A.
General. Any landowner and any person engaged in the
alteration or development of land which may affect stormwater runoff
characteristics shall implement such measures consistent with the
provisions of this chapter, Pennsylvania Act 167, Stormwater Management
and any other applicable statutes and applicable watershed stormwater
plan. In addition thereof, developers shall:
(1)
Assure that the maximum rate of stormwater runoff
is no greater after development than prior to development activities.
(2)
Permit unimpeded flow of natural watercourses, except as may be modified by stormwater detention pond requirements in § 22-31.
(3)
Ensure drainage of all points along streets.
(4)
Intercept stormwater runoff along streets at intervals
related to the extent and grade of the area drained.
(5)
Provide positive drainage away from onsite sewage
disposal systems.
(6)
Take surface water from the bottom of vertical grades
and lead water away from springs. Cross gutters at public street intersections
and elsewhere shall not be permitted.
(7)
In
any instance where the Township is forced by the Pennsylvania Department
of Transportation to be the permit applicant for a highway occupancy
permit for drainage facilities to be constructed by a private developer
on a state roadway, the developer shall be required to enter into
an indemnification agreement with the Township, which shall identify
maintenance responsibilities for the structures. This document shall
be in a form acceptable to the Township Solicitor, and the Township
will not agree to be a permit applicant to any such construction unless
and until this agreement has been executed by both parties.
[Added 6-8-2009 by Ord. No. 2774]
Designs of storm drainage systems shall be prepared
by a professional engineer, licensed to practice in Pennsylvania.
Complete, detailed calculations shall be signed and sealed by the
preparer and submitted with the preliminary plans.
A.
Drainage plan. A site drainage plan for the proposed
land development shall be prepared which illustrates the following
information:
(1)
Mapping of the watershed area or areas in which the
proposed subdivision or land development is located including topography
(at two foot intervals) of the proposed subdivision or land development
and those areas within 400 feet of the proposed subdivision or land
development.
(2)
Calculations of runoff for all points of runoff concentration.
(3)
Complete drainage systems for the land development.
All existing drainage features which are to be incorporated in the
design shall be identified. If the land development is to be developed
in stages, a general drainage plan for the entire subdivision shall
be presented with the first stage and appropriate development stages
for the drainage system indicated.
(4)
The existing points of natural drainage discharge
and the mode of drainage onto adjacent property shall not be altered,
unless the notarized, written consent of affected landowner(s) is
obtained by the developer.
B.
Diversion of runoff. No stormwater runoff or natural
drainage shall be so diverted so as to overload existing drainage
systems, create flooding or create the need for additional drainage
structures on other private properties or public lands, without safe
and adequate provisions being made by the developer for properly handling
such conditions and the developer obtaining the written consent of
downstream landowners.
C.
Deed restrictions. Where a land development is traversed by watercourses other than permanent streams, there shall be provided a deed restriction conforming substantially with the line of such watercourse. The width of the restricted area shall be adequate to provide for unimpeded flow of storm runoff based on the 100-year storm and to provide a freeboard allowance as determined by using the calculations set forth in Appendix A.[1] The terms of restriction shall require periodic cutting
and maintenance of the vegetation by the landowner and shall prohibit
the alteration, obstruction or encroachment of any kind within the
restricted area. The restriction shall further reserve a right-of-entry
to the Township in the event of danger to public safety, exercisable
only in the case of breach of responsibility by the landowner. These
terms shall be secured through covenants included in the deeds of
conveyance. If such area is determined by the Township Engineer to
be integral to the stormwater system of the Township, a drainage easement
must be provided.
(1)
Drainage structures that are located in state highway
rights-of-way shall be approved by the Pennsylvania Department of
Transportation.
(2)
All streets shall be so designed as to provide for
the collection and conveyance of surface water from their rights-of-way.
[1]
Editor's Note: Appendix A is included at the end of this chapter.
D.
Erosion of watercourse channels. Storm drainage facilities
and appurtenances shall be so designed and provided so as to minimize
erosion in watercourse channels and at all points of discharge.
E.
Storm drainage easements. All storm drainage systems
must be located within a public right-of-way or easement. The minimum
easement width shall be 20 feet centered over the system.
G.
DEP approval. Any proposal storm drainage plans which
affect the drainage basin of any watercourse shall be approved by
Pennsylvania Department of Environmental Protection, Division of Dam
Safety and Waterway Management, if the drainage basin so affected
has an area of 0.5 square miles or more.
A.
Applicability of Act 167. If the land development
is within a watershed with an approved Stormwater Management Plan
enacted pursuant to Act 167, the criteria in the applicable plan shall
be used.
(1)
Any downstream analysis conducted to determine adequacy
for accepting increased rates of runoff shall consider the 100-year
storm event.
