No person, firm, corporation, public agency, partnership or association shall develop any real property as hereinafter described or connect or cause to be connected any building or structure, either directly or indirectly with a drain for the removal of surface, roof, ground or other water to be discharged into a ditch, swale, waterway, stream or an existing storm drainage system from any real property hereinafter described without complying with the performance standards set forth in this chapter.
(a) Pavement Inlets. In most developments the street system provides a path for the stormwater to reach the stormwater system. Pavement, gutters and inlets must be designed with the movement of stormwater in mind. In order to provide for the movement of stormwater and to minimize flooding, pavement drainage shall be designed in accordance with the following: Inlet location and spacing.
(1) Curb inlets shall be provided upstream of radius turns, at all pavement sag points and at the low points of street intersections. Runoff will not be allowed to enter the intersection, except for approved "v" pavement areas. The maximum curb inlet spacing shall be 350-400 feet. A double inlet shall be used in sag points.
(2) Consideration must be given to the location of proposed curb ramps. Curb inlets shall be located upstream from the curb ramp. Curb inlets shall be located on the property line wherever possible to avoid conflicts with driveways and other utilities.
(b) Storm Sewers. While streets provide the initial collection of stormwater, storm sewers convey the stormwater to the outlet. Storm sewers shall be designed to adequately convey the design storm within the pipe system and minimize the surface ponding of water at inlets.
(1) Design Criteria.
A. Storm sewers shall be designed to receive stormwater from the entire tributary area.
B. The minimum cover for storm sewers crossing streets with curb and gutter shall be nine inches from the subgrade, but shall be concrete encased where the cover is less than thirty inches.
C. Storm sewers outside the pavement but inside the right-of-way shall have a minimum of thirty inches of cover. All other storm sewers shall have a minimum of two feet cover. If this control cannot be maintained, concrete encasement will be required.
D. Trench backfill shall be as set forth in the Uniform Standards for Sewage Improvements as adopted by the Northeast Ohio Regional Sewer District, the Cuyahoga County Sanitary Engineering Division, the Municipal Engineers Association of Northeast Ohio and the City of Cleveland.
E. The maximum cover shall be determined based on the supporting strength of the conduit, as installed, divided by a suitable factor of safety.
F. The minimum storm sewer size is twelve inches for all mainline storm sewers and twelve inches for storm laterals (excluding individual building service connections).
G. Storm sewers shall be sized to flow just full for a ten-year frequency storm using Manning's equation:
V – (1.486/n) x (R) 213 x(S)
Where:
V =- average velocity (ft/s)
n = Manning's roughness coefficient
R = hydraulic radius (ft)
S = channel slope (ft/ft)
A Manning's "n" of 0.015 shall be used for conduit sizes up to and including twenty-seven inches; "n" = 0.013 shall be used for pipe sizes including thirty inches through eighty-four inches and "n" = 0.011 for ninety inches and larger.
H. The storm sewer shall be designed to insure self-cleaning. The minimum velocity shall be three feet per second. The maximum velocity shall be fifteen feet per second.
I. The flow line of pipes should be set such that the crowns of the pipes, at junctions, are at the same elevation; if the outlet elevation permits, the crown of the outlet pipe may be lower. The flow line elevations of sewers should be set to avoid using concrete encasement.
J. The hydraulic gradient shall be such that the twenty-five-year storm does not exceed the window or grate elevation. Hydraulic grade calculations shall be submitted to the City Engineer if requested.
(2) Pipe Standards. All storm sewers within the public street right of way shall be constructed of reinforced concrete pipe Class IV. Alternative materials may be approved by the City Engineer under special design conditions.
(3) Manholes and Catch Basins.
A. Manholes and catch basins shall be designed to meet the standards set forth in the Uniform Standards for Sewerage Improvement and/or the Ohio Department of Transportation Construction and Material Specifications, latest edition.
B. Manholes shall be located at points in the storm sewer where the following occur:
1. Junctions of pipes
2. Change in direction
3. Change in slope
4. Change in pipe size
5. Change in pipe material
6. End of pipe run
7. Maximum spacing of three hundred feet
C. Where surface drainage is needed, the manhole will be equipped with a grate top or a catch basin will be substituted. Catch basins and manholes located in paved areas where there are no curb underdrains shall be provided with a minimum of ten feet of underdrain upstream of the storm sewer to remove subsurface drainage.
