HomeMy WebLinkAbout10 SE48_3115 Epsilon Presentation 11_05_18
PRINCIPALS
Theodore A Barten, PE
Margaret B Briggs
Dale T Raczynski, PE
Cindy Schlessinger
Lester B Smith, Jr
Robert D O’Neal, CCM, INCE
Andrew D Magee
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
ASSOCIATES
Richard M. Lampeter, INCE
Geoff Starsiak, LEED AP BD+C
Marc Bergeron, PWS, CWS
3 Mill & Main Place, Suite 250
Maynard, MA 01754
www.epsilonassociates.com
978 897 7100
FAX 978 897 0099
Projects:\21597 Lighthouse\2018\Expanded Project\NOI
November 7, 2018
Mr. Jeff Carlson Via U.S. Mail & Electronic Mail
Natural Resources Director, Town of Nantucket
Conservation Commission Office
2 Bathing Beach Road
Nantucket, MA 02554
Subject: DEP File No. SE048-3115 - Expanded Baxter Road and Sconset Bluff
Storm Damage Prevention Project
Dear Mr. Carlson:
Attached please find for the record a hard copy of the Power Point file presented at
the November 5, 2018 Notice of Intent Public Hearing for the above referenced
project.
An electronic copy of this presentation is also being submitted by email for your
use.
Sincerely,
EPSILON ASSOCIATES, INC.
Dwight R. Dunk, LPD, PWS, BCES
Principal
encl.: Power Point Presentation “Expanded Baxter Road and Sconset Bluff Storm
Damage Prevention Project” dated November 5, 2018
cc: J. Posner, SBPF
S. Cohen, Cohen & Cohen Law
G. Wood, Rubin and Rudman
Notice of Intent
Expanded Baxter Road and Sconset Bluff
Storm Damage Prevention Project
November 5, 2018: Meeting #3
Sept 2018
Existing Project
Jute/Coir
Envelopes
Meeting Agenda
1.Overview
2.Sediment Transport
3.Sand Mitigation
•Mitigation Requirement
•Beach Profile Surveys
•Bathymetry Profile Surveys
•Nearshore Cobble/Boulder Surveys
•Sand Source
2
1. Overview
3
4
Existing Geotube Project
5
Proposed Geotube Project
6
Proposed Geotube Project
Sand Mitigation Summary
Protocol Summary:
Complete construction placing 22 cy/lf of compatible sand on the
template.
Periodically contribute sand to the littoral drift system by covering exposed
tubes after erosion events.
“What was Contributed from the Template?” Determine volume of sand
contributed to the littoral drift system during the winter storm season.
Replace sand on the template with the volume of sand contributed to the
littoral drift system the previous year or up to 22 cy/lf, whichever is greater, to
“top it off.”
7
Sand Mitigation Consistent with Regulations
and Policy
Proposed sand mitigation complies with the MA Wetlands Protection Act
regulations/performance standards and the Nantucket Wetlands Bylaw
regulations/performance standards:
–Protects the stability of the Coastal Bank, and
–Is the best available measure to supply sediment to other downdrift
coastal wetland resource areas.
Proposed adaptive sand mitigation is the “best available measure” and
meets the MA CZM Coastal Hazard Policy #1.
Evaluation of coastal profile data and nearshore cobble/boulder survey
results reveal the existing geotube project has no apparent negative
effects to adjacent coastal wetland resource areas and sand mitigation
has been maintaining the coastal system.
The sand mitigation volume each year will be based on the losses the
previous year, i.e. short-term contribution rate rather than long-term
average erosion rate.
8
Adaptive Management Protocol Comparison
9
Comparison of Existing Sand Replenishment Requirements and the Proposed Adaptive Management Protocol
Existing Requirements (OOC SE 48-2824) Proposed Protocol
32. Sand mitigation shall be at a rate of 22 cubic yards per linear foot (cy/lf) per year in accordance with the following schedule:
Place sand on the template before the winter storm season equal to the volume of sand contributed off the template the previous storm season or to refill the template to 22 cy/lf, whichever is greater.
32(b). Maintain a minimum 2 foot cover over the Geotubes to protect them from UV degradation
Maintain 2 feet of sand cover on the template to protect the tubes from UV degradation.
32(c). Annually in September-November: ensure a substantial portion of the sand template volume (l0-15 cy/lf) is available at the onset of the winter storm season.
