In addition to one-family detached home residential subdivision,
other types of subdivisions may occur for which special requirements
may apply, including but not limited to the following:
The Board shall require subdivision plans to show a park or
parks suitably located for recreational and other public purposes
and to provide light and air. The Board shall require by appropriate
endorsement on the plan that no buildings be erected within such park
or parks without the Board's written consent for three years
following the subdivision approval. Such parks can reasonably comprise
7 1/2% of subdivisions of under 50 acres and 5% of larger subdivisions.
A park design plan showing location and equipment shall be submitted
as part of the application.
A.
Due regard shall be shown for the preservation and enhancement of
natural features, such as large trees, wooded areas, watercourses
and bodies, scenic points, historic sites, and similar community assets
which add value and attractiveness to the subdivision and the Town.
If, in the opinion of the Board, excessive foliage growth is removed
due to proposed grades, a planting plan, for the areas affected by
the regrading, shall be submitted for approval together with the definitive
plan. In no case shall areas larger than 100 feet in width be clear
cut to accommodate siting of such structures. The applicant shall
strive to maintain clear cutting within the roadway, and where necessary,
within the planting strip.
(1)
Topsoil. Topsoil removed during the course of construction shall
be redistributed so as to provide at least four inches of cover to
all areas of the subdivision and shall be stabilized by seeding and
planting.
(2)
Floodplains. Proposed subdivisions shall comply with the so-called
Hatch Act, entitled "An Act Relating to the Protection of Floodplains,"
MGL c. 131, § 40 (and any acts in amendment thereof in addition
thereto or in substitution therefor). Written notice to the Plainville
Conservation Commission will be given by the developer if any portion
of the proposed subdivision involves wetlands.
[Amended 3-14-2012]
(3)
Grading and topography. Efforts shall be taken to maintain the continuity
of the natural topography. Cut and fill shall be avoided in all instances
possible. Except in areas where terracing is used, when excavation
is necessary, grading shall be done in such a way that the resulting
contours allow smooth natural curves that conform to the curves of
the surrounding landscape. Straight or angular slopes or cuts which
interrupt natural topography shall not normally be allowed. Existing
contours shall be preserved insofar as it is possible through optimal
location of streets and dwellings to the satisfaction of the Planning
Board. In any event, no change shall be made in existing contours
which adversely affects any land abutting the proposed subdivision.
B.
Street layouts shall generally follow (parallel) the existing contours,
or existing stream valley and natural swales, and should be designed
with the objective of the preservation of natural features identified
on the plan, as required above. All work on the ground hereinafter
specified shall be performed by the applicant in accordance with these
rules and regulations, in conformity with approved definitive plans
and specifications and other construction requirements of the Town
agencies concerned, and to the satisfaction of such agencies. In particular,
all design, material, and construction specifications of the Plainville
Public Works Department relative to road and utility construction
shall be adhered to unless otherwise provided for in these regulations.
Where no detail is given under Plainville DPW specifications, reference
shall be made to construction details of the Massachusetts Highway
Department. All streets in the subdivision shall be designed so that,
in the opinion of the Board, they shall provide safe vehicular travel.
Electric, telephone, fire alarm, and cable TV conduits shall
be placed underground. Size and materials of these conduits and lateral
spacing between conduits shall meet the requirements of the respective
utility company. Conduits shall have a thirty-inch cover, and a bedding
of four inches of sand above and below the conduit. The main line
location of these utilities within the street right-of-way shall be
as shown on the plate for the respective street cross section. The
utilities shall not be located under sidewalks. For streets of fifty-foot
and sixty-foot right-of-ways, with two sidewalks, it is required that
a five-foot-wide communication utilities easement be provided adjacent
to the right-of-way, for the installation of these utilities.
A.
All areas within street right-of-way not used for walks, driveways,
pavement, or structures shall be loamed and seeded at a transverse
slope of 3/16 inch per foot, unless the Board allows otherwise. Maximum
slope outside right-of-way shall be 3 to 1.
B.
T-junctions separated by at least 200 feet between center lines shall
be used whenever feasible in preference to four-way intersections,
and streets shall not join or cross at an angle of less than 70°,
nor shall the 120 feet of street nearest the junction or intersection
be on a curve of less than 500 feet center-line radius.
D.
Turnarounds at the end of dead-end streets shall have outside right-of-way radius of 70 feet and a minimum outside roadway radius of 60 feet, unless an alternative special design has been approved by the Planning Board. See Plate 4.[2]
[2]
Editor's Note: Said plate is included at the end of this chapter.
