HomeMy WebLinkAbout20131001-Cohen email re Memo on Baxter Rd Protection_201404071113189448From:Steven Cohen
To:Erika Mooney
Cc:Libby Gibson; George Pucci; Kara Buzanoski; Andrew Vorce
Subject:Memo on Baxter Road Protection
Date:Tuesday, October 01, 2013 9:22:40 AM
Attachments:Memo EmergencyRoadProtectionOptions 092513.pdfFigure 1 Distance Transects_117-87.pdf
Erika,
My understanding is that M&M has produced a report to the Town. This is not a report to the BOS,
but just FYI, this is what was provided to M&M. I want to make sure that there is no concern about
nonpublic information.
Best,
Steven
Steven L. Cohen
Reade, Gullicksen, Hanley, Gifford & Cohen, LLP
P.O. Box 2669 (6 Youngs Way)
Nantucket, MA 02584
508-228-3128 W
508-228-5630 F
SLC@readelaw.com
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From: Smith, Les Sent: Wednesday, September 25, 2013 5:31 PMTo: Nicolle Burnham - Milone & MacBroom; kbuzanoski@nantucket-ma.govCc: Maria Hartnett ; Helmut Weymar; Posner Josh; Steven Cohen; Arthur Reade; Jamie FeeleySubject: Memo on Baxter Road Protection
Nicolle and Kara,
Attached please find a memo and figure on Baxter Road temporary protection that we prepared on
behalf of SBPF for your consideration.
M E M O R A N D U M
Date: September 25, 2013
To: Kara Buzanoski, Nantucket DPW
Nicolle Burnham, Milone & MacBroom
From: Les Smith and Maria Hartnett, Epsilon Associates, Inc. (for SBPF)
Subject: Protection of Baxter Road and the Sconset Bluff from imminent danger
Following please find a discussion of options that could provide immediate protection for sections
of Baxter Road prior to the coming winter.
‘Sconset, Nantucket 1 Options for Protection of Baxter Road
OPTIONS FOR IMMEDIATE PROTECTION OF BAXTER ROAD
The purpose of this document is to review options that would allow the Town of Nantucket to
protect the most critically threatened sections of Baxter Road prior to the start of the winter storm
season.
Baxter Road is a public way in the village of Siasconset in Nantucket. It serves as the primary
access for about 100 properties and also contains multiple utilities (water, sewer, communication,
and electric lines or services) for those properties. Most of these properties contribute to the Town
significantly, including as a community of historic homes and as a portion of the Town’s tax base.
Of legal significance, most of these properties also pre-date 1978.
The erosion of the “Sconset Coastal Bank to the east of the road has reached a critical point.
Although the erosion of the top of the bank along northern Baxter Road has averaged about 3.2 feet
per year since 1994, the worst locations have lost 20-30 feet in seasons with severe storm events.
There is now an approximately 551 foot section of Baxter Road, from 99-105 Baxter Road, where
the minimum distance on each property between the edge of the road to the top of the coastal bank
is less than 50 feet (see Figure 1), and the distance from the water line to the east of the paved
surface to the top of the coastal bank is even less (as little as 10 feet from the water line to the top of
the coastal bank). There is an additional adjacent section from 93-97 Baxter Road, where the
distance between the road to the top of the coastal bank is less than 74 feet (the variable distance
ranges from 61 to 74 feet) (see Figure 1). This adjacent section should also be protected, for a total
project length of approximately 780 feet1.
It is plausible, if not likely, that Baxter Road may become impassable due to safety concerns, or that
it may be breached, in as little as one season. The factors leading to this conclusion include the
following: 1) Sconset is a very high-energy environment for storms (especially storm surge and
wave action, but also rain/wind), 2) the coastal bank is at a steep angle already, 3) due to prior
erosion, there is little or no vegetation on the face of this over-steepened portion of the bank, and 4)
if some of the larger losses from last year occur in the coming winter at the narrowest locations, the
edge of the road’s pavement would be at the edge of the bank. If the road is lost, the infrastructure
for and access to many homes and the Sankaty Head Lighthouse would be impacted or lost. In
such a case, the Town faces potentially significant costs for its obligations and liabilities, as
previously outlined by Town Administration and Town Counsel.
The Siasconset Beach Preservation Fund Inc., with the assent of the Town and abutting property
owners, is seeking approval from the Conservation Commission for long-term protection of a large
section of the ‘Sconset Coastal Bank, including this location, but that process will not protect the
road this year. If the Town chooses to protect the public infrastructure from erosion before the
1 The cited distance does not include the northern one-third of lot 105, where the lot widens enough such
that immediate protection is not required.
‘Sconset, Nantucket 2 Options for Protection of Baxter Road
upcoming storm season, there are multiple primary and secondary aspects of erosion that should be
considered: 1) Primary erosion at the toe of the bank and associated sloughing (predominantly
caused by wave action and storm surges) and 2) Secondary erosion from the top and face of the
bank (due to wind, rain and downslope slumping). Any decision by the Town should address both
aspects of erosion, although the primary erosion at the toe of the bank is clearly the most
threatening. The Town also needs to consider that protection for the road will likely be installed in
part or in whole both from and on abutting private property.
