[Amended 6-13-2011]
Refer to the Lancaster Stormwater Management Bylaw that was
adopted in October 2007 for the process of securing a local stormwater
management permit.
A. General approach. Storm drains, culverts, swales, detention basins,
and related facilities shall be designed to permit the unimpeded flow
of all natural watercourses, to endure adequate drainage at all low
points along the streets, to control erosion, and to intercept stormwater
runoff along streets at intervals reasonably related to the extent
and grade of the areas being drained. Where determined to be appropriate
by the Planning Board, stormwater shall be carried on the ground surface
and recharged ("open system") rather than piped to surface water ("closed
system"). Peak storm flows and runoff at the boundaries of the development
in a twenty-five-year frequency storm shall be no higher following
development than prior to development, unless an increase is authorized
by the Planning Board, following consultation with the Conservation
Commission and consideration of the ability of receiving wetlands
or water bodies to absorb the increase and the consequences of providing
detention capacity. In the Floodplain District, adequate drainage
systems shall be provided to reduce exposure to flood hazards. Drainage
systems shall be designed based on a twenty-five-year frequency storm,
except that culverts shall be based on a fifty-year storm, detention
basins shall be based on a one-hundred-year storm, and in a one-hundred-year
storm streets shall remain passable and drainage shall not enter buildings.
[Amended 4-27-1987]
B. Storm drains.
(1) Except where drainage swales are used, catch basins will generally
be required on both sides of the roadway on continuous grades at intervals
of not more than 300 feet. Storm drains and culverts shall be no less
than 12 inches inside diameter and shall be of greater size if required
by design considerations. All drains shall have a minimum of three-foot
cover, except where reinforced concrete pipe is used and there the
minimum cover shall be two feet. A catch basin to manhole configuration
shall be used.
[Amended 4-27-1987]
(2) Proper connections shall be made with any existing drains in adjacent
streets or easements where they may exist and prove adequate to accommodate
the drainage flow from the subdivision. If the surface water drains
will discharge into adjacent existing streets, or onto adjacent properties
not under the control of the applicant, the latter shall clearly indicate
what course the discharge will take, and shall present to the Board
evidence from the owner of the adjacent property that such discharge
is permitted.
[Amended 4-27-1987]
(3) Subdrains or interceptor drains are required where necessary to preclude
flowage of groundwater threatening to the integrity of the road surface.
(4) Drainage calculations shall normally assume all tributary area to
be developed as zoned. Water velocities shall be between two and 10
feet per second in pipes, and not over five feet per second in swales.
C. Catch basins. Catch basins shall be provided with grates installed
and approved as to design by the Board. Manholes shall be provided
at changes in direction, and wherever there is a change in size of
pipe. Not more than two catch basins may be connected in series rather
than to manholes. Catch basins and manholes shall be constructed with
standard concrete blocks, with brick and mortar or, if required by
depth, of reinforced concrete. Catch basins shall have a three-foot
deep sump.
D. Detention basins.
[Added 6-13-2011]
(1) An operations and maintenance plan must be submitted as part of the
stormwater management permit application. This plan shall outline
a maintenance schedule for all drainage structures, including swales
and detention basins. The Planning Board may require that a maintenance
bond, or other such instrument, be posted to insure that the ongoing
maintenance is addressed.
(2) Invasive aquatic weeds must be removed from all new detention basins
and stormwater channels for a period of one full year.
E. Water Resource Districts. Within Water Resource Districts as established in Chapter
220, Zoning, of the Code of the Town of Lancaster, provisions for contaminant removal shall be made employing detention basins with subsurface drains or perforated risers, oil and grit separator catch basins, or other devices where appropriate.