E.
Roadway corner roundings at street junctions or intersections shall
be at least 25 feet radius for minor and local streets in single-family
residence subdivisions and 35 feet for other classes of streets and
types of subdivisions. The street right-of-way line shall be rounded
at the same distance from the roadway as in the straight segments
of street. In commercial subdivisions and at junctions of collector
and local streets sloping ramps between sidewalks and roadways shall
be provided for wheelchair users.
F.
Reverse and broken-back curves shall not be permitted in collector
and arterial streets, nor in subdivisions other than single-family.
G.
Leveling areas for a distance of at least 60 feet from street line
at a grade of not over 1% shall be provided at intersections.
H.
Streets shall be of uniform width, without jogs or abrupt changes
in direction of street line; all changes in streets shall be by means
of horizontal curves. All changes in grade will use vertical curves.
Super-elevation or horizontal curves shall be provided in accordance
with good engineering practice.
I.
The Planning Board shall assign and may change the names of private
ways in a subdivision in the same manner as revising other aspects
of a subdivision street. All street names will be submitted to the
Police Department and Fire Department for their review and recommendations
prior to the approval of the subdivision.
J.
A period of no more than one year shall elapse between the rough
and finish coats.
K.
Multiple intersections involving a junction of more than two streets
shall be prohibited.
L.
Road foundations. All peat, mud, etc., will be replaced with gravel,
at least one foot in thickness, and four inches of crusher run gravel
and finished with the required bituminous concrete pavement thickness.
M.
In cases where access to a subdivision crosses land in another municipality,
the Board may require certification from appropriate authorities that
such access is in accordance with the Master Plan and subdivision
requirements of such municipality and that a legally adequate performance
bond had been duly posted or that such access is adequately improved
to handle prospective traffic.
N.
The Planning Board may require space reserved for future streets
(shown on said plan as paper streets) to provide for interconnecting
ways and to avoid excessive dead-end streets. All portions of the
tract being subdivided shall be taken up in lots, streets, public
lands, or other proposed uses, so that remnants and land-locked areas
shall not be created.
O.
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.
P.
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.
Q.
Roadways, culs-de-sac, sidewalks and other required infrastructure
or improvements shall not be placed within easements but within the
right-of-way or on parcels not buildable for residential, commercial
or industrial structures. Sewer, water and drainage lines may be exempted
from this provision by the express waiver of the Board.
R.
The permanent street sign will be approved and/or accomplished through the Town's highway superintendent (see § 540-71).
S.
When an applicant is required to cut into existing pavement, the
applicant shall repave the full width of the roadway pavement and
for a distance of five feet in each direction from the end of the
cut. The pavement shall provide for a smooth transition from the existing
to new surface. Such repaving shall meet the subdivision street standards
and recommendation of the superintendent of the Plainville Department
of Public Works.
T.
The developer shall submit the recommended local utility plan, including
the streetlight for service within the subdivision.
U.
Streetlights shall be in place prior to issuance of occupancy permits.
The layout shall be as per the Street Light Committee. Location of
the streetlight pole within the right-of-way shall be as shown on
the plate for the respective street cross section. Cost of installation
and operation shall be borne by the applicant until acceptance by
the Town of Plainville as a Town road.
V.
Granite curbing on a radius connecting to an existing street edge
which has no berm must have tapered end pieces.
W.
The construction of ramps and curb cuts to facilitate the use of
the project by the physically handicapped is required. Ramps shall
be located at intersections, crosswalks, and other locations as required
by the Board.
X.
Driveways will not be located within 20 feet of hydrants or catch
basins.
[1]
Editor's Note: Said table is included at the end of this chapter.
Prior to the application of building permits, the developer
will notify the Board that temporary street signs with three-inch-tall
letters on contrasting background have been placed at intersections.
Permanent street name signs of the type in use in the Town of Plainville
shall be securely installed by the developer at all street intersections
or junctions at least eight feet above ground level.
Granite bounds three feet long and five inches square with a
one-half- inch drill hole in top shall be set by a registered land
surveyor flush with the ground in the street right-of-way lines at
all points of change in direction, beginning and end of curves and
angle points. Where this is impossible, such as in rock, lead-filled
drill holes or other acceptable means of permanent monumentation will
be used.
