HomeMy WebLinkAbout20180311_NantucketCoastalConservancy_Email_re_Addl_Sand_CalcsFrom:danneatherton@comcast.net
To:Dawn Hill Holdgate; Matt Fee; Jim Kelly; Jason Bridges; Rita Higgins
Cc:Libby Gibson; Erika Mooney
Subject:ADDITIONAL SAND CALCULATIONS
Date:Sunday, March 11, 2018 8:21:52 AM
Attachments:More about sand.pdfPAGE 61 BOS PACKET 3.7.18.pdfBarbara Bund Presentation 3.7.18.pdf
TO: MEMBERS OF THE SELECT BOARD AND TOWN MANAGER
FROM: NCC TEAM
RE: ADDITIONAL SAND CALCULATIONS
We have done additional calculations to determine how long it would take for
the proposed geotube expansion to exhaust the entire supply of sand in the
two island pits. We present those calculations in the attachment More About
Sand.
Our calculations are based on:
One: A letter from Epsilon Associates responding to questions we posed to the
Conservation Commission. That letter is included in the March 7 BOS packet.
For your convenience, we have included as an attachment the relevant page
from that letter (page 4 from the letter, page 61 from the BOS packet).
Two: The calculations presented at the March 7 BOS meeting by our team
member Barbara Bund. Those calculations are based on the SPBF sand logs
and on the Order of Conditions for the original project. Again for your
convenience, we have included those calculations as an attachment.
If you have any questions about this information, please do not hesitate to
contact us.
ATTACHMENTS: (3)
MORE ABOUT SAND
EPSILON LETTER (page 4)
SAND CALCULATIONS/BARBARA BUND
www.savenantucketbeaches.org
info@savenantucketbeaches.org
PO Box 2050 | Nantucket, MA | 02584
MORE ABOUT THE SAND
1.In our presentation to the BOS on 3/7/18, which was based on numbers from the
SBPF sand logs:
The proposed extended project would require at least
83,600 cubic yards of sand per year. (See note below)
2.From page 4 of the SBPF 3/2/18 letter to the ConCom:
The island’s two sand pits contain an estimated
400,000 to 700,000 cubic yards
3.Dividing the total sand by the annual requirement gives the time before the sand
supply is exhausted if it is used ONLY for the SBPF project (with none for other
uses such as construction):
400,000/83,600 = 4.8 years
700,000/83,600 = 8.4 years
Note: SBPF proposes 4 layers of geotubes. We did not include any increase in sand
because of the fourth layer, although it seems reasonable to assume that the sand
requirement per linear foot would increase.
Nantucket Conservation Commission 4
March 2, 2018
Where will SBPF obtain the sand needed for future replenishment of the current
installation? At the present rate required (a minimum of 2000 dump truck round trips
a year), how long will the current supply of available sand in the two on- island pits
last?
The owners of the two sand pits on the island regard information on the sand capacity
of their pits as proprietary information. SBPF estimates that the existing capacity is on
the order of approximately 200,000 to 350,000 cubic yards (cy) in each pit for a total
of 400,000 to 700,000 cy total.
Other sand pits have existed in the past and it is expected that others will be created
in the future as conditions require. SBPF is exploring a number of other sand sources.
The Town’s protection on this aspect of the project is the condition in the OOC that
the sand be supplied. If it cannot be supplied for any reason, the permit is in default
and the Town could require removal of the project. One of the benefits of a geotube
project instead of a rock revetment, for example, is that the geotubes could be
removed much more easily than a rock revetment. SBPF has provided the Town with
an escrow account to cover the costs of removal in the unlikely event that is necessary.
The state CZM is also involved in planning for offshore sources of sand for sand
nourishment projects which will likely be available in the future.
Sincerely,
EPSILON ASSOCIATES, INC.
Lester B. Smith, Jr Maria Hartnett
Principal, Coastal Geologist Associate