(2)
The design or analysis of all natural or man-made
overland drainage systems shall have adequate capacity for the 10-
to 100-year return storm.
(3)
For all development, the extent of the 100-year storm
event shall be shown. Items such as overland flow (width and depth)
and inlets which would backsurge shall be identified.
B.
Design to protect from 100-year storm. In lieu of the requirements set forth in this § 22-30, storm drainage systems required by this chapter shall be designed to provide protection from a 10- to 100-year storm, unless a more conservative design is required by another regulation, or is required because of conditions particular to an individual development.
C.
Design criteria standards. See Table 2.
|
Table 2
| |||
|---|---|---|---|
|
Area
|
Design Storm Return
(years)
| ||
|
Residential Areas:
|
Fixed Pipe
|
10
| |
|
Total Conveyance
|
100
| ||
|
Nonresidential Area:
|
Fixed Pipe
|
25
| |
|
Total Conveyance
|
100
| ||
D.
Watersheds less than 200 acres. Stormwater runoff from watersheds of 200 acres or less shall be calculated by the rational method (See Appendix A[1]), except as the watershed size criteria may be modified
by an approved Act 167 Stormwater Management Plan.
[1]
Editor's Note: Appendix A is included at the end of this chapter.
E.
Watersheds greater than 200 acres. Stormwater runoff
from watersheds of more than 200 acres shall be calculated using the
soil cover complex method developed by the Soil Conservation Service
or other appropriate method acceptable to the Township Engineer.
F.
Verification. The design of any detention facility
shall be verified by routing the proposed post-development hydrograph
through the basin using storage indication techniques.
G.
Submission of calculations. Complete detailed drainage
calculations and applicable charts and hydrographs certified by the
design engineer shall be submitted to the Township Engineer with the
preliminary plan submission.
A.
Compliance with Act 167. Whitehall Township has been designed in its entirety as a provisional no detention area pursuant to Act 167. As such all proposed developments must adhere to the regulations stated therein and in the attached watershed plans. (See Appendix C[1]).
[1]
Editor's Note: Appendix C is included at the end of this chapter.
B.
When required. Stormwater detention facilities may
be required for all land development proposals whenever the following
two criteria have been met:
(1)
The proposed rate and volume of runoff cannot be accommodated
by all downstream fixed pipe or surface drainage system.
(2)
Written permission has not been granted by the adjoining
downstream owner(s) where runoff discharges onto the adjoiner, via
a subsurface and/or surface drainage system to the main channel.
C.
Maximum post peak rates. Whenever stormwater detention
facilities are required, the maximum post-development peak rates of
flow shall be governed by the following provisions:
(1)
Post-development rates of runoff for the 2- , 5- ,
10- , 25- , 50- and 100-year storm events shall not exceed predevelopment
rates.
(2)
Within watersheds for which there is an approved Act 167 Stormwater Management Plan, the detention facilities shall at minimum be designed to discharge post-development peak runoff rates consistent with the plan criteria except in the instance of off-site detention facilities implemented as per Subsection C(4).
(3)
Within watersheds for which there is not an approved Act 167 Stormwater Management Plan, the detention facilities shall be designed to provide that the peak rate of runoff at all points of discharge from the site, when developed, will not exceed the peak rate of runoff at each of those points prior to development, except in the instance of off-site detention facilities implemented as per Subsection C(4).
(4)
In certain instances, regional detention facilities
and other off-site stormwater management facilities to provide runoff
control for multiple development sites may be implemented in lieu
of individual development site detention basins. Peak runoff rates
of discharge from regional detention basins and other off-site stormwater
management facilities shall be based upon maintaining existing peak
runoff rates for the tributary area, except that other criteria for
discharge may apply for regional detention facilities and other off-site
stormwater management facilities located within a watershed with an
approved Act 167 Stormwater Management Plan.
D.
Design requirements. Where stormwater detention facilities
are included as part of the storm drainage system, the following provisions
will apply:
(1)
Detention basins shall be designed so that they empty
completely and no standing water remains.
(2)
The developer shall demonstrate that such basins are
designed, protected and located to assure that public safety is maximized
and health problems are prevented. The following minimum criteria
shall apply:
(a)
Top berm width shall be minimum of 10 feet.
(b)
Side slopes shall be three horizontal to one
vertical or flatter.
(c)
Any basin shall be enclosed with a four foot
high durable chain link fence that includes a 10 foot wide gate with
locking device and vehicle access to floor of the pond.
(d)
All basins shall be screened from view with
a dense, low maintenance, year round vegetative screen that will reach
a height of four feet within two years.
(e)
All basins shall incorporate a four inch impervious
clay liner with a permeability coefficient of 1 x 10-7 cm/sec, verified by test results and a minimum of four inches of
topsoil over the clay.