Whenever connection to the Town fire alarm system is feasible
in the opinion of the Board, the developer shall install to the specifications
of the Fire Chief and connect a fire alarm system. Alternatively,
the Town may have the fire alarm system installed in the subdivision
at the developer's expense. At least one fire alarm box shall
be installed for each 1,000 feet of street or portion thereof. Location
of the fire alarm box within the right-of-way shall be as shown on
the plate for the respective street cross sections and as approved
by the Fire Chief.
Potable water of quality and quantity acceptable to the Board
of Health for domestic use and fire protection water with a minimum
open hydrant flow of 500 gallons per minute shall be provided in each
subdivision at minimum residual pressure of 20 pounds per square inch.
Water lines shall be installed at minimum five feet depth below street
surface and shall be at least six-inch-diameter cement-lined cast
iron one-hundred-fifty pound class or equivalent and shall be furnished
with adequate valves and appurtenances to the specifications of the
Town. Whenever possible, water pipes shall be extended and connected
to form a loop, if need be using easements across lots. Where no municipal
water supply is available within a reasonable distance of the subdivision,
the Board will not approve a subdivision plan unless adequate groundwater
supply is available at the site in the opinion of the Planning Board,
acting with the advice of the Board of Health.
Sewerage disposal system to serve each buildable lot in the
subdivision shall be located and installed to the satisfaction of
the Planning Board and the Board of Health. No lot in a subdivision
shall be approved for building without Board of Health approval of
the individual disposal system for that lot and of the entire subdivision
or parts thereof for subsurface sewage disposal. Design of sewage
disposal facilities shall conform to Title 5 of the Massachusetts
Environmental Code and the rules and regulations of the code due to
high water table or unsuitable soils shall not be approved as building
lots.[1]
[1]
Editor's Note: Wording is so in original.
A stormwater management plan shall be designed by a registered
professional engineer for a subdivision or site to the satisfaction
of the Planning Board. The applicant should be aware that the Board
of Health has stormwater regulations which might supplement those
of the Planning Board and should be considered as well during the
design.[1] The requirements for stormwater management are intended
to protect the public and environment by providing adequate protection
against flooding, siltation, pollutants, and other drainage problems.
The system may take use of gutters, inlets, culverts, catch basins,
manholes, subsurface piping, surface channels, natural waterways,
and detention basins. The Board will not approve any design or component
which in its opinion does not meet the standards of engineering practice,
will not function without frequent maintenance, or is unsuited to
the character of the subdivision. When the project causes a requirement
for stormwater improvements off site, the applicant shall be required
to secure the necessary approvals and provide such improvements in
the public interest.
A.
Drainage criteria:
[Amended 10-21-2002]
(1)
Capture and treat the "first flush" of storm, usually the runoff
from the first two inches of precipitation for a small land area or
other value as may be designated by the Board. Such treatment shall
be by extended detention providing a minimum of 24 hours' average
detention time, unless other methods are specifically allowed by the
Board.
(2)
Not cause an increase or decrease in either the total volume of runoff
discharged off site, or total rate of runoff prior to the development.
Such condition shall be required for storms of one-, ten-, fifty-,
and one-hundred-year frequency events.
(3)
Include source controls and design of BMPs and infiltration and detention
structures in accordance with procedures acceptable to the Board such
as are described in the following publications:
(a)
"Controlling Urban Runoff: A Practical Manual for Planning and
Designing Urban BMPs" — Department of Environmental Programs,
Metropolitan Washington Council of Governments.
(b)
"Stormwater Detention for Drainage, Water Quality, and CSO Management"
— Peter Stahre and Ben Urbones, Prentice Hall, 1990.
(c)
ASCE Publications entitled "Design of Urban Runoff Quality Controls,"
1988, and "Urban Runoff Quality — Impact and Quality Enhancement
Technology," 1986.
(d)
"Urban Surface Water Management" — Stuart G. Walesh, John
Wiley and Sons Inc., 1989.
(e)
"Underground Disposal of Stormwater Runoff — Design Guidelines
Manual," February 1980, of the Federal Highway Administration, Department
of Transportation.
(f)
"Erosion and Sediment Control in Site Development — Massachusetts
Conservation Guide — Volume 1."
(4)
In cases where runoff infiltration cannot, in the opinion of the
Board, be appropriately implemented because of the possibility of
contamination of water supply, or because of extremely poor infiltrative
and permeability characteristics of the soil, the requirement as regards
volume may be waived by the Board, provided the applicant provides
such additional preventive measures to prevent any increase in elevation
or duration of downstream flood elevations. Such additional measures
may be, but are not restricted to, the construction of compensatory
flood storage facilities and/or the creation of additional wetlands.
