" Drainage" shall mean the control of surface
water within the tract of land to be subdivided.
A. Storm drains, culverts and related facilities shall
be designed to permit the unimpeded flow of all natural watercourses,
to ensure adequate drainage of all low points along streets, to control
erosion and to intercept stormwater runoff along streets at intervals
reasonably related to the extent and grade of the area drained and
to meet best stormwater management practices as outlined in the Stormwater
Policy and Technical Handbooks prepared by Massachusetts Department
of Environmental Planning and Massachusetts Coastal Zone Management.
B. Storm sewers shall be based on a twenty-five-year
storm frequency, cross culverts at a fifty-year storm frequency, culverts
on a fifty-year storm frequency and detention areas at a one-hundred-year-storm
frequency. In addition, compilations shall be made on two-, ten-,
twenty-five- and fifty-year frequency storms for the contributing
area of the detention area.
C. Design shall be based upon either the Rational Method
or the Soil Conservation Method Modified Soil Complex as defined in
the National Engineering Handbook, Section 4, Site Hydrology. The
minimum water velocity shall be two (2) feet per second. The coefficient
of runoff used shall be not less than three-tenths (0.3) for the subdivided
areas. All developable land attributed to facilities being designed
shall be assumed to be subdivided. A catchbasin-manhole system of
drainage is required, with no storm sewers with an inside diameter
of less than twelve (12) inches near the corners of intersectioning
streets and at intervals of not more than three hundred (300) feet
on continuous grades. Double catch basins are required at all low
points in sag curves. Said double catch basins shall be constructed
perpendicular to the roadway edge (berm/granite curbing). (See typical
cross section in Appendix.)
D. The main drainage system shall be installed on the
high side of the street.
E. Property shall be developed in such a manner as to
maximize stormwater recharge on the site and to minimize direct overland
runoff into adjoining lots, streets and watercourses. Peak flows and
runoff at the boundaries of the subdivisions shall be no higher following
development than before development. There shall be no volumetric
increase or increase in peak runoff off the site. There will be no
more increase of off-site drainage than existing off the site prior
to disturbance of the total development site including both site drainage
and roadway drainage.
F. Volumetric increases in runoff generated by the proposed
development shall be handled as follows:
(1) The flow from storms having a twenty-five-year-storm
frequency and twenty-four-hour duration shall be conveyed through
the subdivision site in a manner which will maintain the ratio of
runoff to infiltration at the same percentage as under normal conditions.
(2) Detention facilities shall be provided to handle all
runoff which exceeds the percolation capacity of the site, up to and
including the runoff generated by the one-hundred-year-storm frequency
and twenty-four-hour duration.
Before approval of a plan by the Planning Board,
said Board shall also, in proper cases, require the plan to show a
park or parks suitably located for playground or recreation purposes
or for providing light and air, and not unreasonable in area in relation
to the area of land being subdivided and the prospective uses of such
land, and if so determined, said Board shall, by appropriate endorsement
on the plan, require that no building may be erected on such park
or parks without its approval for a period of not more than three
(3) years from acceptance of the last street in the subdivision by
the Town.
Due regard shall be shown for all natural features,
such as large trees, watercourses, scenic points, historic spots and
similar community assets, which, if preserved, will add attractiveness
and value to the subdivision.
No definitive plan shall be approved by the
Planning Board unless evidence satisfactory to the Board is presented
that adequate provisions have been made for underground cable utilities
(e.g., to each lot in the subdivision which is to be built upon).
All underground cables within the ways shall be contained within protective
tubing, and handholes for replacement of the same shall be provided
at appropriate intervals.