[Ord. 8/12/1999, § 3.1]
1. 
From and after the effective date of this Part, a stormwater management system and drainage plan, along with all other required information and processing fee, shall be prepared and submitted to the Township for all regulated activities.
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 Part.
B. 
The existing points of concentrated drainage that discharge onto adjacent property shall not be relocated and shall be subject to any applicable release rate criteria specified in this Part.
C. 
Areas of existing diffused drainage discharge shall be subject to any applicable release rate 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 or streams, a drainage easement shall be provided conforming substantially to the line of such watercourses or streams. 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 Part that would be located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PA DOT).
F. 
Any stormwater management facilities regulated by this Part that would be located in, or adjacent to, waters of the commonwealth or potential wetlands shall be subject to approval by PA DEP through the joint permit application process, or, where deemed appropriate by PA DEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the developer or his agent to show that the land in question cannot be classified as wetlands otherwise approval to work in the area must be obtained from PA DEP.
G. 
When it can be shown that, due to topographic conditions, natural drainageways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by PA DEP through the joint permit application process, or, where deemed appropriate by PA DEP, through the general permit process.
H. 
Stormwater resulting from land development activities shall not be discharged into sinkholes.
I. 
For design purposes the pre-development runoff rate shall be presumed to be meadow unless the site-specific ground cover is confirmed on-site and different runoff rate is approved by the Township Engineer.
[Ord. 8/12/1999, § 3.2]
1. 
Districts.
A. 
For the purposes of managing stormwater within Montour Township the Township is hereby divided into the following stormwater management districts:
(1) 
Stormwater District 1 — Mahoning Creek Watershed.
(2) 
Stormwater District 2 — Sechler Run Watershed.
(3) 
Stormwater District 3 — remainder of Montour Township.
B. 
The location and boundaries of the stormwater management districts are shown on the map in the Appendix.[1]
[1]
Editor's Note: The Appendix is included as an attachment to this chapter.
[Ord. 8/12/1999, § 3.3]
1. 
District Standards.
A. 
All regulated activities occurring within Stormwater District 1 shall comply with the Mahoning Creek-Sechler Run Watershed Stormwater Management Plan, dated June, 1995, and all other applicable provisions of this Part.
B. 
All regulated activities occurring within Stormwater District 2 shall comply with the Mahoning Creek-Sechler Run Watershed Stormwater Management Plan, dated June 1995, and all other applicable provisions of this Part.
C. 
All regulated activities occurring within Stormwater District 3 shall comply with all other applicable provisions of this Part and shall:
(1) 
Ensure that the maximum rate of stormwater runoff is no greater after development than prior to development activities for the two-, ten-, twenty-five- and fifty-year storms.
(2) 
Manage the quantity, velocity and direction of resulting stormwater runoff in a manner which otherwise adequately protects health and property from possible injury.
2. 
General Standards. The following general standards shall be applied to all development within Montour Township to promote flow attenuation, erosion and sediment control and flood control.
A. 
The developer of any development in the Township, unless exempted in § 26-132 of this Part, shall submit a drainage plan consistent with the provisions of this Part to the Township for review and approval.
B. 
Runoff from impervious areas shall be drained to pervious areas of the property, unless a direct stream discharge or storm sewer connection is possible without adverse effect, and unless a drainage easement is granted by an adjacent property owner.
C. 
Roof drains and sump pumps shall not be connected to sanitary sewers, septic systems, streets or roadside ditches.
D. 
Runoff from the site shall not be concentrated nor shall increased runoff be discharged onto adjacent property without the written consent of the adjacent landowners in the form of a drainage easement.
E. 
Impervious surface shall include, but not be limited to, any roof, parking or driveway areas and any new streets or sidewalks. Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious for the purpose of comparison to the exemption criteria in § 26-132 of this Part.
F. 
Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, porous paving, etc. are encouraged, where soil conditions permit, to reduce the size or eliminate the need for detention facilities.
G. 
It shall be the responsibility of the Township Engineer to determine whether site specific soil conditions permit the use of infiltration practices.
3. 
