1.   Purpose and objectives

     The technique is used to establish or extend stage-discharge ratings; to define areas which will be inundated by flood flows of a given frequency; and to compute profiles through various reaches and past control structures.

2.   Description

     The standard step-backwater method of computing water-surface profiles is described, the hydraulic principles and assumptions are reviewed, and field data requirements are given. A brief description of the analysis of floodways and the effects of encroachments is also included.

3.   Input

     A survey of the geometry of the stream channel along the reach for which the profiles are needed produces the data required: principally cross sections of the channel drawn to a common datum at intervals along the reach, and the value of the roughness coefficient.

4.   Output

     The water-surface profile for any known or assumed discharge.

5.   Operational requirements and restrictions

     Procedure is not satisfactory on streams with extremely small slopes or very steep slopes.

6.   Form of presentation

     Manual in English.

7.   Operational experience

     Extensive.

8.   Originator and technical support

     U.S. Geological Survey.

 
9.   Availability

     From the HOMS National Reference Centre for USA.

10.  Conditions on use

     None.