HomeMy WebLinkAboutBeach Nourishment Monitoring Recommendations 5.11.20CAPE COD ENGINEERING, INC.
Robert M. Perry, P.E.
P.O. Box 1517
East Dennis, MA 02641
Tel./Fax 508-385-1445 / Fax 508-385-1446
bobuerrvna caiwod.net
May 11, 2020
Town of Yarmouth
Conservation Commission
1146 Route 28
South Yarmouth, MA 02664
RE - 182 Baxter Ave. West Yarmouth - Green Harbor Resort - Beach Monitoring
SE83- 2227
182 BAXTER AVENUE, WEST YARMOUTH
GREEN HARBOR RESORT BEACH NOURISHMENT MONITORING
RECOMMENDATIONS
The subject beach is an open, flat, sandy expanse of coastal beach fronting the tidal
waters of Lewis Bay. Elevation ranges from approx. el. 4 to 2 NAVD 88 above the tide
lines. The beach is directly exposed to southerly winds and the related wave chop of the
tidal embayment. Wave energy from the larger Nantucket Sound water body enters the
bay via the dredged inlet channel of Hyannis Harbor. Within the sheltered bay the
combined effects of wind, tides and boat wake activity is the character of the day to day
tidal impact to the beach deposit./ Astronomical and storm tides and winds cause for less
frequent but higher wind and water levels that surcharge the beach.
The beach has been routinely cleaned of occasional wrack material and less intense guest
related materials for several decades. The beach has been sand nourished in the past with
upland source material and from appearances, dredged material as well as wind and tide
delivered sediment. For most of the year the beach remains vacant of any recreational
activity.
Future nourishment shall be triggered in accordance with the guidelines established
through the Conservation review process but initiated by the interest of the resort
management.
Recalling from the hearing discussion, two more profiles can be added to the site plan to
proceed with monitoring. The profiles will show graphically what the spot grades of the
plan view indicate: a very flat beach.
There are two conditions which would logically and reasonably give rise to interest in
providing sediment nourishment.
1. A low beach elevation permitting high course tides to surcharge the beach. This
is the condition that the proposed plan presents. Nourishment causes for a minor,
but recreationally meaningful change in the beach elevation.
2. Inland retreat of the tidal boundary due to shoreline erosion with potential to
diminish the beach area. Such a condition does not appear on the site plan because
the shoreline retreat is a future condition.
Monitoring - Upon initiation of a sediment nourishment activity, a monitoring program
as suggested by the Conservation authority would be undertaken to evaluate the impacts
and beach sediment behavior. The extent and intensity of the monitoring for practical
reasons must be commensurate with the scope of the project. Interest in subsequent
beach terrain changes related to wind and tide effects, dune development, near shore
shoaling are physical factors to be observed and, if necessary, quantified. Given the low
profile alterations in grade, visual assessment is suggested as a good source for
determination of immediate impact. Limited topographic update of the 3 profiles and
accompanying photos will provide information relating to the initial grade change. The
scope of the nourishment project does not warrant intense off site or off shore study. The
array of various coastal engineering structures and small harbor inlet jetties along the
south facing shore of Lewis Bay and dredged navigational improvements in several areas
creates both a highly complex sediment system and fosters a general basis for periodic
sediment deposits since segments of armored shore bank contributes nothing, dredging
affects currents and sediment transport, etc. Interruption of sediment transport by groins
and jetties and occasional dredging offset potential adverse impacts from sand
nourishment. The general observations of the ongoing beach behavior accompanied by
observable triggers for elevation measuring will provide adequate data for understanding
the project impacts. Control of source material quality will offer the greatest
environmental protection benefit. Many Orders of Conditions rely upon language that
allows for reconsideration or terms or Conditions going forward upon discovery of an
unforeseen impact.
Recommendations:
• The site plan can be updated to include two additional profiles representing pre -
nourishment conditions.
• Sieve test report of the source material when selected shall be provided to the
Conservation Dept. for review.
• Update of the 3 profiles upon work completion for any nourishment episode.
• Visual observation is recommended with a photographic record of conditions after
a 6 month term is suggested. Observations will include indications of dune
development, vegetation, general beach condition.
• If the 6 month post- nourishment site inspection indicates that sufficient storm
tide over wash has meaningfully altered the beach grade the profiles would be
updated within a suitable time frame, within a month, for example.
• Following the 6 month inspection a schedule of annual periodic site inspections
is adequate for the first term of the Order of Conditions. It is anticipated that the
Order will be extended to be a practical management guideline. Should a need for
amendment of the Order be indicated the Commission may raise topics of concern
in connection with the extension request.
The applicant seeks the Commissions concurrence on these above recommendations at
the next available hearing.
a
E ' eering, Inc.
Perry