[Amended 3-22-2004 by Ord. No. 2004-2]
The management of stormwater on the site, both during and upon completion of the disturbances associated with the proposed subdivision or land development, shall be accomplished in accordance with the standards and criteria set forth in this section and in the Stormwater Management Ordinance set forth at Chapter
162 of this Code.
A. General requirements.
(1) In order to prevent accelerated erosion and resulting sedimentation, land disturbance activities relating to an approved subdivision or land development shall be conducted only in conformity with §
168-25 and the Stormwater Management Ordinance set forth at Chapter
162.
(2) No stormwater runoff or natural drainage water shall
be so diverted as to overload existing drainage systems or create
flooding or the need for additional drainage structures on other private
properties or public lands, without approved provisions being made
by the developer for properly handling such conditions.
(3) Drainage structures that are located on state highway
rights-of-way shall be approved by the Pennsylvania Department of
Transportation, and a letter from that office indicating such approval
shall be directed to the Commissioners.
(4) Blocks and lots shall be graded to secure proper drainage
away from buildings and to prevent the collection of stormwater in
pools. A minimum two-percent slope away from structures shall be required.
(5) To minimize the effect of increased runoff in multifamily
and nonresidential areas, roof drainage shall be conveyed by downspouts
and other drainage facilities constructed under the sidewalk and through
the curb or to a storm sewer, swale, stormwater detention and control
structure or natural watercourse. Approval of such facilities shall
be determined by the Township Engineer.
(6) Drainage across drives, road and walkways shall not
be permitted.
(7) Water from sump pumps shall not be discharged onto
streets, walks or driveways; developers are encouraged to provide
for sump pump discharge directly into the stormwater drainage system.
B. Storm sewers, culverts, bridges and related installations
shall be provided:
(1) To permit unimpeded flow of natural watercourses.
Such flow may be redirected as required, subject to the approval of
the Department of Environmental Protection.
(2) To ensure adequate drainage of all low points along
the line of streets.
(3) To intercept stormwater runoff along streets at intervals
reasonably related to the extent and grade of the area drained and
to prevent substantial flow of water across intersections or flooded
intersections during storms up to and including a ten-year frequency.
(4) To ensure adequate and unimpeded flow of stormwater
under driveways in, near or across natural watercourses or drainage
swales. Suitable pipes or other waterway openings shall be provided
as necessary.
C. Design of storm sewers and related installations.
(1) Storm sewers, as required, shall be placed immediately
in front of the curb, when parallel to the street, within the right-of-way.
When located in undedicated land, they shall be placed within an easement
not less than 20 feet wide, as approved by the Township Engineer.
Open ditches per se shall be avoided, but properly designed, graded
and turfed drainage swales shall be permitted in lieu of storm sewers
where approved by the Township Engineer. Such swales shall be designed
not only to carry the required discharge without excessive erosion,
but also to decrease the time of concentration, reduce peak discharge
and velocity, and permit the water to percolate into the soil. Where
a subdivision is traversed by a watercourse, a drainage easement or
right-of-way conforming substantially to the line of such watercourse
and of such width as will be adequate to preserve natural drainage
and provide sufficient width for maintenance may be required. All
storm sewers or drainage swales shall discharge to a detention facility
for the control of peak runoff discharge, unless otherwise provided
for in the plan or a hydraulic analysis demonstrates a detention facility
is not required.
(2) Storm sewers shall have a minimum diameter of 15 inches
and a minimum grade of 1/2%. Reinforced concrete pipe or high-density
polyethylene (smooth-lined interior) pipe may be used for storm sewers.
Changes in alignment shall be by straight sections connected by inlets
or manholes. A minimum cover of 18 inches shall be provided over all
storm drains. Storm sewer systems shall be designed to handle a ten-year
frequency storm, except from sump (low point) areas to detention facilities
or discharge points in open watercourses, in which case a fifty-year
frequency storm shall be used. If no detention facilities are required
and the storm drainage system is connecting to an existing pipe, then
a ten-year frequency storm can be used throughout. Trench backfill
will be in accordance with Township specifications. Rainfall intensity
curves and other hydraulic design data provided by the Pennsylvania
Department of Transportation and/or Natural Resources Conservation
Service shall be used for design purposes.
(3) Manholes shall be not more than 300 feet apart on
sizes up to 24 inches and not more than 450 feet apart on greater
sizes. Inlets may be substituted for manholes on approval by the Township
Engineer.
