Appendix D Storm Sewers

Storm Water Rules and Regulations (SWRR)
Version: October, 2008

Appendix D

Storm Sewers

1. Storm Sewers
   
   
   1. General
      The subdivider or developer shall provide the necessary means to assure complete drainage in and adjacent to the development. Storm sewer systems shall be constructed of an adequate size to carry away the runoff produced by the development. The drainage area shall include all of the pavement surface, front, side and back of all lots and future plat extensions utilizing the same system.
      
      
   2. Design Formula for “Rational Method”
      The quantity of stormwater runoff to be used in the design of the system shall be determined when using the “Rational Method” and the “Manning Formula” for areas less than 200 acres.
      
      The equation is Q=CxIxA.
      
      Where:
      Q= Ratio of runoff in cubic feet per second.
      C= Ration of runoff to rainfall.
      I= Rainfall intensity in inches per hour.
      A= Area of the watershed in acres.
      
      When using the Soil Conservation Service Methods that programs values will be used.
      
      
   3. Runoff Coefficient
      The following runoff coefficients shall be used in single family residential subdivisions including right-of-way:
      
      

      Runoff Coefficient Table 1

      Average Lot Size in Subdivision	Runoff Coefficient "C"
      5,000 sq. ft. or less	0.50
      5,000 sq. ft. to 6,999 sq. ft.	0.40
      7,000 sq. ft. to 10,000 sq. ft.	0.35
      Over 10,000 sq. ft.	0.30

      
      
      These coefficients shall be used in residential subdivisions unless actual coefficients are determined by engineering analysis.
      
      Coefficients for surfaces and occupancies other than one family residential subdivisions shall be based on the following values:
      
      
      

      Runoff Coefficient Table 2

      Character of Surface	Runoff Coefficient "C"
      Pavement	0.95
      Roofs	0.95
      Lawns	0.15

      
      
      

      Runoff Coefficient Table 3

      Description of Area	Runoff Coefficient "C"
      Business:
      Downtown	0.95
      Neighborhood	0.75
      Residential:
      Multi-units, detached	0.75
      Multi-units, ettached	0.85
      Apartments	0.85
      Industrial:
      Light	0.80
      Heavy	0.95

      
      
      The coefficients in these tabulations are applicable for storms of 5 to 10 year frequencies and shall be called minimum coefficients.
      
      
   4. Rainfall Intesity
      The rainfall intensity, “I” can be taken from the appropriate curves for Erie County, Ohio as published by the U.S. Weather Bureau, the Ohio Department of Transportation Location and Design Manual, or the Urban Hydrology for Small Watersheds TR-55.
      
      A maximum of twenty (20) minutes shall be used as time of concentration to the first collection point in the system for residential areas. Preferred runoff pattern design of streets and lot grading shall be such that runoff from roofs, driveways and other impervious surfaces shall be toward the street or rear lot swales/tile systems. The subsurface system shall be designed such that each lot will have an outlet for footer tile, perimeter drains, sump pumps, etc. The runoff/discharge shall be collected in either system and both systems shall be directed to a detention/retention facility.
      
      
   5. Design Storm Frequency
      Minimum frequencies for various types of occupancies or land use shall
      be as follows:
      
      Residential Area 5 year frequency
      Industrial Area 5 year frequency
      Commercial Area 5 year frequency
      
      Storm sewers shall be designed to flow just full for the five-year frequency storm. The detention/retention facility shall be designed for a ten-year frequency storm plus the volume needed for Water Quality Compliance if the detention basin serves both functions.
      
      Catch basin type and spacing shall be designed using the five-year intensity duration frequency curve.
      
      
   6. Drainage Calculations Presentation
      An overall drainage layout plan showing the limits of the contributing runoff area broken down into areas contributing to each drainage pick-up point, shall be submitted with the paving and drainage plans. Drainage design within the development shall be adequate to handle the entire contributing watershed area and its existing, proposed and probably future development and not the area under submission only. When the design makes use of an existing storm sewer or open ditch, cross sections and profiles shall be submitted which show the existing conditions at least 500 feet downstream from the plat being considered.
      
      If future plat extensions will utilize the same drainage system, the overall drainage plan shall be submitted with the first plat plans. Complete drainage calculations shall be submitted for pipe size determinations, five year hydraulic gradient checks and catch basin type and spacing designs.
      
