(a) Verification of Proposed Hydraulic Design. A professional engineer, licensed to practice in Ohio, shall submit detailed storm calculations and drainage maps of sufficient scale and contour interval to verify the proposed hydraulic design. A map indicating specific drainage basins shall be submitted.
(b) Surface Run-off. Surface run-off quantity shall be determined by one of the following methods:
(1) 100 acres or less - Rational Method (Q = CIA).
Where: Q = the peak run-off rate (cfs), and
C = the run-off coefficient (assumed to be dimension-less).
Note: The run-off coefficient can be assumed to be dimension-less because 1.0 acre-inch/hour is equivalent to 1.008 cubic feet per second (Ft3/sec or cfs).
I = the average rainfall intensity (in/hr) lasting for a critical period of time.
A = the size of the drainage area in acres.
A. Intensity of precipitation for any given storm duration (concentration time off). Ohio Department of Transportation (ODOT) curves show the average precipitation intensity of storms of two, five, ten, twenty-five, fifty and 100-year frequencies. These values may be used for drainage calculations using the Rational Method for tributary areas of 100 acres or less.
B. Inlet time. At the head of the system the inlet may vary from five to twenty minutes, depending upon the size of the area and factors affecting rapid run-off.
C. Run-off coefficient. Compute a weighted value of the drainage areas, using generally accepted engineering criteria.
(2) More than 100 acres - Urban Hydrology for Small Watersheds, Technical Release No. 55, U.S. Department of Agriculture, Soil Conservation Service.