HomeMy WebLinkAboutCorrespondence on update plan 2.23.2021
Grant, Kelly
From:Grant, Kelly
Sent:Tuesday, February 23, 2021 12:47 PM
To:'Bob Perry'
Cc:'Paul Muzyka'
Subject:RE: Revetment design
Attachments:Herbaceous Plant List.pdf
Hi Bob
This looks good to me, though I would like to see additional plant species. See below excerpt from the CZM fact sheet
on bank stabilization. You are OK to use the beach grasses and golden rod but I would like to see a bit more
diversity. How about an interspersed seed mix using a few of the species on the attached list – lower growing species
are fine.
“On banks, switchgrass, saltmeadow cordgrass, little bluestem, and other grasses can stabilize exposed areas
quickly with their fast-growing, fibrous root systems. While American beachgrass is helpful for initial bank
stabilization, it will not thrive on banks that receive little blowing sand. In these areas, it should be planted with
other recommended species that will take over as the beachgrass fades."
"Shrubs, low groundcovers, and perennials that have extensive surface areas and root systems can be used to
intercept heavy rainfall and help shelter and stabilize the underlying soils. Northern bayberry, bearberry, and
marsh elder are excellent shrubs for protecting underlying soil in coastal areas. Shrubs are best used higher up
on the bank where they are not exposed to waves, and planting a mix of grasses around newly planted shrubs
can help stabilize the area while the shrubs become established. Trees and large shrubs should not be planted on
the face of a bank because their height and weight can destabilize the bank and make them vulnerable to
toppling by erosion or high winds. Existing trees on banks can be pruned back to help address this problem."
Send through the paper copies of the plan with an attached planting list and I will get the Order issued.
Thanks
Kelly Grant
Conservation Administrator
Town of Yarmouth
508-398-2231 Ext 1288
kgrant@yarmouth.ma.us
From: Bob Perry \[mailto:bobperry@capecod.net\]
Sent: Monday, February 22, 2021 12:28 PM
To: Grant, Kelly <KGrant@yarmouth.ma.us>
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Cc: 'Paul Muzyka' <paul.muzyka@gmail.com>
Subject: Revetment design
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Hi Kelly,
I received your letter. It was helpful to have the requirements listed so thank you for that. I’m hoping to deliver the
revised plan to accommodate the request to accomplish the re-shaping of the revetment at 45 Crosby Street Ext.
I was not aware that the buried portion of the stone array would lead to encroachment concern. That problem is now
corrected. I think it’s best if you could take a look before we deliver plans.
The 10 ft. plant strip is measured from the landward edge of stone which is the approximate soon – to – be - former top
of the bank. This seemed a reasonable choice rather than chase the c. bank top as it drifts landward. The reshaping of
the coastal bank may not result in a discernable break.
An explanation and a few comments:
The position of the toe stones shifting approx.. 2 to 3 ft. seaward in the last drawing was a practical result of the
Commission’s request for a flatter slope. The reduced face slope, while keeping the toe stones as previously located
created a physical condition where the elev. = 6 upper course of stone is directly below the lip of the coastal bank top
but 3 ft. below it. Carving back the coastal bank crest can be done but is rare.
The opinion repeated at the hearing about conventional revetment face slope values being optimized at 1.5 H to 1.0 v. is
a design preference relating to wave run-up and reflection relationships having more importance in cases with long
fetch, and greater energy environments. Bass River has a great number of vertical seawalls of various materials. Bass
River also has revetments but fewer cases of them. The ones I am familiar with are not laying down below 1 to 1, but
are inclined adequately compared with the more prolific vertical seawalls. The observable variation and effect of the 16
degree slope reduction of such a small feature with the assigned surface roughness will be in the vicinity of “less- than
noticeable” hydraulically but such a change represents an approx. one third size increase in the stone surface ground
occupation measurement.
The purpose of the original 1 to 1 slope initially proposed was founded on two main factors:
1. Recognizing the energy in the river environment was not of the scale requiring strict adherence to
“conventional” face slope preference.
2. Minimize to the degree possible the alteration coverage of the embankment. A 45 degree slope covers approx..
520 s.f. of ground; the 34 degree slope has 715 s.f. of ground coverage.
The beach grass is to be mixed with Seaside Goldenrod. Other coastal plants are expected to arrive as part of the
natural process along this short reach of coastline. If the planting is not satisfactory please let me know and we can
provide additional plants perhaps specified in a letter. Fiber rolls above the stone have been dropped from the
application. If this is an acceptable arrangement please let me know and we’ll proceed with the two paper copies
delivery to the drop box..
Thank you,
Bob
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