Stormwater Control Standards.
A. 
Stormwater District 1 - Mahoning Creek Watershed.
(1) 
Fifty-year post-development flow is to be reduced to the fifty-year pre-development flow.
(2) 
Two-year post-development flow is to be reduced to the one year pre-development flow.
B. 
Stormwater District 2 - Sechler Run Watershed.
(1) 
Fifty-year post-development flow is to be reduced to the twenty-five-year pre-development flow.
(2) 
Twenty-five-year post-development flow is to be reduced to the ten-year pre-development flow.
(3) 
Two-year post-development flow is to be reduced to the year pre-development flow.
C. 
General District 3 - Remainder of Montour Township.
(1) 
Two-, ten-, twenty-five- and fifty-year post-development flow is to be reduced to pre-development levels.
[Ord. 8/12/1999, § 3.4]
1. 
Any stormwater management facilities required or regulated by this Part shall be designed to meet the performance standards set forth in § 26-122 of this Part.
2. 
The height of the settled embankment shall be set to provide a minimum one foot of freeboard above the maximum pool elevation when the facility functions for design storm post development inflow. Should any stormwater management facility require a dam safety permit under 25 Pa. Code Chapter 105, the facility shall be designed in accordance with Part and meet the regulations of Chapter 105 concerning dam safety.
3. 
Any facilities that constitute waterway obstructions (e.g., culverts, bridges, outfalls or stream enclosures) and any work involving wetlands as described in 25 Pa. Code Chapter 105 regulations (as amended or replaced from time to time by PA DEP), shall be designed in accordance with Chapter 105 and will require a permit from PA DEP. Any other drainage conveyance facility that does not fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the ten-year design storm with a minimum one 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 one-hundred-year design storm with a minimum one foot of freeboard measured below the lowest point along the top of roadway. Any facility that constitutes a dam as defined in 25 Pa. Code Chapter 105 regulations may require a permit under dam safety regulations. Any facility located within a PA DOT right-of-way must meet PA DOT minimum design standards and permit submission requirements.
4. 
Storm sewers must be able to convey post-development runoff from a ten-year design storm without surcharging inlets.
5. 
Storm sewer inlet spacing and road cross section design must ensure that post-development runoff resulting from a ten-year design storm does not flood more than 1/2 of a driving lane.
6. 
Easements along open channels shall be provided. The minimum width of the required easement shall be equal to the width of the one-hundred-year water surface (for post-development conditions), including a minimum one foot of freeboard or 20 feet, whichever is greater.
7. 
For development sites that would be located in two or more subareas the applicable release rate for the portions of the site located in different subareas shall be based on natural subarea drainage boundaries. The natural drainage boundaries between subareas shall not be modified, nor shall drainage from a development site be diverted or otherwise conveyed from one subarea to another, except where runoff naturally crosses subarea drainage boundaries.
8. 
For any development site the developer has the option of discharging post-development runoff at a higher rate than pre-development runoff if the developer can prove that no harm would be caused to any person or property located upstream or downstream of the development site. The developer must assume that the entire subarea in which the site is located is developed. The type and amount of development that the developer must consider shall be based on the maximum amount of imperviousness which can be reasonably anticipated under current zoning. Proof that no harm would be caused must be demonstrated in conformance with the hydraulic capacity criteria specified in this Part. Areas that drain through documented drainage problem areas are precluded from utilizing this provision, based on peak runoff increases, except where hydraulic capacity improvements are to be provided consistent with this Part.
9. 
Regional or Subregional Stormwater Management Facilities. The funding for any regional or subregional stormwater management alternatives are the responsibility of prospective developers. The design of any regional stormwater management facilities prospective developers. The design of any regional stormwater management facilities must assume development of the entire area that would drain to the regional facility. When regional or subregional stormwater management facilities are utilized, the effect of all phased growth on stormwater runoff flows must be considered. At no time from the initial phase through ultimate development shall the peak runoff flows exceed the pre-development peak multiplied by the applicable release rate.
10. 