Poor infiltrative and permeability conditions are defined as a soil
permeability of less than 1 x 10-4 centimeters
per second. Unless, in the opinion of the Board of Health, such testing
is not applicable for a particular site, all permeability tests shall
be in-situ field bore hole tests for permeabilities in the acceptable
range as specified above. If permeability testing is desired to be
performed in soils of lesser permeability, laboratory tests for hydraulic
conductivity shall be performed on undisturbed samples by the Falling
Head Permeability Test using flexible membrane triaxial test cells
with back pressure (Army Corps of Engineering Manual EM 1110-2-1906
Appendix VII).
(5)
If detention or retention ponds are utilized, slopes shall be no
steeper than four horizontal to one vertical. Maximum design water
depth shall not exceed three feet except in permanent ponds. Minimum
bottom slope for "dry" detention areas shall be 2%. A safety bench,
a minimum of 10 feet wide, shall be provided. Detention or retention
areas shall not be constructed within existing stream bed or wetland
areas.
(6)
Not result in channelization of surface runoff off site without the
written consent of the owner of the land affected, in the form of
a permanent grant of easement, recorded at the Registry of Deeds.
(7)
Include hydrologic and hydraulic calculations and data to support
the proposed design for the runoff drainage system. Both volume and
flow rate of runoff, before and after development, must be clearly
stated. Calculations shall be performed using the most recent procedures
of the USDA Soil Conservation Service such as are described in National
Engineering Handbook, Section 4, Hydrology (SCS 1985), TR-20 "Computer
Program for Project Formulation — Hydrology" (SCS 1983), and
Technical Release No. 55 "Urban Hydrology for Small Watersheds" (SCS
1986). Structure design shall comply with the standards of USDA SCS
Publication TR-60 for containments for detention and retention areas
or other designated references. Additional design guidelines may be
on file with the Board. Rainfall event amounts shall be as derived
from the latest Atlases of Precipitation as published by the Northeast
Regional Climate Center, Cornell University, Ithaca, New York.
(8)
The stormwater management plan shall include a complete drain system
designed for each street in the subdivision. It shall be of sufficient
size to permit unimpeded flow of all natural waterways, to provide
adequate drainage of all portions of the street system so that water
does not accumulate thereon, to intercept stormwater from adjacent
lots of the subdivision and to eliminate ponding of storm runoff except
in designated areas.
(a)
The roadway drainage system shall designed to intercept and
carry the ten-year peak rate of discharge as determined using the
Rational Method. The proper drain size may be calculated by using
Manning's Formula.
(b)
Drains must be large enough to pass the design storm without
surcharge. At depressions in the road where ponded water can only
be removed through the roadway drainage system, the inlet and outlet
capacity of the system shall be increased to handle the one-hundred-year
storm runoff to the depressed area.
(9)
Culverts and open channels shall be designed on the basis of a one-hundred-year
storm using the SCS method. Culverts and open channels shall be designed
using a two-foot freeboard allowance. Unsubmerged culverts and open
channels shall be designed using Manning's Formula. Open channels
shall be designed at subcritical flow with a minimum slope of 0.005
feet/foot. Submerged culverts shall be designed by use of hydraulic
engineering circular (HEC) No. 5 and/or No. 10. Minimum culvert sizes
shall be fifteen-inch diameter for driveways and eighteen-inch diameter
for roadway cross culverts.
(10)
Lots shall be graded in such a manner that development of one
shall not cause detrimental drainage on another; if provision is necessary
to carry drainage to or across a lot, an easement of adequate width
shall be provided.
B.
Drainage design.
(1)
Drainage analysis. The stormwater management analysis shall include
at least the following information: watershed area calculations, coefficient
of runoff calculations, determination of time concentration, rainfall
intensity, calculation of design discharge, selection of Manning's
coefficient of roughness, slope of pipe or channel, capacity and velocity
of pipe or channel flow full, velocity of flow for design discharge,
inverts and rim elevations, hydraulic gradeline calculations, and
submit a copy of the drain profile sheets with the hydraulic gradeline
drawn in red pencil. The SCS method analysis should also include a
soil map for the site, and determination of the curve number for each
watershed area. A flow diagram for routing procedures should be provided
similar to that which is outlined in Section 3.5 or TR-20 (U.S. Soil
Conservation Service, Technical Release Number 20 User's Manual).
