[Amended effective 2-15-1995]
A.
Soil and drainage.
(1)
No land shall be subdivided for residential use if, after
adequate investigation, the Planning Board determines that it cannot be used
for building purposes without danger to health or safety or welfare.
(2)
The Board shall require satisfactory evidence that soil
conditions and natural drainage are suitable for the proposed subdivision
from the point of view of sanitation and public health.
B.
Natural features.
(1)
To ensure a minimal adverse impact on the natural environment,
due regard shall be shown for all natural features, such as large trees, wetlands,
watercourses, boulders or rock outcrops, as well as for scenic points, historic
spots and similar community assets, which, if preserved, will add attractiveness
and value to the property.
(2)
The applicant shall maintain the existing topography
to the greatest extent possible.
(3)
Retention and detention basins.
(a)
Retention and detention basins or similar man-made drainage
basins are hereby specifically prohibited unless the following conditions
are satisfied:
(b)
Any retention or detention basin required to control
runoff shall be provided only within the landform and contours of undisturbed,
naturally occurring topography and terrain, except that a pipe and earth fill
required for such pipe may be installed to control flow, provided that all
of the following conditions are met:
[1]
The area of existing land surface disturbed by clearing,
cutting trees, filling, regrading or other work shall not exceed 20% of the
area defined by the proposed high water contour line of the basin.
[2]
The storage depth shall not exceed 2 feet.
[3]
No cut shall exceed 4 feet.
[4]
The slope of regraded areas shall not exceed 1 vertical
to 3 horizontal.
[Amended 7-16-2007]
[5]
The basin shall be located within the natural drainage
area that it serves to control.
[6]
Construction shall be done with minimum disturbance to
the existing topography, and all disturbed areas shall be graded and replanted
to blend with adjacent natural land and vegetation.
[7]
All work shall conform to standard construction details (See Appendix A).[1]
[1]
Editor's Note: Appendix A is included at the end of this chapter.
The proposed streets shall conform in width and alignment with those
shown on the master or study plan of the town, as adopted, in whole or in
part, by the Planning Board, except as the same purposes may be shown, to
the satisfaction of the Board, to be better served by a modification thereof
in the general area of the proposed subdivision.
A.
Location.
(1)
Design.
(a)
All streets in the subdivision shall be designed so that,
in the opinion of the Planning Board, they will:
[1]
Provide safe and convenient vehicular travel.
[2]
Permit prompt and efficient means of access for protective
agencies and for other municipal services.
[3]
Have natural drainage with no drainage pockets.
[4]
Provide the minimum number of intersections with major
streets.
[5]
Provide blocks of not less than 600 feet in length nor
more than 1,200 feet in length.
(b)
All streets shall be designed according to Planning Board
specifications and give due consideration to the rural character of the Town.
(2)
Provision satisfactory to the Board shall be made for
the proper projection of streets or for access to adjoining property which
is not yet subdivided.
(3)
Reserve strips prohibiting access to streets or adjoining
property shall not be permitted, except where, in the opinion of the Board,
such strips shall be in the public interest.
(4)
Streets will ordinarily be required adjacent to parks,
schools and the Conservancy District to provide access to and proper policing
of such areas.
B.
Alignment.
(1)
Alignment of street center lines at intersections shall conform to standard construction details. (See Appendix A.)[1]
[1]
Editor's Note: Appendix A is included at the end of this chapter.
(3)
All reverse curves on major and secondary streets shall
be separated by a tangent at least 100 feet long.
(4)
Streets shall be laid out so as to intersect as nearly
as possible at right angles. No street shall intersect any other street at
less than 60°.
(5)
Property lines at street intersections shall be rounded
or cut back to provide for a curb radius of not less than 25 feet.
C.
Widths. The minimum width of streets shall be as follows,
exclusive of berms:
D.
Grades.
(1)
The center line grade for any street shall not be less
than .75%.
(3)
All changes in grade exceeding 1% shall be connected
by vertical curves of sufficient length to afford, in the opinion of the Planning
Board, adequate sight distances.
(4)
Within the right-of-way lines along streets, no cut or fill relative to the proposed finished street center line grades shall exceed 14 feet. (See Appendix A, standard construction details.)[2]
[2]
Editor's Note: Appendix A is included at the end of this chapter.
E.
Dead-end streets. Dead-end streets are not permissible
except in extraordinary circumstances. If such circumstances exist, a waiver
will be required. For any dead-end street allowed, a turnaround with an outer
curb radius of 45 feet and a landscaped, ellipse-shaped center shall be required.
Layout and engineering shall be determined on a case-by-case basis.
[Amended 4-27-1998]
A.
General drainage, subsurface drains.
