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Home My WebLink AboutSE48_2824 2020 Annual Review - Sconset Geotextile Tube Project2020 Annual Review Submitted by: Siasconset Beach Preservation Fund P.O. Box 2279 Nantucket, MA 02584 Prepared by: Epsilon Associates, Inc. 3 Mill & Main Place, Suite 250 Maynard, MA 01754 March 16, 2021 Sconset Geotextile Tube Project (SE48-2824) Nantucket,MA Submitted to: Nantucket Conservation Commission 2 Bathing Beach Road Nantucket, MA 02554 PRINCIPALS Theodore A Barten, PE Margaret B Briggs Dale T Raczynski, PE Cindy Schlessinger Lester B Smith, Jr Robert D O’Neal, CCM, INCE Michael D Howard, PWS Douglas J Kelleher AJ Jablonowski, PE Stephen H Slocomb, PE David E Hewett, LEED AP Dwight R Dunk, LPD David C Klinch, PWS, PMP Maria B Hartnett Richard M Lampeter, INCE Geoff Starsiak, LEED AP BD+C Marc Bergeron, PWS, CWS ASSOCIATES Alyssa Jacobs, PWS Holly Carlson Johnston Brian Lever 3 Mill & Main Place, Suite 250 Maynard, MA 01754 www.epsilonassociates.com 978 897 7100 FAX 978 897 0099 Projects:\21597\2013 Emergency Project\Monitoring and Work Reports\2020 Annual Report March 16, 2021 Mr. Jeff Carlson Nantucket Conservation Commission 2 Bathing Beach Road Nantucket, MA 02554 Subject: DEP File No. SE48-2824 | Sconset Bluff Stabilization Project 2020 Annual Review Dear Mr. Carlson: Epsilon Associates, Inc. (“Epsilon”) submits the attached 2020 Annual Review on behalf of our clients, the Siasconset Beach Preservation Fund (“SBPF”). This annual report was prepared in accordance with the Order of Conditions and reports on: sand delivered in the 2020 Sand Year, bluff monitoring, shoreline monitoring and underwater video monitoring. The Sand Delivery and Contribution Report for 2020 (“2020 Sand Report”) is provided as Attachment A to the Annual Report. The sand deliveries to the template were challenging in 2020 due to COVID, concluding sand coloration and quality issues with the Nantucket Conservation Commission (“Commission”), and working with the Town of Nantucket to evaluate an extended shoreline protection project. As reported in the attached documents one will see that there was ample sand on the template – approximately 33,020 cubic yards (“cy”) – in January 2020 at the start of the 2020 Sand Year, and that correlates to 34.9 cubic yards per linear foot (“cy/lf”) of sand. During the winter and spring of 2020 approximately 16,459 cy of sand were contributed off the template to back fill end returns, re-cover exposed geotubes after erosion events, and to remove sand containing topsoil. During the year (between June and January) 10,656 cy of sand from the Polpis Harbor dredging project was delivered and placed on the template, making available 27,449 cy (29.0 cy/lf) of sand for the 2020 – 2021 storm season. Recovering exposed geotubes following erosion events from October to December means the actual volume of the template on January 15, 2021 was less than 27,449 cy. The SBPF has diligently managed the template to provide adequate sand to the system to compensate for the sediment that would have been contributed off the bluff based on Mr. Jeff Carlson 2 Nantucket Conservation Commission March 16, 2021 pre-construction, site-specific contribution rates. From project construction to the end of the 2020 Sand Year (seven years) SBPF has delivered 133,398 cy of sand to the template and 91,279 cy has been contributed off the template into the littoral drift system. The average of the annual contribution rates is 14.3 cy/lf/yr, see Table 2 in Attachment A. The volume of sand placed on the template over the past seven years exceeds the standard mitigation sand volume of 80,186 cy (53,212 cy or 66% more sand) than is typically required based on the mitigation sand volume formula of length x height x retreat rate for seven years (for this reach of Sconset Bluff that is [(947 feet x 71 feet x 4.6 ft/year) / 27 cf/cy] x 7 years = 80,186 cy). Further, the average sand contribution rate is greater than the pre-construction sediment contribution rate determined for this reach of the bluff, i.e. 14.3 cy/lf/yr contributed versus 12 cy/lf/yr pre-construction contribution rate. Therefore, SBPF has managed the template to provide a greater volume of sand to the littoral system than the bluff would have contributed over this seven-year period had the geotube system not been in place. SBPF will continue to re-cover exposed geotubes after erosion events and plans to deliver and place sand on the template prior to the 2021 – 2022 storm season, after the completion of the Arcadis study assuming the project continues. Please contact me via email at ddunk@epsilonassociates.com or by phone at (978) 897-7100 with any question regarding this annual report. Sincerely, EPSILON ASSOCIATES, INC. Dwight R. Dunk, LPD, PWS, BCES Principal cc. J. Posner, SBPF S. Cohen, Cohen & Cohen Law PC Encl. 2020 Annual Review - Sconset Geotextile Tube Project (SE48-2824) 21597/Sconset i Annual Review Epsilon Associates, Inc. TABLE OF CONTENTS TABLE OF CONTENTS I EXECUTIVE SUMMARY 1 1.0 Introduction 1 2.0 Key Findings 1 3.0 Monitoring Reports 2 4.0 Summary of Monitoring Results 3 4.1 Sand Delivery 3 4.2 Bluff Monitoring 4 4.3 Shoreline Monitoring 5 4.4 Underwater Video Monitoring 6 5.0 Recommended Changes to Monitoring and Mitigation Program 7 5.1 Monitoring Program Adjustments 7 5.2 Mitigation Volume Adjustment 8 ATTACHMENT A JANUARY 2020 – JANUARY 2021 SAND DELIVERY AND CONTRIBUTION REPORT ATTACHMENT B SCONSET BLUFF JUNE 2020 AERIAL SURVEY REPORT ATTACHMENT C EXCERPT FROM SOUTHEAST NANTUCKET BEACH MONITORING, DECEMBER 2020, 84TH SURVEY REPORT ATTACHMENT D SCONSET BEACH JUNE 2020 AND OCTOBER 2020 UNDERWATER VIDEO SURVEY REPORTS 21597/Sconset E-1 Annual Review Epsilon Associates, Inc. EXECUTIVE SUMMARY 1.0 Introduction Pursuant to the Order of Conditions (DEP File No. SE48-2824), the Siasconset Beach Preservation Fund (“SBPF”) was authorized to install geotextile tubes at the base of the coastal bluff below 87- 105 Baxter Road, cover the geotubes with a stockpile of sand as mitigation for installing the tubes at the base of the Coastal Bank (i.e. the sand template), vegetate the natural bluff, and install a coastal drainage system (including a catch basin) at 91 Baxter Road (collectively these activities are referred to as the “Project”). The Project was constructed in two phases. The initial phase was constructed in late December 2013 and January 2014 in accordance with an Emergency Certification approval issued by the Nantucket Conservation Commission, and that authorized construction and maintenance of three stacked tiers of 45-foot circumference geotextile tubes covered by sand at the base of the eroding Sconset Bluff, regulated as Coastal Bank (“bank”). That geotextile tube installation was approximately 852 feet long located along the toe of the bank from 87-105 Baxter Road. The second phase, constructed in October 2015 through February 2016, included the installation of a fourth tier of geotextile tubes on lots 91-99, intermediate returns, end returns, and a surface runoff drainage system. With the returns included, the total Project length is now 947 feet. As part of the Order of Conditions for the Project, an annual review of the Project is required to review information gathered through the Project’s monitoring and mitigation programs. This Annual Report was prepared to review the existing monitoring data and provide recommended changes to monitoring and mitigation programs for the future. 2.0 Key Findings Significant monitoring has occurred during the greater than 7-year period since the geotextile tubes were initially constructed in late 2013: twenty-five shoreline surveys, nine underwater video surveys, five wetland wells monitoring events, beach invertebrate monitoring at four locations, four drainage system reports, and five aerial surveys of the bluff. SBPF has also regularly submitted work reports describing template re-grading activities. After more than seven years of monitoring, there is no indication of adverse effects to adjacent beaches, the nearshore hard bottom environment, the wetlands at the top of the bluff, or beach invertebrates. Following are the key findings from the monitoring data. ♦ The shoreline monitoring data shows that the measured shoreline positions and the rate of shoreline change are similar to historic patterns. There is no indication of accelerated erosion in excess of historical observations in front of or adjacent to the geotubes. ♦ The bluff survey indicates that the mitigation sand template has contributed more than two times more sand (14.3 cubic yard/linear foot/year [cy/lf/yr], although more than this 21597/Sconset E-2 Annual Review Epsilon Associates, Inc. has been delivered to the site) than the unprotected bluff (6.6 cy/lf/yr) over the last seven years. ♦ Underwater video surveys show that a productive cobble habitat area is located just offshore from the geotextile tubes, with no indication that this cobble habitat is being adversely affected by the sand mitigation. ♦ The significant mitigation required at Sconset is uniquely conservative. The sand mitigation volume of 22 cy/lf/yr is 1.5- to 1.8-times the average bank contribution rate1. Ten comparable bank and dune protection projects2 on the Cape & Islands provided mitigation equivalent to the average bank contribution volume; in most cases, the mitigation volume was estimated by multiplying the average annual erosion of the bank or shoreline by the height and length of the shoreline protected, and was only required to be placed one time per year. The largest annual sand delivery for these 10 projects is 1,100 cy/yr. If the same method were used for the Sconset project area, a mitigation volume of only 12.0 cy/lf/yr would be required. ♦ The conservative nature of the sand mitigation program is noted by the greater volume of mitigation sand required to be placed on the sand template than is contributed off the sand template to the littoral drift system. Simply put, the annual volume of sand that is currently required to be placed on the template has exceeded the volume of sand that is typically lost off the sand template each year, and this can result in a surplus of sand in the template. If this were to continue, further addition of sand could eventually cover vegetation on the upper portion of the bank and exacerbate slope erosion, additionally that would steepen the access ramps, making equipment access and template re-grading difficult or impossible. Therefore, an adaptive sand management approach of simply refilling the template each year to 22 cy/lf is advocated. 3.0 Monitoring Reports Individual monitoring reports are presented herewith as Attachments A-D: ♦ January 2020 – January 2021 Sand Delivery and Contribution Report (Attachment A) ♦ Sconset Bluff June 2020 Aerial Survey Report (Attachment B) ♦ Excerpt from Southeast Nantucket Beach Monitoring, December 2020, 84th Survey Report (Attachment C) 1 The volume of 22 cy/lf/yr is 1.8 times to 1.5 times the bank contribution volume of 12.0 cy/lr/yr to 14.3 cy/lf/yr calculated using the standard equation of bank height X bank length X bank recession rate. The volume range varies based on how Coastal Bank recession rate is measured. 2 A review of these ten comparable projects was presented in Attachment B of the 2016 Annual Report. 21597/Sconset E-3 Annual Review Epsilon Associates, Inc. ♦ Sconset Beach June & October 2020 Underwater Video Survey Reports (Attachment D) The following sections provide a summary of each of the referenced monitoring reports. 4.0 Summary of Monitoring Results 4.1 Sand Delivery As presented in Attachment A the “January 2020 – January 2021 Sand Delivery and Contribution Report” (also referred to as the “Sand Report”), the Project incorporates a substantial sand mitigation volume. Table 1 in the Sand Report (Attachment A) summarizes the sand deliveries and Attachment B provides a description of the bluff monitoring results. The aerial survey of the bluff (see Section 4.2 of this Executive Summary below) indicated that not all mitigation sand eroded off the sand template over the winter and that approximately 16,793 cy of sand remained in the template as of June 2020, prior to the additional 10,656 cy delivered between June 2020 and January 15, 2021. These sand deliveries bring the volume of sand within the template available for the 2020 – 2021 storm season to approximately 27,449 cy. During the course of the sand year 16,227 cy of sand, or 16.9 cy/lf, was contributed off the sand template and into the littoral drift system. While it was a fairly calm storm season, the 2020 volume contributed by the template is the result of various project activities associated with the re-covering of the geotubes post-storm events, rebuilding the end returns, and to push excess sand off the template to remove sand containing topsoil from the template. The SBPF proposed to the Commission a more adaptive mitigation approach in previous annual reports, as well as in the Notice of Intent to expand the geotube system (SE48-3115), because the last few years have had lower erosion, leading to a significant portion of the mitigation sand remaining in the sand template. Continuing to place 22 cy/lf/yr on the sand template would cover up the vegetation on the bluff face and steepen the access ramps, making pedestrian or equipment access and template management activities (such as re-grading) more difficult or impossible. During a meeting with the Massachusetts Department of Environmental Protection (“MassDEP”) in early 2017, options for making the sand mitigation volume more adaptive to actual conditions were discussed. MassDEP suggested on option may be to simply refill the template to 22 cy/lf each spring. In this manner, whatever portion of sand that erodes each winter is replaced each year so that a minimum of 22 cy/lf are available each year, prior to the start of the winter storm season. SBPF believes this is a reasonable option that ensures a conservative volume of sand is available while recognizing that actual bluff contribution rates are typically less than 22 cy/lf/yr. As shown in Attachment A, at the end of the 2019 Sand Year there was 33,020 cy of sand on the template, exceeding the 20,834 cy for a full template based 22 cy/lf (22cy/lf x 947 ft = 20,834 cy). As measured in June 2020 after the winter storm season and before any 2020 sand deliveries, the 21597/Sconset E-4 Annual Review Epsilon Associates, Inc. sand volume of the template was determined to be 16,793 cy. Based on that template volume, 4,041 cy of sand was required to refill the template to 20,834 cy (22 cy/lf) (volume of sand on the template in June 2020 of 16,793 cy (20,834 cy – 16,793 cy = 4,041 cy)). An additional 10,656 cy of sand was placed between June 2020 and January 15, 2021, which increased the volume of sand on the template to 27,449 cy for the 2020-2021 storm season, and which is equivalent to a distance-weighted average of approximately 29.0 cy/lf. There was an unknown amount of sand contributed off the template to re-cover exposed geotubes after storms in the fall of 2020 which reduced the actual volume of the sand in the template on January 15, 2020 to less than 27,449 cy. The sand volume delivered to the template exceeded the minimum volume required to refill the template to 22 cy/lf/yr and provides for a “mathematical surplus” of sand in an adaptive sand management protocol based on the calculations summarized above and presented in Attachment A. 4.2 Bluff Monitoring As presented in the “Sconset Bluff June 2020 Aerial Survey Report” included as Attachment B, an aerial survey of Sconset Bluff was performed by AirShark on June 9th, 2020. An unmanned aerial vehicle (“UAV”) was used to survey the bluff face and geotextile tube area. The data from the survey were processed and used to produce a digital surface model (“DSM”) of Sconset Bluff. The survey yielded the following findings: ♦ The results of the 2020 aerial survey were used to calculate the changes in the bluff volume from September 2019 to June 2020 for those unprotected areas immediately adjacent to the geotextile tube project (Figure 1 in Attachment B). During review of the topography generated from this survey and the updated profile views, it was determined that the break in slope between the beach and bluff (toe of the slope) generally varies between elevation +10 and +11 feet North American Vertical Datum of 1988 (“NAVD 88”) but is best represented by using elevation +11 feet NAVD 88. 3 This contour was used to provide a constant toe elevation and for consistency across the survey area. Therefore, the change in the bluff volume in these unprotected areas was calculated from the toe of the bluff (elevation +11 feet NAVD 88) to the top of the bluff. ♦ As of June 2020, the volume in the sand template was 16,793 cy, which is approximately 17.7 cy/lf. This volume was calculated prior to the delivery of an additional 10,656 cy between June 2020 and January 2021. ♦ The Sand Report (Attachment A) and the June Aerial Survey Report (Attachment B) show that, of the total volume of sand delivered and placed for the 2019 – 2020 winter storm 3 The conversion from Mean Low Water 92 to NAVD88 is -1.88 feet. 21597/Sconset E-5 Annual Review Epsilon Associates, Inc. season, approximately 16.9 cy/lf was contributed to the littoral system. Although the 2019 – 2020 storm season was not particularly active, additional sand was pushed off the template during maintenance activities, to rebuild end returns, re-cover exposed geotubes and to remove sand containing topsoil, which all lead to higher than needed sand contribution off the template in the 2020 Sand Year. ♦ The Project has contributed more sand (14.3 cy/lf) than the unprotected bluff (6.6 cy/lf/yr) over the last seven years (July 2013 – January 2021). 4.3 Shoreline Monitoring Shoreline monitoring occurred quarterly at 46 profiles located along six miles of shoreline. Each shoreline survey includes information on the change in position of the shoreline, the Mean Low Water (“MLW”) line, and the change in volume for each profile. Bathymetry is conducted each spring and fall which extends from the surf zone to either a distance of 3,000 ft offshore or -35 ft MLW92, whichever is reached first. Adverse impacts from the geotextile tubes would be expected to be the most apparent in the areas immediately adjacent to the geotextile tubes. One of the purposes of the shoreline monitoring is to ensure the long-standing pattern of shoreline retreat in the Project area and immediately adjacent areas is not accelerating due to the presence of the geotextile tubes. To provide a comprehensive assessment, shoreline monitoring also occurs at profiles that were established in the 1990’s farther to the north and south of the geotextile tubes, for a total monitoring distance of approximately six miles. Quarterly reports provide data for all profiles and include plots from nine beach profiles that represent the stretch of beach subject to monitoring, to help visualize long-term trends. These nine profiles include: ♦ Near the south of the monitoring area (Profile 84) ♦ Approximately 1,000 feet and 500 feet south of the geotubes (Profiles 90 and 90.6) ♦ Within the geotube area (Profiles 91, 91.5, and 92) ♦ Approximately 500 feet and 1,000 feet north of the geotubes (Profiles 9.5 and 93) ♦ Near the north end of the monitoring area (Profile S) Shoreline data charts from these nine representative profiles are included in the “Southwest Nantucket Beach Monitoring, December 2020, 84th Quarterly Report” prepared by Woods Hole Group (“WHG”) and previously submitted to the Commission; the charts are reproduced here as Attachment C. General observations derived from the plotted shoreline data included the following: 21597/Sconset E-6 Annual Review Epsilon Associates, Inc. ♦ Each profile includes times of shoreline advance and shoreline retreat, demonstrating a high degree of variability on short and long-time scales. This high degree of variability, which observed short-term period of erosion or accretion, suggests that adverse effects from the geotextile tubes could only be reliably determined through years of sustained erosion that deviate from historic observations. ♦ Each profile responds differently on variable time scales. ♦ This variability does not lend itself to fitting a long-term trend line with a high degree of statistical accuracy. ♦ The current December 2020 shoreline position at many profiles is generally similar (within about 20 feet) to the shoreline position in the ~2006-2008 timeframe. ♦ The short-term variability shown by surveys since geotube installation in January 2014 is similar to short-term variability (~2- to 3-year periods) observed over many years of surveys before the geotubes were installed. Surveyed post-geotube shoreline changes are not materially different from previous observations as related to rates and duration of shoreline change. No accelerated erosion post-geotube installation in excess of historical observations is evident. 4.4 Underwater Video Monitoring As presented in the “Sconset Beach Underwater Video Survey Report” submissions, included in Attachment D, on June 18, 2020 and October 22, 2020, CR Environmental, Inc. (“CR”) and Epsilon conducted underwater video surveys offshore from the geotube project site and directly adjacent areas at the base of the bluff from 87-105 Baxter Road. Underwater video data was collected with CR’s portable towed video sled along the transects shown on the figures within Attachment A in both reports (see Attachment D). The surveys shows that a productive habitat area is located just offshore from the geotextile tubes, with no indication that such cobble habitat is being covered by mitigation sand. During the underwater video survey in June, 13 invertebrate species, three fish species, and five marine plant and algal species were observed. During the underwater video survey in October, 14 invertebrates, two fish species, and five marine plant and algal species were observed. The dominant biota across both surveys and all transects included unidentified branching brown algae, unidentified branching red algae, Irish moss algae, rockweed brown algae, hydroids, common slipper shells, bread crumb sponge, sulfur (boring) sponge, and hermit crabs. Most of the survey area had a 25-54% cobble coverage, and there is no indication that such habitat is being covered by the mitigation sand. A comparison of the 2020 underwater video surveys with the survey conducted in 2019, two surveys conducted in 2018, two surveys conducted in 2017, and the two surveys conducted in 2016, demonstrates that results were broadly consistent and did not indicate loss of cobble habitat due to the Project. 