This flow diagram shows subwater shed delineation and the relationship
of subwatersheds, structures and reaches. The analysis should also
describe all assumptions and provide a copy of all charts and nomographs
used by the designer. Each design shall be accompanied by a suitable
topographic plan of the site and sufficient surrounding area to show
complete drainage patterns that will affect the site and abutting
properties. This plan may, in many cases, be a modified site plan,
but to avoid confusion, should be submitted as a separate sheet and
labeled "watershed plan." The plan shall show existing and proposed
topography and shall clearly indicate: the contributory areas to each
collection structure and catchment area, the route of overland flow,
and the slope used to determine the time of concentration. Each area
is to be labeled with the same designations on the plan as described.
(2)
Drainage structures. Catch basins and manhole structures shall be
reinforced precast concrete with minimum four-foot inside diameter.
Structures shall have a minimum six-inch concrete base. Man covers
and catch basin grates shall be cast iron, conforming to patterns
L-3460 and L-3210, as manufactured by the E.L. Lebaron Foundry, or
equivalent, and be machined to fit their frames securely and evenly.
The top precast section shall be set at an elevation that will allow
for installation of a minimum of two courses and a maximum of five
courses of brick and mortar for setting the cast iron frame and cover
or gate. All construction shall conform to Plates 5 and 6 of these
rules and regulations[2] and to applicable details of the Commonwealth of Massachusetts
DPW Standard Specifications for Highway and Bridges, latest edition.
Cases not specifically covered by this section shall be in accordance
with good engineering practice.
(a)
Materials.
[1]
Materials shall conform to the following requirements:
[a]
Precast reinforced concrete units shall conform
to ASTM C478 and shall be of the sizes indicated on the referenced
detail or shown on the definitive plan.
[b]
Brick shall be new, whole clay brick or equal,
conforming to ASTM C32 Grade MS.
[c]
Concrete for paved inverts and similar uses shall
be 3,000 psi concrete.
[d]
Mortar for use in setting brick and joining precast
sections shall be composed of one part portland cement (ASTM C-150)
to two parts sand (ASTM C-144) with 20% hydrated lime (ASTM C207).
[2]
Structures are to be inspected by the Planning Department Engineer
prior to backfilling.
(b)
Catch basins. Catch basins with two-and-one-half-foot sumps
shall be located on both sides of the roadway, at all low points in
the roadway, uphill of an intersection with the center line of the
basin located three feet before the point of curvature of the curb
rounding of the intersection, at intervals of not more than 300 feet,
and closer as necessary so that the capacity of the gutter and grate
will not cause flooding above 0.2 feet in the gutter line for the
design storm. Additionally, the subdivision drainage system shall
be extended into any existing uphill intersecting street, with a catch
basin installed at the upstream side of the existing street. In no
instance shall catch basins be located along a driveway cut. All catch
basins shall be provided with a cast iron grate and vertical granite
curb inlet. The grate and curb inlet shall be positioned on the structure
in a manner that will not obstruct the grate and gutter mouth openings.
(c)
Manholes. All catch basins shall be connected to the drainage
system through manholes. Manholes shall be required at every change
in direction, slope or diameter of pipe size. The maximum distance
between manholes shall not exceed 300 feet.
[1]
Manhole sizes will be greater than four feet for pipe sizes
larger than 30 inches, and as needed for structural integrity for
multiple pipe entrances at close angles and elevations.
[2]
All manholes shall be constructed with shaped concrete or brick
inverts and shall be provided with cast aluminum or equivalent steps
12 inches apart incorporated in the construction.
[3]
All drop manholes or inlets with a drop of six feet or more
shall be provided with a splash pad.
[2]
Editor's Note: Said plates are included at the end of this
chapter.
(3)
Drain pipe.
(a)
Drain pipes shall be a minimum of Class III reinforced concrete.
In general, they should be designed to flow full with the hydraulic
gradeline (HGL) at the crown. The minimum pipe diameter shall be 12
inches and shall have a minimum grade of 0.4%; larger pipes shall
be governed by the minimum velocity. The minimum velocity at design
flow should be three feet per second and the maximum 12 feet per second,
unless otherwise approved by the Board. All pipe shall have a minimum
2.5 feet of cover over the top of the pipe. Also it is required that
the hydraulic grade line of the storm drain not rise to a level that
would flood any subdrain outfalling into the storm drain system.
(b)
At structures where the outlet pipe is larger than the inlet
pipe, the crown of the outlet pipe shall be at the same elevation
or lower than the crown of the inlet pipe. If there are elevation
problems, pipes may be set to the same energy gradient, which is approximately
obtained by aligning the 0.8 depth point of both pipes.
