HomeMy WebLinkAboutSE48_2824 SBPF Response to G Berman 2020 Annual Review Comments 05_07_21
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
May 7, 2021
Mr. Jeff Carlson
Natural Resources Director
2 Bathing Beach Road
Nantucket, MA 02554
Subject: DEP File No. SE48-2824 | 2020 Annual Report Review Comments
Dear Mr. Carlson:
We received the memorandum written by Mr. Greg Berman dated April 16, 2021
presenting his review on the 2020 Annual Review. Thank you for sending that along. Upon
review of his comments, we offer the following responses to his review. The major topics
that he identified are paraphrased or copied verbatim and presented in italics followed
by responses is in normal typeface.
Executive Summary / Key Conclusion
Mr. Berman’s memo presents a comprehensive review of the 2020 Annual Review,
commenting on the major elements of: sand delivery, bluff monitoring, shoreline
monitoring and underwater video monitoring. His major comments are on the topic sand
delivery to the template, with the implication that the reported shortfall in sand delivered
to the template is depriving the fronting and adjacent beaches of sand. As we describe
below it is not. Spring 2020 sand deliveries were halted by order of the Commission
because of the perceived poor sand quality (which turned out not be the case after two
rounds of testing and over 5 months of review) plus delays related to COVID-19. However,
because a large volume of sand was stored in the template, the delivery deficit only
effected the volume of sand on top of the template. That large stockpiled volume
provided adequate sand to re-cover exposed geotubes after all erosion events (i.e.
contribute sand to the littoral system). The tubes were re-covered after each erosion
event in 2020. Sand was delivered to the template in December 2020 to rebuild the
stockpile volume and is being used to re-cover exposed geotubes presently.
During the preceding seven years approximately 14.3 cy/lf/yr of sand was contributed off
the template to the littoral system as designed when sand washes off the face of the
template during erosion events, and that volume exceeds the site-specific historical
Mr. Jeff Carlson 2 Nantucket Conservation Commission May 7, 2021
annual average contribution rate of 12.0 cy/lf/yr of sediment from the pre-construction
unprotected bluff. The materials in the 2020 Annual Review, quarterly reporting by the
Woods Hole Group (“WHG”), and summaries presented herein show that sand off the
template has contributed more sand to the littoral system than the unprotected bluff
would have contributed based on the pre-construction retreat rate. See Table 1 below
and Figure 1 attached.
Following are our responses to Mr. Berman’s review comments.
Section 4.1 Sand Delivery:
1. … Line 13 of Table 1 that there is 26,637 cy of sediment deficient from the required
volume as of 01/15/2021. Similar to last year, the report also indicates on Line 14 of
Table 1 that if the applicant were only required to fill the template to 22 CY/LF then
would currently be a surplus instead of a deficiency. However, this type of adaptive
management has not been approved, and the surplus in the template combined with
a deficit in nourishment volume may indicate that the template may not be providing
sediment to the beach system during non-storm periods. …
The volumes delivered to the template are not in dispute, neither is the deficiency from
the permit volume new information nor disputed. In terms of deficits, one needs to
distinguish between permit volume and natural bluff contribution volume (coastal
process perspective). As has been stated many times, the permit volume is 1.83 times
the natural pre-construction bluff contribution rate, 22 cy/lf/yr versus 12 cy/lf/yr. As
summarized in Table 1 below, the sand delivered to the template annually and
cumulatively has exceeded the unprotected bluff contribution volume.
Table 1. Cumulative Sand Contributed 2015 - 2020
Sand
Year
A
Sand Volume
Delivered (cy)
B
Sand Volume at
12/cy/lf/yr (cy)
Difference
(A-b)
(cy)
Sand Volume at
22 cy/lf/yr (cy)
2015 23,951 10,224 +13,727 18,744
2016 38,380 20,448 +17,932 37,488
2017 53,465 31,812 +21,653 58,322
2018 68,603 43,176 +25,427 79,156
2019 76,755 54,540 +22,215 99,990
2020 100,090 65,904 +34,186 120,824
This is also presented graphically in Figure 1, attached.