Throughout the winter, place additional sand on an as-needed basis,
1. Place sand on the template before the winter storm season: a) volume of sand contributed off the template the previous storm season or b) refill template up to 22 cy/lf, whichever is greater.
2. Re-cover exposed geotubes within 10 business days, in accordance with the replenishment trigger in the Milone & MacBroom November 12, 2013 letter
32(d). Delivery tickets from sand supplier shall be provided annually to the Department and the NCC
Will continue to follow this condition to document the total volume of sand provided on a yearly basis.
34(c.) Failure to repair and/or replace damaged geotextile tubes in a timely manner. If repair or replacement cannot be accomplished within 30 days from the date of the damage, SBPF shall notify the Department and the NCC before 30 days have elapsed and provide a repair schedule for Department review and approval.
Follow this condition for repairs or replacement of damaged geotubes.
Sand management, re-cover exposed geotubes within 10 business days unless unsafe work condition. SBPF will notify the Conservation Commission if geotubes cannot be re-covered within 10 business days and provide a schedule to re-cover exposed tubes.
Offshore Submarine Bars
Dynamic Littoral Drift System
10
Sediment Transport – Northward
With Great Point and Submarine Bar Buildup
Dynamic Littoral Drift System
11
Expanded Baxter Road and Sconset Bluff
Storm Damage Prevention Project
DEP File#: SE48-3115
Anticipated Topics for October 22, 2018
•Sediment Transport
•Sand Replenishment Protocols
Sediment Transport – Southward
with beach/dune accretion at Sewer Beds
Dynamic Littoral Drift System
12
Figure 3. Shoreline change plot utilizing data from the 77th Southeast Nantucket Beach MonitoringReport, dated
September 2018. This figure is set-up differently than Figure 3 from the September 2018 Monitoring Report. This figure
is set up to assist the reader in visualizing the shoreline changes pre- and post-geotube installation. The perspective is
that you are looking at the shoreline (x-axis) from the ocean. South is to the left, north is to the right. The average rate of
shoreline retreat (erosion of land) is plotted above the x-axis (negative y-axis values toward the top) while the average
rate of shoreline advance (beach expansion toward the ocean) is plotted below the x-axis (positive y-axis values toward
the bottom).
Applied Coastal Research and Engineering Comments
Rate of Shoreline Change
13
Woods Hole Group Data
Rate of Shoreline Change
14
Woods Hole Group Data
Rate of Shoreline Change
15
South
North
Woods Hole Group Data
Rate of Shoreline Change
16
Station ID
Pre-Geotube Annual Erosion Rate (cy/yr) Post-Geotube Annual
Erosion Rate (cy/yr)
11/94 to 12/01 12/01 to 9/13 9/13 to 9/18 South of Existing Geotube System 88 -5.9 -4.3 0.5
89 -7.8 -1.6 -1.4
90 -8.7 -0.6 -0.3
90.6 -7.3 -0.7 -0.1
Project Area North of Existing Geotube System 92 -1.8 -1.2 -0.8
92.5 -3.0 -0.1 -2.1
93 -4.4 0.2 -2.1
94 -3.7 -0.4 -2.0
95 -3.6 -1.1 -2.5
Annualized Volumetric Changes for Three Time Periods
2. Sediment Transport
17
Sediment Transport Mechanisms
•Cross-shore transport
•Longshore Transport
•Diffusion
18
Cross-shore Transport
•Movement of sand onshore and offshore
•Results in movement of shoreline but is not
technically erosion as the volume remains the
same
•Landward extent is the top of the unprotected bluff
•Seaward extent is between -25 feet and -35 feet,
MLW.