(4)
Outfalls.
(a)
All drain outfalls shall be extended to, and be compatible with,
either a natural waterway or an existing drainage system. Exposed
ends of all storm drainage pipes shall be provided with flared end
sections or headwalls, appropriate energy dissipaters and security
bars. The ground elevation of all outfall pipes, swales, channels
or drainage ditches discharging to retention basin, detention basin
or to a stream, brook, pond, marsh or other wetland shall be at or
above the ten-year flood elevation to allow free discharge from the
outfall structure.
(b)
Connection to an existing drainage system will require that
the applicant prove that the existing drainage system is adequate
to handle the increased flow from the subdivision. In the absence
of an existing drainage facility, or the inadequacy of the same, it
shall be the responsibility of the applicant to extend drains from
the subdivision as required to properly dispose of all drainage from
the subdivision. Provisions shall be made for the disposal of the
drainage in such manner that no flow is conducted over Town ways,
or over the land of others unless a drain easement is obtained. The
definitive plans will include the plan view and profile of the existing
system that the new subdivision will tie into.
(c)
Where adjacent property is not subdivided, provisions shall
be made for extensions of the system by continuing appropriate drains
to the boundary of the subdivision at such size and grade as will
allow their proper connections.
(d)
Culverts shall have a headwall or flared end section at each
end, and any culvert over 36 inches in diameter shall include at the
upstream end additional protection as approved by the Board for the
roadway side slopes.
(e)
No drainage outfall shall discharge below the high water line
of a swamp, stream, or body of water as defined in MGL c. 131, § 40.
(f)
Pipe outfalls shall be located downgradient from dwellings,
at a position subject to the approval of the Planning Board.
(5)
Security bars.
(a)
Security bars in the form of grates shall be provided at all
accessible openings to open pipe drains. At outfalls of twelve-inch
diameter pipes, a single bar grate which passes through the center
of the opening is sufficient. At outfalls of fifteen-inch diameter
pipes, a two-bar grate which divides the opening into thirds is sufficient.
(b)
At all other locations, including upstream openings of all pipes,
grates are required as follows: the grate shall be constructed of
steel bars not less than 1/2 inch diameter welded together to provide
a grate not smaller than the pipe opening. The vertical bars shall
be placed with four inches clear openings between them, and the horizontal
bars shall be placed six inches on center. The grate shall be installed
at the face of the headwall or flared end sections in such a manner
as to allow removal for maintenance purposes. A suitable sketch of
the grate and method of installation shall be submitted for approval
with the plans for the drains and appurtenances.
(6)
Headwalls and flared end sections. Field stone masonry or stone-veneered
reinforced concrete headwalls or reinforced concrete flared end sections
shall be provided at both ends of culverts and the discharge end of
storm drains.
(7)
Scour protection.
(a)
Description. The discharge end of all storm lines shall be protected
with a riprap apron. Said riprap apron shall be installed so as to
coincide in elevation exactly with the elevation of the bottom of
the pipe and the ground line.
[1]
At straight headwalls, the width of the apron shall equal the
length of the headwall. At headwalls with wingwalls, the width of
the apron shall equal the width of the opening between the wingwalls.
At flared end sections the width of the apron shall equal the nominal
pipe diameter plus six feet. The riprap shall also be placed on the
embankment to a point one foot above the top of the flared end section.
[3]
The riprap apron shall be composed of a layer of stone 12 inches
or more in thickness, placed upon a gravel filter layer six inches
in thickness, unless, in the opinion of the Board or the Board's
Engineer, the quality of the existing subgrade is of a gradation equivalent
to the filter layer material specified.
[4]
The stone used for riprap shall consist of a protective covering
of angular shaped stones laid on the slopes in front of and around
drainage ends to ensure protection of the headwall or flared end unit,
the embankment and the downstream channel.
[5]
In areas where riprap must be placed on slopes equal to or greater
than 5%, the stone shall be grouted and shall be extended in a channel
to a point where the slope of the land is less than 5%, at which point
unmortared riprap shall be placed.
(b)
Materials.
[1]
Stone for riprap shall consist of sound, durable angular boulders,
quarry stone or rock fragments. Bounded stones, boulders, sandstone
or similar stone or relatively thin slabs will not be acceptable.