(1)
New storm drainage construction shall consist of a subsurface,
closed catch basin to drain manhole systems. Stormwater carried on the street
surface shall be collected by catch basins with sumps and hoods on the outlet
pipe discharging to drain manholes. Storm sewers connecting drain manholes
shall be discharged to a detention basin, if a waiver for such detention basin
has been granted, and or recharge areas. Catch basins in series will not be
permitted. The minimum size storm drain is 12 inches.
[Amended 12-15-1997]
(2)
Where it appears that any street may be extended so as
to connect with an existing or proposed street on land adjoining the subdivision,
the Board may require that provision be made for extension of the drainage
system to a point at or near the property line at such size as will allow
for such extension.
(3)
A stormwater management plan incorporating the Department
of Environmental Protection (DEP) policy for the improvement of water quality
in stormwater runoff shall be required. The design of stormwater collection
systems shall conform to the best management practices (BMP's) established
by the DEP.
[Added 12-15-1997]
(4)
Erosion control measures shall conform to the following
specifications to prevent down gradient or adjacent areas from being adversely
impacted. Erosion Control Notes must be shown on the Definitive Plan.
[Added 7-16-2007]
(a)
Prior to any disturbance or alterations on any portion
of the site, a hay bale and silt fence sediment barrier shall be installed
and inspected in the locations shown on the site plan.
(b)
Barriers shall be constructed in accordance with hay
bale and silt fence detail shown in the construction standards.
(c)
Once installed, the staked hay bale and silt fence sediment
barriers shall be maintained in place until all areas up gradient from the
barriers have been stabilized as specified herein. Upon completion and stabilization
of the project, the hay bales and silt fence shall be removed.
(d)
The staked hay bales and silt fence sediment barriers
are intended to act as a limit of disturbance. Any land down gradient from
the barrier accidentally disturbed shall be immediately repaired and restored
to its original condition.
(e)
All disturbed areas are not otherwise developed or incorporating
special stabilization measures or landscape plantings shall be loamed and
seeded. No less than 4 inches of loam topsoil shall be spread and the area
shall be seeded with conservation mix.
(f)
All areas outside the limit of work shall be undisturbed.
During site work all persons and equipment shall stay outside these areas.
Existing vegetation shall be preserved.
(g)
All slopes caused by excavation of existing ground conditions
or fill placement over existing ground to create berms of earth materials
or result from recontouring land for proposed house locations shall be no
greater than 3:1 horizontal to vertical. The toe of slopes in fill areas or
top of slope in excavated areas shall be no closer than 5 feet from adjacent
lot lines. Failure to comply with these requirements will result in enforcement
action.
B.
Drainage easements.
(1)
Where it is necessary to carry storm drains across lots
within the subdivision, easements shall be provided of such width to accommodate
the size of the pipe to be installed.
(2)
Where it is necessary to extend the drainage system across
land beyond the subdivision boundaries to an approved point of discharge,
the easement shall be secured by the applicant and shown on the Definitive
Plan.
C.
Drainage patterns.
(1)
Natural drainage patterns shall be used wherever possible.
All existing watercourses shall be left open unless approval to enclose with
a piped system is obtained through the Conservation Commission.
(2)
Proposed alteration of land on the site shall be such
that changes in existing drainage patterns shall not adversely affect properties
outside the subdivision by increasing the predevelopment peak flows.
D.
Maintenance. The Planning Board may require that a lot
owner trust or association be created to operate, maintain and repair the
drainage and detention facilities and any appurtenances thereto. The trustee
of the trust or association shall be authorized and required to assess and
collect charges for the operation, maintenance and repair from the beneficiaries
of the trust or members of the association. The owners of the record of lots
within the subdivision shall be the beneficiaries of the trust or members
of the association. The town shall be a third party beneficiary of the trust
or association with the right, but not the duty, to enforce the obligations
of the association and trustees. The requirements of the section shall be
included on and referenced in the deed of each lot of the subdivision and
on the Definitive Plan and recorded at the Registry of Deeds or Land Court,
whichever is appropriate. A model declaration of trust for the purposes is
attached to these subdivision rules and regulations as Exhibit A.[1]
[1]
Editor's Note: Exhibit A is included at the end of this chapter.
E.
Drainage calculations.
(1)
Pre-development peak flows. To substantiate the proposed
subdivision drainage system, the drainage calculations shall be prepared by
a Massachusetts registered professional engineer and filed as part of the
Definitive Plan. A stormwater runoff plan within the perimeter of the proposed
subdivision shall be drawn to a scale of 1 inch equals 40 feet and, beyond
the perimeter of the subdivision, contributing watershed areas shall be drawn
to a scale of 1 inch equals 200 feet. Predevelopment peak flows shall be calculated
for two-, ten-, twenty-five-, fifty- and one-hundred-year storms. The runoff
plans and calculations shall be submitted as part of the Definitive Plan.