D. Catch basins will be located outside of the pavement at points where drainage is collected. Where "v" pavement is approved, catch basins may be used in lieu of manholes.
E. Catch basins located in paved areas or in the right-of-way will be equipped with a heavy-duty grate and frame suitable for the application.
(4) Headwalls.
A. Storm sewers that discharge to surface waters shall be provided with a suitable concrete headwall meeting the requirements of the Ohio Department of Transportation Standard Construction Drawing HW – 2.1 and HW – 2.2. The invert of the storm sewer shall be set no lower than six inches above the bottom of the channel.
B. Channel erosion control shall be provided at the outlet of all storm sewers. The length, depth and type of Rock Channel protection shall be per ODOT Location and Design Manual, Volume 2, Figure 1107-1.
(c) Culverts. A culvert is a pipe with open ends, designed to carry water across an obstruction in a drainage course such as roadways. This ensures the movement of stormwater while protecting the roadway from flooding. The size and shape of the culvert should be such that it will carry a predetermined design peak discharge without exceeding the allowable headwater elevation at the culvert entrance.
(1) Design Criteria.
A. Single span culverts, including concrete box or slab top, should always be considered in lieu of multiple cell pipe culverts when they are the only structures that will meet the physical requirements introduced by headwater controls. Culverts should be located along the flowline of the ditch or swale that it is draining.
B. The plan for each culvert shall have the drainage area in acres and the estimated runoff or design discharge in cubic feet per second shown.
C. The culvert inlet flow line elevation should be set such that it will be deep enough to provide an adequate outlet for future storm sewer improvements upstream.
D. Culverts shall be sized using computer software such as the Federal Highway Administration HY-8 program, ODOT's CDSS Software package or the Army Corps of Engineers HEC-RAS program. Inlet and outlet control homographs may also be utilized to evaluate culvert hydraulics.
E. Culverts shall be designed for the twenty-five-year frequency design storm with a maximum allowable headwater elevation of:
1. Eighteen inches below top of curb
2. Two feet below the near, low edge of the pavement for drainage areas one thousand acres or greater and twelve inches below for culverts draining less than one thousand acres
3. Two feet above the inlet crown of the culvert or above a tailwater elevation that submerges the inlet crown
4. Elevation set forth by the City Engineer if the above headwater control elevations would cause upstream flooding
F. The one-hundred-year frequency storm shall be used as a check storm for all proposed culverts. The check storm shall not exceed any of the following criteria:
1. Two feet below the lowest ground elevation adjacent to an occupied building
2. Twice the diameter or rise of the conduit
3. Roadway overtopping
4. A replacement structure should be sized such that flooding of upstream land is not increased when compared to the existing structure
5. There shall be no increase in the one-hundred-year headwater elevation for culverts located within a FEMA designated floodway.
G. The one-hundred-year frequency storm headwater pool shall be delineated on a topographical map and submitted with the culvert sizing calculations.
H. The minimum and maximum cover shall be determined based on the supporting strength of the conduit. The structural design criteria for culverts will be the same as that required by the Ohio Department of Transportation.
(2) Pipe Standards. All culverts shall be constructed of reinforced concrete meeting the requirements of the Ohio Department of Transportation, Construction and Material Specifications, latest edition, items 706.02, 706.03, 706.04, 706.05, 706.051 or 706.052. The City Engineer, under special design conditions, may approve alternative materials.
(3) Headwalls and End Treatments. Headwalls or other approved end treatments will be required for all culverts. Half height headwalls may be approved on a case-by-case basis.
(4) Channel Protection and Erosion Control. Channel erosion control shall be provided at the outlet of all culverts and at the inlet wingwalls of full height headwalls. The length, depth, and width of Rock Channel Protection shall be per ODOT Location and Design Manual, Volume 2, Figure 1107-1.
(Ord. 9477-2008. Passed 5-20-08.)