Stone shall be free of overburden, spoil, shale, and organic material
and shall meet the following gradation requirements:
|
Size of Stone Weight
(pounds)
|
Maximum Percent of Total Weight Smaller Than Given Size
| |
|---|---|---|
|
150
|
100%
| |
|
100
|
80%
| |
|
50
|
25%
| |
|
25
|
10%
|
[2]
No more than 5% by weight shall pass a two-inch sieve. Each
load of riprap shall be reasonably well-graded from the smallest to
the maximum size specified. Control of gradation shall be by visual
inspection.
[3]
Gravel for the filter layer shall conform to the requirements
of road gravel.
[4]
Mortar for grouted riprap shall conform to Section M4.02.15
of the Commonwealth of Massachusetts Department of Public Works Standard
Specifications for Highways and Bridges, 1973.
(c)
Construction methods.
[1]
Prior to placement of the riprap, all unsuitable material such
as topsoil, vegetation, roots, sand, etc. shall be removed from the
area to be protected by riprap. The area shall be filled to the subgrade
of the riprap with material hereinbefore specified for the filter
layer and compacted as for roadway embankments. All slopes adjacent
to the headwall or the flared end unit shall be graded to a slope
not to exceed two horizontal to one vertical. The slope immediately
downstream of the outfall structure shall be graded generally in the
shape of a trapezoidal channel, flaring to a flat cross section at
the terminus of the riprap apron.
[2]
Stone for riprap shall be placed on the filter layer or, when
the filter layer is not required, directly on the prepared slope or
area in a manner which will produce a specified. The riprap shall
be placed to its full course thickness in one operation and in such
a manner as to avoid displacing the underlying material. Placing riprap
by methods likely to cause segregation will not be permitted.
[3]
The larger stones shall be well distributed and the entire mass
of stone shall conform approximately to the gradation specified. The
riprap shall be so placed and distributed that there will be no large
accumulations of either the larger or smaller sizes of stone. All
voids, measuring four inches or larger in any dimension, shall be
filled with stone (chinked) to the satisfaction of the Planning Board
or its agent.
[4]
It is the intent of these specifications to produce a fairly
compact riprap protection in which all sizes of material are placed
in their proper proportions. Hand placing, chinking, or rearranging
of individual stones or existing stone may be required to the extent
necessary to secure the results specified.
[5]
The stone for grouted riprap shall conform to the gradation
requirements for riprap as hereinbefore specified. The stone shall
be clean and free of fines which prevent penetration of grout. Care
shall be taken in placing the stone to keep earth or sand from filling
the spaces between the stones. The stones shall be placed on a prepared
slope and shall be thoroughly moistened. Any excess of fines shall
be sluiced to the underside of the stone blanket before grouting.
The grout shall be delivered to the site by means that will insure
uniformity and prevent segregation of the grout. Penetration of the
grout shall be to the full depth of the riprap apron and the grout
shall fill the interstices to within one inch of the surface.
C.
Performance standards. On-site drainage systems, including detention
areas, must meet the following performance standards:
(1)
A fifty-foot buffer zone of existing vegetation shall be retained
between all detention or siltation structures and adjacent uses or
structures for protection of scenic corridors, surface water and wetlands
subject to MGL Ch. 130 and Ch. 131, and/or local wetland bylaws.[4] However, the provisions of this section shall not prohibit
the selective clearing of trees and shrubs, the establishment of new
vegetation better suited to the proposed considerations, or the discharge
of stormwater across such buffer areas, and, if these actions may
be permitted by the Conservation Commission under an order of conditions.
(2)
Use of retention basins shall not be permitted except in combination
with detention facilities and for the express purpose of containing
the design storm for a twenty-four-hour to forty-eight-hour period.
Detention facilities shall be permitted insofar as such systems are
designed to function as natural wetlands, having characteristics of
side slopes, gradients, vegetation and topographic location which
follow naturally occurring wetland types. Use of such artificial drainage
systems shall not substitute for proper erosion control measures including
appropriate design for soil and slope conditions. Design of such facilities
shall observe the following guidelines:
(a)
Side slopes of wetland/detention areas should be no steeper
than 4:1 horizontal to vertical relationship unless steeper slopes
can be shown to be typical for conditions on the site.
(b)
A maximum of 2% slope shall be permitted for the bottom of the
wetland/basin.
(c)
Where clearing and/or regrading of the site may be unavoidable
for installation of the basin and necessary structures, vegetation
shall be reestablished in conformance with the proposed landscape
plan.
(d)
The prohibition of undesirable or unnatural accumulation of
water shall refer to stagnant, ponded waters, but not to wet systems
which are designed to have continuous stream flow through the basin.