21597/Sconset E-7 Annual Review Epsilon Associates, Inc. As described in the June 2016 report, the volume of the sand template is minimal compared to volume of sand in the littoral system, and natural sand and shoal movements. It is our ongoing recommendation that a reduction in the frequency of underwater video monitoring is warranted, as meaningful data could only be generated in the event that regular monitoring indicates that the sand mitigation template is contributing several times more sand than the unprotected bluff. 5.0 Recommended Changes to Monitoring and Mitigation Program The Project’s mitigation and monitoring programs were reviewed to determine those types of monitoring that provide the most useful data and value to assess the potential effects from the Project. The recommended changes are the same as presented in the December 2016 Annual Report and are summarized briefly below. 5.1 Monitoring Program Adjustments ♦ Aerial bluff monitoring should occur annually to provide an assessment of bluff volume change in protected and unprotected areas, as well as the volume of sand remaining in the sand template. ♦ Shoreline surveys should be adjusted to collect the most meaningful data. Seven years of quarterly surveys have now been completed.  Shoreline monitoring frequency should be changed to a maximum of two times a year. Analysis by WHG included in the December 2016 Annual Report indicates that quarterly sampling and observation does not inform the analysis to any greater degree. Therefore, a survey frequency of two times a year is recommended, consistent with the monitoring suggestions in the MassDEP Beach Nourishment Best Practices Guide (MassDEP, 2007) and recommendations from The National Research Council (National Academy Press, 1995). One survey is recommended in late winter / early spring and the other is recommended in late summer/early fall.  Wading shots should be eliminated from the shoreline surveys. As presented in the December 2016 Annual Report, an analysis of extrapolating the data from 0 to -5 feet MLLW, as opposed to using a rodman to collect the data, shows that associated errors are small (the average difference in the volume of sand estimated for each profile was 1.1 cy/ft, which equates to a 1.4% difference). The surveys can be completed in approximately half the time if there are no wading shots, which would add tremendous flexibility to completing the surveys in timely fashion, and also reduces inherent risks to the survey crew.  Bathymetry monitoring frequency should be changed to once per year. The December 2016 Annual Report described how bathymetry surveys conducted once per year are sufficient to characterize regional morphology. Reducing the total number of bathymetry survey profiles to ~22 that extend no more than 3,000 ft 21597/Sconset E-8 Annual Review Epsilon Associates, Inc. offshore would potentially allow for the survey to be completed in a single calm sea/weather day without sacrificing substantive information. To provide useful data for present and long-term comparisons, the subset of ~22 profiles would include the historic whole number profiles 81 through 99 plus profiles Q, S, and W. Additionally, it is proposed that bathymetry monitoring be re-evaluated annually to assess its continued value. ♦ Underwater video monitoring should only be required once every three years or in the event that regular monitoring indicates that the sand mitigation template is contributing several (3-5) times more sand than the unprotected bluff. ♦ Drainage system reporting. The drainage system monitoring had been conducted for six years. At this time, it is proposed that the Town Director of Public Works monitor the catch basin for maintenance, as is done for other Town catch basins. 5.2 Mitigation Volume Adjustment The mitigation requirement for the Project is to place 22 cy/lf/yr annually. As has been noted in previous submissions, the average annual pre-construction bank contribution volume, calculated from 1994-2013, is 12-14.3 cy/lf/yr (depending on bank recession methodology). The conservative volume of 22 cy/lf/yr is 1.5- to 1.8-times the average pre-construction bank contribution. A review of ten comparable bluff and dune protection projects presented in Attachment B of the December 2016 Annual Report, shows that sand mitigation volumes for other Coastal Bank stabilization projects are mostly based upon average annual erosion of the bluff or shoreline multiplied by the height and length of the shoreline protected. That review demonstrated that the significant sand mitigation volume required at Sconset (equivalent to 1.5- to 1.8-times the bluff contribution volume) is uniquely conservative. The conservative nature of the sand mitigation volume is evidenced by the fact that significant volumes of mitigation sand remain on the template at the end of each winter. As the end of sand year 2020 the volume of sand remaining on the template was approximately 27,449 cy; at the end of sand year 2019, 33,020 cy remained on the template; at the end of sand year 2018, 10,200 remained on the template; at the end of sand year 2017, 17,000 cy remained the template; and at the end of sand year 2016, 15,000 cy remained on the template. SBPF recommends an adaptive mitigation program, where the full mitigation volume of 22 cy/lf would be available each year for the winter storm season, but will not be indiscriminately placed annually regardless of how much sand remains in the template. The proposed mitigation plan is to place the full 22 cy/lf in the sand template prior to the start of the storm season each fall. Consistent with current practice, each time the seaward portion of the sand cover is eroded, during storm events as designed, the sand template will be re-graded (sand from the top will be pushed down) so that the geotextile tubes remain covered and sand is available to the littoral system. Each following year (prior to the start of the storm season), a sufficient volume of sand 21597/Sconset E-9 Annual Review Epsilon Associates, Inc. will be added to refill the sand template to 22 cy/lf/yr, so that 22 cy/lf is always available at the start of each storm season. We believe this mitigation approach will be much more adaptive and will allow the mitigation sand requirement to provide adequate sand to maintain an adequate volume of sand to littoral system. The proposed mitigation approach recognizes that not all of the sand on the template is contributed to the littoral system each year. As noted above, approximately 16,793 cy remained on the template in June 2020 with an additional 10,656 delivered in subsequent months, even though the volume of sand contributed from the sand template was higher than the volume of sand contributed from the unprotected bluff. The proposed approach avoids increasing the height of the template each year to accommodate another full placement of 22 cy/lf even though ample sand remains, and instead simply refills the sand template to the 22 cy/lf mark each year. Continuing to increase the height of the sand template each year is not recommended because it covers the existing bank vegetation and steepens the access ramps, making pedestrian and equipment access and template management activities (such as re-grading) more difficult or impossible. Attachment A January 2020 - January 2021 Sand Delivery and Contribution Report January 2020 - January 2021 Sand Delivery and Contribution Report Baxter Road and Sconset Bluff Stabilization Project Nantucket, MA March 2021 Submitted by: Siasconset Beach Preservation Fund PO Box 2279 Nantucket, MA 02584 Prepared by: Epsilon Associates 3 Mill & Main Place, Suite 250 Maynard, MA 01754 In Association with : Cottage + Castle, Inc. 37 Old South Road, Unit #6 Nantucket, MA 02554 PRINCIPALS Theodore A Barten, PE Margaret B Briggs Dale T Raczynski, PE Cindy Schlessinger Lester B Smith, Jr Robert D O’Neal, CCM, INCE Michael D Howard, PWS Douglas J Kelleher AJ Jablonowski, PE Stephen H Slocomb, PE David E Hewett, LEED AP Dwight R Dunk, LPD David C Klinch, PWS, PMP Maria B Hartnett Richard M Lampeter, INCE Geoff Starsiak, LEED AP BD+C Marc Bergeron, PWS, CWS ASSOCIATES Alyssa Jacobs, PWS Holly Carlson Johnston Brian Lever 3 Mill & Main Place, Suite 250 Maynard, MA 01754 www.epsilonassociates.com 978 897 7100 FAX 978 897 0099 March 16, 2021 Nantucket Conservation Commission 2 Bathing Beach Road Nantucket, MA 02554 Subject: Annual Sand Delivery and Contribution Report File No. SE 48-2824, Sconset Bluff Geotextile Tube Project, Nantucket MA Dear Commissioners: On behalf of the Siasconset Beach Preservation Fund (“SBPF”), Epsilon Associates, Inc. submits the attached Annual Sand Delivery and Contribution Report (prepared as required in Special Condition 32.d). If you have any questions regarding this transmittal, please contact me at 978-897-7100 or ddunk@epsilonassociates.com. Sincerely, EPSILON ASSOCIATES, INC. Dwight R. Dunk, LPD, PWS, BCES Principal 21597/Sconset 1 2020 Annual Sand Delivery Report Epsilon Associates, Inc. ANNUAL SAND DELIVERY REPORT 1.0 Introduction The Baxter Road and Sconset Bluff Stabilization Project (the “Project”) was constructed in two phases. The first phase was constructed in late December 2013 and January 2014 via an Emergency Certification approval issued by the Nantucket Conservation Commission. The first phase consisted of the installation of three stacked tiers of 45-foot circumference geotextile tubes at the base of the eroding Sconset Bluff. The geotextile tube installation was approximately 852 feet long and extended along the toe of the bank from 87-105 Baxter Road. The second phase was constructed in October 2015 through February 2016 and included the installation of a fourth tier of geotextile tubes on lots 91-99, intermediate returns, end returns, and a surface runoff drainage system. With the returns included, the total project length is now 947 feet. The purpose of the annual sand delivery report is to present the sand mitigation volumes and corresponding delivery tickets for each “Sand Year” initially from April 1 through March 31 of any given year. SBPF has previously submitted detailed Sand Reports for the first six sand years associated with the Project: • November 2013 through March 31, 2014 (referred to as the “2014 Sand Year”) • April 1, 2014 through March 31, 2015 (referred to as the “2015 Sand Year”) • April 1, 2015 through March 31, 2016 (referred to as the “2016 Sand Year”) • April 1, 2016 through January 31, 2018 (referred to as the “2017 Sand Year”) • February 1, 2018 through April 30, 2018 (referred to as the “2018 Sand Year”) • May 1, 2018 through December 31, 2019 (referred to as the “2019 Sand Year”) This report presents information on sand deliveries during the period from January 1, 2020 through January 15, 2021 (referred to as the “2020 Sand Year”). 2.0 Sand Delivery Requirements The Project incorporates a substantial mitigation volume of 22 cubic yards/linear foot/year[cy/lf/yr]. Given the project’s length of 947 feet, the total annual mitigation volume required is currently 20,834 cy. As required by the Project’s Order of Conditions (SE48-2824), annually in Sept. – Nov. place sand to ensure a substantial volume of sand (10 – 15 cy/lf) is available at the onset of the winter storm season, place additional sand as needed during the winter and if the total volume is not placed before March 1, the balance shall be placed by March 31. Delivery tickets are to be provided annually to document the total volume of sand provided on a yearly basis. 21597/Sconset 2 2020 Annual Sand Delivery Report Epsilon Associates, Inc. 3.0 Volume of Mitigation Sand Delivered The following ten tables document the sand delivery amounts. ♦ Tables 1-2 present a summary of the volume of sand delivered and contributed from December 2013 through January 15, 2021. Table 3 presents a comparison of the volume of sand eroded from the bluff in adjacent unprotected areas from July 2013 – June 2020. ♦ Table 4 presents the volume of sand delivered during the period from December 2013 – March 31, 2014, which includes construction of the initial Project. ♦ Table 5 presents the total volume of mitigation sand delivered during the period from April 1, 2014 – March 31, 2015. ♦ Table 6 presents the total volume of sand delivered during the period from April 1, 2015 – March 31, 2016, which includes supplementary construction of the fourth tier and returns. ♦ Table 7 presents the total volume of sand delivered during the period from April 1, 2016 – January 31, 2018. ♦ Table 8 presents the total volume of sand delivered during the period from February 1, 2018 – April 30, 2018. ♦ Table 9 presents the total volume of sand delivered during the period from May 1, 2018 – December 31, 2019. ♦ Table 10 presents the total volume of sand delivered during the period from January 1, 2020 through January 15, 2021. Each of these tables is discussed in further detail below. 3.1 Table 1. Summary of Sand Delivery Volume Lines 1-4 of Table 1 describe the total volume of sand delivered to the site, and separate this total into the following categories: mitigation sand, sand used on the bluff face, and sand used for construction (inside or behind the geotextile tubes). Neither sand placed on the bluff face nor sand used for construction is counted towards the mitigation requirement. Lines 5-11 of Table 1 provide a summary of the required mitigation volume. The base mitigation volume is determined by multiplying the 22 cy/lf/yr by the Project’s length (Line 5). This volume is then adjusted by subtracting out the surplus sand from the previous year and the amount of sand eroded from the bluff face. The surplus sand is calculated as that sand delivered the previous year that is in excess of the base mitigation requirements and that is still in the sand template at the end of the sand year (see Line 6-8). The bluff erosion volume accounts for that portion of the bluff face that continued to erode and is discussed further in Section 5.0 below. 21597/Sconset 3 2020 Annual Sand Delivery Report Epsilon Associates, Inc. Lines 13 and 14 of Table 1 presents the final calculation of whether the project’s mitigation requirement was met. Any surplus of sand delivered during one year, up to but not in excess of the amount remaining on the sand template on the beginning of the new sand year, is carried forward and counted towards the following year’s requirement. 3.2 Table 2. Summary of Sand Contribution Table 2 presents a summary of the volume on sand contribution for the period from December 2013 – December 31, 2020. Table 2 provides a breakdown of the sand contribution from the sand template, bluff face, construction, and the total contribution. Line 9 of Table 2 provides the total volume of sand contributed during the 2020 Sand Year. Line 10 provides the average of annual sand contribution from December 2013 – January 15, 2021. 3.3 Table 3. Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes Tables 3a-c present a comparison of the volume of sand eroded from the bluff in adjacent unprotected areas from July 2013 – June 2020. Table 3a provided the bluff volume change from September 2019 – June 2020. During this period the unprotected bluffs to the north and the south of the geotextile tubes eroded approximately 4,623 cy which is equivalent to a distance-weighted average of 6.6 cy/lr/yr. Table 3b presents the bluff volume loss during the period of May 2013 – September 2019. Table 3c presents the bluff volume loss in the unprotected areas adjacent to the geotextile tubes from July 2013 – June 2020. 3.4 Table 4. Sand Delivery December 2013 – March 31, 2014 Table 4 presents the volume of sand delivered during the period from December 2013 – March 31, 2014, which includes construction of the initial Project. Table 4 provides a detailed breakdown of that portion of sand placed within and behind the geotextile tubes and presents the total volume of mitigation sand placed over, in front of, and at the ends of the geotextile tubes. All delivery tickets for the total volume delivered of 39,204 cy were previously submitted to the Conservation Commission, most recently as part of the 2015 Sand Report. 3.5 Table 5. Sand Delivery April 1, 2014 – March 31, 2015 Table 5 presents the total volume of mitigation sand delivered during the period from April 1, 2014 – March 31, 2015. Three separate deliveries were made over this period of time. All delivery tickets for the total volume of 14,428 cy were submitted as part of the 2015 Sand Report. 3.6 Table 6. Sand Delivery April 1, 2015 – March 31, 2016 Table 6 presents the total volume of sand delivered during the period from April 1, 2015 – March 31, 2016. Table 6 provides a detailed breakdown of the sand delivered for construction, sand delivered for mitigation, and sand delivered to the bluff face. All delivery tickets for the total volume of 22,485 cy delivered during the 2016 Sand year were provided in the 2016 Sand Report, including the 19,066.7cy delivered during the most recent construction period in November, December, and January and the 3,418 cy delivered in April 2015. 21597/Sconset 4 2020 Annual Sand Delivery Report Epsilon Associates, Inc. 3.7 Table 7. Sand Delivery April 1, 2016 – January 31, 2018 Table 7 presents the total volume of sand delivered during the period from April 1, 2016 – January 18, 2018. Deliveries occurred in the latter half of 2016, in May and December 2017, and in January 2018. All delivery tickets for the total volume delivered of 15,138 cy were submitted as part of the 2017 Sand Report. 3.8 Table 8. Sand Delivery February 1, 2018 – April 30, 2018 Table 8 presents the volume of mitigation sand delivered during the period from February 1, 2018 – April 30, 2018. Three separate deliveries were made over this period of time. All delivery tickets for the total volume delivered of 8,152 cy were submitted as part of the 2018 Sand Report. 3.9 Table 9. Sand Delivery from May 1, 2018 – December 31, 2019 Table 9 presents the total volume of sand delivered during the period from May 1, 2018 – December 31, 2019. Deliveries occurred between October 2018 to February 2019, and between October 2019 to December 2019. A table of all deliveries for the total volume delivered of 23,335 cy were submitted as part of the 2019 Sand Report. 3.10 Table 10. Sand Delivery from January 1, 2020 – January 15, 2021 Table 10 presents the total volume of sand delivered during the period from January 1, 2020 – January 15, 2021. Deliveries occurred in June, November, and December 2020, and in January 2021. A table of all deliveries for the total volume delivered of 10,656 cy are included in with this report. 3.11 Summary Table 1 shows that sand delivery requirements were met during the first three years of the Project1, with a surplus of sand delivered in the Project’s first two years. At the end of the Project’s fourth winter in 2017, SBPF proposed using an adaptive mitigation approach, whereby the sand template was refilled to 22 cy/lf/yr. (This adaptive mitigation approach was discussed with the Commission during the Project’s March 2018 Annual Review and is also described in the 2017 Sand Report). The UAV survey in June 2020 indicated there was approximately 16,793 cy within the template at the time of the survey. An additional 10,656 cy was delivered before January 15, 2021 bringing the total volume delivered to the sand template to be approximately 27,449 cy which correlates to approximately 29.0 cy/lf. There was an unknown amount of sand from the template used to re-cover exposed geotubes after storms in the fall of 2020 which reduced the actual volume of sand in the template to less than 27,449 cy. 1 As described in the 2017 Sand Report, a small deficit was apparent in spring 2016 after bluff erosion contribution values were recalculated and slightly reduced. 21597/Sconset 5 2020 Annual Sand Delivery Report Epsilon Associates, Inc. 4.0 Annual Aerial Survey of Bluff SBPF contracted AirShark to perform the annual aerial survey of the bluff in June 2020. AirShark is the same firm that previously performed the 2017, 2018 and 2019 aerial surveys. A separate report on the aerial survey is attached (the “Sconset Bluff June 2020 Aerial Survey Report” or the “2020 Survey Report”). 5.0 Changes in Bluff Volume Changes in Bluff Volume are also reported in the Sconset Bluff September 2019 Aerial Survey Report. To understand changes in the bluff volume since Project construction, the results of the 2020 survey were compared to the previous aerial surveys of the Project area that were conducted in September 2019, May 2018, August 2017, and July 2013. The July 2013 survey was conducted about 6 months prior to the installation of the geotextile tubes. 