§ 151.31  DETERMINATION OF RUNOFF QUANTITIES.
   (A)   Because topography and the availability and adequacy of outlets for storm runoff vary with almost every site, the requirements for storm drainage tend to be an individual matter for any project. It is required that each proposed project be discussed with the County Surveyor at the earliest practical time in the planning stage.
   (B)   Runoff quantities shall be computed for the area of the parcel under development, plus the area of the watershed flowing into or through the parcel under development. The quantity of runoff which is generated as the result of a given rainfall intensity must be calculated as follows.
      (1)   For areas up to and including 20 acres, the Rational Method may be used to determine runoff quantities. The procedure is described in the HERPICC Storm Water Design Manual. Other design methods as described below in division (B)(2) below may also be used.
      (2)   For areas larger than 20 acres, hydrograph techniques and/or computer drainage modeling methods must be used. The techniques or methods used shall be proven methods in the practice of hydrology, subject to approval of the Board. The Advanced Interconnect Pond and Channel Routing, SWMM, HEC-HMS, NRCS TR-20 (Project Formulation, Hydrology) and NRCS TR-55 (Urban Hydrology for Small Watersheds) models are approved by the Board for appropriate use in analysis of the runoff and routing of storm water.
(Ord. 8-2014, passed 7-21-2014)