PROTECTING THE TOE OF THE COASTAL BANK:
There are a number of possible ways to protect the toe of the bank from erosion. However, given
time constraints, cost, and the immediate threat to the road, the best temporary and removable
choice in this situation is the installation of an appropriately-sized geotube system (approximately
18 feet wide and 7 feet high) at the base of the bank to protect the toe of the bank from wave action
and storm surges. Protecting the toe stops erosion at that point, and prevents sloughing of the face
of the bank except where it is extremely oversteepened. A geotube is fabricated from high strength,
woven polyester or polypropylene sewn together into a tube shape and then filled and covered
with clean sand. Geotubes are extremely durable and can be designed to withstand significant
storm events, and to mitigate scour and flanking. Once filled with sand, the geotubes would
prevent the bank from eroding and contributing sand into the littoral system, which would require
sacrificial sand mitigation. While winter storms may expose the geotube system in whole or in
part, from late spring through early fall it would generally be covered by sand. Geotubes generally
require little maintenance, but if they are punctured they just release compatible sand into the
system. Given the length of large-scale geotubes and the strength of the geotextile fabric, they are
generally not a source of debris as a result of storm damage and could be interlaced with straps
attached to anchors in the unlikely event that the geotube was damaged enough that an empty tube
could be released into the environment. Geotubes stood up very well in New York and New Jersey
during Sandy. They can be installed relatively quickly and have the advantage of being readily
emptied and removed if necessary.
There are several other forms of hard armoring that could be considered, but none are a good
choice in these circumstances given the short time frame for installation and the desire to be cost
effective and removable, but also strong enough for the environment. A marine mattress/gabion
system (small rocks in anchored high density plastic containers), riprap (larger rocks in a free-form
pile), a revetment (even larger rocks installed in an engineered design), or a sea wall (a solid steel or
concrete wall) could provide effective protection in a high-energy environment like Sconset, and
could be designed to mitigate scour, flanking and sand starvation, but none could be installed
before the coming storm season and all would be significantly harder to remove if the protection is
considered short-term (1-3 years).
Alternatives that are designed to reduce wave force, such as off shore breakwaters, and options that
are designed to protect the toe by building out the beach, such as beach nourishment and
dewatering, have not proven effective or sustainable in this location, are very expensive or
‘Sconset, Nantucket 3 Options for Protection of Baxter Road
complicated, are not a viable short term solution, or may have other impacts, such as cost, debris
and impact on local fisheries.
Softer forms of protection, such as dune fencing and sand-filled coir or jute bags are also not a
viable short term solution. The sand-filled jute bags currently in use are porous and designed to
release sand during storm events, which has proven problematic in substantial or successive storm
events, such as last season. Since they lose much of their sand in a storm relatively quickly, they
may not protect against a 3-4 day nor’easter, and may not be quickly enough repaired in the event
of even moderate storms occurring in close succession. This was evident in last winter’s storm
season as areas that could not be rebuilt quickly enough suffered substantial damage.
PROTECTING THE TOP AND FACE OF THE COASTAL BANK:
The preferred option to protect a coastal bank is to plant native vegetation on the bank, which can
be reinforced with terraces and netting. Plants hold together the bank, reduce impact of wind and
rain, and remove excess moisture. However, due to timing, it may not be possible to plant the
bank this fall before the next storm season. Nonetheless, various forms of geogrid fabric, jute
netting, and other soil reinforcement and retaining systems (which are often used in conjunction
with plantings) could be used to secure the upper portion of the face of the bank except where it is
excessively oversteepened. This soil reinforcement is porous and still allows some sand to pass
through, and it could be planted with native vegetation in the spring. Such a system can be
installed quickly, with relatively little impact on the environment, and is readily removable after the
plants take hold. However, the fabric and anchors do pose some risk of debris getting into the
system during a severe storm event. Further, these systems do not prevent the bank from sloughing
where it is excessively oversteepened or if the toe is undermined. In the steepest areas of the bank,
sloughing can be prevented by augmenting the bank face with beach compatible sand deposited
from the top of the bank.
The alternative of driving steel sheeting along the east side of Baxter Road to protect it from bank
erosion has been evaluated by geotechnical engineers from Haley & Aldrich. This alternative is not
recommended as it could be very detrimental to the stability of the bank.
CONCLUSIONS:
Installing some type of toe protection is critical for the 551-foot section of Baxter Road between 99-
105 Baxter Road; protection of the adjacent section of Baxter Road from 93-97 Baxter Road is also
recommended, for a total project length of approximately 780 feet. Given the available timeframe
for permitting and installation, a geotube is the best short-term option. Geotubes can provide
sufficient protection, are easy to install and remove, and held up well during Sandy in other
locations. At Sconset, a 780-foot geotube system could be installed in 2-3 weeks. Additional
measures to protect the bank from secondary erosion, such as augmenting the bank face with beach
compatible sand, reinforcing and then vegetating the bank face and redirecting stormwater away
from the top of the bank, could be included.
Thanks,
Les
Lester B. Smith, Jr.
Principal & Coastal Geologist
Epsilon Associates, Inc.
3 Clock Tower Place, Suite 250
Maynard, Massachusetts 01754
Direct: 978.461.6212
Epsilon: 978.897.7100
lsmith@epsilonassociates.com
https://twitter.com/EpsilonAssoc
www.epsilonassociates.com
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G:\Projects\Lighthouse\2013\Geotube\Revised\transects_117-87.mxd
Figure 1Geotube Analysis
Baxter Road and Sconset Bluff Storm Damage Prevention Project Nantucket, Massachusetts
LEGEND
Basemap: 2013 Aerial Imagery, Col-East, Inc.
Edge of Pavement
2013 Top of Bank
Transects (feet)
Parcels
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