5.1 Changes in Bluff Volume in Adjacent Unprotected Areas The results of the 2020 aerial survey were used to calculate the changes in the bluff volume from September 2019 to June 2020 for those unprotected areas immediately adjacent to the geotextile tube project (Figure 1). During review of the topography generated from this survey and the updated profile views, it was determined that the break in slope between beach and bluff (toe of the slope) generally varies between elevation +10 and +11 feet North American Vertical Datum of 1988 (“NAVD 88”) but is best represented by using elevation +11 feet NAVD 882. This contour was used to provide a constant toe elevation and for consistency across the survey area. Therefore, the change in the bluff volume in these unprotected areas was calculated from the toe of the bluff (elevation +11 feet NAVD 88) to the top of the bluff. ♦ For the north unprotected area, the section of the bluff within 802 feet immediately to the north of the geotextile tubes was used. ♦ For the south unprotected area, the section of bluff within 138 feet immediately to the south of the geotextile tubes was used. Areas farther south than this could not be used because they had coir or jute terraces installed so were not representative of the unprotected bluff. ♦ No areas with a bulge of sand from sand delivery activities at the accessway between 85 and 87 Baxter Road were used in the calculations. In particular, the size of the south unprotected area was reduced in 2019 (i.e. the northern boundary was moved farther south) to account for sand delivery activities and the associated accretion of sand on the bluff face extending farther south in 2019 than in previous years. 2 The conversion from Mean Low Water 92 to NAVD 88 is -1.88 feet. 21597/Sconset 6 2020 Annual Sand Delivery Report Epsilon Associates, Inc. As shown in Tables 3a-c, this analysis indicates that the unprotected areas immediately adjacent to the geotextile tubes eroded at the following rates: ♦ For the most recent year (September 2019 – June 2020), the unprotected areas eroded approximately 4,623 cy (Table 3a). This is equivalent to a distance-weighted average of 6.6 cy/lf/yr. ♦ For the period from geotextile tube installation to the previous reporting period (July 2013 – September 2019), the unprotected areas eroded approximately 41,000 cy (Table 3b). This is equivalent of a distance weighted average of 6.8 cy/lf/yr. As discussed in the 2019 Bluff Survey Report, the apparent accretion in the previous reporting period was within the vertical accuracy range and likely represents no changes. ♦ For the period from geotextile tube installation to present (July 2013 – June 2020), the unprotected areas eroded approximately 45,623 cy (Table 3c). This is equivalent to a distance-weighted average of 6.6 cy/lf/yr. The 2019-2020 estimate of the annual loss of sand from unprotected areas was calculated to be 6.6 cy/lf/yr. This annual loss from September 2019 to June 2020 is consistent with the less energetic winter storm season than in previous years. This loss is greater than the annual loss of the previous reporting period for reasons more thoroughly described in the 2019 Bluff Survey Report. The 2019-2020 estimate is equal to the annualized loss of sand from the geotextile tube installation in 2013 to the June 2020 survey of 6.6 cy/lf/yr. 5.2 Changes in Bluff Volume Above Geotextile Tubes The 2020 aerial survey was also used to calculate the changes in the bluff volume above the geotextile tubes for the period between September 2019 and June 2020. Based on this aerial survey the bluff above the geotubes eroded approximately 267 cy. As described in the 2020 Bluff Survey Report, the accuracy of the survey data was 2.3cm, which applied across this area correlates to approximately ±181 cy, or a distance weighted average of ±0.19 cy/lf.3 With a net loss of 267 cy, and an accuracy range of approximately ±181 cy, this suggests there was some loss of sediment off the bluff face above the template. Reviewing Figure 1, the locations of red are indicative of “gain” and represent maintenance activities at the Project area, specifically rebuilding of the end returns that were washed away during winter storms and general template maintenance to re-cover the geotubes. The template maintenance can also be seen with the creation of the windrows, visible as the relatively north- to-south narrow linear strips of “gain” shown along the westerly edge of the template. 3 The vertical accuracy was used to calculate the sand volume and presented as a volume rather than vertical accuracy based on comments from Greg Berman on the 2019 Annual Report. 21597/Sconset 7 2020 Annual Sand Delivery Report Epsilon Associates, Inc. 6.0 Volume of Sand in Template The volume of sand in the template was calculated by determining the total volume of the template at the time of the 2020 aerial survey and subtracting out the known volume of sand within the geotextile tubes and returns located above beach level. The total volume of sand above the beach level was 28,506 cy and the total volume of sand in the geotubes is 11,713 cy. This yields a sand cover volume in June 2020 of approximately 16,793. This was prior to the delivery of an additional 10,656 cy between June 2020 and January 15, 2021. As described in Section 3.11, this results in an estimate of approximately 27,449 cy of sand available for the 2020-2021 storm season. Calculations were also performed on that portion of the sand template that is located above the fourth tier. Per the Project’s Order of Conditions, the sand on the top of the fourth tier is not counted as mitigation sand. This volume is calculated as approximately 1,974 cubic yards. It is anticipated that sand on top of the sand template, including san don top of the fourth tier, will continue to be pushed down to re-cover the geotextile tubes as needed. Therefore, the volume above the fourth tier will become available through time. 7.0 Volume of Sand Contributed to Littoral System Table 2 presents the approximate volume of sand contributed to the littoral system. The amount contributed is that portion of the sand delivered to the site that is no longer in place in the sand template and therefore is deemed to have been contributed to the littoral system. As has been previously notes, the mitigation sand is delivered to the top of the geotextile tubes and then is pushed over to cover the face of the tubes. On an as-needed basis after erosion events, the sand on top of the geotextile tubes is pushed from the top of the tubes to the face of the tubes whenever needed to re-cover exposed geotextile tubes. Table 2 provides a reasonable estimate of how much mitigation sand has been contributed off the template and into the littoral system over the past seven years, which totals 91,279 cy. For each of the seven sand years (Sand Year 2014, Sand Year 2015, Sand Year 2017, Sand Year 2018, Sand Year 2019, and Sand Year 2020), this estimate was calculated by the following steps shown in Table 2: 1. Beginning with the volume of sand in the sand template at the start of each year (this was estimated in Sand Years 2014 – 2016 and measured in Sand Years 2017 – 2020); 2. Adding the total amount of mitigation sand delivered each year (this is a known amount for each Sand Year); 3. Subtracting the volume of sand in the sand template at the end of each sand year (this was estimated in Sand Years 2014 – 2016 and measured in Sand Years 2017 – 2020); 21597/Sconset 8 2020 Annual Sand Delivery Report Epsilon Associates, Inc. 4. Adding the bluff volume eroded (this is a known total from 2013 through 2017 and was apportioned to Sand Years 2015 and 2016 as described in Section 5.1 of the 2017 Sand Report); 5. Adding the volume of sand contributed during construction (this is known from 2013); and 6. Determining the total volume of sand contributed (both as a total volume and as a rate expressed in cy/lf/yr), including as an average rate from 2013 – 2020. A review of Tables 2 and 3a-c indicates that the sand template has consistently contributed more sand than the unprotected bluff to the north and south of the project: ♦ During the first six years, the unprotected bluff contributed an average of 6.8 cy/lf/yr, while the sand template contributed an average of 13.8 cy/lf/yr. ♦ During the most recent year, the unprotected bluff contributed 6.6 cy/lf/yr, while the sand template contributed 16.9 cy/lf/yr. While it was a calmer storm year, this volume contributed by the template is the result of various Project activities associated with the re-covering of the geotubes post-storm events, rebuilding the end returns, and to push excess sand off the template to remove sand containing topsoil from the template. ♦ Over the nearly seven years from July 2013 – January 2021, the unprotected bluff contributed an average of 6.6 cy/lf/yr compared to 14.3 cy/lf/yr of sand contributed an average off the template (although more than this has been delivered to the site). Tables Line Sand Amounts 12/13-3/31/14 4/1/14-3/31/15 4/1/15-3/31/16 4/1/16-1/31/18 2/1/18-4/30/18 5/15/18-12/31/19 1/1/20-1/15/21 1 Total Volume Delivered for Geotube Construction (See Line 5 in Table 4 and Line 5 in Table 6)12,653 0 2,931 0 0 0 0 2 Total Volume Delivered for Mitigation (see Tables 4-10)23,951 14,429 15,085 15,138 8,152 23,335 10,656 3 Total Volume Delivered to Bluff Face (Not Counted as Mitigation; See Ln 10 in Tbl 4 & Ln 12 in Tbl 6)2,600 0 4,469 0 0 0 0 4 Total Volume Delivered by Truck (Sum Lines 10-12)39,204 14,429 22,485 15,138 8,152 23,335 10,656 5 Required Mitigation Volume (22 cy/lf * Project Length of 852' for 3 tiers, 947' for 4 tiers w/ret.)18,744 18,744 20,834 20,834 20,834 20,834 20,834 Surplus Sand From Prior Year 6 Surplus Delivered in Prior Year (From Line 13 in Preceding Column)0 5,207 3,029 -583 -6,278 -18,960 -16,459 7 Volume on Template at Start of Sand Year 0 5,900 8,500 15,000 17,000 10,200 33,020 8 Countable Surplus Present in Sand Template (Line 6; Not to Exceed Line 7)0 5,207 3,029 -583 -6,278 -18,960 -16,459 9 Volume on Template at End of Sand Year 5,207 8,500 15,000 17,000 10,200 33,020 27,449 Bluff Erosion 10 Net Contribution from Erosion of Bluff Face (pre-veg & during 4th tier const.; see Table 6)0 2,138 2,138 0 0 0 0 11 Adjusted Required Mitigation Volume (Line 5 - Line 8 - Line 10)18,744 11,400 15,667 21,417 27,112 39,794 37,293 12 Total Volume Delivered for Mitigation (Line 2 above)23,951 14,429 15,085 15,138 8,152 23,335 10,656 13 Mitigation Surplus or Deficit (-) ( Line 12 - Line 11)5,207 3,029 -583 -6,278 -18,960 -16,459 -26,637 14 Mitigation Surplus or Deficit (-) to Refill Template to 22 CY/LF 755 -10,634 12,186 6,615 Table 2. Summary of Sand Contribution in Cubic Yards (CY), December 2013 - January 15, 2021 Line Sand Amounts 12/13-3/31/14 4/1/14-3/31/15 4/1/15-3/31/16 4/1/16-5/31/17 6/1/17-5/14/18 5/15/18-12/31/19 1/1/20-1/15/21 1 Volume on Template at Start of Sand Year (Line 7 in Table 1)0 5,900 8,500 15,000 17,000 10,200 33,020 2 Total Volume Delivered for Mitigation (Line 2 in Table 1; Lines 1 through 4 in Table 10)23,951 14,429 15,085 10,550 12,741 23,335 10,656 3 Volume on Template at End of Sand Year (Line 9 in Table 1)5,900 8,500 15,000 17,000 10,200 33,020 27,449 4 Total Volume Contributed from Sand Template (Line 1 + 2 - Line 3)18,051 11,829 8,585 8,550 19,541 515 16,227 5 Total Volume Contributed from Sand Template (cy/lf/yr)21.2 13.9 9.1 8.9 20.3 0.5 16.9 6 Net Contribution from Erosion of Bluff Face (Line 10 in Table 1)0 2,138 2,138 0 0 0 0Construction Contribution 7 Contribution from Construction (Line 8 in Table 4)3,707 0 0 0 0 0 0 Total Annual Sand Contribution 8 Total Volume Contributed 21,758 13,966 10,723 8,550 19,541 515 16,227 9 Total Volume Contributed in cy/lf/yr 25.5 16.4 11.3 8.9 20.3 0.5 16.9 10 Average of Annual Sand Contribution from 2013-2020 (cy/lf/yr)14.3 Template Sand Contribution Bluff Face Contribution Note: 2020 Sand Template was measured in June, 2020. Minor template maintenance was performed during Fall months following storms. Mitigation Volume Summary Sconset Bluff and Baxter Road Geotextile Tube Project, 87-105 Baxter Road, Nantucket, MA Table 1. Summary of Sand Delivery in Cubic Yards (CY), December 2013 - January 2021 Sand Delivery Summary Base Required Mitigation Volume Mitigation Volume Adjustments Page 1 of 5 Line Area Volume Eroded (CY)Length (Feet)Duration (Years) Annual Change (CY/LF/YR) 1 North Unprotected Area 4,418 802 0.75 7.3 2 South Unprotected Area 205 138 0.75 2.0 3 Total Bluff Erosion for Adjacent Unprotected Areas (Distance-weighted average)4,623 6.6 Line Area Volume Eroded (CY)Length (Feet)Duration (Years)Annual Change (CY/LF/YR) 1 North Unprotected Area 35,423 802 6.0 7.4 2 South Unprotected Area 5,577 192 6.0 4.8 3 Total Bluff Erosion for Adjacent Unprotected Areas (Distance-weighted average)41,000 6.8 Line Area Volume Eroded (CY)Length (Feet)Duration (Years) Annual Change (CY/LF/YR) 1 North Unprotected Area 39,841 802 7.0 7.1 2 South Unprotected Area 5,782 192 7.0 4.3 3 Total Bluff Erosion for Adjacent Unprotected Areas (Distance-weighted average)45,623 6.6 Table 3a. Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes, September 2019 - June 2020 Table 3b. Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes, July 2013 - September 2019 Table 3c. Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes, July 2013 - June 2020 Note: As described in the 2019 Bluff Survey Report, the apparent accretion was within the vertical accuracy range and likely represent no net change ; therefore, a value of 0 was used for the 2019 Sand Year to calculate the 7-year annual rate of change. Note: The volumes provided in the above table is a comparison of the unprotected areas from the September 2019 survey to the June 2020 survey Note: As described in the 2019 Bluff Survey Report, the apparent accretion was within the vertical accuracy range and likely represents no change; therefore, a value of 0 was used for the 2019 Sand Year to calcualte the annual rate of change over the previous six years. Page 2 of 5 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY 1 Inside Tier 2 Geotube 5 852 3,834 2 Inside Tier 3 Geotube 5 835 3,758 3 Bench Behind Tier 2 Geotube 3 852 2,556 4 Bench Behind Tier 3 Geotube 3 835 2,505 5 Total Sand For Geotube Construction (Sum Lines 1-4)12,653 6 Template on Top 22 852 18,744 7 Template at Ends 1,500 8 Sand Contributed to Littoral System During Construction 3,707 9 Total Mitigation Volume (Sum Lines 6-8)23,951 10 Total Volume Delivered to Bluff Face (Not Counted as Mitigation)2,600 11 Total Sand Delivered (Sum Lines 5, 9, and 10)39,204 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY 1 April 2014 7.1 852 6,015 2 Jan 2015 5.3 852 4,477 3 Feb 2015 4.6 852 3,936 4 Total Sand Delivered (Sum Lines 1-3)14,429 Mitigation Volume Bluff Face Volume Table 4. Sand Delivered December 2013 - March 31, 2014 Geotube Construction Total Sand Delivered Table 5. Sand Delivered April 1, 2014 - March 31, 2015 Mitigation Volume Page 3 of 5 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY Fourth Tier (3) 120' long x 45' circumference tubes(1) 75' long x 45' circumference tubeTotal of 435 linear feetNorthern Returns (4) 25' long x 30' circumference tubesTotal of 100 linear feet Northern Intermediate Returns(1) 35' long x 30' circumference tube(1) 45' long x 30' circumference tubeTotal of 80 linear feet Southern Returns (1) 65' long x 30' circumference tube(1) 70' long x 30' circumference tube(1) 75' long x 30' circumference tube(1) 80' long x 30' circumference tubeTotal of 290 linear feet Southern Intermediate Returns(1) 35' long x 30' circumference tube(1) 45' long x 30' circumference tubeTotal of 80 linear feet 6 Total Sand For Geotube 4th Tier and Returns Construction (Sum Lines 1-5)2,931 7 November and December 2015 (immediately post-construction)15,085 8 Total Mitigation Volume 15,085 9 Total Volume Delivered to Bluff for Vegetation (April 2015)3,418 10 Total Volume Delivered to Bluff to Fill Gully South of Viewing Area (Nov/Dec 2015)931 11 Total Volume Delivered to Bluff to Fill Gully at Viewing Area (Jan 2016)12012Total Volume Delivered to Bluff Face (Not Counted as Mitigation)4,469 13 Total Sand Delivered (Sum Lines 6, 8, and 12)22,485 Mitigation Volume Bluff Face Volume (Not Counted as Mitigation) Total Sand Delivered 5 2.0 80 160 3 2.0 80 160 4 2.0 290 580 Geotube Construction - 4th Tier and Returns 2 2.0 100 200 1 4.21 435 1831 Table 6. Sand Delivered April 1, 2015 - March 31, 2016 Page 4 of 5 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY 1 August through December 2016 1,230 2 May 2017 9,320 3 December 2017 2,090 4 January 2018 2,499 5 Total Sand Delivered (Sum Lines 1-4)15,138 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY 1 February 2018 40 2 March 2018 5,506 3 April 2018 2,606 5 Total Sand Delivered (Sum Lines 1-3)8,152 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY 1 October 2018 2,204 2 November 2018 3,156 3 January 2019 4,120 4 February 2019 2,683 5 October 2019 5,400 6 November 2019 4,266 7 December 2019 1,506 8 Total Sand Delivered (Sum Lines 1-7)23,335 Line Sand Delivery Amounts Cubic Yard (CY)/ Linear Foot (LF) Project Length (LF)Total CY 1 June 2020 1,350 2 November 2020 1,800 3 December 2020 5,454 4 January 2021 2,052 5 Total Sand Delivered (Sum Lines 1-4)10,656 Table 9. Sand Delivered May 1, 2018 - December 31, 2019 Mitigation Volume Table 7. Sand Delivered April 1, 2016 - January 31, 2018 Mitigation Volume Table 8. Sand Delivered February 1, 2018 - April 30, 2018 Mitigation Volume Table 10. Sand Delivered January 1, 2020 - January 15, 2021 Mitigation Volume Page 5 of 5 Sand Delivery Table Cottage + Castle Ventures, Inc. Sconset Beach Preservation Trust2021-2021 Sand Season Delivery Schedule Truck Delivery Date Loads Per Load CYD's Total CYD's Hours Amount Source Delivery Vendor Delivery Location AH Invoice Number Invoice Date Delivery Qtr 656 6/17/2020 18 18 324 1,800.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 361 7/29/2020 Q2, 2020 97 6/17/2020 7 18 126 675.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 361 7/29/2020 Q2, 2020 500 6/17/2020 19 18 342 1,950.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 361 7/29/2020 Q2, 2020 207 6/17/2020 11 18 198 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 361 7/29/2020 Q2, 2020 473 6/17/2020 20 18 360 2,100.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 361 7/29/2020 Q2, 2020 083 11/20/2021 12 18 216 8.00 1,200.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 2020 473 11/20/2021 11 18 198 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 2020 097 11/20/2020 11 18 198 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 2020 083 11/23/2021 13 18 234 8.50 1,275.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 2020 473 11/23/2020 11 18 198 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 2020 097 11/23/2020 9 18 162 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 2020 083 11/30/2020 13 18 234 8.50 1,275.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202047311/30/2020 11 18 198 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202009711/30/2020 9 18 162 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202008312/3/2020 11 18 198 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202047312/3/2020 12 18 216 8.00 1,200.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202009712/3/2021 12 18 216 8.00 1,200.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202008312/8/2020 9 18 162 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202047312/8/2020 13 18 234 8.50 1,275.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202009712/8/2020 11 18 198 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202008312/12/2020 14 18 252 9.00 1,350.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202047312/12/2020 10 18 180 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202009712/12/2020 7 18 126 6.00 900.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 399 1/8/2021 Q4, 202047312/14/2020 12 18 216 8.50 1,275.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 202009712/14/2020 9 18 162 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 473 12/16/2020 11 18 198 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 097 12/16/2020 11 18 198 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 473 12/17/2020 10 18 180 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 097 12/17/2020 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 473 12/18/2020 13 18 234 9.00 1,350.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 097 12/18/2020 8 18 144 6.00 900.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 473 12/19/2020 10 18 180 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 097 12/19/2020 11 18 198 8.00 1,200.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 473 12/21/2020 12 18 216 8.50 1,275.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 097 12/21/2020 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 473 12/22/2020 13 18 234 9.00 1,350.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 2020 097 12/22/2020 8 18 144 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 202047312/23/2020 12 18 216 8.50 1,275.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 202009712/23/2020 12 18 216 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 402 1/12/2021 Q4, 202047312/28/2020 7 18 126 6.00 900.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q4, 202009712/28/2020 10 18 180 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q4, 202047312/30/2020 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q4, 202009712/30/2020 8 18 144 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q4, 20204731/1/2021 7 18 126 6.00 900.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20210971/1/2021 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20214731/2/2021 10 18 180 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20210971/2/2021 8 18 144 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20214731/5/2021 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20210971/5/2021 10 18 180 7.50 1,125.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20214731/6/2021 8 18 144 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021 097 1/6/2021 6 18 108 5.50 825.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021 473 1/9/2021 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021 097 1/9/2021 9 18 162 7.00 1,050.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021 473 1/11/2021 6 18 108 5.50 825.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021 097 1/11/2021 8 18 144 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021 473 1/12/2021 8 18 144 6.50 975.