      
   7. Pipe, Catch Basin and Manhole Materials
      • All catch basin and manhole structures shall conform to the Ohio Department of Transportation (ODOT) “Construction and Materials Specifications” (CMS) manual Item 604.
      • All storm sewer pipe proposed in the plan must conform to the ODOT CMS manual Item 603. This includes mandrill testing of any flexible pipe used.
      • Storm sewers within the road right-of-way shall be either reinforced concrete pipe (RCP) or polyvinyl chloride (PVC) corrugated pipe with smooth walled interior with a minimum pipe stiffness of 46 psi. The County Engineer reserves the right to require reinforced concrete pipe within the road right-of-way if ground conditions exist that in his judgment would be detrimental to the long term life of a pvc corrugated pipe.
      • Rear lot storm sewer collectors can be designed using either of the afore named types of pipe in addition to corrugated polyethylene smooth walled interior pipe approved in ODOT “CMS” manual Item 603. The polyethylene type of pipe can only extend to the road right-of-way, where it will be connected to either RCP or PVC extending to a catch basin or manhole.
      • Driveway culverts, for crossing a roadside ditch within the public right-of-way to access a property, must be constructed of RCP of not less than 12 inches in diameter and having a minimum length of 32 feet.
      • Flexible (PVC) pipe crossing under the roadway must have at least 18 inches of cover from the outside top of the pipe to the pavement sub-grade and have a maximum diameter of 36 inches. Pipe larger than 36 inches shall be RCP.
      • RCP will be required if it is determined by the Erie County Engineer that insufficient cover will exist during construction prior to the pavement installation such that construction equipment can damage the pipe.
      • Road culverts that have exposed ends and whose function is to convey a watercourse under a roadway shall be RCP. PVC corrugated pipe will not be considered for this type of application.
        
        
      Drainage systems outside the public right-of-way for private developments that public improvements are not dependant upon may be constructed using the developer’s choice of pipe materials with the exception of metal pipe and single walled polyethylene pipe. Installation and design will still have to meet ODOT design and installation standards found in the CMS manual.
      
      
   8. Conduit Design Factors
      Velocity when flowing full or half full shall not be more than twelve feet (12 ’) per second.
      
      Drop manholes shall be used to keep the velocity below twelve feet (12’) per second.
      
      Storm sewers shall be designed so that the projected accumulated 5-year discharge from the watershed is within the full flow capacity of proposed pipe. Top to top design is preferred at the structures when there is a pipe size change however in some areas there is not sufficient grade to allow for this. In those cases center to center or invert to invert design is acceptable with center to center being the second preferred and invert to invert the last.
      
      
   9. Manholes and Catch Basins
      Manholes and catch basins are required as follows:
      
      
      1. At all changes in grade.
      2. At all changes in alignment.
      3. At all points of intersection of sewers.
      4. At the point of all changes in pipe size.
      5. At all locations where inlets from catch basins connect to the main sewer.
         
         
   10. Transitions in Size and Flow
       Where the sewer size or shape changes, a manhole or structure shall be constructed. Special attention must be given where smaller sewers enter larger sewers to prevent blocking of the flow in either sewer. In some instances, special transition junction structures may be required. Smooth flow at all manholes and junction structures is vital which requires all manholes and catch basins to have poured inverts.
       
       
   11. Outfall Ends
       The outfall ends of storm sewers shall be properly protected by concrete headwalls, rock channel protection of the banks and bottom of open channels, paved inverts of open channels or similar means as required by standard engineering practices and approved by the County Engineer.
       
       
       
2. Special Drainage Structures
   
   
   1. General
      Special drainage structures are considered to be such items as open drainage channels, culverts, bridges and detention ponds. The design of these items must be discussed with all concerned departments or agencies prior to commencement; they are:
      
      
      1. County Highway Engineer
      2. Soil and Water Conservation District
      3. Township Trustees
      4. Regional Planning Commission
         
         
   2. Open Drainage Channels
      As a general rule, stormwater runoff in subdivisions shall be collected in a system of closed conduits (storm sewers) of adequate design and properly constructed to conduct the runoff to a proper and adequate outlet. Open drainage channels may be used to collect and convey stormwater runoff in subdivisions where approved by the various agencies, The approved open drainage channel shall be so located on an individual lot so that there is a minimum distance of not less than fifteen feet (15’) from the top of the bank of the drainage channel and the property line, or to any physical encroachment, obstacle or structure. It is intended by this requirement, to provide a permanent easement along the top of each bank of the drainage channel at least fifteen feet (15’) in width in which to move equipment for maintenance of the open drainage channel.
      
      The above does not preclude an open drainage channel, where permitted, to be so located so that its centerline follows a property line dividing individual lots of a subdivision, or along a boundary line or tract of property, provided the minimum width of fifteen feet (15’) along the top of each bank is provided.
      
      Permanent easements shall be dedicated for all open drainage channels and right of ingress provided so the County may have its maintenance forces enter upon the easement to maintain the open drainage channel or have this work done by a Contractor. The width of the easements shall be determined after the open drainage channels have been designed.
      
      Open drainage channels shall be designed to adequately carry the stormwater runoff, which shall be determined as if closed conduits or storm sewers were to be constructed as provided in this manual. The slopes shall be protected from erosion and the grade of the invert of the channel shall be such that will not cause erosion of the bottom of the channel. Cross-sections shall show the type of channel at each fifty-foot (50’) along the channel centerline. Check dams or grade stabilization structures shall be constructed as required to preserve the channel from, excessive velocities.
      
      Existing drainage channels shall be enlarged, repaired, realigned, graded and sloped as required for new channels and shall be adequately sized.
      
