HomeMy WebLinkAbout2013_8_8 SBPF Submission_201405230853376460BAXTER ROAD AND SCONSET BLUFF STORM DAMAGE PREVENTION PROJECT
NOTICE OF INTENT
RESPONSES TO QUESTIONS FROM NANTUCKET CONSERVATION COMMISSION ASKED AT
PUBLIC HEARING ON JULY 30, 2013
Below is a summary of issues raised at the July 30, 2014 hearing for the above-referenced project,
organized by topic.
1. Sand Mitigation
a. Initial Sand Cover on Revetment:
The Notice of Intent Engineering Plans included an initial veneer of sand on the surface
of the revetment, although we noted in the NOI text in section 3.2.2 that sand is
typically not placed on the face of revetments, but may be included for aesthetic
purposes. We have decided that rather than placing the sand on the face of the
revetment, we will place the sand mitigation both in front of and at the ends of the
revetment. This revised approach will make the sand more available to adjacent
beaches to mitigate the armoring of the coastal bank. Sand will be placed at the toe of
the revetment in the form of a terrace or sacrificial dune and will extend approximately
300 feet at revetment ends to help prevent end scour. This sand cover mitigation will
be added to the design plans which will be revised next week using recent LIDAR
survey results.
b. Sediment Budget:
We will submit sediment budget information separately.
c. Mitigation Calculation Using Coastal Bank Retreat Rate
See response #2 to Applied Coastal memo
d. What if sand mitigation isn’t sufficient and end scour occurs?
SBPF will monitor areas immediately adjacent to the revetment to determine if end
scour is occurring and if so, additional sand mitigation will be provided to abate the
situation. Also, SBPF will continue to monitor the extensive existing shoreline
monitoring transects to determine if the project is causing impacts to downdrift beaches.
e. What if sand mitigation isn’t sufficient and toe erosion occurs?
SBPF will monitor the beach elevation in front of the revetment to determine if
excessive toe erosion is occurring. If SBPF engineers determine that toe scour is
excessive either sand mitigation will be supplied or additional rocks will be placed in
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front of the revetment. These will gradually sink into the beach and will augment the
existing toe scour protection of the revetment.
f. Long term Funding of Mitigation?
Funding of construction and the ongoing mitigation and maintenance commitment
would be funded by the creation of a betterment district, i.e. assessments on the
properties on both sides of Baxter Road fronted by the revetment.
2. Inventory of Public Coastal Engineering Structures in Massachusetts
At the last meeting we reviewed some of the results of the inventory of public coastal
engineering structures in Massachusetts prepared by the Department of Conservation and
Recreation, Division of Waterways. One of the Commissioners requested a copy of the
inventory and we have sent Jeff Carlson a copy so it can be posted on your website.
3. What will happen if the revetment fails?
The various modes of revetment failure were discussed at the last ConCom meeting and we
reviewed how this project has been designed to not fail. Also, we discussed failure if the
fronting beach eroded to the point where toe scour threatened the structure. We discussed a
pre-emptive plan to provide additional toe protection by dumping boulders in front of the
revetment to prevent failure by toe scour.
4. Why not Retreat Alternative?
As Sara Alger stated retreat is usually treated as moving a house back on the same lot, not requiring
the acquisition of additional land. Also the town has conducted a preliminary evaluation of
providing additional access to Baxter Road. This would involve the need for takings, large damage
awards and substantial costs to relocate the road and utilities, if this is even feasible.
The Town is not planning for alternative access at the moment. The Town has entered into a MOU
allowing the SBPF to try to protect the road. As Phase 3 of the MOU, SBPF has agreed to use its best
efforts to design and arrange for approval and legal releases to identify a viable alternative access.
The Town began the process of looking at relocating Baxter Road and utilities and it has stopped
working on it until it sees whether SBPF is successful.
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5. Public Access?
We have described that the beach may thin somewhat after the revetment is constructed and
high water after storm events and before sand mitigation is provided may restrict access along
the beach. However, SBPF has proposed additional public access including the following:
Walkway along the top of the revetment with stairs to the beach
Use of existing stairs from top of bluff to revetment walkway
Possible future stairs
Use of the existing bluff walk and possible future expansion
These locations of public access are shown on the attached three public access figures.
6. Article on California Beach Fleas
Sarah Oktay referred to an article that she added to the record entitled “Local extirpations and
regional declines of endemic upper beach invertebrates in southern California” published in
Estuarine, Coastal and Shelf Science (2013), http://dx.doi.org/10.1016/j.ecss.2013.06.017.
This article focuses on two species of isopods (beach or sand fleas) that reside in the supratidal
or high intertidal beach zones along the California coast. This particular study focused on their
distribution between Santa Barbara and San Diego. The article indicates that various coastal
urbanization activities have caused a reduction in numbers of these two species. Coastal
urbanization includes activities such as large beach nourishment, beach grooming and coastal
armoring that affects sediment supply to the beach. The armoring projects in the areas of this
study typically do not include sand mitigation associated with them, thus these are not
comparable to Sconset where sand mitigation is proposed.
7. Nantucket Land Council and Applied Coastal Research and Engineering, Inc.
See the separate response to the NLC letter and Applied Coastal memo.