A drainage system shall be designed and constructed by the subdivider to provide for the proper drainage of the surface water of the subdivision and the drainage area of which it is a part. Said drainage system shall be designed so that the post-development runoff discharged from the subdivision shall be less than or equal to predevelopment runoff for all storms, with a return period less than or equal to twenty-five years.
(a) Storm Water Calculations. The subdivider shall submit storm runoff and flood routing calculations prepared by a registered engineer for the two-year and twenty-five-year storms. The subdivider's engineer shall also prepare and submit a plan showing the major routing path through the subdivision for a 100-year storm.
(b) Drainage System Design. The design criteria for the drainage systems shall be based on the State of Ohio Department of Transportation Location and Design Manual. The subdivider shall submit calculations proving conformance of all portions of the drainage system to the requirements of such regulations.
Runoff or design discharge for sewer design, where the contributing area generally consists of pavement and a narrow strip back of the pavement, shall be obtained from the Rational Method formula: Q=CIA. The following minimum design frequencies are to be used:
Description Years
Roadway ditches 5
Storm sewers 5 to 10
Culvert under roadways 25
Watercourses 10
In system design, the high end of the runoff coefficient range, as set forth in the following table, shall be used, unless calculations are provided which indicate a lower coefficient. Such calculations shall consider both soil type and the percentage of impervious area. In no case, however, shall the coefficient used be less than the low end of the range, as set forth in the table:
Description of Area | Rainfall Frequency (yrs.) | Range of Runoff Coefficient |
Description of Area | Rainfall Frequency (yrs.) | Range of Runoff Coefficient |
Open Space-Conservation | 5 | 0.25 - 0.40 |
Rural Residential | 5 | 0.25 - 0.40 |
Low-Density Urban Residential | 5 | 0.30 - 0.50 |
Medium-Density Urban Residential | 5 | 0.30 - 0.50 |
High-Density Urban Residential | 5 | 0.30 - 0.50 |
Multifamily Urban Residential | 5 | 0.40 - 0.60 |
High-Density Multifamily Urban Residential | 10 | 0.50 - 0.70 |
High-Density Multifamily Commercial Urban Residential | 10 | 0.50 - 0.70 |
Local Commercial | 10 | 0.50 - 0.70 |
Office and Limited Business | 10 | 0.50 - 0.70 |
Community Commercial | 10 | 0.70 - 0.90 |
Central Retail-Office Intensive and Automotive | 10 | 0.70 - 0.90 |
Oriented Commercial | 10 | 0.70 - 0.90 |
Highway Interchange Commercial | 10 | 0.70 - 0.90 |
Industrial Research and Office | 10 | 0.50 - 0.70 |
Industrial | 10 | 0.40 - 0.90 |
Manufacturing, Storage and Disposal | 10 | 0.40 - 0.90 |
Railroad Yard Areas | 10 | 0.20 - 0.40 |
Any commonly accepted engineering practice which has been pre-approved by the Development Engineer may be used for sewer design in situations with larger contributing areas.
(c) Street Drainage Systems. The street storm drainage system shall serve as the prime drainage system. It shall be designed to carry roadway, adjacent land and house storm water drainage.
On streets with curbs, inlet spacing shall be based on a five-year frequency, fifteen-minute duration design storm. In no case, however, shall the contributing length of roadway in any one direction exceed 300 feet. The spread of water on the pavement shall be limited to two feet into the traveled lane.
Standard manholes or combination manhole inlets for cleaning purposes shall be placed no further than 300 feet apart.
(d) Storm Laterals. A storm lateral shall be provided for each lot to accommodate footer drains and downspouts. Direct connection of footer drains shall be prohibited, unless the lowest floor elevation is above the street elevation.
(e) Open Channels. All open channels used for storm drainage shall be provided with appropriate measures, as approved by the Development Engineer, to control the flow of water and limit erosion.
(f) Storm Sewer Pipe. All pipe proposed to be installed as part of a storm drainage system shall conform to the current City of Geneva standards regarding type, usage and installation.
(g) Grading. An overall grading plan shall be submitted which indicates how each lot shall be surface-drained. Said plan shall conform to the following:
(1) Roadway grading shall extend the full width of the right-of-way.
(2) Planting strips shall have gradients of not less than two percent nor more than three percent from the curb to the sidewalk or property line.
(3) Lots shall be graded to provide positive drainage away from each building.
(4) Swales shall have a minimum grade of 0.5 percent.
(5) Driveways shall have grades of not less than 0.4 percent nor more than fifteen percent.
(6) When topsoil is removed, it shall be saved and spread over the lots as grading is finished.
(7) Trees shall be preserved to the greatest extent possible.
(h) Storm Outlet. The subdivider shall provide sufficient evidence to show that the proposed outlet for the storm drainage from the subdivision is capable of handling the projected flows.
(Ord. 2381. Passed 11-22-93.)