19
Cross-shore Transport
•Best evident in summer and winter profiles
From: Steve Earle,
Physical Geology, Pressbooks. 20
Cross-shore Transport
•Interestingly, profiles on the east coast of
Nantucket do not show markedly different winter
and summer profiles
•However, the principle is similar in that sand is
redistributed across the profile based on storms
and then calmer periods
21
Cross-shore Transport
~2,000’
22
Cross-shore Transport
•Profile 95
23
Cross-shore Transport
•Profile 95
24
Cross-shore Transport
•Profile 95
25
Cross-shore Transport
~1,500’
26
Cross-shore Transport
•Profile 88
27
Cross-shore Transport
•Profile 88
28
Cross-shore Transport
•Profile 88
29
Cross-shore Transport
•Bluff face collapse is a cross-shore transport
process
•Undercutting at the base of the bluff occurs during
a storm event
•Timing of bluff failure could be during the storm event
or well after the storm event
30
Cross-shore Transport
•Relevance to the Geotextile Tube System
•Cross-shore transport does not directly result in
downdrift erosion
•The geotextile tubes avoid periodic loss of sand from
the bluff (and the bluff cannot be naturally rebuilt)
•This can/will happen periodically on adjacent
shorelines regardless of the geotextile tube project given a large enough storm event
31
Longshore Transport
•North and south movement of sand
32
Longshore Transport
33
Longshore Transport
•Driven by waves arriving at an angle to the beach
Oblique
Waves
34
Longshore Transport
•Variation in longshore transport causes erosion
and accretion
•Transport in > transport out accretion
•Transport out > transport in erosion
•This can happen naturally along different sections
of the shoreline
•The geotextile tube project area has a naturally higher erosion rate than areas to the north and south
35
Longshore Transport
•The magnitude of longshore transport is a
function of:
•Wave height
•Wave angle
•Wave period
•Grain size
•Offshore beach slope
36
Longshore Transport
•Where does longshore transport occur?
•Mostly in the breaker zone
•Some in the swash zone
Swash
Breaking
Zone
Longshore Transport
•Greatest longshore
component in the
breaking zone
•Second maxima in the
swash zone (beach
face)
From Pilkington (2007). Coastal Hydrodynamics and
Transport Processes, Danish Hydraulics Institute.
38
Longshore Transport
•Relevance to Geotextile Tube System
•Sand is not transported longshore at the highest
elevations along the beach face
•Sand transport is primarily in the wave breaking zone
and secondarily as part of runup
•Once there is sufficient sand in the system as a whole,
then sand will be moved alongshore at natural rates
39
Diffusion
•A form of longshore
transport
•Spreading loss due to
a “perturbation” (bump)
in the shoreline
From Dean, R.G. (2002). Beach Nourishment: Theory and
Practice, World Scientific 40
Diffusion
•Relevance to the Geotextile Tube system
•Potentially applicable at Sconset due to excess sand being
placed in front of the geotube system
•Would increase movement of sand from in front of the
geotube system to adjacent beaches
•Not readily apparent reviewing existing shoreline data
•Small offset, short length and large wave climate creates quick
diffusion
•Increases longshore distribution of sand placed by SBPF
41
Summary
•Sand from higher portions of the bluff are pulled to
lower sections of the beach profile and then
transported alongshore
•SBPF’s overfilling in front of the geotextile tube
system puts additional sand in the system
adjacent to the project as well
42
3. Sand Mitigation
43
3. Sand Mitigation
44
•Mitigation Requirement
•Beach Profile Surveys
•Bathymetry Profile Surveys
•Nearshore Cobble/Boulder Surveys
•Sand Source
Coastal Bank Performance Standard: 310 CMR 10.30(3)
(a) Coastal engineering structure or modification shall be designed so as to
minimize, using best available measures, adverse effects on adjacent or
nearby coastal beach.
45
Project Compliance:
Sand Mitigation is incorporated into the design to minimize adverse effects to
adjacent beaches because it is a best available measure.
Mitigation – Requirement
Coastal Bank Performance Standard: 310 CMR 10.30(3) continued
46
Best Available Measures is defined at 310 CMR 10.4 as: “..the most up-
to-date technology or the best designs, measures or engineering
practices that have been developed and that are commercially
available.”
In the Notice of Intent and at our last Conservation Commission meeting
(October 1, 2018) we reviewed the extensive alternatives analysis that this
project has evaluated over the last 20 plus years and we demonstrated that the
Proposed Project meets the above definition.
Mitigation – Requirement
47
Project Compliance (a. continued):
Sand Mitigation
Coastal bank Sediment contribution rate for Proposed Project has been
calculated using standard approach:
Sediment Contribution = Project Length x Bank Height x Retreat Rate
Project Length = 2,873 ft
Bank Height = 74 ft
Retreat Rate = 2.8 ft/yr
Calculated Coastal Bank Sediment Contribution Rate = 7.7 cy/lf/yr
Coastal Bank Performance Standard: 310 CMR 10.30(3) (continued)
Mitigation – Requirement
(Calculating Mitigation Volume)
48
Lots Length
59-87 1,978 ft
105-119 895 ft
Total 2,873 ft
Length
Mitigation – Requirement
(Calculating Mitigation Volume)
49
Average Coastal Bank Height = 74 feet
74 ft
Height
Mitigation – Requirement
(Calculating Mitigation Volume)
50
Annual Retreat Rate = 2.8 ft/yr
Average of transects in NOI:
Table 2-2 provides transects for 107-119 Baxter Rd and
Table 2-3 provides transects for 71-85 Baxter Rd.