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 20210971/12/2021 7 18 126 6.00 900.00 Industrial Road/Purchased Town Sand AH Construction To Bluff 412 2/19/2021 Q1, 2021Total592 10,656 376.00 64,050.00 57 Attachment B Sconset Bluff June 2020 Aerial Survey Report Sconset Bluff September 2020 Aerial Survey Report Baxter Road and Sconset Bluff Stabilization Project Nantucket, MA February 2021 Submitted by: Siasconset Beach Preservation Fund PO Box 2279 Nantucket, MA 02584 Prepared by: Epsilon Associates 3 Mill & Main Place, Suite 250 Maynard, MA 01754 21597/Sconset 1 2020 Bluff Aerial Survey Report Epsilon Associates, Inc. 2020 ANNUAL BLUFF AERIAL SURVEY REPORT 1.0 Introduction The Baxter Road and Sconset Bluff Stabilization Project (the “Project”) consists of three and four tiers of geotextile tubes, sand covering the geotubes (i.e. the sand template), vegetation planting on the bluff face, and the installation of stormwater runoff drainage system. The Project was constructed in two phases by the Sconset Beach Preservation Fund (“SBPF”). The first phase was constructed in late December 2013 and January 2014 via an Emergency Certification approval issued by the Nantucket Conservation Commission (“Commission”). The first phase consisted of the installation of three stacked tiers of 45-foot circumference geotextiles tubes at the base of the eroding Sconset Bluff. The geotextile tube installation was approximately 852 feet long and extended along the toe of the bank from 87-105 Baxter Road. The second phase was constructed in October 2015 through February 2016 and included the installation of a fourth tier of geotextile tubes on lots 91-99, intermediate returns, end returns, and a surface runoff drainage system. With the returns included, the total project length is now 947 feet. SBPF intends to perform an annual survey of the bluff face each year, to facilitate the calculation of the following parameters: ♦ Annual change in volume of the bluff face above the geotubes; ♦ Annual change in volume of the unprotected bluff sections to the north and south of the geotextile tubes; and ♦ Volume of sand in the sand template. The 2020 drone LiDAR survey described below is the fifth aerial survey conducted since the Project’s Order of Conditions was issued in Fall 2015. 2.0 Annual Aerial Survey and Data processing An aerial survey of Sconset Bluff was performed by AirShark on June 9th, 2020. As described in the “Southeast Nantucket Beach Monitoring, June 2020, 82nd Survey Report” prepared by Woods Hole Group and dated August 2020, this aerial survey included the bluff, dune, and beach areas within the Siasconset Monitoring Area from Low Beach to Wauwinet that have been monitored by Woods Hole Group and others for over 20 years. A subset of the aerial survey data was processed and used to produce a digital surface model (“DSM”) of those parts of Sconset Bluff within and immediately adjacent to the area of the geotextile tubes. The remainder of this report focuses on the aerial survey data from the area of Sconset Bluff within and immediately adjacent to the geotextile tubes. 2.1 2020 Survey Details AirShark was contracted by the SBPF to conduct a UAV flight on June 9th, 2020 of Siasconset Bluff. Airshark is the same firm that previously performed the 2017, 2018, and 2019 aerial surveys. The 21597/Sconset 2 2020 Bluff Aerial Survey Report Epsilon Associates, Inc. UAV utilized Light Detection and Ranging (“LiDAR”) to map the bluff, geotextile tubes, and beach along Baxter Road. LiDAR measures distance to a target by illuminating that target with a pulsed laser light, and measuring the reflected pulses with a sensor. The June 2020 LiDAR mission at Siasconset Beach was flown with a customized DJI M600 Pro Aircraft Platform equipped with a Phoenix Aerial Systems LiDAR System Mini Ranger-UAV that can operate at up to 100 meter above ground level and collected 30-50 points per square meter. The drone flew the same flight path for the June 2020 survey as it did for the September 2019 survey. This system relies on Real Time Kinematic (“RTK”) GPS to achieve a 2.5 cm horizontal and a 5 cm vertical accuracy classes, produced to meet the American Society for Photogrammetry and Remote Sensing (“ASRPS”). To achieve this level of accuracy the drone requires a base station while the drone is operating. This survey employed the Base Station #277, which is a capped rebar set inside the fence by Sankaty Lighthouse at the northern end of Baxter Road, to the north of the Project area. In addition to the base station, Aeropoints, manufactured by Propeller Aero were deployed across the flight area to provide a QA/QC accuracy check. These Aeropoints are “mapping grade” GNSS receivers which can provide point locations with 1-3 cm accuracy. Comparing the LiDAR data against the available Aeropoints, the June 2020 LiDAR Survey, and the Woods Hole Group 82nd Report1, yields a Root Mean Square Error (“RMSE”) of 2.3 cm for this survey. 3.0 Changes in Bluff Volume To understand the changes in the bluff volume since Project construction, the results of the 2020 survey were compared to the previous aerial surveys of the Project area that were conducted in September 2019, May 2018, August 2017, and July 2013. The July 2013 survey was conducted about 6 months prior to the installation of the geotextile tubes. 3.1 Changes in Bluff Volume in Adjacent Unprotected Areas The results of the 2020 aerial survey were used to calculate the changes in the bluff volume from September 2019 to June 2020 for those unprotected areas immediately adjacent to the geotextile tube project (Figure 1). During review of the topography generated from this survey and the updated profile views, it was determined that the break in slope between the beach and bluff (toe of the slope) generally varies between elevation +10 and +11 feet North American Vertical Datum of 1988 (“NAVD 88”) but is best represented by using elevation +11 feet NAVD 88.2 This contour was used to provide a constant toe elevation and for consistency across the survey area. Therefore, the change in the bluff volume in these unprotected areas was calculated from the toe of the bluff (elevation +11 feet NAVD 88) to the top of the bluff. 1 Southeast Nantucket Beach Monitoring, June 2020, 82nd Survey Report. Prepared by Woods Hole Group. 2 The conversion from Mean Low Water 92 to NAVD 88 is -1.88 feet. 21597/Sconset 3 2020 Bluff Aerial Survey Report Epsilon Associates, Inc. ♦ For the north unprotected area, the section of the bluff within 802 feet immediately to the north of the geotextile tubes was used. ♦ For the south unprotected area, the section of bluff within 138 feet immediately to the south of the geotextile tubes was used. Areas farther south than this could not be used because they had coir or jute terraces installed so were not representative of the unprotected bluff. ♦ No areas with a bulge of sand from sand delivery activities at the accessway between 85 and 87 Baxter Road were used in the calculations. In particular, the size of the south unprotected area was reduced in 2019 (i.e. the northern boundary was moved farther south) to account for sand delivery activities and the associated accretion of sand on the bluff face extending farther south in 2019 than in previous years. As shown in Tables 1a-c, this analysis indicates that the unprotected areas immediately adjacent to the geotextile tubes eroded at the following rates: ♦ For the most recent year (September 2019 – June 2020), the unprotected areas eroded approximately 4,623 cy (Table 1a). This is equivalent to a distance-weighted average of 6.6 cy/lf/yr. ♦ For the previous reporting period (May 2018 – September 2019), the unprotected areas showed a calculated net accretion of approximately 1,082 cy (Table 1b). This is equivalent to a distance-weighted average accretion rate of 1.2 cy/lf/yr. As discussed in the 2019 Sconset Bluff Survey Report, this apparent accretion appears to be a mapping anomaly and likely represents no net change. ♦ For the period from geotextile tube installation to present (July 2013 – June 2020), the unprotected areas eroded a distance weighted average of 6.6 cy/lf/yr (Table 1c). Table 1a Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes for the Most Recent Year, September 2019 – June 2020 Line Area Volume Eroded (CY) Length (Feet) Duration (Years) Annual Change (CY/LF/YR) 1 North Unprotected Area 4,418 802 0.75 7.3 2 South Unprotected Area 205 138 0.75 2.0 3 Total Bluff Erosion for Adjacent Unprotected Areas 4,623 6.6 Note: The volumes provided in the above table is a comparison of the Unprotected Bluff from the September 2019 survey to the June 2020 survey. 21597/Sconset 4 2020 Bluff Aerial Survey Report Epsilon Associates, Inc. Table 1b Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes for the Previous Reporting Period, May 2018 – September 2019 Line Area Volume Eroded (CY) Length (Feet) Duration (Years) Annual Change (CY/LF/YR) 1 North Unprotected Area -797 802 1.0 -1.0 2 South Unprotected Area -285 138 1.0 -2.1 3 Total Bluff Erosion for Adjacent Unprotected Areas -1,082 -1.2 Note: The negative eroded volume correlates to accretion rate. The calculated erosion is within the error range of the survey and likely represent no net change (refer to 2019 Sand Report). Table 1c Bluff Volume Loss in Unprotected Areas Adjacent to Geotextile Tubes for the Seven Years since Geotextile Tube Installation, July 2013 – June 2020 Line Area Volume Eroded (CY) Length (Feet) Duration (Years) Annual Change (CY/LF/YR) 1 North Unprotected Area 39,841 802 7.0 7.1 2 South Unprotected Area 5,782 192 7.0 4.3 3 Total Bluff Erosion for Adjacent Unprotected Areas 45,623 6.6 Note: Bluff face accretion is shown in Table 1b for the 2019 Sand Year. As described in in the 2019 report no net change is reported; therefore, a value of 0 was used for the 2019 Sand Year to calculate the 7-year average annual rate. The 2019-2020 estimate of the annual loss of sand from unprotected areas was calculated to be 6.6 cy/lf/yr. This annual loss from September 2019 to June 2020 is consistent with the less energetic winter storm season than in previous years. This loss is greater than the annual loss of the previous reporting period for reasons more thoroughly described in the 2019 Bluff Survey Report. The 2019-2020 estimate is equal to the long-term annualized loss of sand from the geotextile tube installation in 2013 to the June 2020 survey of 6.6 cy/lf/yr. 3.2 Changes in Bluff Volume Above Geotextile Tubes The 2020 aerial survey was also used to calculate the changes in the bluff volume above the geotextile tubes for the period between September 2019 and June 2020. Based on this aerial survey the bluff above the geotubes eroded approximately 267 cy. As described above, the accuracy of the survey data was 2.3 cm, which applied across this area correlates to approximately ±181 cy, or a distance weighted average of ±0.19 cy/lf.3 With a net loss of 267, and an accuracy 3 The vertical accuracy was used to calculate the sand volume and presented as a volume rather than vertical accuracy based on comments from Greg Berman on the 2019 Annual Report. 21597/Sconset 5 2020 Bluff Aerial Survey Report Epsilon Associates, Inc. range of approximately ±181 cy, this suggests there was some loss of sediment off the bluff face above the template. Reviewing Figure 1, the locations of red are indicative of “gain” and represent maintenance activities at the Project area, specifically rebuilding of the end returns that were washed away during winter storms and general template maintenance to re-cover the geotubes. The template maintenance can also be seen with the creation of the windrows, visible as the relatively north- to-south narrow linear strips of “gain” shown along the westerly edge of the template. 4.0 Volume of Sand in Template The volume of the sand in the template was calculated by determining the total volume of the template at the time of the 2020 aerial survey and subtracting the known volume of sand within the geotextile tubes and returns located above the beach level. The total volume of sand above the beach level was 28,506 cy and the total volume of sand in the geotubes is 11,713 cy. This yields a sand cover volume in June 2020 of approximately 16,793 cy. While it was a calmer storm season in 2020, various Project activities contributed to the increased use sand associated with template maintenance to re-cover the geotubes after storm events, rebuild the northern and southern end returns after large erosion events in March 2020, and to push excess sand off the template to remove dark sand (i.e., the sand with topsoil present) from the template. These activities contributed to the increased sand use during this Sand Year. Calculations were also performed of that portion of the sand template that is located above the fourth tier. Per the Project’s Order of Conditions, the sand on the top of the fourth tier is not counted as mitigation sand. This volume is calculated as approximately 1,974 cubic yards. It is anticipated that sand on top of the sand template, including sand on top of the fourth tier, will continue to be pushed down to re-cover the geotextile tubes as needed. Therefore, the volume above the fourth tier will become available through time. G:\Projects\Lighthouse\2020\Lighthouse_2020_ArcPro\Lighthouse_2020_ArcPro.aprx Figure 1 2019 to 2020 Sand Volume Comparison Baxter Road and Sconset Bluff Storm Damage Prevention Project Nantucket, Massachusetts Data Source: Office of Geographic Information (MassGIS), Commonwealth of Massachusetts, Information Technology Division Basemap: 2019 Orthophotography, MassGIS °0 112.5 225 Feet Scale 1:2,700 1 Inch = 225 Feet Net Gain Net Loss LEGEND 92cy Gain 297cy Loss 214cy Gain 4,632cy Loss 263cy Gain 539cy Loss Attachment C Excerpt from Southeast Nantucket Beach Monitoring, December 2020 84th Survey Report SOUTHEAST NANTUCKET BEACH MONITORING December 2020 84th SURVEY REPORT 107 Waterhouse Road Bourne, MA 02532 January 2021 Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 19 January 2021 “See Proprietary Note on Title Page” 3.3 LONG-TERM TRENDS To help visualize long-term trends at select profiles along the monitoring area, a series of figures illustrate cumulative change (feet) in shoreline position relative to a 1994 baseline position (zero on the vertical axis) over time on the horizontal axis for a representative subset of beach profiles. The figure captions include profile-specific observations. Nine (9) beach profiles are shown in Figures 5 through 13 to represent the stretch of beach subject to monitoring including: • Near the south of the monitoring area (Profile 84) • Approximately 1,000 ft and 500 ft south of the geotubes (Profiles 90 and 90.6) • Within the geotube area (Profiles 91, 91.5 and 92) • Approximately 500 ft and 1,000 ft north of the geotubes (Profiles 92.5 and 93) • Near the north end of the monitoring area (Profile S) Individual data points on each plot represent the change in shoreline position at mean low water (MLW), based on the surveyed beach profile at that time. Positive numbers indicate shoreline advance and negative numbers indicate shoreline retreat relative to the 1994 baseline (assumed zero). Blue dots represent data obtained from surveys before the installation of geotubes, while red dots represent data since geotube installation. The plots differentiate the pre- and post-geotube installation periods as a known geographic and temporal reference point highlighting results subject to the current regulatory requirements and expected to be subject to future monitoring. The plots demonstrate temporal variability as can be seen with the following examples: • Periods of stability with little cumulative change in shoreline position as seen in Figure 6 from December of 1996 to May of 2002; • Periods of shoreline advance as seen in Figure 6 from May 2002 to February 2005; and • Periods of shoreline retreat as seen in Figure 7 from December 1996 to February 2005. General observations derived from the data plotted on Figures 5 through 13 are summarized below. This collection of long-term observations accentuates the high degree of variability at this site: • Each profile includes times of shoreline advance and shoreline retreat, demonstrating a high degree of variability on short and long-time scales. This high degree of variability, with observed short-term periods of erosion or accretion, suggests that adverse effects from the geotextile tubes could only be reliably determined through years of sustained erosion that deviate from historic observations. Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 20 January 2021 “See Proprietary Note on Title Page” • Each profile responds differently on variable time scales. • This variability does not lend itself to fitting a long-term trend line with a high degree of statistical accuracy. • The current December 2020 shoreline position at many profiles is generally similar (within about 20 feet) to the shoreline position in the ~2006-2008 timeframe. • The short-term variability shown by surveys since geotube installation in January 2014 is similar to short-term variability (~2-3 year periods) observed over many years of surveys before the geotubes were installed. Surveyed post-geotube shoreline changes are not materially different from previous observations as related to rates and duration of shoreline change. No accelerated erosion in excess of historical observations is evident. Figures 5 through 13 follows below with observations made for each profile. Figure 5. Cumulative Shoreline Change (ft) at Profile 84 since November 1994. • Figure 5 shows the shoreline position trend for Profile 84 located in Codfish Park. • There was an overall shoreline advance of ~+90 ft since 1994 • Relatively stable shoreline position with modest retreat from 1996 to late 2001 • 200 ft of shoreline advance from September 2001 to January 2004 • Variable alternating periods of relative stability with modest shoreline advance and retreat spanning multiple years since 2004 • Relative stability since ~2013, excepting latest two surveys. Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 21 January 2021 “See Proprietary Note on Title Page” Figure 6. Cumulative Shoreline Change (ft) at Profile 90 since November 1994. • Figure 6 shows the shoreline position trend for Profile 90 located on bluff just south of the geotubes • There were variable periods of shoreline retreat, stability, and advancement • Maximum and net shoreline erosion on the order of -170 ft and -110 ft, respectively since 1994 • Relatively consistent erosion from 1996 through April 2001 • Sharper short-term shoreline retreat between June 2005 and February 2006 • Shoreline advance from February 2006 to November 2007 • Substantial trend of beach accretion from April 2011 to April 2014 • Relative stability since ~2013. Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 22 January 2021 “See Proprietary Note on Title Page” Figure 7. Cumulative Shoreline Change (ft) at Profile 90.6 since November 1994. • Figure 7 shows the shoreline position trend for Profile 90.6 located on bluff just south of the geotubes • There were variable periods of shoreline erosion, stability, and accretion • General trend of shoreline erosion between 1996 and 2003 • Substantial advance from October 2003 to February 2005 • Sharp retreat from 2005 to 2006 • Net shoreline retreat on the order of -100 ft since 1994 • Current shoreline position similar to 2006, with relative stability since ~2013. Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 23 January 2021 “See Proprietary Note on Title Page” Figure 8. Cumulative Shoreline Change (ft) at Profile 91 since November 1994. • Figure 8 shows the shoreline position trend for Profile 91 located on bluff and geotubes • Net shoreline loss since 1994 on the order of -120 ft • Substantial trend of beach erosion at variable rates through 2007 • Variable shoreline position since 2005 with reversing trends of beach accretion and erosion • Substantial shoreline advance from September 2012 to March 2013 • Little net change in the shoreline position since 2006; similar to other profiles • Trend of milder shoreline erosion in September 2010 to September 2012, October 2003 to June 2005, and December 1998 to June 2000 • Current trend shows relative stability. Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 24 January 2021 “See Proprietary Note on Title Page” Figure 9. Cumulative Shoreline Change (ft) at Profile 91.5 since November 1994. • Figure 9 shows the shoreline position trend for Profile 91.5 located on bluff and geotubes • Net shoreline retreat on the order of -100 ft since 1994 • Relatively consistent long-term shoreline erosion from 1996 through September 2012; with short-term variability • Substantial beach accretion occurred from September 2012 to March 2013 • Current shoreline position similar to 2012; the observation that the current shoreline position is similar to the condition 8-10 years ago is common to other profiles Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 25 January 2021 “See Proprietary Note on Title Page” Figure 10. Cumulative Shoreline Change (ft) at Profile 92 since November 1994. • Figure 10 shows the shoreline position trend for Profile 92 located on bluff just north of the geotubes • Net erosion on the order of -70 ft since 1994 • Current shoreline position similar to observations since 2005; similar to other profiles • Recent trend of beach stability since October 2015, excepting latest two surveys. Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 26 January 2021 “See Proprietary Note on Title Page” Figure 11. Cumulative Shoreline Change (ft) at Profile 92.5 since November 1994. • Figure 11 shows the shoreline position trend for Profile 92.5 located on bluff north of the geotubes • Net erosion on the order of -70 ft since 1994 • Current shoreline position similar to observations since 2005; similar to other profiles • Trend of beach stability for ~10 years, excepting the summer survey likely related to hurricane activity Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 27 January 2021 “See Proprietary Note on Title Page” Figure 12. Cumulative Shoreline Change (ft) at Profile 93 since November 1994. • Figure 12 shows the shoreline position trend for Profile 93 located on bluff north of the geotubes • Relatively stable shoreline position since 1998 • Majority of net losses occurred between 1994 and 1998 • Net erosion on the order of -70 ft since 1994 Woods Hole Group, Inc. • A CLS Company Siasconset 84th Survey 2000-162 28 January 2021 “See Proprietary Note on Title Page” Figure 13. Cumulative Shoreline Change (ft) at Profile S since November 1994. • Figure 13 shows the shoreline position trend for Profile S located on at Sesachacha Pond north of the geotubes • Variable shoreline response • Net shoreline advance on the order of 25 ft since 1994 • Majority of accretion occurred up to 2011, with sharp alternating periods of erosion between • Recent trend of beach stability since 2015 • As with other profiles, the current shoreline position similar to 2005 3.4 WAVE AND WATER LEVEL CONDITIONS For the current 84th survey, defined by the time period of September 17th, 2020 through December 11th, 2020, no nearshore wave data was available since the Woods Hole Oceanographic Institution’s (WHOI) Martha’s Vineyard Coastal Observatory (MVCO) has not operational. Offshore wave data was taken from the National Oceanic and Atmospheric Administration’s (NOAA’s) National Data Buoy Center (NDBC) Station 44008, located 54 nautical miles southeast of Nantucket Island. A time series of wave heights (meters) recorded since the last survey in June 2020 are shown in Figure 14 below. At NDBC Station 44008, there were approximately twelve (12) significant wave events that exceed 1.5 m (~4.9 ft) during the last three months with an overall energy- weighted average wave height for the time period of 2.47 meters, which is an increase since the last quarter’s 1.27 meters (Figure 14). Only one of these events coincided with Attachment D Sconset Beach June & October 2020 Underwater Video Survey Reports Submitted to:Nantucket Conservation Commission2 Bathing Beach RoadNantucket, Massachusetts 02554 Submitted by:Siasconset Beach Preservation FundP.O. Box 2279Nantucket, Massachusetts 02584 November 2020 Sconset Beach Underwater Video Survey Report Prepared by: Epsilon Associates, Inc. 3 Mill & Main Place, Suite 250 Maynard, Massachusetts 01754 CR Environmental, Inc. 639 Boxberry Road East Falmouth, Massachusetts 02536 Nantucket, MA Sconset Beach Underwater Video Survey Report Nantucket, MA Submitted to: Nantucket Conservation Commission Submitted by: Siasconset Beach Preservation Fund Prepared by: Epsilon Associates, Inc. CR Environmental, Inc. November 2020 Table of Contents 21597/Sconset Geotextile Tube Project i Table of Contents Underwater Video Survey Report Epsilon Associates, Inc. Table of Contents UNDERWATER VIDEO SURVEY REPORT 1 1.0 Introduction 1 2.0 Vessel Operations, Navigation, and Survey Design 1 3.0 Survey Data Acquisition and Processing 2 4.0 Survey Results 3 4.1 Biota 4 4.2 Bottom Sediment Coverage 5 5.0 Conclusions 7 ATTACHMENT A Video Survey Maps Figure 1 Underwater Video Trackline Map Figure 2 Percent Cobble/Boulder Present at Trackline Intersections (June 2020) Figure 3 Percent Cobble/Boulder Present at Trackline Intersections (November 2019) Figure 4 Percent Cobble/Boulder Present at Trackline Intersections (November 2018) Figure 5 Percent Cobble/Boulder Present at Trackline Intersections (June 2018) Figure 6 Percent Cobble/Boulder Present at Trackline Intersections (November 2017) Figure 7 Percent Cobble/Boulder Present at Trackline Intersections (June 2017) Figure 8 Percent Cobble/Boulder Present at Trackline Intersections (October 2016) Figure 9 Percent Cobble/Boulder Present at Trackline Intersections (June 2016) ATTACHMENT B Video Survey Screenshot Figures LIST OF TABLES Table 1 Sconset Beach Video Survey – Bottom Sediment Coverage and Biota Underwater Video Survey Report 21597/Sconset Geotextile Tube Project 1 Underwater Survey Report Epsilon Associates, Inc. UNDERWATER VIDEO SURVEY REPORT 1.0 Introduction On June 18, 2020, CR Environmental, Inc. (“CR”) and Epsilon Associates, Inc. (“Epsilon”) on behalf of the Siasconset Beach Preservation Fund (“SBPF”) conducted the spring 2020 underwater video survey offshore from the geotube system, at the base of the bluff fronting 87-105 Baxter Road, Nantucket, MA. These geotubes were installed in December 2013 and January 2014 (with an approximate length of 852-feet) and were then expanded in November and December 2015 to a total length of 947-feet. As part of the Order of Conditions (DEP File No. SE48-2824) for the geotube project, underwater video monitoring is required as described in Special Conditions 28 of the Order of Conditions, which reads in part: “… Photographs and/or video shall be taken along the transects within the project area and the area directly adjacent to the project area. The underwater video shall be able to characterize the bottom sediments, species present and relative abundance including the calculating of the percent cobble where appropriate…” The purpose of the underwater video survey monitoring is to evaluate if mitigation sand that washes off the sand template and carried into the littoral system, i.e. that sand on top of the geotextile tubes, is causing a significant alteration or loss of cobble/boulder habitat located directly offshore of the geotube system. The June 2020 survey marks the eighth underwater video survey since the geotubes were installed. This document describes the data acquisition and processing methods, equipment used for the survey, and survey results. 2.0 Vessel Operations, Navigation, and Survey Design The underwater video monitoring survey activity was conducted on June 18, 2020 from the 35- foot fishing vessel Althea K. The vessel was configured to accommodate navigation and video acquisition systems and was furnished with a portable generator to power survey electronics. The survey crew on the underwater video survey consisted of a boat captain and one mate, a field biologist, an oceanographic technician, and an environmental scientist. The survey was conducted to visually characterize bottom sediments, biota, and type of bottom cover offshore from the geotube project site (see Figures 1-9 in Attachment A). Navigation for the survey was accomplished using a Hemisphere VS-110 12-channel sub-meter (GPS) system. The GPS system was interfaced to a laptop computer running HYPACK 2013A hydrographic survey software. HYPACK recorded vessel position, water depth, and provided a steering display for the vessel captain. During the June 2020 survey, a total of eleven (11) 3- to 6-minute video drifts were performed and bottom coverage was obtained at all 35 survey point intersections. The air temperature was between 65- to 70-degrees Fahrenheit, wind speed at 5- to 10-knots (nautical miles per hour), 21597/Sconset Geotextile Tube Project 2 Underwater Survey Report Epsilon Associates, Inc. swells at 1- to 2-feet for the first four hours of the survey; conditions changed later in the day with winds increasing to a steady 10-knots with increased swells following the change in tide. Due to these workable ocean conditions, good quality underwater video data were obtained at most of the stations. At a few of the stations, the vessel was forced to maneuver (power) into the seas to achieve the correct drift direction. In these cases, the video sled was at times towed sideways and the video data quality reduced. Additionally, at times the vessel and sled speed were too fast causing reduction in video data quality. However, classification of the major substrate types and biota could still be performed by selecting the highest available video quality near each survey point intersection. 3.0 Survey Data Acquisition and Processing Underwater video operations were conducted using a real-time high-resolution color underwater video data acquisition system which permitted the characterization of bottom habitat and the species present. Maps showing the location of the video transects offshore are provided in Attachment A. Underwater video data was collected with CR’s portable towed video sled consisting of a lightweight aluminum frame, Outland Technologies’ high-resolution low light color camera, and two wide-angle 250-watt lights with variable output control. The video camera was cabled to the surface to an OTI-960 DVR recorder and topside monitor. A GoPro 4 Black color camera with internal data storage was also mounted to the towed sled and recorded footage simultaneously with the Outland camera as a second source of data. The video sled was lowered and raised using a lifting davit and lobster pot hauler mounted on the stern and the height of the system off the bottom was continually adjusted to achieve the best bottom coverage and video quality. The vessel speed varied between 0.5 to 1.7 knots. Mounted lasers on the video sled frame were used for scaling purposes, and a calibrated scale template was overlain on the video frame or screen captures. The distance between template grid lines in both the X and Y directions was equal to approximately 6 inches. This grid system permitted scaling and estimating of bottom biota and determining substrate classes and their percent coverage. When the video camera was one foot off the bottom, the viewing area of the camera was approximately 1.5 ft x 1.5 ft (18 in. x 18 in.) and the video quality was optimal for bottom sediment characterizations and biota identifications. HYPACK navigation files were recorded during each video drift. Video data were transferred to a processing computer and viewed by a staff scientist at Epsilon. Representative screen captures (frame images) were extracted along each video drift to characterize bottom sediments and biota offshore from the project. To analyze the bottom characteristics of each video drift, screenshots were taken at points as close as possible to the June 2017 survey’s seven shore-parallel and three shore-perpendicular transect intersections (Figure 6). The June 2020 survey collected video drifts over these intersections. In addition, coordinates for two previously-established, shore-perpendicular 21597/Sconset Geotextile Tube Project 3 Underwater Survey Report Epsilon Associates, Inc. survey transects (90.6 and 92.5) were added to the figure, then screenshots were pulled from points nearest the June 2017 survey’s intersections between those two transects and the seven shore-parallel transects. Using the GPS data collected simultaneously with the video, the time stamps for each of these intersection points were extracted into a spreadsheet. The intersection coordinates were found by scrolling through the video until the time matched as closely as possible to the time recorded to the GPS data coordinates. Sometimes the view closest to the intersection point was not optimal due to the camera position being either too far from or too close to the bottom, or the video sled was towing on its side so that the scale lasers were not visible. In these instances, a screenshot was captured as close as possible to the intersect position where the view was improved. The scale grid was overlain on the video view. Live video (not shown) was reviewed concurrent with the screenshots for the most accurate assessment of biota and bottom substrate. Once the scale grid was in place, the bottom coverage was classified along a gradient of grain sizes using the Auster hierarchical approach (Auster 1998). Bottom sediment and habitat types within the offshore area included: flat sand, sand ripples, sand waves, pebble, cobble, and boulder. The percent cover for bottom sediment types present in each screenshot was approximated using the scale grid. Each of the nine grid sections was reviewed and bottom sediment was categorized individually, then an average was calculated for the complete screenshot. The percent bottom type numbers were rounded to the nearest five percent for presentation in Table 1. To maintain consistency across the 35 screenshots, the same individual reviewed all final percent cover estimates concurrently with the live video. Each screenshot is given three identifiers in Table 1. First, the intersection location is indicated by the name of the transect, which is the same as the distance in feet from the shore (see Figure 1). The June 2020 intersection locations followed the November 2018 survey transect, therefore these distance labels are unchanged (see Figures 1 and 2). Second, the shore perpendicular transect that crosses the shore-parallel transect is listed. Lastly, each screenshot is given a number consistent with the order of all the past surveys’ intersection numbering (i.e. the June 2020 intersection numbering is consistent with all previous surveys, back to June 2016). 4.0 Survey Results Table 1 provides the bottom sediment coverage and biota present in the underwater video drifts collected in June 2020 offshore from the geotube system. Screenshots captured from the underwater video are numbered 1-35 and are presented in Attachment B – Video Survey Screenshot Figures. Note, the June 2020 screenshot numbering 1-35 corresponds to the intersection numbers depicted on Figure 1 – Underwater Video Trackline Map, found in Attachment A – Figures. Results of each screenshot are tabulated in terms of bottom sediment coverage percentages and biota. Screenshots between intersection numbers 1 through 21 were taken at intersection locations between shore-parallel and shore-perpendicular survey transects established for the 21597/Sconset Geotextile Tube Project 4 Underwater Survey Report Epsilon Associates, Inc. underwater video monitoring, while screenshots between intersection numbers 22 through 35 used shore-perpendicular transect locations taken from the previously-established Woods Hole Group shoreline monitoring transects. Table 1 provides an assessment of the biota present and the bottom type at each of the 35 screenshot locations. 4.1 Biota During the underwater video survey, 13 invertebrate species, three fish species, and five marine plant and algal species were observed. The dominant biota across all transects included unidentified branching brown algae, unidentified branching red algae, Irish moss red algae, rockweed brown algae, hydroids, barnacles, common slipper shells, bread crumb sponge, sulfur (boring) sponge, orange encrusting bryozoan, and hermit crabs. Additional biota observed at the transect intersections included northern star coral, red beard sponge, rock crab, surf clam shell, moon snail, and unidentified shell fragments. Additionally, while either not captured or identifiable in the intersection screenshots, the following biota were observed during the video survey fieldwork: common skate, striped bass, and black seabass. ♦ Branching brown and red algae were abundant and were observed in the entire survey area. This was likely Irish moss and rockweed algae, which are often difficult to distinguish if the camera is not close, or the sled speed is not slow enough. ♦ Sulfur sponge and hydroids were abundant and were found in nearly every transect, with the exception of the transect closest to shore: TR-250. ♦ Hermit crabs and Common Slipper Shell were the most abundant invertebrates. ♦ Bread crumb sponge was abundant and was found in all transects, but not identified at every intersection. ♦ Common slipper shells were abundant in the entire survey area, mostly beyond 700 feet offshore. ♦ Moonsnails were observed in transect TR-725 near intersections 8, 9, and 31. ♦ Rock crabs were observed in all transects, except for TR-250, closest to shore. ♦ Common skates were observed in TR 1300 and TR1915. ♦ Black seabass specimens were observed along TR-1050, TR-1915, and TR-1595; and Striped bass were observed near TR-1300 and TR-1595. 21597/Sconset Geotextile Tube Project 5 Underwater Survey Report Epsilon Associates, Inc. Overall, the June 2020 survey continues to show a biologically productive habitat is located just offshore from the geotube bank stabilization system. The June 2016, October 2016, June 2017, November 2017, June 2018, November 2018, and November 2019 surveys had similar dominant biota to the June 2020 survey of the branching brown and red algae, sulfur sponge, bread crumb sponge, and common slipper shells. Besides some expected seasonal variability of the species present, the June 2020 survey had results consistent with the dominant biota observed in 2016, 2017, and June 2018 and there is no indication of adverse effect of marine biota from the geotube system and sand contributed off the sand template. 4.2 Bottom Sediment Coverage In addition to biota, Table 1 listed the bottom coverage types observed in the survey area. The bottom sediment categories include sand flat, sand waves, sand ripples, pebble, cobble, and boulder. An additional category shows the cobble and boulder percentage combined into one percentage. These percentages were combined to show a more representative picture of the bottom substrate differences across the survey area. These combined data were used to create Figure 2, which shows the abundance of cobble/boulder from the June 2020 survey. The cobble/boulder surface was calculated using a geoprocessing tool that interpolates a surface from points using an inverse distance weighted (IDW) technique. The percentage of cobble/boulder coverage ranges from green gradients colors (0-24%), to blue gradient colors (25-69%), and finally to red gradient colors (70-100%) (Figure 2). The percent cobble/boulder coverage varies significantly across the survey area, from <10% to 80%. In June 2020, most of the survey area has 25-54% cobble/boulder coverage. A comparison was made between this June 2020 survey and the 2016, 2017, 2018, and 2019 survey results. An understanding of the natural variability in the nearshore environment provide important context for interpreting results between surveys. Although the presence of cobble/boulder habitat is widespread just offshore from the geotextile tubes, there is significant natural variability within this habitat. As explained in the October 2016 survey report, the percent cobble/boulder coverage can vary by 20% or more when reviewing video from locations even one or two seconds (this time correlates to about 4 to 10 feet) either before or after the intersection point selected for screenshot capture. While each survey collects video data along similar transects, it is nearly impossible to collect video data at absolutely identical locations between surveys, due to both minor variation in the position of the vessel during video survey data collection and due to the occasional need to adjust screenshot capture locations by one or two seconds in order to capture the clearest view. Accordingly, some variation is expected in the cobble/boulder percent cover in each survey, since each survey will represent slightly different locations. With these considerations in mind, the results of the June 2020 survey were compared with the previous seven surveys conducted in June 2016, October 2016, June 2017, November 2017, June 2018, November 2018, and November 2019. Following are the key findings from this comparison: 21597/Sconset Geotextile Tube Project 6 Underwater Survey Report Epsilon Associates, Inc. ♦ All seven surveys showed that most of the sampling area has 25-54% cobble coverage. ♦ All seven surveys indicated that the nearshore survey areas had the lowest cobble/boulder percent coverage, from <10% to 24%. ♦ The cobble/boulder cover was found to increase farther offshore. In the June 2020, November 2019, November 2018, June 2018, November 2017, and June 2017 surveys, the increased cobble/boulder cover started closer to shore (at about 415 feet offshore) than in the June 2016 and October 2016 surveys (where increased cobble/boulder coverage was observed starting around 700 feet offshore). ♦ All eight surveys identified the same general areas as having the highest concentration of cobble/boulder: o June 2016 intersection 9, 11, 12, 15, 33, and 35 had 65-90% cobble/boulder coverage, o October 2016 intersections 9, 11, 15, 22, and 35 had 65-90% cobble/boulder coverage, o June 2017 intersections 6, 8, 9, 11, 13, 33, and 35 had 65-85% cobble/boulder coverage, o November 2017 intersections 8, 13, 18, 33, and 35 had 65-95% cobble/boulder o June 2018 intersections 7, 8, 11, 12, 13, 15, 17, 18, 33, and 35 had 65-100% cobble/boulder coverage. o November 2018 intersections 8, 9, 11, 13, 15, 18, 31, 33, and 35 had 65-100% cobble/boulder coverage o November 2019 intersections 8, 9, 14, 15, 16, 18, 33, and 35 had 65-85% cobble/boulder coverage. o June 2020 intersections 8, 9, 14, 15, 16, 18, 33, and 35 had 60-85% cobble/boulder coverage. While these results were generally consistent with each other, there was some variation. As explained above, the differences in percent cobble/boulder coverage between the eight surveys are considered to be the results of natural variability. A couple locations where the percent cobble/boulder appeared to decrease in June 2020 from the previous surveys (intersections 6, 12, 18, 30 and 35). These intersections were checked, and all were within 10% of the past three surveys, except intersection 6. Intersection 6 decreased approximately 15% from the November 2019 survey, however, is within 10% of the November 2017 and is greater than the November 2018 survey. Intersections 1, 7, 8, 9, 10, 14, 19, 27, 32 and 34 showed increased cobble/boulder 21597/Sconset Geotextile Tube Project 7 Underwater Survey Report Epsilon Associates, Inc. percentages than the previous survey with a difference of 5-10%. Intersection 4 showed increased cobble/boulder percentage by approximately 20% from the previous two surveys but is less than the percent cobble/boulder in the June 2018 survey. These observations suggest that the apparent difference between the two 2016 surveys, the two 2017 surveys, the two 2018 surveys, the 2019 survey, and the June 2020 survey reflects the slightly different locations chosen for screenshot capture between the eight surveys, and is not indicative of change in cobble/boulder habitat. Overall, the June 2020 underwater video survey indicates that a productive widespread cobble/boulder habitat area is located just offshore from the geotextile tubes, and there is no indication that such habitat is being covered by the sand mitigation. 