Regarding sand contributed off the template during non-storm periods that has nothing
to do with template sand volume. As described numerous times, there are two
Mr. Jeff Carlson 3 Nantucket Conservation Commission May 7, 2021
components to the template: (1) the face – from which sand is contributed to the beach
and littoral system when waves erode sand from the face; and (2) the top of the template
– an on-site stockpile used to replenish the face after erosion events. SBPF contracts to
have eroded sand replaced from the sand atop the template after erosion events, and
that is performed.
Sand can be washed off the face whenever waves lap against the toe of the template
slope, and that can occur during storms or during non-storm times if the surf is high
enough. Just like the natural bluff, sediment is only contributed off the natural bluff and
carried to the beach and littoral system when waves lap against the bluff toe. Therefore,
the template is contributing sand as effectively as the bluff, that occurs whenever waves
wash against the template face and erode sand off the face.
2. The 2020 sand year is much closer to the calendar year (1/1/2020 to 1/15/2020) and
is a positive step towards a less confusing reporting system. … despite irregular time
periods used in defining the Sand Years, it does not appear to significantly impact the
surplus or deficit for a given year.
Comment acknowledged
3. The project site has received the required volume of sand in only one of the sand years
since 2015. While there is some fluctuation, the net deficit has been increasing over
time and the current deficient volume is 26,636 CY (significantly more than one year’s
requirement). While the deficit was somewhat reduced from 2018-2019, it has
increased even more in 2020. The trend of increasing deficit nourishment volumes is
concerning and should be addressed. As the trendline in the graph above shows,
continuing this trend will lead to a potential deficit of >50,000 CY by 2025.
Reexamining the appropriateness of the required mitigation volume is not part of this
review. Assuming the required volume is appropriate, then there is a significant
disruption in the supply of sediment to this region.
Please see response to #1 above. The deficits referred to in the comment are relative to
the permit volume. The actual volume delivered to template has exceeded the volume
that would have been contributed off the unprotected bluff.
4. The nourishment sand does not need to be placed on the template. Some of this
material could be placed at the ends of the geotube array (an area of noted erosion)
or immediately seaward of the array. This material would be transported away from
the site more quickly than if placed on the template, but would serve its purpose as
compensatory nourishment providing sediment to downdrift beaches and dunes.
The nourishment sand serves several functions: (1) it is used to keep geotubes covered
with sand to protect them from UV damage and physical damage, (2) the sand atop the
template is an on-site sand stockpile so there is an adequate supply of sand to re-cover
exposed geotubes after erosion events (this limits truck deliveries to a few concentrated
Mr. Jeff Carlson 4 Nantucket Conservation Commission May 7, 2021
times per year), and (3) to contribute to sand to the littoral system to compensate for the
placement of the geotubes in front of the bluff.
The purpose of placing sand (an expensive commodity on Nantucket) on top of the
template is to receive the benefit of all three functions. Placing sand on either side of the
template would not achieve all the functions of mitigation sand. Additionally, placing
excess sand in front of the template would narrow the fronting beach, something the OOC
seeks to avoid.
5. The uncertainty in the volume is now shown and is very helpful in putting the data in
context. It would also be helpful if the Total Bluff Erosion for Adjacent Unprotected
Areas, reported as 4,623 CY, also had the uncertainty provided (ex. 4,623 CY ±??? CY).
Using the equation ((802’+138’)*+0.19 cy/lf) the Total Bluff Erosion for Adjacent
Unprotected Areas is estimated as 4,623 CY ±179 CY. For the next report I would still
urge the Gain/Loss map to provide a different color for the range of uncertainty (for
2020 this was ±2.3 cm).
Comment acknowledged. We will confer with the GIS specialist to ascertain if this visual
presentation as suggested will be legible at these scales.