(f)
All basins shall be seeded with PennDOT, formula
B.
(3)
The developer shall verify that the operation of the
stormwater detention facility will not aggravate potential downstream
peaking conditions.
(4)
An emergency overflow spillway weir, constructed of
concrete, six inches in thickness, shall be provided for stormwater
detention facilities to handle runoff in excess of 100-year storm.
(5)
If a portion of the land development will remain in
common ownership, the developer shall provide an annotation on the
record plan imposing a covenant running with the land requiring perpetual
maintenance of the stormwater detention basin by either the owner
of the development or lot owner.
(6)
All detention basins in all areas must contain easements
for Township emergency maintenance. Routine maintenance such as mowing
of grass, etc., will be the responsibility of lot owner.
(7)
All stormwater detention basin outlet structures shall
be constructed of concrete.
(8)
The bottom of the stormwater detention basin must
slope to the outlet structure at a grade not less than 1%.
(9)
Stormwater retention basins are not permitted.
(10)
When the outflow of a stormwater detention basis
flows downstream and into another detention basin the routed outflow
hydrograph must be added to the existing inflow hydrograph and routed
through the existing stormwater detention basin to determine the impact,
if any. If there is a negative impact on the existing detention basin,
the proposed stormwater detention basin must be altered to eliminate
this impact.
(11)
All stormwater detention basins must be provided
with a minimum of one foot of freeboard above the maximum water elevation
over the emergency spillway.
(12)
All stormwater detention basin outlet structures
smaller than four inches must be fitted with a debris deflector.
(13)
Underground detention must be constructed with
inspection ports (no less than 12 inches in diameter) and a clean
out access hatch (no less than 36 inches in diameter).
(14)
Regulations for the pumping of stormwater detention
facilities.
(a)
The stormwater detention facility shall provide
sufficient capacity to hold runoff volume from the 100-year storm
event plus an additional 40% thereof, without the pumps being in operation.
(b)
All pumping systems shall be housed in a separate
chamber.
(c)
All pumping systems shall be a duplex model
(two pumps).
(d)
An emergency generator shall be part of the
system, with automatic switchover feature.
(e)
The pumping system shall, in the event of the
failure of the pump or the generator, provide an alarm which shall
send a signal to a monitoring service which shall immediately authorize
and effect a service call. The name, address, telephone number and
contact person of the then current monitoring service and the then
current service company shall be provided to the Township.
(f)
The pumping system shall be capable of completely
dewatering the drainage facility within 48 hours after a storm event.
(g)
A note shall be placed on the final plan stating
that: the owner of this property shall, at the property owner's sole
cost and expense, operate, maintain, repair and keep in proper working
order, the stormwater drainage facility and the pumping system so
as to properly accommodate and remove, in a timely and safe manner,
the stormwater collected in the stormwater detention facility situate
on this property. This obligation shall be a covenant running with
the land and shall bind the owner and the owner's successors, heirs
and assigns.
(h)
In the event the property is abandoned, the
pumping system shall remain functional. To that end, the electrical
supply to the pump shall be designed to accept a separate and independently
metered service without energizing any other equipment on the site.
(i)
The developer shall execute an easement in favor
of the Township, in form and content acceptable to the Township Solicitor,
that permits the Township to have access to the property in order
to facilitate the changes to said electrical service to the pump station.
A.
Flanking inlets. When inlets are placed at a low point
on a vertical curve, flanking inlets shall be provided two feet above
the low point inlet or a maximum of 100 feet on either side of the
low point inlet(s).
B.
Design requirements. All storm sewer pipes must be
reinforced cement concrete pipe and a minimum of 15 inches diameter.
Pipes must be provided with a minimum of two feet of cover. When pipe
sizes change in a junction, the crown of the pipes must match. If
the pipe size does not change, developer shall provide a 0.10 foot
minimum drop through the junction. If the Township Engineer deems
it necessary, the energy grade shall control.
D.
Inlet capacity. Inlet capacity calculations must be
provided for all inlets involved in a stormwater drainage system.
E.
Minimum velocity. All storm sewer pipes shall be designed
so as to have a minimum velocity of 3.0 f.p.s.
F.
G.
Sumping of inlets. All inlets shall be sumped one
inch below final road grade elevation. Initially, all inlets within
the cartway shall be sumped one inch below the elevation of the base
course. This practice will allow the inlets to effectively collect
stormwater runoff prior to the placement of the wearing/surface course.
Immediately prior to the placement of the wearing/surface course,
the inlets tops shall be raised to achieve the one inch sump required
herein. The developer shall ensure that sufficient clearance is provided
in order to set the inlet top at the interim elevation required hereinabove.
(See Detail Plate WT-D-02.[2])
[2]
Editor's Note: The Detail Plates are included
at the end of this chapter.