(4) Inlets, manholes, covers and frames shall conform
to Pennsylvania Department of Transportation specifications. At street
intersections, inlets shall be placed in the tangent and not in the
curved portion of the curbing. When precast concrete inlets or manholes
are used, a minimum of two courses of brick masonry or grade ring
shall be placed to bring the grate or cover to proper elevation.
(5) Stormwater roof drains shall not discharge water directly
over a sidewalk, driveway or into any sanitary sewer line.
D. Bridges and culverts.
(1) Bridges and culverts shall have ample waterway to
carry expected flows, based on a minimum storm frequency of 50 years.
Bridge and/or culvert construction shall be in accordance with the
Pennsylvania Department of Transportation specifications and shall
meet the requirements of the Pennsylvania Department of Environmental
Protection.
(2) Culverts shall be provided with wing walls and constructed
for the full width of the right-of-way. The cartway area over the
bridge shall be 24 inches wider, on either side, than the road connecting
with the bridge, or, if the character of the road is expected to change
for future planning, the cartway of the bridge shall be made to anticipate
this condition. Provision shall also be made for present or future
sidewalks. Final cartway, sidewalk and total width between parapets
shall be subject to Township Engineer approval.
E. Detention basins shall meet the standards and criteria set forth in the Stormwater Management Ordinance at Chapter
162.
(1) Basins shall be installed prior to any earthmoving
or land disturbances which they will serve. The phasing of their construction
shall be noted in the narrative and on the plan.
(2) Emergency spillway. Whenever possible, the emergency
spillway for detention basins shall be constructed on undisturbed
ground. Emergency spillways shall be constructed of reinforced concrete,
vegetated earth or riprap. All emergency spillways shall be constructed
so that the detention basin berm is immediately protected against
erosion. The minimum capacity of the emergency spillway shall be such
that it will permit passage of flow equivalent to the peak flow produced
in a one-hundred-year storm. After construction, one foot of freeboard
shall be required between design flow elevation through the emergency
spillway and the top of the berm.
(3) Energy dissipaters and/or level spreaders shall be
installed to prevent erosion at points where pipes or drainageways
discharge to or from basins.
(4) The following restrictions shall apply to basins:
(a)
Exterior slopes of compacted soil shall not
exceed one foot vertical for three feet horizontal and may be further
reduced if the soil has unstable characteristics.
(b)
Interior slopes of the basin shall not exceed
one foot vertical to three feet horizontal where maximum water depth
exceeds three feet.
(c)
Slope of the basin bottom shall not be less
than 2% for all sheet flow and a minimum grade of 1/2% for all channel
flow.
(d)
The minimum top width of detention basin berms
shall be 10 feet for all basins exceeding four feet in depth.
(5) Outlet structures within basins which will control
peak discharge flows and distribute the flows by pipes to discharge
areas shall be constructed of concrete or brick and shall have childproof,
nonclogging trash racks over all design openings exceeding 12 inches
in diameter, except those openings designed to carry perennial stream
flows. Antiseep collars shall be installed around the principal pipe
barrel within the normal saturation zone of the detention basin berms.
(6) Inlet and outlet structures shall be located at maximum
distances from one another. The Township Engineer may require a rock
filter berm or rock-filled gabions between inlet and outlet areas
when the distance is deemed insufficient for sediment trapping.
(7) Temporary and permanent grasses or stabilization measures
shall be established on the sides of all earthen basins within 15
days of initial construction.
(8) Notwithstanding the above, all requirements of the
Pennsylvania Department of Environmental Protection and/or the Natural
Resources Conservation Service, United States Department of Agriculture,
shall be met, and evidence of approvals by those agencies shall be
submitted to the Township.
(9) For all proposed developments, plans for erosion and
sedimentation control and stormwater management must be submitted
to the Township for review and approval by the Township Engineer as
part of the subdivision and land development approval process. The
developer and/or owner shall assure the Township, in writing, that
all stormwater management facilities will be properly maintained.
(10)
Any noncompliance with the applicable provisions of this section, as specified in the approved subdivision or land development plan, that is identified by the Township Engineer or his designee in the course of inspections shall be remedied by the developer immediately, but in no case shall such remedy fail to be completed within 10 days and to the satisfaction of the Township. Failure to comply shall be deemed a violation of the approved plan and this Article
IV.
Street name signs shall be installed at all
street intersections. The design and placement of such signs shall
be done by the Township, the cost to be borne by the developer.