HomeMy WebLinkAboutRiverwalk Park_ Boardwalk Design Elevation_BETA Memorandum 01.04.2023
MEMORANDUM
BETA GROUP, INC.
www.BETA-Inc.com
During the Design Development phase, BETA Group, Inc. (BETA) evaluated multiple types of structural
support systems capable of supporting the performed the proposed elevated boardwalk. Alternates
assessed included traditional wooden piles, composite piles, and helical piles, with several ‘hybridized’
alternates of each, which were also evaluated, with design criteria and qualities of each system compared
in a matrix format. The final selection was made to utilize helical piles as the boardwalk structural support
system, based on several factors including minimization of permanent impacts to both the marsh, the
upland woodland access points, probable construction costs, anticipated ease of maintenance /repairs
and minimization of negative visual impacts from surrounding areas.
The two-design elevation(s) of the boardwalk surface (Elev.10.17 and Elev. 11.85) were set by balancing
the different design criteria noted above while maintaining no less than a clearance ratio of 1H:1W
between the boardwalk width and the surface of the saltmarsh. The proposed boardwalk is 6’-0”wide,
with three overlook areas. The 6’-0” width allows for greater spatial clearance between users of the
boardwalk, accommodating pedestrians, walkers with strollers and people using wheelchairs, and avoids
the need for construction of ADA compliant wheelchair turning spaces as appurtenances to the boardwalk
system. The height of the boardwalk is increased for the east-west portion of the route, along the length
where the wider overlooks and bench areas are located. For the highest section of boardwalk (Elev.11.85),
the height to width ratio for the 6’-0” wide straight sections of the boardwalk that are not overlooks or
bench areas attain an average clearance of over 8’-3” over the saltmarsh, translating to a ratio of 1.4H:1W.
In response to the question regarding the proposed height to width ratio differing from guidance provided
by the Division of Marine Fisheries (DMF), elevating the boardwalk to higher elevation(s) than those
presently shown in the NOI Plans, it is foreseeable the action would result in the following outcomes:
• Greater permanent impacts in the salt marsh due to an increase in the overall number of
vertical helical pile supports and/or bracing.
• Greater permanent structural impacts in resource area buffers due to increased ADA
compliant ramp and landing structural systems required for the boardwalk approaches.
• Increased physical presence of structural systems and overall building material mass in
the saltmarsh.
• Increased negative visual impacts from abutting properties, including documented
Environmental Justice Populations to the west of the proposed boardwalk location.
• Increased construction duration and increased public project costs.
Date: January 4, 2023 Job No.: 10056
To:
Brittany DiRienzo, Conservation Agent
Kathleen Williams PE, Yarmouth Town Planner
Cc: Laura Krause, Lead Scientist, BETA Group
Chris Jones, PE, Senior Associate, BETA Group
From:
Arek Galle, RLA Project Manager, BETA Group
Subject: Yarmouth – Riverwalk Park –Elevated Boardwalk Design Considerations