Comments on Section 4.3 Shoreline Monitoring:
6. The Conservation Commission may want to request a different representation of the
shoreline monitoring data. The excerpt of the WHG report represents the change in
position of Mean Low Water (MLW) over time, however concerns about the geotube
array are based on a potential reduction in the volume of Longshore Sediment
Transport (LST). It is feasible to construct a sediment budget (example below) that
illustrates the volume flowing past points along the shoreline. Then updrift, geotube,
and downdrift rates can be compared over time. If there is a reduction in flow
downdrift of the geotubes then negative impacts might be inferred regardless of the
overshadowed signal. The data to perform this analysis is not readily available and
this level of effort is outside the scope of this review.
The underlined themes in this comment will be addressed out of order. First, the WHG
monitoring program is the long-term shoreline program that was started in 1994 and is
the method that is prescribed in the OOC (SE42-2824). An amendment to the OOC would
be needed to change the monitoring program. Second, the purpose of the mitigation
sand is to compensate for the sediment that can no longer be contributed from the
eroding bluff into the littoral system because the geotube array prevents bluff erosion.
The use of the standard compensatory sand volume calculation (length x retreat rate x
height) is a practical and pragmatic method to provide an adequate volume of mitigation
sand to compensate for the erosion prevention. The basis for this mitigation approach is
to ensure there is no net loss of sediment to the littoral system because of a CES. As
demonstrated above in Table 1 and depicted on Figure 1, the existing geotube project has
Mr. Jeff Carlson 5 Nantucket Conservation Commission May 7, 2021
provided more sand to the littoral system than the unprotected bluff would have based
on this standard calculation.
Third, this project is but a very short segment of the Nantucket shoreline and the sand
within this reach of shoreline is but a very small proportion of the total sand volume
moving within the littoral drift system, which is comprised of the entire shoreline plus
nearshore and offshore shoals off the east coast of Nantucket. Any changes of sand
migration throughout the entire littoral system would overshadow any signal generated
from this short stretch of shoreline. Examination of the WHG data1 shows that the study
area was experiencing erosion (reduced volume in most profiles during the periods 1994
- 2001 and 2001 - 2013 and retreat of the MLW position for the periods 1994 – 2020 and
2001 – 2020). Since the geotubes were installed, that trend is generally observed, but
due to shorter timeframes, i.e., 7-years, 1-year and 1-quarter, some variation is observed,
that is some profiles exhibit accretion while others exhibit erosion. I’d posit that the
overall trend of erosion as evidenced in the WHG data back to 19914 is due to the
conditions in the larger system than the installation of the geotube array.
Comments on Section 4.4 Underwater Video Monitoring
7. While this type of video surveillance is adequate for ground truthing, Sidescan
(backscatter) sonar images would provide a much more complete picture of the
bottom. This has been mentioned in previous reviews, but is not a requirement of the
Order of Conditions. The migration of the large (several feet high) underwater sand
forms in the area overshadow any potential impact from the geotube sand
contribution. One survey (06/2018) shows more cobble/boulder than any of the other
surveys. There does not appear to be a significant difference between any of the
remaining surveys. It is possible that the bottom type varies too abruptly to allow for
fine scale parsing using this method. If the areas were more simply classified (>50%
or <50%) there would likely be little to no significant change between the maps. An
expert in fisheries could be consulted to determine the minimum acceptable
percentage of Cobble/Boulder. It should also be noted that no June 2019 survey was
provided.
We agree this is the monitoring method prescribed in the OOC. The purpose of this
monitoring was to ascertain if increased sand off the template (1.8 times the pre-
construction unprotected bluff contribution rate) might cover the offshore cobble habitat
with sand contributed off the template. The monitoring shows there has been no
discernable change in cobble coverage.
Monitoring was required to demonstrate the project resulted in no adverse effect on
grain size distribution in accordance with 310 CMR 10.25(6)(c). There was no assessment
1 Southeast Nantucket Beach Monitoring 84th Survey - Tables 2. and 3.
Mr. Jeff Carlson 6 Nantucket Conservation Commission May 7, 2021
of habitat quality before the geotube array was constructed and none is needed now. The
performance is no adverse effect from the pre-construction condition and that standard
has been met, as demonstrated by the video monitoring.