If the developer can prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the existing drainage network the adequate capacity improvements may be provided by the developer in lieu of stormwater management facilities on the development site. Any capacity improvements shall be designed based on development of all areas tributary to the improvement and the capacity criteria specified in this Part. The type and amount of development that the developer must consider shall be based on the maximum amount of imperviousness which can be reasonably anticipated under current zoning. It shall be assumed that all new development upstream of a proposed capacity improvement would implement applicable stormwater management techniques, consistent with this Part.
11. 
Adequate erosion protection shall be provided along all open channels and at all points of discharge.
12. 
The design of all stormwater management facilities shall incorporate sound engineering principles and best management practices. The Township reserves the right to disapprove any design that would result in the occurrence or perpetuation of an adverse hydrologic or hydraulic condition within the watershed.
[Ord. 8/12/1999, § 3.5]
1. 
Any stormwater runoff calculations involving drainage areas greater than 20 acres, including on- and off-site areas, shall use any generally accepted calculation technique that is based on the SCS (now NRCS) Soil Cover Complex Method. Table 1 below summarizes acceptable computation methods. It is assumed that all methods will be selected by the design professional based on the individual limitations and suitability of each method for a particular site. The Township Engineer may approve the use of the rational method to estimate peak discharges from drainage areas that contain less than 20 acres.
2. 
The design of any stormwater detention facilities intended to meet the performance standards of this Part shall be verified by routing the design storm hydrograph through these facilities using the Storage Indication Method or Modified Puls Routing System. 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 Township Engineer may approve the use of any generally accepted full hydrograph approximation technique which uses a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.
3. 
All calculations consistent with this Part using the Soil Cover Complex Method shall use the appropriate design rainfall depths for the various return period storms presented in the references in the Appendix of this Part. 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.
4. 
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the design storm curves in the references in the Appendix of this Part. Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, SCS, TR 55 (as amended or replaced from time to time by SCS, now NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's equation.
5. 
Runoff Curve Numbers (CN) for both existing and proposed conditions to be used in the Soil Cover Complex Method shall be obtained in the references in the Appendix of this chapter,[1] with adjustments in accordance with TR 55 methods.
[1]
Editor's Note: The Appendix is included as an attachment to this chapter.
6. 
Runoff coefficients (c) for both existing and proposed conditions for use in the Rational Method shall be obtained in the references in the Appendix of this Part.
7. 
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. Where nonuniform flow is anticipated the hydraulic effects of backwater caused by hydraulic obstructions (e.g., culverts, bridges, dams, reservoirs etc.) shall be evaluated using the Standard Step Method for determining water surface profiles. Values for Manning's roughness coefficient (n) shall be consistent with the references in the Appendix of this chapter.
8. 
Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this part using any generally accepted hydraulic analysis technique or method.
[Ord. 8/12/1999, § 3.6]
1. 
Permits Required. Unless specifically exempted hereunder, and except for minor repairs, no stormwater management facility or structure shall be erected, constructed, reconstructed, extended, moved, demolished or removed until a stormwater permit has been secured from the Code Enforcement Officer in accordance with this Part.
2. 
Permit Approval. If the plans and specifications set forth by the applicant in the application are in conformity with this Part and all other applicable statutes, the Code Enforcement Officer shall issue a permit. If a stormwater permit is denied, the Code Enforcement Officer shall state such denial, in writing, with the cause(s) and shall mail notice of such denial to the applicant at the address indicated on the application within 90 days following submission of the completed application. The Code Enforcement Officer shall grant or deny the permit only after the Township Engineer has approved the drainage plan.
3. 
Application Requirements. The complete application for a stormwater permit shall consist of the application form provided by the Township, executed in its entirety and duly executed, together with the drainage plan, including all applicable calculations, maps and plans with specifications.
4. 
Life of a Permit. Any construction requiring a stormwater permit shall be completed within one year from date of issuance of the permit unless part of a staged stormwater management system approved for a multi-year completion schedule in conjunction with related subdivision or land development. However, the permit may be extended annually without payment of additional fees for an aggregate period of not more than three years; provided, the construction pursuant to said permit has commenced within the first one-year period.