(A) Authority for the improvement or disturbance. The authority for the construction, improvement, or disturbance of open channels and water courses is with the city engineer. Open channels, such as vegetated swales, may be used for the collection of surface flows from relatively small areas, generally lying within a city block.
(B) Degree of protection. The stormwater drainage channels and watercourses shall be adequate to handle the runoff from storms of the frequencies of occurrence shown for the degree of site development as follows:
(1) For all residential, commercial, and industrial areas with drainage areas of less than one square mile - 10-year frequency.
(2) For concentrated high value districts, and for all areas providing drainage flows in excess of the capacity of an 84-inch diameter sewer pipe - 25-year frequency.
(3) For main flood control channels - 100-year frequency. The runoff computed from these storms shall be that from the area within the subdivision, and from all other areas considered as fully developed in accordance with the ultimate development planned in the master plan.
(C) Determination of quantity of runoff. Each portion the stormwater system of drainage channels and watercourses shall be capable of handling the peak flows as determined by the "Rational Method."
(D) Drainage channel capacities.
(1) Drainage channels shall be designed to carry the peak flows as determined by the methods given in the preceding divisions. Channel cross section areas shall be determined by Manning's formula, based on the following chart:
DESCRIPTION | COEFFICIENT |
DESCRIPTION | COEFFICIENT |
Channels - Concrete | 0.0130 |
Channels - Gunite | 0.0170 |
Channels - Earth | 0.0200 |
Channels - Cut in Rock | 0.0250 |
Channels - Fine Gravel | 0.0240 |
Channels - Coarse Gravel | 0.0280 |
Dense Turf / Tree Switches | 0.0750 |
Stemmy Grass / Brushy Growth | 0.0175 |
Weeds, Brush, & Bushy Willows | 0.0375 |
Cattails, Brush, & Trees | 0.0750 |
(2) When open drainage channels require pavement lining to attain their ultimate design capacity, the earth sections of the drainage channel and its structure shall be designed and constructed to the ultimate design required. Lining will not be required in the initial construction, and may be delayed until the development of the area produces runoff quantities large enough to result in erosive channel flows, unless drainage channel velocities are excessive initially.
(E) Erosion control for drainage channels.
(1) The design velocity shall be less than 4 feet per second. The bottom and sides of the earth channel shall be completely sodded to an elevation of 3 feet above the design water surface. The sod on the sides shall be sufficiently pegged to remain in place. Velocity 4 feet per second and higher. The bottom shall be paved with a reinforced turf product. Sides shall be completely sodded and fertilized as detailed above.
(2) Where sodding or seeding is required, and the soil is not capable in its natural state of supporting vegetation (such as excessively sandy soil or certain types of clay), appropriate actions shall be taken to bring the soil to a condition which will support the growth of sod or seed.
(3) Consideration may be given to the construction of check dams and drop structures for drainage channel erosion control, with the approval of the city engineer.
(F) Swales.
(1) Turfed swales shall be permitted with lots of 1/2 acre or larger. They may be located at the rear of lots or along common property lines. The swale flow shall discharge into an open drainage channel or into an inlet-manhole. Inlet-manholes shall be provided with a paved apron and transition section to funnel the swale flow into the inlet.
(2) If an owner desires to eliminate a swale through his property, he shall first secure approval by the city engineer and a work permit for the installation therein, of a yard drain of adequate capacity, with a sewer connection to a stormwater sewer or drainage channel. This process may also entail the requirement of a post-construction best management practice.
(G) Culverts and bridges. Culverts and bridges shall be designed in accordance with the methods given in the "Manual of Location and Design," published by the Department of Transportation of the State of Ohio.
(H) Headwalls. Standard headwalls or wingwalls shall be constructed for all culvert inlets and outlets in swales, and at the out fall of all storm sewers.
(I) Other drainage improvement measures. Drainage improvement measures other than the foregoing may be undertaken to provide the necessary hydraulic characteristics required for adequate drainage. These other measures may be stream bed clearing, removal of obstructions, reduction of construction, stabilization of banks or areas to eliminate erosion; widening, deepening, or realignment of streams; or the construction of ponds behind dams or pump stations.
(J) Specifications for construction and material. In all other respects, the material and construction shall be as specified in §§ 603, 604, 706, and 707, State of Ohio Department of Transportation “Construction and Material Specifications.”
(Ord. 26-1978, passed 6-21-78; Am. Ord. 40-2010, passed 12-15-10; Am. Ord. 20-2023, passed 4-19-23)