Measures used to collect and carry stormwater
on any site ("stormwater management facilities") shall be designed
to meet the following minimum performance standards:
A. Prevent erosion damage and satisfactorily carry off
or detain and control the rate of release of surface waters.
B. When subsurface soil conditions are suitable, require
runoff control measures to percolate the stormwater into the ground
to aid in the recharge of groundwater and the preservation of baseflow.
C. Carry surface water to the nearest adequate street,
storm drain, detention basin, natural watercourse, or drainage facility.
D. Take surface water from the bottom of vertical grades,
to lead water away from springs, and to collect water upgrade of all
street intersections at the earliest or most efficient point.
E. Control/accommodate not only the anticipated peak
discharge from the on-site disturbed area but also the existing runoff
being contributed from all land at a higher elevation in the same
watershed.
F. Maintain the adequacy of the natural stream channels.
Accelerated bank erosion shall be prevented by controlling the rate
and velocity of runoff discharged to these watercourses so as to avoid
increasing the occurrence of stream bank overflow.
G. Preserve the adequacy of existing culverts and bridges
by suppressing the new flood peaks created by the new earth disturbances.
H. If in the course of preparing or reviewing the stormwater
management plan the Township Engineer determines that off-site improvements
are necessary to satisfactorily control the stormwater from the site,
the applicant shall be responsible for such off-site improvements.
I. All stormwater detention and retention facilities
shall be in place and functioning prior to the creation of any impervious
surface.
J. Whenever a watercourse, stream or intermittent stream
is located within a grading site, it shall remain open in its natural
state and location and shall not be piped unless permitted by the
Pennsylvania Department of Environmental Protection (DEP) and the
Township.
K. The existing points of natural drainage discharge
onto adjacent property shall not be altered without written approval
and a drainage easement from the affected landowners.
L. No stormwater runoff or natural drainage 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.
M. All stormwater management facilities shall be designed
to satisfy the following requirements:
(1) They shall be capable of withstanding the discharge
associated with the one-hundred-year return rainfall event without
failing or resulting in damage to downstream areas. Some nondetention
facilities may be designed to bypass stormwater discharges which are
in excess of the appropriate design storm. In this case, conveyance
must be provided to transport the one-hundred-year surcharge flow
to downstream facilities, a natural watercourse or storm drainage
system inlet.
(2) All groundwater recharge devices shall be protected
from sedimentation. Areas designated for recharge shall not receive
runoff until the contributory drainage areas have achieved final stabilization.