1.   Purpose and objectives

     The program computes water surface profiles for steady, gradually varied flow in rivers of any cross section.

2.   Description

     Flow may be sub-critical or super-critical. Extensive analysis of water surface profiles through structures such as bridges, culverts and weirs is performed. Variable channel roughness and variable reach length between adjacent cross sections can be accommodated. Several energy and/or 
momentum methods are used to define the flow. Digital elevation data may be used to define the channel and floodplain using the HEC-Geo RAS support software with the ArcView GIS. Inundated areas may be plotted on the digital elevation model. The following assumptions are implicit in the 
analytical expressions used in the program: (1) flow is steady; (2) flow is gradually varied; (3) flow is one dimensional (i.e., velocity components in directions other than the direction of flow are not accounted for); and (4) river channels have small slopes, say less than 1:10.

3.   Input

     Graphic user input, including: flow regime, starting elevation, discharge, loss coefficients, cross-section geometry, and reach lengths. A digital terrain pre-and post-process is available to prepare data and display results.

4.   Output

     Tabular and graphical data can be produced on the screen and printer from a choice of numerous variables and formats.  

5.   Operational requirements and restrictions

     a.  Persons with knowledge and experience in open channel flow and a 
         basic understanding of computers can run the program.

     b.  One week of training is required.

     c.  The program was written for use Windows 95 or better PC’s. C and 
         Fortran languages are used.

6.   Form of presentation

     CD or download from www.hec.usace.army.mil 

     Support documentation consists of a Users, Hydraulic Reference, and Applications Manuals and Training Documents. Instructional videotapes are also available.

7.   Operational experience

     Extensive, worldwide, with predecessor HEC-2 Software.

8.   Originator and technical support

     The Hydrologic Engineering Center, HEC, U.S. Army Corps of Engineers.

9.   Availability

     Direct download via the Internet at www.hec.usace.army.mil or from the HOMS National Reference Centre for USA.

10.  Conditions on use

     A standard handling fee is charged for the CD, downloading is free.