As used in this chapter, the following terms
shall have the meanings indicated:
The normally occurring small flow in a stream.
June 15, 1988, or the adoption by County Council of subsequent
watershed plan updates.
A statistically determined rainfall event having a specific
distribution of rainfall (inches of precipitation) over a specific
time interval with an associated frequency.
A basin designed to retard stormwater runoff by temporarily
storing the runoff and releasing it at a predetermined rate.
Any improvement of one lot or two or more contiguous lots,
tracts or parcels of land for any purpose (including the expansion
of, or addition to, existing improvements) resulting in the creation
of an additional 7,500 or more square feet of impervious land area.
A stormwater management option which allows for the discharge
of the total stormwater runoff flows from a development site through
outfalls directly into Ridley Creek.
The flow rate at which runoff is allowed to leave a development
site.
One of two hydrologic studies which may relieve a developer
from implementing the release rate percentage stormwater runoff control
criterion.
Surface water runoff.
Natural features, pipes, swales and other man-made improvements
to carry drainage.
Those conditions which were present on any site prior to
the date of adoption of the stormwater management plan or subsequent
updates by the County.
See "rate of runoff."
The likelihood of a storm occurrence developed from recorded
events, typically expressed as a return period such as the twenty-five-year
storm.
Replenishment of existing natural groundwater supplies.
A record of the flow rate leaving a site or passing a point
in a stream channel with respect to time, and displayed as a graph
of flow rate vs. elapsed time or as a listing of flow rates at respective
times of occurrence. For the purpose of this chapter, the hydrographs
developed as part of the Ridley Creek Stormwater Management Plan shall
be used.
A surface which prevents the absorption of water into the
ground. All buildings, driveways, roads, sidewalks and any areas in
concrete, asphalt, etc., are considered impervious within this definition.
Any man-made, immovable structure or facility which becomes
part of, is placed upon, or is affixed to real estate.
The penetration and movement of water through the earth's
surface.
A municipal civil division of the County of Delaware contained
wholly or partly within the Ridley Creek watershed.
See "baseflow."
The maximum rate of flow of water at a given point and time
resulting from a specified storm event.
Expression (in cubic feet per second) of the volume of water
passing a particular point at defined time intervals as specified
by the Act 167 Stormwater Management Plan for the Ridley Creek Watershed.
The primary performance standard of the watershed plan which
defines the percentage of the predevelopment peak stormwater runoff
rate that shall be considered the base runoff rate for a particular
site. The specific release rate percentage for each subarea prescribes
the percentage of the predevelopment rate of runoff which may leave
the site after development.
A storm event which is expected to occur over specific time
intervals (i.e., twenty-five-year storm, which is expected to occur
every 25 years, or has a four-percent chance of occurring in any given
year). See "frequency."
Stormwater runoff.
Facilities which control the stormwater runoff from more
than one development site.
Any facility used for temporary or permanent storage of stormwater
runoff.
Any and all elements of stormwater control systems, including
basins, swales, pipes, conduits, etc.
The portion of the development plan which indicates the existing
site conditions and method(s) for the postdevelopment control of stormwater
runoff in conformance with Act 167[1] and the watershed plan.
The excess water resulting from a precipitation event which
exceeds the amount that can percolate (infiltrate) or be absorbed
into the ground, collects in channels and conduits, and is carried
by receiving streams.
One of the 63 subwatersheds contained within the Ridley Creek
watershed as indicated on Plate 1 of the Act 167 Stormwater Management
Plan for the Ridley Creek Watershed.
A low-lying stretch of land which gathers or carries surface
water runoff.
The total drainage area of a stream and its tributaries.
Act 167 Stormwater Management Plan for the Ridley Creek Watershed,
adopted by Delaware County as required by the Act of October 4, 1978,
P.L. 864 (Act 167), and known as the "Pennsylvania Stormwater Management
Act."[2]