This average retreat rate for the Proposed Project is significantly lower than
the retreat rate for the reach of bluff at the Existing Project of 4.6 ft/yr.
Retreat Rate
*
*
Mitigation – Requirement
(Calculating Mitigation Volume)
•Greater Sand Volume with Project: Sand is eroded from the template during
coastal storms and sediment transport makes this sand available to the regional
Sconset littoral drift system at a greater volume than would be available without
the Project.
•Provides Interest of Storm Damage Prevention: Mitigation sand is available
to downdrift Coastal Beaches and Land Under the Ocean which rebuilds the
volume of sand in these Resource Areas that is lost to sediment transport. This in
turn enables these downdrift coastal landforms to continue to provide a buffer
from coastal storm waves (Interest of Storm Damage Prevention).
•Bulldozer Speeds Geotube Re-covering: Proposed adaptive sand
management program involves SBPF funding the use of a project-dedicated
bulldozer so that sand can be moved to cover exposed geotubes as quickly as
possible after coastal storms. 51
Coastal Bank Performance Standard: 310 CMR 10.30(3) (continued)
Mitigation – Requirement
Coastal engineering structures (other than bulkheads and groins) may be permitted only
upon a clear showing that no other alternative exists to protect a structure that has not
been substantially improved or public infrastructure built prior to 9/78, from imminent
danger.
Project Compliance:
•Alternatives Analysis: previously reviewed.
•Project Protects: Baxter Road and other public infrastructure.
•Project Preserves: an entire historic largely pre-78 community, which includes pre-78
homes to which various alterations have been made and a number of post-78 homes.
52
Nantucket Coastal Bank Performance Standard: 2.05 B(1)
Existing
Project
Jute/Coir Envelopes
Mitigation – Requirement
Projects shall be restricted to activity determined by the Commission to have no
adverse effect on bank height, bank stability, ...or the use of a bank as a sediment
source.
Project Compliance:
No adverse effect on:
•Bank Height: Project will preserve rather than adversely affect bank height.
•Bank Stability: Project will maintain bank stability by protecting the lower bank from
wave-induced erosion. Vegetation plantings on the upper bank face will also prevent
rain- and wind-induced erosion.
•Sediment Source: Project provides sand mitigation and includes monitoring of
adjacent and downdrift beaches.
53
Nantucket Coastal Bank Performance Standard: 2.05 B(3)
Mitigation – Requirement
Mitigation - Requirement
Follows MA Office of Coastal Zone Management (CZM) Coastal
Hazards Policy #1:
Preserve, protect, restore, and enhance the beneficial functions of storm damage
prevention and flood control provided by natural coastal landforms, such as dunes,
beaches, coastal banks, land subject to coastal storm flowage, etc.
Coastal Engineering Structure requirement:
•Only feasible alternative
•Compatible sediment must be periodically placed in the littoral system to
compensate for sediment lost to the system
* Lost to system = volume of sand no longer available to system due to presence of
coastal engineering structure.
54 54
Mitigation - Requirement
Follows MA Office of Coastal Zone Management (CZM) Coastal
Hazards Policy #1 (continued):
Sediment Mitigation Volume based on:
•Calculation of the long-term average annual erosion rate of the coastal
landform at the site.
•Short-term rates* can be considered if the issuing authority determines that the
short-term rate is more indicative of current and future conditions due to alterations
along the shore.
•Proposed Project has calculated project site specific rates.
55 55
Mitigation – Existing Project
Calculated Sediment Contribution for the Coastal Bank at the Existing
Project Site was 12-14.3 cy/lf/yr for pre-construction condition.
Annual Placement of 22 cy/lf/yr – Even if the sand template already contains a
substantial volume of sand.
Existing Sand Template: Contributed on average 13.5 cy/lf/yr (2016-2018)* which
is generally consistent with pre-construction conditions.
* This three-year period does not include initial construction sand volume and better
represents annual average template maintenance volume:
(2016 = 11.3 cy/lf; 2017 = 8.9 cy/lf; 2018 = 20.3 cy/lf)
Problem: Annual placement of 22 cy/lf/yr leaves significant volume of sand in
template at end of each season.
