A. 
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this chapter.
B. 
The existing points of concentrated drainage that discharge onto adjacent property shall not be relocated and shall be subject to any applicable discharge criteria specified in this chapter.
C. 
Areas of existing diffused drainage discharge shall be subject to any applicable discharge criteria in the general direction of existing discharge, whether proposed to be concentrated or maintained as diffused drainage areas. If diffused flow is proposed to be concentrated and discharged onto adjacent property, the developer must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding, or other harm will result from the concentrated discharge.
D. 
Where a development site is traversed by watercourses other than permanent streams, a drainage easement shall be provided conforming substantially to the line of such watercourses. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may affect adversely the flow of stormwater within any portion of the easement. Also, maintenance and mowing of vegetation within the easement shall be required.
E. 
Any stormwater management facilities regulated by this chapter that would be located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PADOT).
F. 
The Pennsylvania DEP, Chapter 105, Rules and Regulations, apply to the construction, modification, operation or maintenance of both existing and proposed dams, water obstructions and encroachments throughout the watershed, including work in wetlands. Inquiries on permit requirements or other concerns should be addressed to the soils and waterways section of the applicable DEP Regional Office.
A. 
General. The following general standards shall be applied to all development within the Borough of Lansford to promote flow attenuation, erosion and sediment control and flood control.
(1) 
All site development in Lansford Borough creating an area of impervious cover shall submit to this municipality for review a drainage plan consistent with this chapter.
(a) 
A site shall be considered exempt from review under the following criteria:
Total Parcel
Size
Minimum Distance*
(Feet)
Impervious Areas
Exempt
(square feet)
<1 acre
0
5,000
1 to 2 acres
100
10,000
2 to 5 acres
250
15,000
>5 acres
500
20,000
*
The minimum distance between the proposed impervious area and/or stormwater controls/structure discharge point to the downslope property line.
(b) 
This criteria shall apply to the total proposed development even if development is to take place in stages. Impervious cover shall include, but not be limited to, any roof, parking or driveway areas and any new streets and sidewalks. Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious for the purposes of comparison to the waive criteria.
(2) 
Runoff from impervious areas must be drained to pervious areas of the property.
(3) 
Roof drains must not be connected to streets, sanitary or storm sewers or roadside ditches.
(4) 
Runoff from a site should not be concentrated or increase runoff discharged onto adjacent property without the written consent of the adjacent landowners.
B. 
Detention/infiltration standards.
(1) 
Post-development rates of runoff from any regulated activity shall not exceed the peak rates of runoff prior to development for the two-year and ten-year design storms. That is, facilities for the control of stormwater from a development site must be designed for both the two-year and ten-year design storms.
(2) 
Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., are encouraged, where soil conditions permit, to reduce the size or eliminate the need for detention facilities.
A. 
Any stormwater facility located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation.
B. 
Any stormwater management facility required or regulated by this chapter shall be designed to provide an emergency spillway to handle flow up to the 100-year post-development conditions. The height of embankment must be set as to provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed when the facility functions for the 100-year post-development inflow. However, criteria for design and construction of stormwater management facilities are not the same criteria that are used in the permitting of dams under the DEP Dam Safety Program. Depending upon the physical characteristics of a dam, a dam permit may be required and the design will have to meet the provisions of 15 Pa. Code Chapter 105 regulations of the Dam Safety and Encroachments Act.[1] Depending on the physical characteristics of a dam, the design could require that anywhere from a fifty-year to a PMF storm event be considered.
[1]
Editor's Note: See 32 P.S. § 693.1 et seq.
C. 
Any drainage conveyance facility that doesn't fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway. Roadway crossings located within designated floodplain areas must be able to convey runoff from a 100-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of roadway. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.
D. 
Storm sewers must be able to convey post-development runoff from a twenty-five-year design storm without surcharging inlets.
E. 
Adequate erosion protection shall be provided along all open channels, and at all points of discharge.
Stormwater runoff from all development sites shall be calculated using either the Rational Method or a Soil Cover Complex methodology.
A. 
Runoff curve numbers listed in TR-55 are to be used in NRCS methodologies.
B. 
Rational "C" values listed in PennDOT Design Manual 2 are to be used for the Rational formula.
C. 
The design of any stormwater detention facilities intended to meet the performance standards of this chapter shall be verified by routing the design storm hydrograph through these facilities using the storage-indication method. For drainage areas greater than 20 acres in size, the design storm hydrograph shall be computed using a calculation method that produces a full hydrograph. The municipality may approve the use of any generally accepted full hydrograph approximation technique that shall use a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.
D. 
All calculations consistent with this chapter using the Soil Cover Complex method shall use the appropriate design rainfall depths for the various return period storms. If a hydrologic computer model such as PSRM or HEC-1 is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours.
E. 
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods. Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's equation.
F. 
Where uniform flow is anticipated, the Manning equation shall be used for hydraulic computations, and to determine the capacity of open channels, pipes, and storm sewers. All hydraulic computations shall be reviewed and approved by Lansford Borough Engineer.
G. 
Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this chapter using any generally accepted hydraulic analysis technique or method.
The methodology for determining required stormwater controls for a regulated activity is shown in Figure 7-1 and outlined below:
A. 
Compute:
(1) 
Pre-development hydrograph at the site discharge point for the two- and ten-year, twenty-four-hour storm.
(2) 
Post-development hydrograph at the site discharge point incorporating any "non-detention" techniques such as pervious areas, swales, infiltration trenches, etc.
Note: Hydrographs may be obtained from NRCS methods such as TR-55, or from use of the "modified" Rational formulas.
B. 
Compare post-development hydrographs with predevelopment hydrographs. If the peak rate of runoff and the shape of the hydrographs are nearly identical, stormwater management has been achieved. Detention will not be required. If not, proceed to § 378-14C.
C. 
Design detention/retention facilities, in conjunction with any non-detention techniques, such that post-development peak rates from the site will not exceed pre-development levels for both the two and ten-year storms.
Figure 7-1
Stormwater Control Determination Flow Chart