5.0 Conclusions An underwater video survey of the area located just offshore of the geotube system and surrounding areas was conducted in June 2020, approximately seven years after the installation of the geotextile tubes at the base of the bluff. During this survey, 12 invertebrate species, three fish species, and five marine plant and algal species were observed. The dominant biota across all transects included branching brown algae, branching red algae, Irish moss red algae, rockweed brown algae, hydroids, barnacles, common slipper shells, bread crumb sponge, sulfur (boring) sponge, orange encrusted bryozoan, and hermit crabs. Northern star coral and red beard sponge were common in most of the offshore survey area. Common skates, striped bass, and black seabass were also observed within the offshore survey area. Besides some expected seasonal variability of the species present, the June 2020 survey continues to show biologically productive benthic habitat just offshore from the geotextile tubes, and there is no indication of adverse effect on marine biota from the geotextile tube project. The bottom sediment type was also surveyed. The percent cobble/boulder coverage varied significantly across the survey area, from <10% to 75% with increasing percentage of cobble/boulder coverage correlated with increasing distance offshore. The June 2020 survey results were broadly consistent with the survey results from 2016, 2017, 2018, and 2019: most of the survey area in June 2020 had 25-54% cobble/boulder coverage, similar to the previous surveys, and localized areas of higher cobble/boulder coverage were found at similar locations in all eight surveys. While some variation was found between the eight surveys, an analysis of the survey results described in the October 2016 survey report showed that the percentage of cobble/boulder coverage at video locations within just a few feet of one another could vary by up to 20-30%, indicating that much of the observed differences between the eight surveys can be attributed to natural variability. Based on the continued prevalence of cobble/boulder habitat located directly offshore of the geotextile tube Project, there is no evidence that cobble/boulder habitat is being covered by the mitigation sand. 21597/Sconset Geotextile Tube Project 8 Underwater Survey Report Epsilon Associates, Inc. As described in the June 2016 report, the volume of sand contributed off the template is minimal compared to the volume of native sand moving in the littoral system and shoal movements. It is our ongoing recommendation that a reduction in the frequency of underwater video monitoring is warranted, as meaningful data could only be generated in the event that regular monitoring indicated that mitigation sand is contributing to the loss of, or covering of, cobble/boulder substrate. Results of monitoring completed to date do not indicate covering or loss of cobble/boulder substrate offshore from the geotube system. Table 1. Sconset Beach Video Survey June 18, 2020 - Bottom Sediment Coverage and Biota Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-250 91.9 1 50 5 30 15 45 Unidentified Branching Brown and Red Algae, Rockweed, Common Slipper Shells, Hermit Crabs TR-250 91.35 2 85 0 15 0 15 Unidentified Branching Brown and Red Algae, Barnacles, Shell Hash TR-250 91 3 100 0 0 0 0 Unidentified Floating Algae, Shell Hash TR-415 91.9 4 75 0 10 15 25 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Common Slipper Shells, Hermit Crab, Shell Hash TR-415 91.35 5 80 0 20 0 20 Rockweed, Irish Moss, Unidentified Branching Algae, Northern Star Coral, Hydroids, Rock Crab, Common Slipper Shells, Hermit Crabs TR-415 91 6 40 5 45 10 55 Irish Moss, Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Orange Encrusting Bryozoan, Surf Clam Shell, Common Slipper Shells, Barnacles TR-725 91.9 7 50 0 25 25 50 Unidentified Branching Brown and Red Algae, Common Slipper Shells, Hydroids, Bread Crumb Sponge, Barnacles TR-725 91.35 8 25 0 15 60 75 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Red Beard Sponge, Sulfur Sponge, Common Slipper Shells, Moon Snail, Shell Hash TR-725 91 9 20 10 35 35 70 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Common Slipper Shells, Bread Crumb Sponge, Sulfur Sponge, Hydroids, Moon Snail, Shell Hash Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-1050 91.9 10 30 35 25 10 35 Rockweed, Irish Moss, Common Slipper Shells, Unidentified Branching Brown and Red Algae, Surf Clam Shell, Barnacles, Shell Hash TR-1050 91.35 11 45 5 10 40 50 Unidentified Branching Brown and Red Algae, Rockweed, Bread Crumb Sponge, Barnacles, Shell Hash TR-1050 91 12 50 5 25 20 45 Unidentified Branching Brown and Red Algae, Rockweed, Bread Crumb Sponge, Northern Star Coral, Hydroids, Barnacles, Shell Hash, Black Seabass TR-1300 91.9 13 50 0 15 35 50 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Unidentified Floating Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Red Beard Sponge, Hydroids, Surf Clam Shell, Striped Bass TR-1300 91.35 14 20 5 35 40 75 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Northern Star Coral, Common Slipper Shells, Skate TR-1300 91 15 5 25 65 5 70 Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Hydroids, Common Slipper Shells, Barnacles, Hermit Crabs, Shell Hash Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-1595 91.9 16 20 10 55 15 70 Unidentified Branching Brown and Red Algae, Rockweed, Orange Encrusting Bryozoan, Sulfur Sponge, Bread Crumb Sponge, Hydroids, Hermit Crab, Common Slipper Shells, Shell Hash TR-1595 91.35 17 5 40 50 5 55 Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Northern Star Coral, Hydroids, Barnacles, Common Slipper Shells TR-1595 91 18 10 30 45 15 60 Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Rock Crab, Common Slipper Shells, Shell Hash, Black Seabass TR-1915 91.9 19 45 10 30 15 45 Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Hermit Crab, Common Slipper Shells, Shell Hash, Skate TR-1915 91.35 20 50 5 20 25 45 Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Barnacles, Shell Hash, Skate, Black Seabass TR-1915 91 21 50 20 15 15 30 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Northern Star Coral, Orange Encrusting Bryozoan, Hydroids, Surf Clam Shell, Common Slipper Shells Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-250 92.5 22 85 0 15 0 15 Unidentified Branching Brown and Red Algae, Unidentified Floating Algae TR-415 92.5 23 60 0 15 25 40 Unidentified Branching Brown and Red Algae, Shell Hash TR-725 92.5 24 65 0 5 30 35 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Orange Encrusting Bryozoan, Common Slipper Shells, Shell Hash, Barnacles TR-1050 92.5 25 45 10 25 20 45 Unidentified Branching Red Algae, Irish Moss, Barnacles, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Hermit Crabs, Common Slipper Shell, Shell Hash TR-1300 92.5 26 20 45 35 0 35 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Orange Encrusting Bryozoan, Hydroids, Surf Clam Shell, Common Slipper Shells, Hermit Crab TR-1595 92.5 27 60 0 30 10 40 Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Hydroids, Common Slipper Shells, Hermit Crab, Barnacles, Striped Bass, Shell Hash TR-1915 92.5 28 60 5 25 10 35 Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Hermit Crab, Common Slipper Shells, Skate, Black Seabass TR-250 90.6 29 100 0 0 0 0 Fine Shell Hash, Common Slipper Shell Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-415 90.6 30 75 0 10 15 25 Unidentified Branching Red and Brown Algae, Unidentified Floating Algae, Common Slipper Shells, Hermit Crabs, Surf Clam Shell, Shell Hash TR-725 90.6 31 45 0 15 40 55 Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hydroids, Common Slipper Shells, Moon Snail, Barnacles, Shell Hash TR-1050 90.6 32 25 35 10 30 40 Unidentified Branching Brown and Red Algae, Common Slipper Shells, Sulfur Sponge, Hydroids, Barnacles, Hermit Crabs, Shell Hash TR-1300 90.6 33 25 5 40 30 70 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hermit Crabs, Barnacles TR-1595 90.6 34 40 10 40 10 50 Irish Moss, Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Hermit Crabs, Northern Star Coral, Hydroids, Common Slipper Shells, Surf Clam Shell TR-1915 90.6 35 15 10 45 30 75 Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Rock Crab, Barnacles, Common Slipper Shells, Shell Hash Attachment A Video Survey Maps Figure 1 Underwater Video Trackline Map Figure 2 Percent Cobble/Boulder Present at Trackline Intersections (June 2020) Figure 3 Percent Cobble/Boulder Present at Trackline Intersections (November 2019) Figure 4 Percent Cobble/Boulder Present at Trackline Intersections (November 2018) Figure 5 Percent Cobble/Boulder Present at Trackline Intersections (June 2018) Figure 6 Percent Cobble/Boulder Present at Trackline Intersections (November 2017) Figure 7 Percent Cobble/Boulder Present at Trackline Intersections (June 2017) Figure 8 Percent Cobble/Boulder Present at Trackline Intersections (October 2016) Figure 9 Percent Cobble/Boulder Present at Trackline Intersections (June 2016) 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-725 TR-1,300 TR-1,595 TR-415 TR-250 TR-1,915 TR-1,050 19 20 21 35 27 16 17 18 34 26 13 15 33 25 10 24 7 8 9 31 4 5 6 30 22 1 2 3 29 23 11 12 32 14 28 G:\Projects\Lighthouse\2020\2020_Underwater_Survey\MXD\Underwater_Video_Transects_20200827.mxd Figure 1Underwater Video Trackline Map Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2019 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (June 2020) Video Drift Transects (June 2017) Geotube Area N orth A tl a nti c OceanService Layer Credits: Source: Esri,Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 92.5 90.6 TR-725 TR-1,300 TR-415TR-250 19 20 21 35 27 16 17 18 34 26 13 15 33 25 10 24 7 8 9 31 4 5 6 30 22 1 2 3 29 23 11 12 32 14 28 G:\Projects\Lighthouse\2020\2020_Underwater_Survey\MXD\Percent_Cobble_Boulder_Transects_20200921.mxd Figure 2Percent Cobble/Boulder Present at Trackline Intersections (June 2020) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2019 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (June 2020) Video Drift Transects (June 2017) Geotube Area Service Layer Credits: Source: Esri,Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N ort h A tl a n ti c Ocean TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 92.5 90.6 TR-725 TR-1,300 TR-415TR-250 3 1 22 30 6 5 23 31 9 8 7 24 25 10 11 12 32 26 13 14 15 33 27 16 17 18 34 28 19 21 35 204 G:\Projects\Lighthouse\2019\2019_Underwater_Survey\MXD\Percent_Cobble_Boulder_Transects_20200119.mxd Figure 3 Percent Cobble/Boulder Present at Trackline Intersections (November 2019) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2018 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (November 2019) Video Drift Transects (June 2017) Geotube Area Service Layer Credits: Source: Esri,DigitalGlobe, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N ort h A tl a nti c Ocean !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !(!( !( !( !( !( !( TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 90.6 92.5 22 23 24 25 26 27 28 19161310741 2 5 8 11 14 17 20 21 33 34 12 31 63 9 15 18 29 30 32 35 G:\Projects\Lighthouse\2018\2018_Underwater_Video\MXD\Percent_Cobble_Boulder_Transects_20190221.mxd Figure 4 Percent Cobble/Boulder Present at Trackline Intersections (November 2018) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2017 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 !(Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (November 2018) Video Drift Transects (June 2017) Geotube Area N orth A tl a nti c OceanNotes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-1,050 TR-1,915 TR-250 TR-415 TR-1,595 TR-1,300 TR-725 6 5 4 9 8 7 3 2 12 11 10 15 14 13 18 17 16 20 19 21 30 31 29 32 33 34 23 24 22 25 26 27 35 28 1 G:\Projects\Lighthouse\2018\2018_Underwater_Video\MXD\Percent_Cobble_Boulder_Transects_20180607.mxd Figure 5 Percent Cobble/Boulder Present at Trackline Intersections (June 2018) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2017 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects Geotube Area N orth A tl a nti c OceanNotes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100%TR-91.9 TR-91.35 TR-91.13 24 26 28 7 14 2322 41 52 3 6 29 30 31 32 33 34 35 21 15 9 25 10 8 11 17 19 2013 27 16 1812 G:\Projects\Lighthouse\2017\2017_Underwater_Survey\MXD\Percent_Cobble_Boulder_20171116_30.mxd Figure 6 Percent Cobble/Boulder Present at Trackline Intersections (November 2017) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: ESRI World Imagery °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 N orth A tl a nti c OceanNote: -Transects 92.5 and 90.6 were not video drift transects and were added to the figure so that coordinates could be pulled-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-1,050 TR-1,915 TR-250 TR-415 TR-1,595 TR-1,300 TR-725 Transect Survey Point Intersection Video Drift Transects Shoreline Survey Transects Video Drift Transects (June 2017) Geotube Area% Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% Transect Survey Point Intersection(no data collection November 2017) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 G:\Projects\Lighthouse\2017\2017_Underwater_Survey\MXD\Percent_Cobble_Boulder_20170928.mxd Figure 7 Percent Cobble/Boulder Present at Trackline Intersections (June 2017) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2016 NAIP Imagery, USDA FSA °0 375 750 Feet1 inch = 750 feetScale1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects Geotube Area% Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N orth A tl a nti c OceanNote: -Transects 92.5 and 90.6 were not video drift transects and were added to the figure so that coordinates could be pulled-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-1,050 TR-1,915 TR-250 TR-415 TR-1,595 TR-1,300 TR-725 TR-91.9 TR-91.35 TR-710 TR-1,265 TR-1,590 TR-400TR-250 TR-1,925 TR-1,020 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 G:\Projects\Lighthouse\2016\Percent_Cobble_Boulder_20161221.mxd Figure 8 Percent Cobble/Boulder Present at Trackline Intersections (October 2016) Sconset Beach Video Survey Nantucket, Massachusetts Data Source: Office of Geographic Information (MassGIS), Commonwealth of Massachusetts, Information Technology Division LEGEND °0 350 700 Feet1 inch = 700 feet Scale 1:8,400 Screenshot Location Video Drift Transects Shoreline Survey Transects Geotube Area % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% 90.6 92.5 TR-91.9 TR-91.35 TR-91.13 NorthAtlanticOcean Note: -Transects 92.5 and 90.6 were not videodrift transects and were added to the figureso that coordinates could be pulled-The NAD27 Datum was used for consistency withWoods Hole Group Shoreline Surveys Basemap: 2013 Orthophotography, MassGIS TR-91.9 TR-91.35 TR-91.13 TR-220 TR-370 TR-720 TR-1,020 TR-1,280 TR-1,580 TR-1,900 N orth A t la n ti c Oc e an18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 21 20 19 343332313029 35 272625242322 28 G:\Projects\Lighthouse\2016\Percent_Cobble_Boulder_20161012.mxd Figure 9 Percent Cobble/Boulder Present at Trackline Intersections (June 2016) Sconset Beach Video Survey Nantucket, Massachusetts Data Source: Office of Geographic Information (MassGIS), Commonwealth of Massachusetts, Information Technology Division LEGEND 0 350 700 Feet1 inch = 700 feet Scale1:8,400 Screenshot Location Video Drift Transects Shoreline Survey Transects Geotube Area % Cobble/Boulder 0-10% 10-25% 25-40% 40-55% 55-70% 70-85% 85-100% 90.6 92.5 Note: -Transects 92.5 and 90.6 were not videodrift transects and were added to the figureso that coordinates could be pulled-The NAD27 Datum was used for consistency withWoods Hole Group Shoreline Surveys Attachment B Video Survey Screenshot Figures 1 (Sand Waves 50%, Pebble 5%, Cobble 30%, Boulder 15%) Unidentified Branching Brown and Red Algae, Rockweed, Common Slipper Shells, Hermit Crabs 2 (Sand Waves 85%, Cobble 15%) Unidentified Branching Brown and Red Algae, Barnacles, Shell Hash 3 (Sand Waves 100%) Unidentified Floating Algae, Shell Hash 4 (Sand 75%, Cobble 10%, Boulder 15%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Common Slipper Shells, Hermit Crab, Shell Hash 5 (Flat Sand 80%, Cobble 20%) Rockweed, Irish Moss, Unidentified Branching Algae, Northern Star Coral, Hydroids, Rock Crab, Common Slipper Shells, Hermit Crabs 6 (Sand 40%, Pebble 5%, Cobble 45%, Boulder 10%) Irish Moss, Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Orange Encrusting Bryozoan, Surf Clam Shell, Common Slipper Shells, Barnacles 7 (Sand 50%, Cobble 25%, Boulder 25%) Unidentified Branching Brown and Red Algae, Common Slipper Shells, Hydroids, Bread Crumb Sponge, Barnacles 8 (Sand 25%, Cobble 15%, Boulder 60%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Red Beard Sponge, Sulfur Sponge, Common Slipper Shells, Moon Snail, Shell Hash 9 (Sand 20%, Pebble 10%, Cobble 35%, Boulder 35%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Common Slipper Shells, Moon Snail, Bread Crumb Sponge, Sulfur Sponge, Hydroids, Moon Snail, Shell Hash 10 (Sand 30%, Pebble 35%, Cobble 25%, Boulder 10%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Surf Clam Shell, Barnacles, Shell Hash 11 (Sand 45%, Pebble 5%, Cobble 10%, Boulder 40%) Unidentified Branching Brown and Red Algae, Rockweed, Bread Crumb Sponge, Barnacles, Shell Hash 12 (Sand 50%, Pebble 5%, Cobble 25%, Boulder 20%) Unidentified Branching Brown and Red Algae, Rockweed, Bread Crumb Sponge, Northern Star Coral, Hydroids, Barnacles, Shell Hash, Black Seabass 13 (Sand 50%, Cobble 15%, Boulder 35%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Red Beard Sponge, Hydroids, Surf Clam Shell, Striped Bass 14 (Sand 20%, Pebble 5%, Cobble 35%, Boulder 40%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Northern Star Coral, Common Slipper Shells, Skate 15 (Sand 5%, Pebble 25%, Cobble 65%, Boulder 5%) Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Hydroids, Common Slipper Shells, Barnacles, Hermit Crabs, Shell Hash 16 (Sand 20%, Pebble 10%, Cobble 55%, Boulder 15%) Unidentified Branching Brown and Red Algae, Rockweed, Orange Encrusting Bryozoan, Sulfur Sponge, Bread Crumb Sponge, Hydroids, Hermit Crab, Common Slipper Shell, Shell Hash 17 (Sand 5%, Pebble 40%, Cobble 50%, Boulder 5%) Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Northern Star Coral, Hydroids, Barnacles, Common Slipper Shells 18 (Sand 10%, Pebble 30%, Cobble 45%, Boulder 15%) Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Rock Crab, Common Slipper Shells, Shell Hash, Black Seabass 19 (Sand 45%, Pebble 10%, Cobble 30%, Boulder 15%) Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Hermit Crab, Shell Hash, Skate 20 (Sand 50%, Pebble 5%, Cobble 20%, Boulder 25%) Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Barnacles, Shell Hash, Skate, Black Seabass 21 (Sand 50%, Pebble 20%, Cobble 15%, Boulder 15%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Northern Star Coral, Orange Encrusting Bryozoan, Hydroids, Surf Clam Shell, Common Slipper Shells 22 (Sand Waves 85%, Cobble 15%) Unidentified Branching Algae, Unidentified Floating Algae 23 (Sand Waves 60%, Cobble 15%, Boulder 25%) Unidentified Branching Brown and Red Algae, Shell Hash 24 (Sand 65%, Cobble 5%, Boulder 30%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Orange Encrusting Bryozoan, Common Slipper Shells, Shell Hash, Barnacles 25 (Sand 45%, Pebble 10%, Cobble 25%, Boulder 20%) Unidentified Branching Brown and Red Algae, Irish Moss, Barnacles, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Hermit Crabs, Common Slipper Shell, Shell Hash 26 (Sand 20%, Pebble 45%, Cobble 35%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Orange Encrusting Bryozoan, Hydroids, Surf Clam Shell, Common Slipper Shells, Hermit Crab 27 (Sand 60%, Cobble 30%, Boulder 10%) Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Hydroids, Common Slipper Shells, Hermit Crab, Barnacles, Striped Bass, Shell Hash 28 (Sand 60%, Pebble 5%, Cobble 25%, Boulder 10%) Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Hermit Crab, Common Slipper Shells, Skate, Black Seabass 29 (Sand Waves 100%) Fine Shell Hash, Common Slipper Shell 30 (Sand 75%, Cobble 10%, Boulder 15%) Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Hermit Crabs, Surf Clam Shell, Shell Hash 31 (Sand 45% Cobble 15%, Boulder 40%) Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hydroids, Common Slipper Shells, Moon Snail, Barnacles, Shell Hash 32 (Sand 25%, Pebble 35%, Cobble 10%, Boulder 30%) Unidentified Branching Brown and Red Algae, Common Slipper Shells, Sulfur Sponge, Hydroids, Barnacles, Hermit Crabs, Shell Hash 33 (Sand 25%, Pebble 5%, Cobble 40%, Boulder 30%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hermit Crabs, Barnacles 34 (Sand 40%, Pebble 10%, Cobble 40%, Boulder 10%) Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Orange Encrusting Bryozoan, Hydroids, Northern Star Coral, Common Slipper Shells, Surf Clam Shell 35 (Sand 15%, Pebble 10%, Cobble 45%, Boulder 30%) Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Rock Crab, Barnacles, Common Slipper Shells, Shell Hash Submitted to:Nantucket Conservation Commission2 Bathing Beach RoadNantucket, Massachusetts 02554 Submitted by:Siasconset Beach Preservation FundP.O. Box 2279Nantucket, Massachusetts 02584 March 2021 Sconset Beach Underwater Video Survey Report Prepared by: Epsilon Associates, Inc. 3 Mill & Main Place, Suite 250 Maynard, Massachusetts 01754 CR Environmental, Inc. 639 Boxberry Road East Falmouth, Massachusetts 02536 Nantucket, MA Sconset Beach Underwater Video Survey Report Nantucket, MA Submitted to: Nantucket Conservation Commission Submitted by: Siasconset Beach Preservation Fund Prepared by: Epsilon Associates, Inc. CR Environmental, Inc. March 2021 Table of Contents 21597/Sconset Geotextile Tube Project i Table of Contents Underwater Video Survey Report Epsilon Associates, Inc. Table of Contents UNDERWATER VIDEO SURVEY REPORT 1 1.0 Introduction 1 2.0 Vessel Operations, Navigation, and Survey Design 1 3.0 Survey Data Acquisition and Processing 2 4.0 Survey Results 3 4.1 Biota 4 4.2 Bottom Sediment Coverage 5 5.0 Conclusions 7 ATTACHMENT A Video Survey Maps Figure 1 Underwater Video Trackline Map Figure 2 Percent Cobble/Boulder Present at Trackline Intersections (October 2020) Figure 3 Percent Cobble/Boulder Present at Trackline Intersections (June 2020) Figure 4 Percent Cobble/Boulder Present at Trackline Intersections (November 2019) Figure 5 Percent Cobble/Boulder Present at Trackline Intersections (November 2018) Figure 6 Percent Cobble/Boulder Present at Trackline Intersections (June 2018) Figure 7 Percent Cobble/Boulder Present at Trackline Intersections (November 2017) Figure 8 Percent Cobble/Boulder Present at Trackline Intersections (June 2017) Figure 9 Percent Cobble/Boulder Present at Trackline Intersections (October 2016) Figure 10 Percent Cobble/Boulder Present at Trackline Intersections (June 2016) ATTACHMENT B Video Survey Screenshot Figures LIST OF TABLES Table 1 Sconset Beach Video Survey – Bottom Sediment Coverage and Biota Underwater Video Survey Report 21597/Sconset Geotextile Tube Project 1 Underwater Survey Report Epsilon Associates, Inc. UNDERWATER VIDEO SURVEY REPORT 1.0 Introduction On October 22, 2020, CR Environmental, Inc. (“CR”) and Epsilon Associates, Inc. (“Epsilon”) on behalf of the Siasconset Beach Preservation Fund (“SBPF”) conducted the Fall 2020 underwater video survey offshore from the geotube system, at the base of the bluff fronting 87-105 Baxter Road, Nantucket, MA. These geotubes were installed in December 2013 and January 2014 (with an approximate length of 852-feet) and were then expanded in November and December 2015 to a total length of 947-feet. As part of the Order of Conditions (DEP File No. SE48-2824) for the geotube project, underwater video monitoring is required as described in Special Conditions 28 of the Order of Conditions, which reads in part: “… Photographs and/or video shall be taken along the transects within the project area and the area directly adjacent to the project area. The underwater video shall be able to characterize the bottom sediments, species present and relative abundance including the calculating of the percent cobble where appropriate…” The purpose of the underwater video survey monitoring is to evaluate if mitigation sand that washes off the sand template and carried into the littoral system, i.e. that sand on top of the geotextile tubes, is causing a significant alteration or loss of cobble/boulder habitat located directly offshore of the geotube system. The October 2020 survey marks the ninth underwater video survey since the geotubes were installed. This document describes the data acquisition and processing methods, equipment used for the survey, and survey results. 