Creates an unsafe oversteepened top-heavy bank.
56 56
57
Calculated Sediment Contribution = Project Length x Bank Height x
Retreat Rate
Project Length = 2,873 ft
Bank Height = 74 ft
Retreat Rate = 2.8 ft/yr
Calculated Coastal Bank Sediment Contribution Rate for Proposed
Project = 7.7 cy/lf/yr or 22,122 cy/yr.
Actual Contribution of 22 cy/lf/yr correlates to 63,206 cy/yr which
is 2.9 times calculated sediment contribution rate for Coastal Bank
in Proposed Project area.
Proposed Adaptive Template Management Plan: Refill template to
22 cy/lf before storm season.
Mitigation – Proposed Project
Sand Mitigation – Proposed Adaptive Approach
•Beginning of Storm Season: Refill template with volume of sand contributed off
template previous season, or up to 22 cy/lf, whichever is greater.
•After Storm Erosion: Replenish sand over Geotubes with sand from template.
•Placement with dedicated Bulldozer: Within 10 business days replace sand
over Geotubes using Project dedicated bulldozer funded by SBPF.
•Adaptive Approach is Preferred: Avoids overfilling template which causes:
•Covering existing vegetation.
•Creating overly steep access ramps resulting in difficult pedestrian and vehicle
access for template management.
58
59
Sand Mitigation – Other Projects?
Woods Hole Group’s Report, (NOI, Attachment E)
Supplemental Historic Analysis of Survey Data
a t Siasconset, Nantucket, MA, December 2016
WHG conducted background research on other projects with Orders of Conditions
requiring sand mitigation - 10 projects: 2 on Nantucket, 1 on Martha’s Vineyard
and 7 on Cape Cod.
•Timeframe: 1986-2016
•Hard and soft engineering solutions
•Shoreline reaches: 100 ft – 1,800 ft
•Annual sand mitigation: 65 – 1,100 cy/yr
•Volume based on: bank height, project length & bank retreat rate
•The proposed Sconset project is many times larger than these other approved
projects
Beach Profile Surveys
60
61
Beach Profile Surveys – Summary
Woods Hole Group’s Report,
(NOI, Attachment E)
Supplemental Historic Analysis of
Survey Data at Siasconset,
Nantucket, MA
December 2016
WHG conducted supplemental data
analysis on beach profile survey data in
Existing Geotube area focusing on
shoreline change, volume change and
bathymetry.
62
Beach Profile Surveys – Summary
Woods Hole Group’s Report* (Continued)
Strong correlation (linear relationship) exists between the shoreline position (MLW)
and beach sand volume in representative profiles, before and after Geotube
installation.
* These data are presented quarterly to
the Conservation Commission. To date 77
quarterly surveys have been completed by
WHG.
63
Beach Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Cumulative Shoreline Change in Project Area ~ 20 years.
Profile 91
•Net shoreline loss since 1994 ~ 110 ft
•Since 2005 – long-term erosion with periodic accretion events.
•Post Geotube similar to overall trend.
64
Beach Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Cumulative Shoreline Change in Squam Area .
Profile S
•Net shoreline advance ~30 ft since 1994.
•Variable shoreline – relatively stable since 2007
•Post Geotube similar to overall trend.
65
Beach Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Cumulative Shoreline Change in Codfish Park Area.
Profile 84
•Late 1990’s shoreline threatening Codfish Park Road.
•Overall shoreline advance ~130 ft since 2000.
•Relatively stable since 2003-2004.
•Post Geotube similar to overall trend.
•High degree of variability.
•Post-Geotube similar to Pre-Geotube
•No evidence of accelerated erosion Post-Geotube exceeding historical observations.
66
Beach Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Cumulative Shoreline Change at 6 profiles in Geotube Project Area and
immediately adjacent areas.
Bathymetry Profile Surveys
67
Bathymetry Profile Surveys
68
Woods Hole Group’s Report
Surveys conducted from shoreline (MLW) out to depth of -40 feet
69
Bathymetry Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Bathymetry Transects at Project Area since 2008.
Data depicts a Stable Profile.
70
Bathymetry Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Bathymetry Transects at Squam Area since 2008.
Data Depicts a Stable Profile.
71
Bathymetry Profile Surveys – Summary
Woods Hole Group’s Report (Continued)
Bathymetry Transects at Codfish Park Area since 2008.
Depicts Large-scale Dynamic Shoal Changes.
