The specifications for construction, as referenced in Appendices
I through VI of these rules and regulations, shall be used as a guide for required construction specifications
unless otherwise directed. The Board, upon recommendation from the
Board's designee, shall determine if the standards have been met.
At a minimum, a continuous low-profile, granite edging shall
be provided as an integral part of all new streets. On cul-de-sac
turnarounds and at intersections, vertical granite curbing shall be
required. Vertical granite curb inlets with curb transition sections
shall be required at the back of catch basins, on grades over 6%,
and at the intersections with arterial streets.
Driveway aprons and road pavement shall be installed at the
same time. Aprons shall extend from the street to the street right-of-way
line. In the event that the driveway aprons cannot be installed at
the same time as the street construction, it shall be the responsibility
of the applicant to ensure that the driveway aprons are installed
prior to the acceptance of the street by Town Counsel and the Board's
designee. If a lot is undeveloped, the applicant shall curb the frontage
of the lot until such time as the lot owner obtains a street opening
permit.
Stormwater run-off shall be disposed of through a combination
of storage and controlled release, as indicated in the Rules and Regulations
Governing Stormwater Management. (See Appendix V.) Drainage systems shall be designed according to the following
principles and criteria:
A. Peak flows. Property shall be developed in such a manner as to maximize
stormwater recharge on the site and to minimize direct overland run-off
into adjoining streets and watercourses. Peak flows and run-off at
the boundaries of the subdivision shall be no higher following development
than before development, for the ten-year and one-hundred-year storm
events.
B. Capacity. Drainage systems shall have adequate capacity to carry
all stormwater run-off presently flowing through the subdivision,
as well as to dispose of any additional run-off generated by the proposed
development, up to and including the run-off from a one-hundred-year
storm using the following methods:
(1)
The flow from storms of up to a twenty-five-year frequency and
a twenty-four-hour duration shall be conveyed through the storm drain
system on the subdivision site. Storm drain piping and grate inlets
shall be designed for a twenty-five-year storm event.
(2)
Detention facilities and culverts shall be provided to accommodate
all run-off, up to and including the run-off generated by the one-hundred-year,
twenty-four-hour storm. As a minimum, detention basin routing calculations
shall be prepared for the ten-year and one-hundred-year storm events.
C. Release rate. The combination of storage and design release rate
shall not result in a storage duration of greater than 72 hours. The
maximum depth of stormwater detention/retention areas shall be four
feet.
D. Outlet structures. Outlet control structures shall be designed as
simply as possible and shall require as little maintenance as possible
for proper operation.
E. Emergency overflow. Each stormwater detention area shall be provided
with a method of emergency overflow in the event of a storm in excess
of the one-hundred-year frequency type.
F. Natural patterns. Natural drainage patterns shall be used wherever
possible. All existing watercourses shall be left as existing unless
approval to alter them is obtained through the Conservation Commission.
All new open watercourses shall be protected from erosion with seeded,
sodded, rip-rapped, stone-lined or other treatment required for the
projected volume and velocity of flow.
G. Alteration. Any alteration of land on the site shall be such that
changes in existing patterns of drainage shall not affect properties
outside the subdivision by increasing the amount or rate of peak flow
as designated by the Wetlands Protection Act.
H. Structured systems. If soil conditions or topography make natural
drainage systems impractical and existing drains in adjacent streets
or easements have adequate capacity to accommodate the drainage flow
from the subdivision, a structured system shall be used and appropriate
connection to the existing Town drainage system shall be made.
I. Calculations.
(1)
Hydraulic calculations, prepared by a registered professional
engineer, shall note the specific engineering and/or computer program
to be used. Hydraulic calculations shall be submitted to substantiate
all design features of any proposed drainage system. Computations
for run-off shall be made in accordance with standard engineering
practice, acceptable to the Board's designee. Pipe systems shall be
designed to provide self-cleaning flow velocities.
(2)
The hydrology calculations information shall include the following
information, as a minimum:
(a)
Runoff area boundaries shown on a plan.
(c)
C factors and I values used for existing and proposed conditions.
(d)
Soil conditions/groundwater.
(3)
The hydraulic calculations shall show the following information,
as a minimum:
(a)
Capacity and projected volume of each catch basin or other inlet
grate.
(c)
Detention/Retention pond calculations, including outlet structure
as applicable.
(d)
Total suspended solid (TSS) removal rates.
(e)
Infiltration calculations as applicable.
(f)
Gutter flow calculations.
(g)
Culvert analysis and calculation as applicable.
J. Detention/Retention basin side slopes. Basin area side slopes shall
be kept as close as possible to natural land contours, i.e. 10% or
less wherever possible. A maximum 3:1 side slope shall be constructed
for the interior of the basin areas. For security purposes, fencing
may be required by the Board. Drainage basins shall be designed to
facilitate access for maintenance vehicles and personnel.
K. Drainage easements.
(1) If it is necessary to carry drainage across lots within the subdivision,
storm drainage easements shall be provided, of such width and construction
as will be adequate to accommodate the volume and velocity of the
run-off. However, no such easement shall be less than 30 feet in width.
(2) If a proposed drainage system would carry water across land outside
the subdivision boundaries to an approved outfall, appropriate drainage
rights shall be secured by the applicant at the applicant's expense,
and shall be referenced on the definitive plan.
Guard rails shall be installed in all areas where fill slopes
in excess of the required 3:1 have been approved. Appropriate slope
treatment and erosion control measures shall be provided for all slopes
in excess of 3:1 and rip-rap may be required on all slopes in excess
of 2:1, unless otherwise specified by the Board.
Street signs shall be installed at all intersections in conformity
with the specifications of the Department of Public Works. Until such
time as each street is accepted by the Town as a public way, the sign
posts at the intersection of each street with any other street shall
have affixed thereto a sign designating such street as a private way.
Upon application for acceptance of the streets, the costs for advertising
for hearing, for data collection in support of the street acceptance,
for permanent signs and for any other costs related to the acceptance
of the street shall be paid by the applicant.
Provisions shall be made for street lighting connections at
locations determined by the Board.
The final grading shown on any approved Form C plan shall not be amended or changed without prior review and approval of the Board except as may be deemed minor by the Board's staff as defined in §
255-5.15F. In reviewing proposed amendments or changes, the Board shall consider the impact of such amendments or changes upon the subdivision as:
A. Changes in the direction of stormwater;
B. Changes in velocities of runoff;
C. Impacts on abutting properties;
D. Impacts on street drainage systems;
E. Impacts on natural drainage channels, watercourses or streams.
Lot slope requirements in the residential zoning districts shall
be as follows:
A. The slope of land at any point, stated as a percentage, shall be
defined as the change in elevation over a horizontal distance measured
perpendicular to the contours divided by the distance over which the
change occurs multiplied by 100.
Slope = (Change in elevation/horizontal distance measured perpendicular
to contours) x 100
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B. All natural slopes exceeding 25% over a horizontal distance of 10
feet as measured perpendicular to the contour are protected and shall
remain in their natural state.
C. All cut-and-fill slopes within or contiguous to the street right-of-way
shall be planted with suitable, well-rooted, low-growing plant materials
or grass as determined by the Board, with advice from the Board's
designee. A wood chip or comparable mulch shall be used with ground
cover plants to minimize erosion. Planting of sod may be required.