Any downstream or off-site hydraulic capacity analysis conducted
in accordance with this chapter or as required by the Township shall
use the following criteria for determining adequacy:
A. Natural or man-made channels or swales must be able to convey the
post-development runoff associated with a ten-year return period event
within their banks at velocities consistent with protection of the
channels from erosion. Acceptable velocities shall be based upon criteria
included in the PADEP Erosion and Sediment Pollution Control Program
Manual.
B. Natural or man-made channels or swales must be able to convey the
post-development, 100-year return period runoff without creating any
hazard to persons or property.
C. Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with 25 Pa. Code Chapter 105 regulations (if applicable) and, at a
minimum, pass the post-development, twenty-five-year return period
runoff.
D. It must be demonstrated that the downstream conveyance channel, other
stormwater facilities, roadways, or overland areas must be capable
of safely conveying the 100-year, twenty-four-hour design storm without
causing additional damage to buildings or other infrastructure. Where
the downstream conveyance channel or other facility is located within
a special flood hazard area (as documented on the Flood Insurance
Rate Map), it must be demonstrated that the limits of said flood hazard
area are not increased by the proposed activity.