Hebron Subdivision
Using Grass Swales to Manage Stormwater
Site
Description: "The Settlement" constructed
in 1997 contains 11 residential lots on a cul-de-sac
built on 25 acres. It is located on Martin Road in
Hebron, CT. All homes are served by private drinking
water wells and septic systems.
Design Details: The planning and zoning
commission revised their road standards for private and public roads
to permit a more rural roadway standard that better fit the character
of the community and that reduced impacts on the site and surrounding
area. The changes included permitting open drainage systems, or
swale designs in certain locations where soils, groundwater and
drainage area characteristics permit. Other recent regulation changes
have required a 100 foot wide conservation easement along Town roads
to maintain the area's rural character, and have required a 20%
open space dedication.
In The Settlement, a pavement width of 22 feet
within a 50 foot ROW drains to vegetated swales (Figure 1). These
swales outlet to catch basins (Figure 1, center) that bring any
excess runoff through pipes and to a stilling basin or velocity
dissipator (Figure 2). The wetlands enforcement officer and public
works director report very little runoff ever makes it to the stilling
basin from the swales. This is evidenced by the vegetation that
is in the basin which would not exist if scouring and high water
were present.
Figure 3 depicts a cross-section of a similar swale
built at The Coats Farm Subdivision, also in Hebron.
Maintenance: Homeowners largely maintain
the swales. In any areas where the swales are not mowed by homeowners,
the Town mows periodically in keeping with their regular roadside
mowing schedule. The public works department has a plow fitted with
a sieve-like device to scoop out sediment with little damage to
vegetation.
Notes: The Town recommends taking a bond to enforce
the proper installation of the swales and to support an inspector
for the town during construction. The Town requires that driveway
crossings be designed and built concurrently with the swales to
avoid disruption of the drainage system.
Mike O'Leary, Town Planner (860-228-5971, moleary@hebronct.com
Tom Fenton, Nathan L. Jacobson & Assoc., Inc.,
Chester Ct, Town Engineer (860-526-9591, tfenton@nlja.com
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