      All construction work on open drainage channels shall be completed and approved by the County before any building construction is started in the subdivision.
      
      Open drainage channels shall be protected from scouring on curves, storm sewer outfalls and similar damage by proper placement of rock channel protection. Open drainage channel banks shall be properly sloped, in accordance with standard engineering practice and properly seeded, sodded or paved as may be required.
      
      
   3. Pipe Culverts
      Pipe culverts or other culvert structures conveying an open ditch under public streets or public ways shall be constructed of reinforced concrete. The pipe culverts shall be designed to carry a twenty-five 25-year post development flow.
      
      
   4. Driveway Culverts
      In estate type subdivisions of lots with areas of two acres or more and frontages of 150 feet or more, the Planning Commission may approve open roadside ditches where rights-of-way widths for streets and public ways are not less than 66 feet wide.
      
      Where culverts are provided under driveways from individual lots onto public streets without curbs and utilizing roadside ditches for street drainage, each driveway shall be provided with a reinforced concrete pipe not less than twelve inches (12”) diameter and a minimum length of thirty-two feet (32’). Final sizing will be determined by a ditch flow design to show required capacity.
      
      
3. Storm Pipe and Pipe Specifications
   
   
   1. General
      Pipe and pipe specifications shall be furnished in accordance with the provisions of the following specifications or shall be in accordance with such other specifications as may be shown on the plans or ordered by the Engineer.
      
      
   2. Pipe and Fittings – Type and Kind
      Pipe ten inches (10”) or smaller shall be one of the following:
      
      
      1. PVC corrugated pipe with smooth walled interior with a pipe stiffness rating of 46 PSI or higher.
      2. Polyvinyl Chloride (PVC) SDR-35
      3. Corrugated Polyethylene smooth bore pipe (for off road usage only). This type of pipe is intended for lot drainage only and is not acceptable for any collector main that will convey drainage from or along a public road.
         
         
   3. Pipe twelve inches (12”) to thirty-six inches (36”) shall be:
      
      
      1. Reinforced concrete pipe conforming to the requirements of A.S.T.M. Specification C-76 and of a class as required by the County Engineer.
      2. Reinforced elliptical concrete pipe conforming to the requirements of A.S.T.M. Specification C-507 and of a class as required by the County Engineer.
      3. Polyvinyl Chloride (PVC) SDR.35
      4. Corrugated Polyethylene smooth bore pipe (for off road usage only) as in Paragraph 2c above.
      5. PVC corrugated pipe with smooth walled interior with a pipe stiffness rating of 46 PSI or higher.
         
         
   4. Pipe larger than thirty-six inches (36”) shall be reinforced concrete. No connections shall be permitted to the storm sewer pipe without the use of either a catch basin or manhole unless in special situations connections made where the placement of a structure would be impractical then a manufactured core type insert may be used, i.e. “Inserta-Tee”.
      
      
   5. Joints
      All sewer pipe joints shall be watertight to prevent any trench settlement from leaking joints. Joints for various of pipe shall conform to:
      
      
      1. Polyvinyl chloride (PVC) SDR 35 and PVC corrugated smooth walled, shall be gasketed.
      2. Concrete sewer pipe of a resilient flexible joint as required in A.S.T.M. Specification C-443.
      3. Concrete sewer pipe of a cold application mastic joint filled as required by Ohio Department of Transportation “Construction and Material Specifications Item 706.10 and 603.06.
      4. Corrugated Polyethylene Pipe with smooth walled interior shall be a gasketed manufactured joint fitting.
         
         
   6. Pipe Fittings – Inspection and Rejection
      
      
      1. All pipes shall bear a means to identify the manufacturer and class of the pipe. The markings shall be indented or stenciled on the barrel and shall be plainly legible for purposes of identification.
      2. All pipes shall be subject to inspection at the factory and the job site.
      3. The manufacturer shall furnish a Certificate of Conformance in the form of an affidavit of conformance, test results or copies of test results for the pipe supplied for the project.
      4. Inspection by the County will not relieve the manufacturer of the responsibility of furnishing material performing in all respects to the specifications.
      5. Pipe shall be subject to rejection based on any of the following:
         
         
         • .01 Variations in any dimensions exceeding permissible variations as shown in the appropriate A.S.T.M. Specifications.
         • .02 Fractures, splits or cracks passing through the barrel, bell or socket of a pipe or fitting.
         • .03 Blisters or defects, which indicate imperfect proportioning, mixing or molding.
         • .04 Cracks, which impair the strength, durability or serviceability of the pipe.
         • .05 Variation of more than 1/8 inch per foot in alignment of the pipe intended to be straight.
           
           
   7. Testing
      Infiltration and ex-filtration tests will not usually be required of storm sewers. However, if it is the opinion of the County Engineer that the tests are necessary due to poor workmanship or materials, the Contractor shall perform all tests required to determine the leakage (i.e. run video camera down pipe). Testing for flexible storm sewer lines may include mandrill usage.