2.0 Vessel Operations, Navigation, and Survey Design The underwater video monitoring survey activity was conducted on October 22, 2020 from the 35-foot fishing vessel Althea K. The vessel was configured to accommodate navigation and video acquisition systems and was furnished with a portable generator to power survey electronics. The survey crew on the underwater video survey consisted of a boat captain and one mate, a field biologist, two oceanographic technicians, and an environmental scientist. The survey was conducted to visually to characterize bottom sediments, biota, and type of bottom cover offshore from the geotube project site (see Figures 1-10 in Attachment A). Navigation for the survey was accomplished using a Hemisphere VS-110 12-channel sub-meter (GPS) system. The GPS system was interfaced to a laptop computer running HYPACK 2013A hydrographic survey software. HYPACK recorded vessel position, water depth, and provided a steering display for the vessel captain. During the October 2020 survey, a total of thirty-five (35) 2- to 4-minute video drifts were performed and bottom coverage was obtained at all 35 survey point intersections. The air 21597/Sconset Geotextile Tube Project 2 Underwater Survey Report Epsilon Associates, Inc. temperature was between 60- to 65-degrees Fahrenheit, wind speed at approximately 5-knots (nautical miles per hour), swells at 1- to 2-feet for the first three hours of the survey; conditions changed later in the day with swells of 1-foot following the change in tide. Due to these workable ocean conditions, good quality underwater video data were obtained at most of the stations. At a few of the stations, the vessel was forced to maneuver (power) in the seas to achieve the correct drift direction. In these cases, the video sled was at time towed sideways and the video data quality reduced. Additionally, at times the vessel and sled speed were too fast causing reduction in video data quality. However, classification of the major substrate types and biota could still be performed by selecting the highest available video quality near each survey point intersection. 3.0 Survey Data Acquisition and Processing Underwater video operations were conducted using a real-time high-resolution color underwater video data acquisition system which permitted the characterization of bottom habitat and the species present. Maps showing the location of the video transects offshore are provided in Attachment A. Underwater video data was collected with CR’s portable towed video sled consisting of a lightweight aluminum frame, Outland Technologies’ high-resolution low light color camera, and two wide-angle 250-watt lights with variable output control. The video camera was cabled to the surface to an OTI-960 DVR recorder and topside monitor. A GoPro 4 Black color camera with internal data storage was also mounted to the towed sled and recorded footage simultaneously with the Outland camera as a second source of data. The video sled was lowered and raised using a lifting davit and lobster pot hauler mounted on the stern and the height of the system off the bottom was continually adjusted to achieve the best bottom coverage and video quality. The vessel speed varied between 0.5 to 1.7 knots. Mounted lasers on the video sled frame were used for scaling purposes, and a calibrated scale template was overlain on the video frame or screen captures. The distance between template grid lines in both the X and Y directions was equal to approximately 6 inches. This grid system permitted scaling and estimating of bottom biota and determining substrate classes and their percent coverage. When the video camera was one foot off the bottom, the viewing area of the camera was approximately 1.5 ft x 1.5 ft (18 in. x 18 in.) and the video quality was optimal for bottom sediment characterizations and biota identifications. HYPACK navigation files were recorded during each video drift. Video data were transferred to a processing computer and viewed by a staff scientist at Epsilon. Representative screen captures (frame images) were extracted along each video drift to characterize bottom sediments and biota offshore from the project. To analyze the bottom characteristics of each video drift, screenshots were taken at points as close as possible to the June 2017 survey’s seven shore-parallel and three shore-perpendicular transect intersections (Figure 8). The October 2020 survey collected video drifts over these intersections. In addition, coordinates for two previously established, shore-perpendicular survey 21597/Sconset Geotextile Tube Project 3 Underwater Survey Report Epsilon Associates, Inc. transects (90.6 and 92.5) were added to the figure, then screenshots were pulled from points nearest the June 2017 survey’s intersections between those two transects and the seven shore- parallel transects. Using the GPS data collected simultaneously with the video, the time stamps for each of these intersection points were extracted into a spreadsheet. The intersection coordinates were found by scrolling through the video until the time matched as closely as possible to the time recorded to the GPS data coordinates. Sometimes the view closest to the intersection point was not optimal due to the camera position being either too far from or too close to the bottom, or the video sled was towing on its side so that the scale lasers were not visible. In these instances, a screenshot was captured as close as possible to the intersect position where the view was improved. The scale grid was overlain on the video view. Live video (not shown) was reviewed concurrent with the screenshots for the most accurate assessment of biota and bottom substrate. Once the scale grid was in place, the bottom coverage was classified along a gradient of grain sizes using the Auster hierarchical approach (Auster, 1998). Bottom sediment and habitat types within the offshore area included: flat sand, sand ripples, sand waves, pebble, cobble, and boulder. The percent cover for bottom sediment types present in each screenshot was approximated using the scale grid. Each of the nine grid sections was reviewed and bottom sediment was categorized individually, then an average was calculated for the complete screenshot. The percent bottom type numbers were rounded to the nearest five percent for presentation in Table 1. To maintain consistency across the 35 screenshots, the same individual reviewed all final percent cover estimates concurrently with the live video. Each screenshot is given three identifiers in Table 1. First, the intersection location is indicated by the name of the transect, which is the same as the distance in feet from the shore (see Figure 1). The October 2020 intersection locations followed the June 2017 survey transect, therefore these distance labels are unchanged (see Figures 1 and 2). Second, the shore perpendicular transect that crosses the shore-parallel transect is listed. Lastly, each screenshot is given a number consistent with the order of all the past surveys’ intersection numbering (i.e. the October 2020 intersection numbering is consistent with all previous surveys, back to June 2016). 4.0 Survey Results Table 1 provides the bottom sediment coverage and biota present in the underwater video drifts collected in October 2020 offshore from the geotube system. Screenshots captured from the underwater video are numbered 1-35 and are presented in Attachment B – Video Survey Screenshot Figures. Note, the October 2020 screenshot numbering 1-35 corresponds to the intersection numbers depicted on Figure 1 – Underwater Video Trackline Map, found in Attachment A – Figures. Results of each screenshot are tabulated in terms of bottom sediment coverage percentages and biota. Screenshots between intersection numbers 1 through 21 were taken at intersection locations between shore-parallel and shore-perpendicular survey transects established for the 21597/Sconset Geotextile Tube Project 4 Underwater Survey Report Epsilon Associates, Inc. underwater video monitoring, while screenshots between intersection numbers 22 through 35 used shore-perpendicular transect locations taken from the previously-established Woods Hole Group shoreline monitoring transects. Table 1 provides an assessment of the biota present and the bottom type at each of the 35 screenshot locations. 4.1 Biota During the underwater video survey, 14 invertebrate species, two fish species, and five marine plant and algal species were observed. The dominant biota across all transects included unidentified branching brown algae, unidentified branching red algae, Irish moss red algae, rockweed brown algae, hydroids, common slipper shells, bread crumb sponge, sulfur (boring) sponge, red beard sponge, and hermit crabs. Additional biota observed at the transect intersections included northern star coral, invasive white tunicate, red dulse, sand sponge, orange encrusting bryozoan, rock crab, comb jellyfish and surf clam shell. Additionally, while either not captured or identifiable in the intersection screenshots, the following biota were observed during the video survey fieldwork: common skate, moonsnail, and black seabass. ♦ Branching brown and red algae were abundant and were observed in the entire survey area. This was likely Irish moss and rockweed algae, which are often difficult to distinguish if the camera is not close, or the sled speed is not slow enough. ♦ Sulfur sponge, bread crumb sponge, and hydroids were abundant and were found in nearly every transect. ♦ Hermit crabs were the most abundant invertebrates observed over the whole survey area and were observed in greater numbers in the offshore cobble/boulder habitats. ♦ Common skates were observed throughout the survey area proximate to 11 intersections. ♦ Common slipper shells were abundant in the entire survey area, mostly beyond 700 feet offshore. ♦ Moonsnails were observed near intersections 10 and 19. ♦ Rock crabs were observed in all transects, primarily near intersections with a higher cobble/boulder percentage. ♦ Black seabass were observed in all transects in varying life stages (juveniles to fully- mature). ♦ Unidentified fish were observed in all transects, except for the closest to shore: TR-250 and TR-415. These fish may have been black seabass but were unidentifiable in the video. 21597/Sconset Geotextile Tube Project 5 Underwater Survey Report Epsilon Associates, Inc. Overall, the October 2020 survey continues to show a biologically productive habitat is located just offshore from the geotube bank stabilization system. The June 2016, October 2016, June 2017, November 2017, June 2018, November 2018, November 2019, and June 2020 surveys had similar dominant biota to the October 2020 survey of the branching brown and red algae, sulfur sponge, bread crumb sponge, and common slipper shells. Besides some expected seasonal variability of the species present, the October 2020 survey had results consistent with the dominant biota observed in the Fall surveys in 2016, 2017, and 2018, and there is no indication of adverse effect of marine biota from the geotube system and sand contributed off the sand template. 4.2 Bottom Sediment Coverage In addition to biota, Table 1 listed the bottom coverage types observed in the survey area. The bottom sediment categories include sand flat, sand waves, sand ripples, pebble, cobble, and boulder. An additional category shows the cobble and boulder percentage combined into one percentage. These percentages were combined to show a more representative picture of the bottom substrate differences across the survey area. These combined data were used to create Figure 2, which shows the abundance of cobble/boulder from the October 2020 survey. The cobble/boulder surface was calculated using a geoprocessing tool that interpolates a surface from points using an inverse distance weighted (IDW) technique. The percentage of cobble/boulder coverage ranges from green gradients colors (0-24%), to blue gradient colors (25-69%), and finally to red gradient colors (70-100%) (Figure 2). The percent cobble/boulder coverage varies significantly across the survey area, from <10% to 80%. In October 2020, most of the survey area has 25-54% cobble/boulder coverage. A comparison was made between this October 2020 survey and the 2016, 2017, 2018, 2019, and June 2020 survey results. An understanding of the natural variability in the nearshore environment provide important context for interpreting results between surveys. Although the presence of cobble/boulder habitat is widespread just offshore from the geotextile tubes, there is significant natural variability within this habitat. As explained in the October 2016 survey report, the percent cobble/boulder coverage can vary by 20% or more when reviewing video from locations even one or two seconds (this time correlates to about 4 to 10 feet) either before or after the intersection point selected for screenshot capture. While each survey collects video data along similar transects, it is nearly impossible to collect video data at absolutely identical locations between surveys, due to both minor variation in the position of the vessel during video survey data collection and due to the occasional need to adjust screenshot capture locations by one or two seconds in order to capture the clearest view. Accordingly, some variation is expected in the cobble/boulder percent cover in each survey, since each survey will represent slightly different locations. With these considerations in mind, the results of the October 2020 survey were compared with the previous eight surveys conducted in June 2016, October 2016, June 2017, November 2017, 21597/Sconset Geotextile Tube Project 6 Underwater Survey Report Epsilon Associates, Inc. June 2018, November 2018, November 2019, and June 2020. Following are the key findings from this comparison: ♦ All nine surveys showed that most of the sampling area has 25-54% cobble coverage. ♦ All nine surveys indicated that the nearshore survey areas had the lowest cobble/boulder percent coverage, from <10% to 24%. ♦ The cobble/boulder cover was found to increase farther offshore. In the October 2020, November 2019, November 2018, June 2018, November 2017, and June 2017 surveys, the increased cobble/boulder cover started closer to shore (at about 415 feet offshore) than in the June 2016 and October 2016 surveys (where increased cobble/boulder coverage was observed starting around 700 feet offshore). ♦ All eight surveys identified the same general areas as having the highest concentration of cobble/boulder: o June 2016 intersection 9, 11, 12, 15, 33, and 35 had 65-90% cobble/boulder coverage, o October 2016 intersections 9, 11, 15, 22, and 35 had 65-90% cobble/boulder coverage, o June 2017 intersections 6, 8, 9, 11, 13, 33, and 35 had 65-85% cobble/boulder coverage, o November 2017 intersections 8, 13, 18, 33, and 35 had 65-95% cobble/boulder o June 2018 intersections 7, 8, 11, 12, 13, 15, 17, 18, 33, and 35 had 65-100% cobble/boulder coverage. o November 2018 intersections 8, 9, 11, 13, 15, 18, 31, 33, and 35 had 65-100% cobble/boulder coverage o November 2019 intersections 8, 9, 14, 15, 16, 18, 33, and 35 had 65-85% cobble/boulder coverage. o June 2020 intersections 8, 9, 14, 15, 16, 18, 33, and 35 had 60-85% cobble/boulder coverage. o October 2020 intersections 8, 9, 14, 15, 16, 18, 31, 33, and 35 had 60-85% cobble/boulder coverage. While these results were generally consistent with each other, there was some variation. As explained above, the differences in percent cobble/boulder coverage between the nine surveys are considered to be the results of natural variability. A couple locations where the percent cobble/boulder appeared to decrease in October 2020 from the previous surveys (intersections 21597/Sconset Geotextile Tube Project 7 Underwater Survey Report Epsilon Associates, Inc. 4, 8, 9, 14, 16, 23, 24, 26, and 27). These intersections were checked, and all were within 10% of the past three surveys, except intersection 4. Intersection 4 decreased approximately 15% from the June 2020 survey, however, is within 5% of the November 2018 and November 2019 surveys. Intersections 2, 6, 12, 20, 21, 30, 31 and 34 showed increased cobble/boulder percentages than the previous survey with a difference of 5-10%. These observations suggest that the apparent difference between the two 2016 surveys, the two 2017 surveys, the two 2018 surveys, the 2019 survey, and two 2020 surveys reflect the slightly different locations chosen for screenshot capture between the nine surveys, and is not indicative of change in cobble/boulder habitat. Overall, the October 2020 underwater video survey indicates that a productive widespread cobble/boulder habitat area is located just offshore from the geotextile tubes, and there is no indication that such habitat is being covered by the sand mitigation. 