1.   Purpose and objectives

     This is a quick procedure for estimating peak rates of discharge for use in designing soil and water conservation measures in agricultural areas, and storm water management practices in urban areas.

2.   Description

     Graphs are used to estimate peak rates of discharge for times of concentration (Tc) less than 10 hours and for a range of rainfall amounts, soil types, land use, and cover conditions. The graphs are for a variety of 24-hour rainfall distributions.

3.   Input

     The required data are land use and hydrological soils group to calculate a runoff curve number, 24-hour rainfall amount, drainage area and an estimate of the time of concentration of the watershed.

4.   Output

     Estimates of peak rate of discharge and runoff volume for time of concentrations less than 10 hours are read from the graphs.

5.   Operational requirements and restrictions

     a. An engineering technician who can calculate Tc can easily use this 
        procedure.

     b. One day of training or familiarization with the procedure may be 
        necessary.

     c. The data for the graphs were computed using procedures from the 
        NRCS National Engineering Handbook, Section 4, Hydrology (NEH-4) 
        Chapter 16.

     d. Component K22.3.02 "Computer Program for Project Formulation 
        Hydrology (TR-20)" should be used in lieu of this procedure for 
        special situations and areas, or where this procedure is too 
        general to provide good estimates of discharge.

6.   Form of presentation

     Presented as Chapter 4, Urban Hydrology for Small Watersheds - Technical Release No. 55, Natural Resources Conservation Service, U.S. Department of Agriculture, June 1986.

7.   Operational experience

     The technique is used extensively by the U. S. Natural Resources Conservation Service with good results, and is used worldwide.

  
8.   Originator and technical support

     Water Science Technology Team
     National Water and Climate Center
     Natural Resources Conservation Service
     U.S. Department of Agriculture

  
9.   Availability

     From the HOMS National Reference Centre for USA.

10.  Conditions on use

     None.