Comments on Section Annual Drainage System Report
8. Previous Epsilon Reports have included professional determinations regarding
accumulated sediment in the drainage system. In the past the system has been likely
performing as designed, however there is no mention of the drainage system in the
2020 Epsilon Report.
It was my understanding the drainage system was presently monitored and maintained
by the department of public works as municipal stormwater infrastructure. We will have
an engineer inspect and report on the drainage system.
Key finding for this independent review of the 2020 Epsilon Report:
9. In the 2020 Sand Year less than the required amount of sediment was provided to
the project area resulting in a current net deficiency of 26,637 cy. This continues a
disturbing trend of increasing deficits which may lead to negative impacts, although
the current reporting requirements have not shown such an impact. A more direct
look at potentially changing volumes in longshore sediment transport may of use in
determining downdrift impacts. The annual volume of sediment eroded from a
coastal bank can vary greatly along this section of shoreline, therefore there might
be some leeway in providing the exact volume each year (at least from a coastal
processes point of view, if not the Order of Conditions). However, over the long-term
more sediment will need to be provided to average out these years of deficit.
The themes summarized by Mr. Berman were addressed above, but are summarized
below
(a) The deficit cited by Mr. Berman is the deficit from the permit volume, while there
has been a surplus contributed off the template as compared to the unprotected
pre-construction bluff contribution rate (i.e., the coastal process point of view). See
Table 1 above and Figure 1 attached. As Mr. Berman writes, “… there might be some
leeway in providing the exact volume each year (at least from a coastal processes
point of view, if not the Order of Conditions).”
(b) The WHG monitoring program is the monitoring program prescribed in the OOC.
Data presenting the MLW position and volume along each profile are direct
measures of downdrift beaches, the coastal landform of concern, and from which
one can assess downdrift impacts. The MLW position plots submitted with our
response to Mr. Berman’s comments on the 2019 Annual Report demonstrate the
beaches are not experiencing accelerated erosion (landward movement of the MLW
line) post-construction. The difference along the Sconset shoreline, however, is the
Mr. Jeff Carlson 7 Nantucket Conservation Commission May 7, 2021
bluff landward of the geotube has been stabilized, while the adjacent unprotected
bluff continues to erode.
This project meets the performance standards established for CES’s which were
established to protect the interests of the Wetlands Protection Act and the interests of
Nantucket Wetlands Bylaw. The interests presumed significant to Coastal Bank are storm
damage prevention and flood control. The geotube system has positively affected the
ability of the Coastal Bank to protect those interests. Secondly, the regulations require
that CES’s have no adverse effect to downdrift beaches. As stated many times, the data
shows there has been no adverse effect to fronting and adjacent beaches attributable to
the geotube system. See Table 1 above and the plots of MLW position previously
submitted to the Commission.
We appreciate you taking these responses into consideration when reviewing Mr.
Berman’s review. In accordance with the OOC we expect to discuss the 2020 Annual
Review with the Commission at the meeting scheduled for May 17, 2021.
Contact me at ddunk@epsilonassociates.com or by phone at 978.461.6226 with any
questions regarding this correspondence.
Sincerely,
EPSILON ASSOCIATES, INC.
Dwight R. Dunk, LPD, PWS, BCES
Principal
encl.
cc. J. Posner, SBPF
S. Cohen, Cohen & Cohen Law PC
G. Wood, Rubin and Rudman LLP
0
20000
40000
60000
80000
100000
120000
140000
160000
2014 2015 2016 2017 2018 2019 2020 2021Cumulative Mitigation Volume (cubic yards)Year (Jan-Dec)
Cumulative Mitigation Requirement vs Documented Placement
Required MitigationVolume at 22 cy/lf/yr
Mitigation Volume
Delivered
Standard Mitigation
Volume at 12 cy/lf/yr
Figure 2 - Cumulative Sand Contribution