5.0 Conclusions An underwater video survey of the area located just offshore of the geotube system and surrounding areas was conducted in October 2020, approximately 7 years after the installation of the geotextile tubes at the base of the bluff. During this survey, 13 invertebrate species, three fish species, and five marine plant and algal species were observed. The dominant biota across all transects included branching brown algae, branching red algae, Irish moss red alga, rockweed brown algae, hydroids, common slipper shells, bread crumb sponge, sulfur (boring sponge), red beard sponge, and hermit crabs. Rock crabs, northern star coral, and sand sponge were common in most of the offshore survey area. Common skates and black seabass were also observed within the offshore survey area. Besides some expected seasonal variability of the species present, the October 2020 survey continues to show biologically productive benthic habitat just offshore from the geotextile tubes, and there is no indication of adverse effect on marine biota from the geotextile tube project. The bottom sediment type was also surveyed. The percent cobble/boulder coverage varied significantly across the survey area, from <10% to 75% with increasing percentage of cobble/boulder coverage correlated with increasing distance offshore. The October 2020 survey results were broadly consistent with the survey results from 2016, 2017, 2018, 2019, and June 2020: most of the survey area in October 2020 had 25-54% cobble/boulder coverage, similar to the previous surveys, and localized areas of higher cobble/boulder coverage were found at similar locations in all nine surveys. While some variation was found between the nine surveys, an analysis of the survey results described in the October 2016 survey report showed that the percentage of cobble/boulder coverage at video locations within just a few feet of one another could vary by up to 20-30%, indicating that much of the observed differences between the nine surveys can be attributed to natural variability. Based on the continued prevalence of cobble/boulder habitat located directly offshore of the geotextile tube Project, there is no evidence that cobble/boulder habitat is being covered by mitigation sand. 21597/Sconset Geotextile Tube Project 8 Underwater Survey Report Epsilon Associates, Inc. As described in the June 2016 report, the volume of sand contributed off the template is minimal compared to the volume of native sand moving in the littoral system and shoal movements. It is our ongoing recommendation that a reduction in the frequency of underwater video monitoring is warranted, as meaningful data could only be generated in the event that regular monitoring indicated that mitigation sand is contributing to the loss of, or covering of, cobble/boulder substrate. Results of monitoring completed to date do not indicate covering or loss of cobble/boulder substrate offshore from the geotube system. Table 1. Sconset Beach Video Survey October 22, 2020 - Bottom Sediment Coverage and Biota Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-250 91.9 1 50 5 35 10 45 Unidentified Branching Brown and Red Algae, Common Slipper Shells, Hermit Crabs, Bread Crumb Sponge, Hydroids, Rock Crab, Shell Hash TR-250 91.35 2 85 0 15 0 15 Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Common Slipper Shells, Barnacles, Clam Shell, Black Sea Bass, Rock Crab, Barnacles TR-250 91 3 100 0 0 0 0 Unidentified Floating Algae, Hermit Crabs, Shell Hash TR-415 91.9 4 85 0 15 0 10 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Hermit Crab, Black Sea Bass, Rock Crab, Skate, Shell Hash, Common Slipper Shells TR-415 91.35 5 80 0 15 5 20 Irish Moss, Rockweed, Red Dulse, Unidentified Branching Brown and Red Algae, Hydroids, Orange Encrusting Bryozoan, Common Slipper Shells, Hermit Crab, Surf Clam Shell TR-415 91 6 50 0 35 15 50 Irish Moss, Unidentified Branching Brown and Red Algae, Common Slipper Shell, Bread Crumb Sponge, Sulfur Sponge, Red Beard Sponge, Hermit Crabs, Skate TR-725 91.9 7 55 0 30 15 45 Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Common Slipper Shells, Rock Crab, Hermit Crabs, Black Sea Bass Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-725 91.35 8 25 5 15 55 70 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Rock Crab, Hermit Crabs, Skate, Common Slipper Shells, Shell Hash TR-725 91 9 25 10 30 35 65 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Red Beard Sponge, Sulfur Sponge, Hydroids, Hermit Crab, Rock Crab, Black Sea Bass, Common Slipper Shell, Shell Hash TR-1050 91.9 10 50 10 30 10 40 Rockweed, Irish Moss, Shell Hash, Unidentified Branching Brown and Red Algae, Hermit Crab, Common Slipper Shells, Rock Crab, Moon Snail, Rock, Surf Clam Shell TR-1050 91.35 11 45 5 10 40 50 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Bread Crumb Sponge, Hermit Crab, Shell Hash, Unidentified Fish TR-1050 91 12 50 0 15 35 50 Rockweed, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Northern Star Coral, Hydroids, Rock Crab, Hermit Crabs, Black Sea Bass TR-1300 91.9 13 45 0 20 35 55 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hydroids, Skate, Common Slipper Shell, Shell Hash Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-1300 91.35 14 15 15 35 35 70 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Northern Star Coral, Common Slipper Shells, Shell Hash TR-1300 91 15 5 25 60 10 70 Irish Moss, Rockweed, Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hermit Crabs, Hydroids, Common Slipper Shells, Skate, Rock Crab, Comb Jellyfish TR-1595 91.9 16 20 15 50 15 65 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Hydroids, Orange Encrusting Bryozoan, Hermit Crabs, Rock Crab, Skates, Shell Hash TR-1595 91.35 17 35 10 45 10 55 Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Sulfur Sponge, Bread Crumb Sponge, Sand Sponge, Red Beard Sponge, Northern Star Coral, Orange Encrusting Bryozoan, Common Slipper Shells, Hermit Crabs, Rock Crab, Shell Hash TR-1595 91 18 25 15 40 20 60 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Sand Sponge, Orange Encrusting Bryozoan, Common Slipper Shells, Hermit Crabs, Shell Hash Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-1915 91.9 19 45 10 25 20 45 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Red Beard Sponge, Unidentified Fish, Common Slipper Shells, Hermit Crabs, Rock Crab, Moon Snail, Black Sea Bass, Shell Hash TR-1915 91.35 20 40 10 25 25 50 Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Sand Sponge, Hydroids, Common Slipper Shells, Shell Hash TR-1915 91 21 50 15 25 10 35 Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Sand Sponge, Hydroids, Red Beard Sponge, Hermit Crabs, Common Slipper Shells, Shell Hash TR-250 92.5 22 85 0 15 0 15 Unidentified Branching Algae, Unidentified Floating Algae, Shell Hash, Hermit Crabs TR-415 92.5 23 60 5 15 20 35 Irish Moss, Unidentified Branching Brown and Red Algae, Hermit Crabs, Shell Hash, Unidentified Floating Algae TR-725 92.5 24 65 5 10 20 30 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Rock Crabs, Hermit Crabs, Shell Hash, Unidentified Fish Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-1050 92.5 25 50 10 20 20 40 Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Common Slipper Shells, Hermit Crabs, Black Sea Bass, Shell Hash TR-1300 92.5 26 15 55 30 0 30 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Orange Encrusting Bryozoan, Red Beard Sponge, Common Slipper Shells, Hermit Crabs, Surf Clam Shell TR-1595 92.5 27 65 0 20 15 35 Irish Moss, Unidentified branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Common Slipper Shells, Skate, Hermit Crabs, Hydroids, Common Slipper Shells, Shell Hash TR-1915 92.5 28 40 25 30 5 35 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Invasive White Tunicate, Red Beard Sponge, Common Slipper Shells, Hermit Crabs, Unidentified Fish TR-250 90.6 29 100 0 0 0 0 Unidentified Floating Algae, Hermit Crabs, Shell Hash TR-415 90.6 30 70 0 15 15 30 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hydroids, Hermit Crabs, Barnacles, Surf Clam Shell Shore- Parallel Transect # Shore- Perpendicular Transect # Screenshot Label Bottom Sediment Coverage (Percent) Cobble + Boulder (Percent) Biota Flat Sand/Sand Waves/Sand Ripples Pebble Cobble Boulder TR-725 90.6 31 35 5 20 40 60 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Hydroids, Invasive White Tunicate, Skate, Unidentified Fish, Common Slipper Shells, Shell Hash TR-1050 90.6 32 35 25 10 30 40 Unidentified Branching Brown and Red Algae, Hermit Crab, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Northern Star Coral, Hydroids, Common Slipper Shells, Hermit Crabs, Shell Hash TR-1300 90.6 33 30 0 30 40 70 Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Hydroids, Rock Crab, Hermit Crabs, Skate, Shell Hash TR-1595 90.6 34 40 5 35 20 55 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Red Beard Sponge, Northern Star Coral, Common Slipper Shells, Hermit Crabs, Rock Crab, Skate, Shell Hash TR-1915 90.6 35 15 10 50 25 75 Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Red Beard Sponge, Common Slipper Shells, Hermit Crabs, Rock Crab, Black Sea Bass Attachment A Video Survey Maps Figure 1 Underwater Video Trackline Map Figure 2 Percent Cobble/Boulder Present at Trackline Intersections (October 2020) Figure 3 Percent Cobble/Boulder Present at Trackline Intersections (June 2020) Figure 4 Percent Cobble/Boulder Present at Trackline Intersections (November 2019) Figure 5 Percent Cobble/Boulder Present at Trackline Intersections (November 2018) Figure 6 Percent Cobble/Boulder Present at Trackline Intersections (June 2018) Figure 7 Percent Cobble/Boulder Present at Trackline Intersections (November 2017) Figure 8 Percent Cobble/Boulder Present at Trackline Intersections (June 2017) Figure 9 Percent Cobble/Boulder Present at Trackline Intersections (October 2016) Figure 10 Percent Cobble/Boulder Present at Trackline Intersections (June 2016) 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-725 TR-1,300 TR-1,595 TR-415 TR-250 TR-1,915 TR-1,050 22 1 2 3 29 23 4 5 6 30 24 7 8 9 31 25 10 11 12 32 33 15 14 13 26 34 18 17 16 27 35 21 20 19 28 G:\Projects\Lighthouse\2020\2020_Underwater_Survey\MXD\Underwater_Video_Transects_20201216.mxd Figure 1Underwater Video Trackline Map Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2019 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (October 2020) Video Drift Transects (June 2017) Geotube Area N orth A tl a nti c OceanService Layer Credits: Source: Esri,Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 92.5 90.6 TR-725 TR-1,300 TR-415TR-250 22 1 2 3 29 23 4 5 6 30 24 7 8 9 31 25 10 11 12 32 33 15 14 13 26 34 18 17 16 27 35 21 20 19 28 G:\Projects\Lighthouse\2020\2020_Underwater_Survey\MXD\Percent_Cobble_Boulder_Transects_20201223.mxd Figure 2Percent Cobble/Boulder Present at Trackline Intersections (October 2020) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2019 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (October 2020) Video Drift Transects (June 2017) Geotube Area Service Layer Credits: Source: Esri,Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N ort h A tl a n ti c Ocean TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 92.5 90.6 TR-725 TR-1,300 TR-415TR-250 19 20 21 35 27 16 17 18 34 26 13 15 33 25 10 24 7 8 9 31 4 5 6 30 22 1 2 3 29 23 11 12 32 14 28 G:\Projects\Lighthouse\2020\2020_Underwater_Survey\MXD\Percent_Cobble_Boulder_Transects_20200921.mxd Figure 3 Percent Cobble/Boulder Present at Trackline Intersections (June 2020) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2019 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (June 2020) Video Drift Transects (June 2017) Geotube Area Service Layer Credits: Source: Esri,Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N ort h A tl a n ti c Ocean TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 92.5 90.6 TR-725 TR-1,300 TR-415TR-250 3 1 22 30 6 5 23 31 9 8 7 24 25 10 11 12 32 26 13 14 15 33 27 16 17 18 34 28 19 21 35 204 G:\Projects\Lighthouse\2019\2019_Underwater_Survey\MXD\Percent_Cobble_Boulder_Transects_20200119.mxd Figure 4 Percent Cobble/Boulder Present at Trackline Intersections (November 2019) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2018 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (November 2019) Video Drift Transects (June 2017) Geotube Area Service Layer Credits: Source: Esri,DigitalGlobe, GeoEye, EarthstarGeographics, CNES/Airbus DS, USDA,USGS, AeroGRID, IGN, and the GISUser Community Notes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N ort h A tl a nti c Ocean !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !(!( !( !( !( !( !( TR-725 TR-1,300 TR-1,595 TR-415TR-250 TR-1,915 TR-1,050 TR-91.13 TR-91.35 TR-91.9 90.6 92.5 22 23 24 25 26 27 28 19161310741 2 5 8 11 14 17 20 21 33 34 12 31 63 9 15 18 29 30 32 35 G:\Projects\Lighthouse\2018\2018_Underwater_Video\MXD\Percent_Cobble_Boulder_Transects_20190221.mxd Figure 5 Percent Cobble/Boulder Present at Trackline Intersections (November 2018) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2017 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 !(Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects (November 2018) Video Drift Transects (June 2017) Geotube Area N orth A tl a nti c OceanNotes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-1,050 TR-1,915 TR-250 TR-415 TR-1,595 TR-1,300 TR-725 6 5 4 9 8 7 3 2 12 11 10 15 14 13 18 17 16 20 19 21 30 31 29 32 33 34 23 24 22 25 26 27 35 28 1 G:\Projects\Lighthouse\2018\2018_Underwater_Video\MXD\Percent_Cobble_Boulder_Transects_20180607.mxd Figure 6 Percent Cobble/Boulder Present at Trackline Intersections (June 2018) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2017 World Imagery, ESRI °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects Geotube Area N orth A tl a nti c OceanNotes: -Transects 92.5 and 90.6 were not video drifttransects and were added to the figure so thatcoordinates could be pulled.-Transects TR-91.9, TR-91.35, and TR-91.13 areJune 2017 video drift transects and were added to the figure so that coordinates could be pulled.-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys. % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100%TR-91.9 TR-91.35 TR-91.13 24 26 28 7 14 2322 41 52 3 6 29 30 31 32 33 34 35 21 15 9 25 10 8 11 17 19 2013 27 16 1812 G:\Projects\Lighthouse\2017\2017_Underwater_Survey\MXD\Percent_Cobble_Boulder_20171116_30.mxd Figure 7 Percent Cobble/Boulder Present at Trackline Intersections (November 2017) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: ESRI World Imagery °0 375 750 Feet1 inch = 750 feet Scale 1:9,000 N orth A tl a nti c OceanNote: -Transects 92.5 and 90.6 were not video drift transects and were added to the figure so that coordinates could be pulled-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-1,050 TR-1,915 TR-250 TR-415 TR-1,595 TR-1,300 TR-725 Transect Survey Point Intersection Video Drift Transects Shoreline Survey Transects Video Drift Transects (June 2017) Geotube Area% Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% Transect Survey Point Intersection(no data collection November 2017) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 G:\Projects\Lighthouse\2017\2017_Underwater_Survey\MXD\Percent_Cobble_Boulder_20170928.mxd Figure 8 Percent Cobble/Boulder Present at Trackline Intersections (June 2017) Sconset Beach Video Survey Nantucket, Massachusetts LEGEND Basemap: 2016 NAIP Imagery, USDA FSA °0 375 750 Feet1 inch = 750 feetScale1:9,000 Transect Survey Point Intersection Shoreline Survey Transects Video Drift Transects Geotube Area% Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% N orth A tl a nti c OceanNote: -Transects 92.5 and 90.6 were not video drift transects and were added to the figure so that coordinates could be pulled-The NAD27 Datum was used for consistency with Woods Hole Group Shoreline Surveys 92.5 90.6 TR-91.9 TR-91.35 TR-91.13 TR-1,050 TR-1,915 TR-250 TR-415 TR-1,595 TR-1,300 TR-725 TR-91.9 TR-91.35 TR-710 TR-1,265 TR-1,590 TR-400TR-250 TR-1,925 TR-1,020 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 G:\Projects\Lighthouse\2016\Percent_Cobble_Boulder_20161221.mxd Figure 9 Percent Cobble/Boulder Present at Trackline Intersections (October 2016) Sconset Beach Video Survey Nantucket, Massachusetts Data Source: Office of Geographic Information (MassGIS), Commonwealth of Massachusetts, Information Technology Division LEGEND °0 350 700 Feet1 inch = 700 feet Scale 1:8,400 Screenshot Location Video Drift Transects Shoreline Survey Transects Geotube Area % Cobble/Boulder 0-9% 10-24% 25-39% 40-54% 55-69% 70-84% 85-100% 90.6 92.5 TR-91.9 TR-91.35 TR-91.13 NorthAtlanticOcean Note: -Transects 92.5 and 90.6 were not videodrift transects and were added to the figureso that coordinates could be pulled-The NAD27 Datum was used for consistency withWoods Hole Group Shoreline Surveys Basemap: 2013 Orthophotography, MassGIS TR-91.9 TR-91.35 TR-91.13 TR-220 TR-370 TR-720 TR-1,020 TR-1,280 TR-1,580 TR-1,900 N orth A t la n ti c Oc e an18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 21 20 19 343332313029 35 272625242322 28 G:\Projects\Lighthouse\2016\Percent_Cobble_Boulder_20161012.mxd Figure 10 Percent Cobble/Boulder Present at Trackline Intersections (June 2016) Sconset Beach Video Survey Nantucket, Massachusetts Data Source: Office of Geographic Information (MassGIS), Commonwealth of Massachusetts, Information Technology Division LEGEND 0 350 700 Feet1 inch = 700 feet Scale1:8,400 Screenshot Location Video Drift Transects Shoreline Survey Transects Geotube Area % Cobble/Boulder 0-10% 10-25% 25-40% 40-55% 55-70% 70-85% 85-100% 90.6 92.5 Note: -Transects 92.5 and 90.6 were not videodrift transects and were added to the figureso that coordinates could be pulled-The NAD27 Datum was used for consistency withWoods Hole Group Shoreline Surveys Attachment B Video Survey Screenshot Figures 1 (Sand 50%, Pebble 5%, Cobble 35%, Boulder 10%) Unidentified Branching Brown and Red Algae, Common Slipper Shells, Hermit Crabs, Bread Crumb Sponge, Hydroids, Rock Crab, Shell Hash 2 (Sand Waves 85%, Cobble 15%) Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Common Slipper Shells, Barnacles, Clam Shell, Black Sea Bass, Rock Crab, Barnacles 3 (Sand Waves 100%) Unidentified Floating Algae, Hermit Crabs, Shell Hash 4 (Sand Waves 85%, Cobble 15%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Hermit Crab, Black Sea Bass, Rock Crab, Skate, Shell Hash, Common Slipper Shells 5 (Flat Sand 80%, Cobble 15%, Boulder 5%) Irish Moss, Rockweed, Red Dulse, Unidentified Branching Brown and Red Algae, Hydroids, Orange Encrusting Bryozoan, Common Slipper Shells, Hermit Crab, Surf Clam Shell 6 (Sand 50%, Cobble 35%, Boulder 15%) Irish Moss, Unidentified Branching Brown and Red Algae, Common Slipper Shell, Bread Crumb Sponge, Sulfur Sponge, Red Beard Sponge, Hermit Crabs, Skate 7 (Sand 55%, Cobble 30%, Boulder 15%) Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Common Slipper Shells, Rock Crab, Hermit Crabs, Black Sea Bass 8 (Sand 25%, Pebble 5%, Cobble 15%, Boulder 55%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Rock Crab, Hermit Crabs, Skate, Common Slipper Shells, Shell Hash 9 (Sand 25%, Pebble 10%, Cobble 30%, Boulder 35%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Red Beard Sponge, Sulfur Sponge, Hydroids, Hermit Crab, Rock Crab, Black Sea Bass, Common Slipper Shell, Shell Hash 10 (Sand 50%, Pebble 10%, Cobble 30%, Boulder 10%) Rockweed, Irish Moss, Shell Hash, Unidentified Branching Brown and Red Algae, Hermit Crab, Common Slipper Shells, Rock Crab, Moon Snail, Skate, Surf Clam Shell 11 (Sand 45%, Pebble 5%, Cobble 10%, Boulder 40%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Bread Crumb Sponge, Hermit Crab, Shell Hash, Unidentified Fish 12 (Sand 50%, Cobble 15%, Boulder 35%) Rockweed, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Northern Star Coral, Hydroids, Rock Crab, Hermit Crabs, Black Sea Bass 13 (Sand 45%, Cobble 20%, Boulder 35%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hydroids, Skate, Common Slipper Shell, Shell Hash 14 (Sand 15%, Pebble 15%, Cobble 35%, Boulder 35%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Northern Star Coral, Common Slipper Shells, Shell Hash 15 (Sand 5%, Pebble 25%, Cobble 60%, Boulder 10%) Irish Moss, Rockweed, Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hermit Crabs, Hydroids, Common Slipper Shells, Skate, Rock Crab, Comb Jellyfish 16 (Sand 20%, Pebble 15%, Cobble 50%, Boulder 15%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Hydroids, Orange Encrusting Bryozoan, Hermit Crabs, Rock Crab, Skates, Shell Hash 17 (Sand 35%, Pebble 10%, Cobble 45%, Boulder 10%) Unidentified Branching Brown and Red Algae, Unidentified Floating Algae, Sulfur Sponge, Bread Crumb Sponge, Sand Sponge, Red Beard Sponge, Northern Star Coral, Orange Encrusting Bryozoan, Common Slipper Shells, Hermit Crabs, Rock Crab, Shell Hash 18 (Sand 25%, Pebble 15%, Cobble 40%, Boulder 20%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Sand Sponge, Orange Encrusting Bryozoan, Common Slipper Shells, Hermit Crabs, Shell Hash 19 (Sand 45%, Pebble 10%, Cobble 25%, Boulder 20%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Red Beard Sponge, Unidentified Fish, Common Slipper Shells, Hermit Crabs, Rock Crab, Moon Snail, Black Sea Bass, Shell Hash 20 (Sand 40%, Pebble 10%, Cobble 25%, Boulder 25%) Rockweed, Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Sand Sponge, Hydroids, Common Slipper Shells, Shell Hash 21 (Sand 50%, Pebble 15%, Cobble 25%, Boulder 10%) Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Sand Sponge, Hydroids, Red Beard Sponge, Hermit Crabs, Common Slipper Shells, Shell Hash 22 (Sand Waves 85%, Cobble 15%) Unidentified Branching Algae, Unidentified Floating Algae, Shell Hash, Hermit Crabs 23 (Sand 60%, Pebble 5%, Cobble 15%, Boulder 20%) Irish Moss, Unidentified Branching Brown and Red Algae, Hermit Crabs, Shell Hash, Unidentified Floating Algae 24 (Sand 65%, Cobble 5%, Cobble 10%, Boulder 20%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Rock Crabs, Hermit Crabs, Shell Hash, Unidentified Fish 25 (Sand 50%, Pebble 10%, Cobble 20%, Boulder 20%) Unidentified Branching Brown and Red Algae, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Hydroids, Common Slipper Shells, Hermit Crabs, Black Sea Bass, Shell Hash 26 (Sand 15%, Pebble 55%, Cobble 30%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Orange Encrusting Bryozoan, Red Beard Sponge, Common Slipper Shells, Hermit Crabs, Surf Clam Shell 27 (Sand 65%, Cobble 20%, Boulder 15%) Irish Moss, Unidentified branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Common Slipper Shells, Skate, Hermit Crabs, Hydroids, Common Slipper Shells, Shell Hash 28 (Sand 40%, Pebble 25%, Cobble 30%, Boulder 5%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Invasive White Tunicate, Red Beard Sponge, Common Slipper Shells, Hermit Crabs, Unidentified Fish 29 (Sand Waves 100%) Unidentified Floating Algae, Hermit Crabs, Shell Hash 30 (Sand 70%, Cobble 15%, Boulder 15%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Orange Encrusting Bryozoan, Hydroids, Hermit Crabs, Barnacles, Surf Clam Shell 31 (Sand 35%, Pebble 5%, Cobble 20%, Boulder 40%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Hydroids, Invasive White Tunicate, Skate, Unidentified Fish, Common Slipper Shells, Shell Hash 32 (Sand 35%, Pebble 25%, Cobble 10%, Boulder 30%) Unidentified Branching Brown and Red Algae, Hermit Crab, Sulfur Sponge, Bread Crumb Sponge, Red Beard Sponge, Northern Star Coral, Hydroids, Common Slipper Shells, Hermit Crabs, Shell Hash 33 (Sand 30%, Cobble 30%, Boulder 40%) Rockweed, Irish Moss, Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Hydroids, Rock Crab, Hermit Crabs, Skate, Shell Hash 34 (Sand 40%, Pebble 5%, Cobble 35%, Boulder 20%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Red Beard Sponge, Northern Star Coral, Common Slipper Shells, Hermit Crabs, Rock Crab, Skate, Shell Hash 35 (Sand 15%, Pebble 10%, Cobble 50%, Boulder 25%) Unidentified Branching Brown and Red Algae, Bread Crumb Sponge, Sulfur Sponge, Sand Sponge, Red Beard Sponge, Common Slipper Shells, Hermit Crabs, Rock Crab, Black Sea Bass