(2)
Post-development peak flows.
(a)
The forty-scale plan shall show existing and proposed
contours and the incremental watershed areas contributing runoff to each catch
basin, ditch, stream or detention pond. Peak flows shall be calculated for
two-, ten-, twenty-five-, fifty- and one-hundred-year storms. In no case shall
the post-development flows for each storm event exceed the predevelopment
peak flows.
(b)
Calculations of post-development peak flows shall include
the subcatchment areas of the closed system and the overland flow of mini-watersheds
contributing to the total peak flows at the point of discharge to detention
ponds or leaching basins.
(c)
Provided that soil conditions allow, recharge basins
or leaching trenches may be designed to mitigate or reduce the peak flows.
Recharge basins or leaching basins shall be designed based on the rate of
discharge determined by standard, falling head permeability tests.
F.
Design criteria.
(1)
Hydraulics. The closed system shall be designed using
the Rational Method or TR20 of the Soils Conservation Service. The design
storm shall be 25 years.
(a)
Rational Method.
[2]
Rainfall intensities shall be obtained from the Town
of Dover Rainfall Intensity Curves in Appendix C.[2]
[Amended 7-16-2007]
[2]
Editor's Note: Appendix C is included at the end of this chapter.
[3]
The minimum times of concentration shall be 10 minutes
for closed systems and 20 minutes for cross culverts.
(b)
TR20.
[1]
If TR20 is used, the curve numbers designated by the
SCS for similar areas shall apply.
[2]
All drains shall be designed to flow full by gravity,
using the Manning Formula to determine pipe sizes. Drains shall be sloped
to provide a minimum velocity of 2 feet per second and a maximum velocity
of 10 feet per second.
(2)
Hydrology.
(a)
Watershed analyses shall be made for pre and post development
peak flows using the latest version of HYDROCAD or approved equal.
[Amended 7-16-2007]
(b)
Detention basins shall be designed for a one-hundred-year
storm. The release rate shall result in a storage duration of not greater
than 72 hours. Maximum depth of storage for one-hundred-year peak flows shall
be 2 feet. Side slopes shall not be greater than 10% and shall conform as
closely as possible to the natural contours of the land.
(c)
Outlet structures shall be designed for multistage discharge
to release the peak flows of each design storm at a rate no greater than the
calculated predevelopment peak flows. An emergency overflow shall be provided
to accommodate storms in excess of a one-hundred-year event.
(d)
Cross culverts shall be designed for a one-hundred-year
storm, with inlet control. Submerged outlets during periods of storm flow
or during dry periods will not be permitted.
(e)
Infiltration basins, leaching trenches and leaching basins
intended to recharge rainfall runoff shall be designed based on a permeability
test performed after bore holes and standard constant head permeability tests
have determined the conductivity of the soils. The computed rate of recharge
based on the hydrology analysis of the watershed and catchment areas shall
not exceed the conductivity of the soils as indicated by the foregoing permeability
tests. The design storm selected shall be subject to approval by the Town
Engineer. Infiltration areas having a high groundwater table shall be analyzed
for groundwater mounding and approved by the Town Engineer for adequacy.
[Added 7-16-2007]
[Added 7-16-2007[1]]
A.
Sanitary sewers shall be designed for capacity based
on the average daily flow of 150 gallons per unit of multifamily development
in accordance with the provisions of Title V. The minimum pipe size shall
be six-inch diameter. The pipe shall be sloped to provide a minimum velocity
of 2 feet per second and a maximum velocity of 8 feet per second, with a flow
depth of 0.8 of diameter. Changes in direction and changes in slope shall
be made with a standard size four-foot minimum diameter watertight manhole.
Manholes shall be constructed at the end of the lines.
A.
Easements for utilities across lots or centered on rear
or side lot lines shall be provided where necessary and shall be at least
20 feet wide.
B.
Where a subdivision is traversed by a watercourse, drainageway,
channel or stream, the Planning Board shall require that there be provided
a stormwater easement or drainage right-of-way of adequate width to conform
substantially to the lines of such watercourse, drainageway, channel or stream
and to provide for the free flow of water in its natural course or for construction
or other necessary purposes.
C.
Pedestrianways and easements for bridle paths shall be
required to break up along blocks or to connect open spaces or park areas.
Before approval of a plan, the Planning Board may also, in proper cases,
require the plan to show a park or parks or open areas suitably located for
playground or recreational purposes or for providing light and air. The park
or parks shall not be unreasonable in area in relation to the land being subdivided
and to the prospective uses of such land. The Board may, by appropriate endorsement
on the plan, require that no building be erected upon such park or parks without
its approval.
A variation of these design requirements may be permitted when, in the
opinion of the Planning Board, topography or other physical consideration
necessitates such variation.
