A.
Watersheds. Lower Paxton Township is divided into three
watersheds, including Paxton Creek, Spring Creek, and Beaver Creek
(all contained within the Dauphin County Act 167 Plan). The map indicating
the watershed boundaries is available for inspection at the Township
office. All areas within the districts are subject to the specified
release rates. The one-year, two-year, ten-year, twenty-five-year
and 100-year design storms are all subject to the specified release
rates.
B.
Stormwater management districts.
(1)
If the applicant can show that the post-development
hydrograph matches the predevelopment hydrograph for peak flows and
volume, for all design storms, then meeting the requirements of the
release rates are not required.
(2)
Specific watershed requirements:
(a)
Paxton Creek Watershed: Specified release rate
districts. For all districts in this category, the future runoff must
be controlled to the specified release rate; that is, the post-development
runoff rate must be less than or equal to the predevelopment rate
multiplied by the specified release rate for that district.
(b)
Paxton Creek Watershed: provisional no-detention
districts. These watershed areas may discharge post-development peak
runoff without detention facilities. However, the applicant must prove
that the "local" runoff conveyance facilities which transport runoff
from the site to the main channel have adequate capacity to safely
transport unattenuated increased peak flows for a twenty-five-year
storm in accordance with § 170-114C. If there is inadequate
capacity, the applicant shall either use 100% release rate control
or provide increased capacity within the downstream drainage facilities
to convey increased peak flows consistent with § 170-114C.
When determining if adequate capacity exists in the local watershed
drainage network, the applicant must assume that the entire local
watershed is developed per current zoning and that all new development
will use the least restrictive runoff controls specified by this article.
(c)
Spring Creek Watershed: Specified release rate
districts. For all districts in this category, the future runoff must
be controlled to the specified release rate; that is, the post-development
runoff rate must be less than or equal to the predevelopment rate
multiplied by the specified release rate for that district.
(d)
Beaver Creek Watershed: Specified release rate
districts. For all districts in this category, the future runoff must
be controlled to the specified release rate; that is, the post-development
runoff rate must be less than or equal to the predevelopment rate
multiplied by the specified release rate for that district.
(e)
Areas not within the Paxton, Spring, or Beaver
Creek Watersheds: Standard release rate district. For all areas within
the Township but outside of the Paxton, Spring, or Beaver Creek Watersheds,
the future peak rate of runoff for one-year, two-year, ten-year, twenty-five-year
and 100-year design storms must be controlled equal to or less than
the predevelopment runoff rate for the respective storm frequencies.
(3)
The exact location of any given development site,
or activity regulated by this article relative to the release rate
district boundaries shall be determined by mapping the release rate
district boundaries using two-foot topographic contour mapping provided
as part of the drainage plan.
(4)
For a proposed development site located entirely
within one release rate district, the total runoff from the site shall
meet the required release rate criteria.
(5)
For sites within one release rate district and
having multiple discharge points, any individual point may be designed
to a 100% release rate, provided that the total runoff from the site
is controlled to the applicable release rate for that district and
adequate downstream capacity exists for the unattenuated flow as prescribed
herein.
(6)
For a proposed development site which is located
within two or more release rate districts, the maximum runoff discharged
at any point shall be equal to the release rate for the district in
which the discharge point is located. In the event that a portion
of the site is located in a provisional no detention area, no runoff
from portions of the site located in areas subject to release rate
controls may be drained to or through the provisional no detention
area.
(7)
Each development site shall be considered separately
and shall conform to the criteria of the district in which it is located.
In no case may the release rate for an area be exceeded as "credit"
for a reduction below the criteria or any other restrictions on a
separate site.
(8)
Regional detention facilities may be permitted
provided that adequate conveyance is available or provided from the
site to the facility. The acceptability and discharge characteristics
of the facility will be determined on a case by case basis, by the
Township Engineer, using the calibrated model developed for the Dauphin
County Act 167 Plan.