72
Beach and Bathymetry Surveys – Findings
Woods Hole Group’s Report, (NOI, Attachment E)
Findings:
•No statistically meaningful trend to Long-term shoreline changes:
These data exhibit a high degree of variability on short and long time scales.
•Present shoreline is similar in position to the shoreline position 8-10 years ago.
•Recent shoreline changes since Geotube installation exhibit similar patterns.
•Geotube project influence is not significant and/or the associated
mitigation is effectively helping to maintain the coastal system.
73
Beach and Bathymetry Surveys – Findings
Woods Hole Group’s Report (Continued)
Findings (continued):
•Strong correlation exists between the shoreline position and volume
of sand in the profile.
•Bathymetry data offshore Sconset Project Area features a generally stable
profile.
•Beach response since geotubes were installed is similar to past
measured shoreline changes. These data suggest that the sand
volume required can be reduced to offset the long-term sand volume
erosion rate in the project area.
74
Beach and Bathymetry Surveys – Findings
Woods Hole Group’s Report (continued)
Findings (continued):
•Generally, there have not been apparent adverse effects to
adjacent coastal landforms since the placement of the existing
geotube project.
•Beach performance trends since installation of geotubes are
similar to historic trends before geotubes.
•Documented large natural variability precludes a purely quantitative
statistical measure of project performance and impacts.
•Data indicate that the geotube project influence is not significant
and/or the associated sand mitigation is effectively helping to
maintain the coastal system.
Expanded Baxter Road and Sconset Bluff
Storm Damage Prevention Project
DEP File#: SE48-3115
Anticipated Topics for October 22, 2018
•Sediment Transport
•Sand Replenishment Protocols
Nearshore Cobble/Boulder Surveys
76
Nearshore Cobble/Boulder Surveys
Sconset Beach Underwater Video Survey Report
Epsilon Associates and CR Environmental, October 2018
•Underwater video surveys were conducted in nearshore off Geotube project in
2016, 2017 and 2018.
•2018 report summarizes survey results for 2018 and compares with previous
2016 and 2017 surveys.
•Reports presented to Conservation Commmission after each survey.
77
Underwater Video Trackline Map
78
Percent Cobble/Boulder at Trackline Intersections
JUN 2016
79
Underwater Video - Screen Shot Project Area
Nearshore (200 ft from beach)
JUN 2016
80
Underwater Video - Screen Shot Project Area
(700 ft from beach)
JUN 2016
81
Percent Cobble/Boulder at Trackline Intersections
JUN 2017
82
Underwater Video - Screen Shot Project Area
Nearshore (200 ft from beach)
JUN 2017
83
Underwater Video - Screen Shot Project Area
(700 ft from beach)
JUN 2017
84
Percent Cobble/Boulder at Trackline Intersections
JUN 2018
85
Underwater Video - Screen Shot Project Area
Nearshore (200 ft from beach)
JUN 2018
86
Underwater Video - Screen Shot Project Area
(700 ft from beach)
JUN 2018
87
Nearshore Cobble/Boulder Surveys
JUN 2018
JUN 2017
JUN 2016
88
Nearshore Cobble/Boulder Surveys
Sconset Beach Underwater Video Survey Report
Epsilon Associates and CR Environmental, October 2018
Findings:
• Continues to be significant natural variability of nearshore habitat.
•Cobble/boulder cover increases as you go farther offshore.
• Highest concentration of cobble/boulders continued to be found in same
general areas.
•June 2018 survey indicates that a productive widespread cobble/boulder
habitat continues to be located just offshore the Geotubes and there is no
indication that habitat is being covered by sand mitigation.
89
Sand Sources
Sand Sources
•Proposed Sand Source
–Island and Off-Island Sand Pits
90 90
Sand Mitigation Summary
•Proposed sand mitigation: complies with the MA Wetlands Protection
Act regulations/performance standards and the Nantucket Wetlands Bylaw
regulations/performance standards for coastal wetlands resource areas in
Project Area. Protects the interests of Storm Damage Prevention
and Flood Control.
•Proposed adaptive sand mitigation: meets the Coastal Hazard Policy
of MA CZM.
•Nearshore cobble/boulder surveys:
–Show continued prevalence of cobble/boulder habitat located directly
offshore from Project.
–No apparent negative effects due to Geotube Project.
•Sand mitigation volume each year will be based on the losses the
previous year.
91
92
Thank You
92