The development of all new and modified drainage systems shall be governed by the guidelines set forth in this section as follows:
(a) Preliminary Drainage Plan. A preliminary drainage plan for all subdivisions shall be submitted (in triplicate) to the City for review and approval. It shall include a drawing showing the general runoff pattern of the area, which is to be improved, as well as the runoff patterns of adjacent areas which may affect or be affected by the proposed improvement. A copy of the preliminary plat which is required by the Planning Commission may serve as the preliminary drainage plan providing sufficient data has been supplied to check the feasibility of the drainage system as proposed by the developer.
(b) Adequate Drainage Outlet. Surface water runoff from a development shall be drained through an adequate outlet. The location of the outlet shall be approved by the City. The outlet may be a ditch, stream, storm sewer or approved retention basin, which has sufficient capacity to accommodate the runoff in a reasonable manner.
(c) Drainage Easement. Easements of adequate width shall be required for all existing and proposed drainage courses that are not within the road right of way. The development's owner shall be responsible for obtaining any easements required outside the subdivision boundaries, and have them properly recorded in the Erie County Recorder's Office.
All drainage easements shall be shown on the plat and construction drawings along with their intended purpose specified in writing.
(d) Right of Way for Drainage Structures. When a drainage structure extends beyond the limits of the normal road right of way, additional right of way shall be provided around the structure to allow for adequate maintenance.
(e) Final Drainage Plan.. The final drainage plan shall include drawings of the entire drainage system and be submitted to the City (in triplicate) for review and approval. The plan shall conform to the guidelines herein and to any special requirements of the Planning Commission in approving the preliminary plat. The plan shall also include the engineering calculations used in determining the design of the drainage courses, drainage structures and stormwater runoff control structures.
All drainage construction drawings shall be sealed with the stamp of a professional engineer. The drainage drawings must be approved by the City prior to the construction of any portion of the drainage system.
Minimum requirements for drawings and engineering calculations for drainage systems shall comply with all aspects of Section 1117.01 (Construction Plan; Profile; Cross Sections) of the Codified Ordinances of the City and also the following:
(1) A map showing the existing topography of the development area and adjacent land within 200 feet of its boundary. The topographic map shall use a contour interval appropriate to portray clearly the surface conformation and drainage pattern of the area.
(2) A vicinity map at a scale of not less than 2000 feet to the inch showing the development area in relation to existing road and nearest existing thoroughfares, streams and water areas.
(3) The drainage area for each pipe or drainage structure shall be outlined and have the acreage shown. To show the entire drainage area, additional sheets may be required. If additional sheets are needed, existing aerial mapping or USGS mapping will be sufficient.
(4) The acreage of all tributary drainage areas and their sum.
(5) Times of concentration, intensity and runoff coefficients used in the Rational Method to estimate the amount of runoff.
Overland slopes, curve numbers, hydraulic lengths, etc., used in the SCS Peak Discharge Method.
For methods other than those above, enough information must be provided to the City to allow for an accurate review.
(6) Discharge in cubic feet per second (cfs), velocities in feet per second (fps), and any additional data needed to establish that the drainage system will convey the flow.
(7) The plan and profile of all drainage courses.
(8) Cross sections along the drainage course at 100 foot intervals or as directed by the City.
(9) Size and types of all drainage improvements including the detailed standard drawings of each.
(f) Computation of Stormwater Runoff. Given the type of drainage structure to be designed, the rate of runoff shall be computed using the storm frequencies given below:
Structure | Storm Frequency (years) |
Storm sewer | 5 |
Open ditches | 10 |
Culverts | 25 |
The design frequency to be considered for an individual structure may be altered by the City where the health and safety of the residents would be endangered by the hazards of flood waters or increased flows.
(g) Design Frequency. To prevent damages caused by accelerated stormwater runoff from developing areas, the increased peak rates and volumes of runoff shall be controlled such that:
(1) The peak rate of runoff from a Critical Storm and all more frequent storms occurring on the development area does not exceed the peak rate of runoff from a two year frequency storm (of 24 hour duration) over the same area under pre-development conditions.
(2) Storms of less frequent occurrence than the critical storm, up to the 100 year storm, have peak runoff rates no greater than peak runoff rates from equivalent size storms under pre-development conditions.
The critical storm for a specific development area is determined as follows:
(1) Determine by appropriate hydrologic methods the total volume of runoff from a two year frequency, 24 hour storm occurring over the development area before and after development.
(2) From the volumes determined in (1), determine the percentage increase in volume of runoff due to development, and using this percentage, select the 24 hour critical storm from the following table:
% Increase in Volume of Runoff | “Critical Storm” Discharge Limitation (year) | |
(at least) | (but less than) | |
0 | 20 | 3 |
20 | 50 | 5 |
50 | 100 | 10 |
100 | 250 | 25 |
250 | 500 | 50 |
500 or more | 100 | |
(3) Storage volume does not have to be provided for runoff from off-site upstream areas. Upstream runoff should be conveyed through the site in accordance with the current runoff conditions.
(4) The requirements of this section for runoff rates and volumes shall be satisfied at each location where runoff leaves the development area.
(h) Storm Sewers. All storm sewer installations shall comply with PART ELEVEN, TITLE ONE of the Codified Ordinances of the City in addition to the following:
(1) Drainage easements shall be a minimum width of twenty feet when located outside the road right of way. This easement shall be shown on both the final plat and the construction drawings and labeled "Storm Sewer Easement".
(2) All storm sewers installed in the right of way shall be provided with curb inlets.
(3) The hydraulics of the storm sewer should be arrived at by the use of Manning's Equation:
V = 1.49 R (2/3) S (1/2) also Q = AV |
n |
Where: V = velocity (fps) |
N = Manning's roughness coefficient |
R = hydraulic radius |
S = slope |
Q = flow (cfs) |
A = area (sf) |
Kutter's formula may also be used in the hydraulic computation of storm sewers.
(4) All storm sewers shall be designed with hydraulic slopes sufficient to provide a mean velocity, when flowing full, of not less than three feet per second. Where the velocity exceeds fifteen feet per second, special provisions must be made to protect against erosion and displacement.
(5) All storm sewers shall be properly sized but, in no case, shall a storm sewer be less than twelve inches in diameter.
A. All storm sewers shall be sized to flow approximately full for a five year frequency storm. The size shall be determined by working downstream from the inlet of the first sewer run.
B. Hydraulic gradient for flood flow (ten year) should be kept below catch basin grates. This will eliminate storm water being detained on the pavement surface during this period.
(6) When storm sewers are increased in size in the direction of flow, the invert of the larger pipe shall be lowered to maintain the same energy gradient (place the crowns of both pipes at the same elevations). A larger pipe shall not discharge into a smaller pipe unless specifically approved by the City.
(i) Construction Specifications. All drainage structures and appurtenances shall comply with applicable City specifications and/or the most current edition of ODOT's Construction and Materials Specifications.
(Ord. 1994-2. Passed 3-14-94.)