Post-Construction Storm Water


All residential, commercial, industrial, and other sites developed in unincorporated areas which increase impervious surface must detain the increase storm water runoff.

Runoff Estimation:

In general, storm water runoff can be described as a by-product of rainfall's interaction with the land. In Wood County, the design of storm drainage systems shall be based upon the Rational Method (Q = CiA) for determining peak runoff flow-rates for areas less than 200 acres, where:

  • Q = Peak runoff rate in cubic feet per second (CFS);
  • C = Coefficient of Runoff corresponding to surface imperviousness;
  • i = Average rainfall intensity in inches per hour corresponding to the storm design frequency and for a duration equal to the time of concentration (See the latest edition of ODOT's Location and Design Manual, Volume II, "General Notes - Figures 1101-2 Through 1101-3"). 
  • A = Area in acres of the contributing watershed/design area.

Storm Water Detention:

Wood County requires all new residential, commercial, and industrial developments to have onsite storm water collection facilities, also know as detention/retention basins.

All surface storm water generated by the development must be collected and metered out with the allowable discharge (Q Allowable) being limited to and not to exceed a two (2) year frequency storm for undeveloped conditions of the proposed development site using an intensity time of i = 20 minutes and a coefficient of runoff (C) of 0.10.

The collection facilities shall be able to store or detain the proposed discharge from a 100 year frequency storm minus the allowable discharge.

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