(3)
Drainage outfalls shall be designed in conformance with Subsection B(4)(e), and shall further provide riprap aprons in accordance with the length requirements shown on Plate 9 or 10,[5] and in every case shall provide a minimum of 30 feet of
vegetation swale before the property line and above the high water
line of any stream, swamp, bank, or wetlands bylaw.[6] As with other drainage structures, detention areas shall
have a positive outfall and connection to an existing water body,
including wetlands as defined above.
D.
Subsurface drains or subdrains. In areas where the finished grade
of the roadway is less than four feet above the water table or in
areas where less than four feet of fill is placed above water in swampy
places or any standing water, or in other areas where in the opinion
of the Board the subgrade must be drained, a system of subdrains shall
be designed for such areas. In addition, laterals may be required
as directed by the Board in areas in which an undue amount of water
could accumulate in the subgrade. The system of subdrains shall be
discharged into the storm drainage system or otherwise disposed of
in a manner satisfactory to the Board.
E.
Erosion control facilities.
(1)
Keep disturbed areas small. No more than 50 feet wide, 100 feet long,
and 20% of single lot, or five acres of the overall tract are recommended
guidelines. Consideration of topographic, soil, and vegetative characteristics
shall be demonstrated through identification of erodible soils, steep
slopes, streambanks and drainageways, and measure designed to limit
disturbance of these areas.
(2)
Stabilize and protect disturbed areas quickly. Exposed areas and
stockpiles should be revegetated within 30 to 60 days. Two methods
are available for stabilizing disturbed areas: mechanical (or structural)
methods and vegetative methods. In some cases, both are combined in
order to retard erosion. The selected measure should be identified
in the stormwater management plan submitted with the subdivision application.
(3)
Keep stormwater runoff velocities low. Acceptable overland velocities
shall be less than one foot per second. The removal of existing vegetative
cover during development and the resulting increase in impermeable
surface area after development will increase both the volume and velocity
of runoff. These increases must be taken into account when providing
for erosion control.
(4)
Protect disturbed areas from stormwater runoff. Conservation measures
can be utilized to prevent water from entering and running over the
disturbed area. Diversions and other control practices to intercept
runoff from higher watershed areas, store or divert it away from vulnerable
areas, and direct it toward stabilized outlets should be utilized.
Selected measures should be identified in the proposed stormwater
management plan.
F.
General drainage concerns. Streets and lots shall be graded to provide
for expeditious runoff of water, except that settling basins or other
means of removing pollutants shall be used in draining large parking
areas or streets subject to heavy traffic or other sources of pollutants.
Roof drains may be connected to the drainage system, but no industrial
or domestic waste shall be discharged to or allowed to enter storm
drains.
Existing trees shall be preserved and new trees planted so that
at the time a subdivision is completed trees of 1 1/2 inch or
greater diameter shall be located on each lot within 16 feet of the
street line at a spacing of not less than three trees per 200 feet
street frontage. New trees shall be of species consistent with the
existing trees in the area; they shall be planted in at least 1 1/2
cubic yard of loam, guyed and wrapped as necessary to ensure survival.
The selection, location, and planting of new trees shall be to the
satisfaction of the Tree Warden.
Except for five-foot-wide communication utilities easement adjacent
to the right-of-way, all easements shall be at least 20 feet wide
and shall be centered on lot lines, where feasible, and on natural
watercourses. Easements in favor of the Town shall be provided for
water pipes, subsurface and surface drain lines, fire alarm conduits,
streams and watercourses located outside the street right-of-way,
other than house or building connections. Easements may also be required
for the protection of particularly valuable or unique features, such
as historic site or a vista and for off-street pedestrian, bicycle,
or bridle paths.
Typical Street Cross Section and other typical or standard detail
drawings contained in the Appendix[1] are part of these rules and regulations and should be
consulted as to location and design of these subdivision construction
features.
[1]
Editor's Note: Said drawings are included at the end of this
chapter.
Bituminous concrete or equivalent sidewalks five feet wide shall
be installed along one side of minor, local, and arterial streets
in single-family subdivisions and along both sides of streets on collector
streets in single-family subdivisions and on all streets in apartment,
condominium, commercial, and industrial subdivisions, or extend the
full width to the curb. In all single-family, apartment or condominium
subdivisions some walks or bikeways may be located in ten-foot-wide
easements in lieu of being located within street right-of-way, if
a safer, more convenient and economical pedestrian and bicycle circulation
can be attained thereby. Walks shall be built to the same transverse
and longitudinal slope as the street pavement.
