Possible stormwater control measures, including
on-site infiltration techniques, detention facilities, and other measures,
are described in the Ridley Creek Watershed Plan. Other measures are
acceptable when approved by the municipal engineer. Information and
standards for developing stormwater management controls may be found
in the following references:
A. "Urban Hydrology for Small Watersheds," Technical
Release No. 55, USDA, Soil Conservation Service, January 1975.
B. "Soil Erosion and Sedimentation Control Manual," Pennsylvania
Department of Environmental Resources, May 1976.
C. "Engineering Field Manual for Conservation Practices,"
USDA, Soil Conservation Service, 1975.
D. "Practices in Detention of Urban Stormwater Runoff,"
Special Report No. 43, American Public Works Association, June 1974.
If special geological hazards or soil conditions
are identified on the site, the developer's engineer shall consider
the effect of proposed stormwater management measures on these conditions.
In such cases, the municipality may require an in-depth report by
a competent soils engineer.
Storage facilities shall be designed to control
the postdevelopment peak stormwater runoff rates for the two-, ten-,
and twenty-five-year design rainfall events to the subarea's release
rate percentage or that approved through the downstream impact evaluation.
A. Provisions shall also be made for passing the postdevelopment
one-hundred-year runoff flows through a stormwater detention facility
without damaging or causing failure of (i.e., impairing the continued
function of) the facility.
B. Storage facilities shared by more than one development
site are permitted within a single subarea of the watershed, provided
that they meet the above criteria.
C. Runoff from the development sites involved shall be
conveyed to the facility from its source in a manner so as to avoid
adverse impacts, such as flooding or erosion and scour of natural
channels, to downstream channels and property.
D. Storage facilities shall be located such that they
remain accessible for maintenance based upon the type of equipment
and procedures required.
E. Municipalities may, at their discretion, require any
necessary measures to ensure the security and general safety of proposed
storage facilities.
When storm sewers are proposed, developers must
show:
A. Compliance with all other state and local regulations
and specifications governing the installation of such systems.
B. That there is sufficient channel capacity from the
point where the storm sewer outlets into the natural drainage system
and further downstream to the base of the watershed.
The safety of the public shall be considered
at all times in the design of such facilities and provided for to
the satisfaction of the municipal engineer. Except as otherwise provided
for by municipal ordinances, the standards and specifications of the
Pennsylvania Department of Transportation shall be used in the construction
of stormwater collection system components.
The discharge of concentrated, collected stormwater
runoff from control facilities, such as detention basins or storm
sewers, onto adjacent properties where there is no existing natural
watercourse or drainageway to receive the discharge shall be avoided
unless deemed absolutely necessary. Where such a discharge is absolutely
necessary, easements and/or other provisions shall be proposed, approved,
and implemented to prevent damage to the adjacent properties to the
satisfaction of the municipal engineer. Where discharges are proposed
to natural watercourses and drainageways, such discharges shall be
made in a manner so as not to result in property damage or deterioration
of channel stability.