sac(1) U.S. Geological Survey (wrdapp) sac(1) NAME sac - Slope-Area Computation program ABSTRACT SAC follows USGS standardized procedure for computing discharge by the slope-area method. The source is written in Fortran 77. METHOD The program solves the 1-D steady-state energy and continuity equations for discharge given upstream and downstream water-surface elevations. HISTORY Version 97-01 1997/05/01 - Added new metric conversion to allow input data and the output results to be in either meter-second or feet-second units. A new record implements this feature. Additionally, the previous version did not correct cross-section stationing for skew angles entered on the XS record. The program did not compute correctly for sections with level water surfaces that were described using the method in Open-File Report 94-360 for nonlevel water surfaces. The program did not select the appropriate water-surface elevation for cross sections described by enclosing the figure (Fulford, 1994, p. 21) if a vertical bank existed on the right side of the cross section. These errors have been corrected. Version 96-03 1996/04/19 - The program originally used the mean cross-sectional velocity to compute the Froude numbers listed in the results for each subarea. The Froude computation has been changed to use an estimated subarea velocity for the subarea Froude numbers. Version 94-11 1995/08/16 - Version as documented in USGS Open-File Report 94-360. 1993 - J.M. Fulford changed input format to a modified WSPRO format, output to an 80-column format, and reorganized code. 1983 - Revised by W. Kirby. 1970 - Original code was written by O.G. Lara. DATA REQUIREMENTS Cross-section geometry and roughness values that describe the channel reach geometry along with measurements of high water marks. OUTPUT OPTIONS Text output of discharges and other variables used in the computations. SYSTEM REQUIREMENTS The program is written in Fortran 77 with the following extensions: variable names longer than 6 characters and use of double quotes for character strings. Generally, the program is easily installed on 7 Jul 1998 1 sac(1) U.S. Geological Survey (wrdapp) sac(1) most computer systems. The code has been used on UNIX-based computers and DOS-based 386 or greater computers having a math coprocessor and 2 mb of memory. DOCUMENTATION Fulford, J.M., 1994, User's guide to SAC, a computer program for computing discharge by the slope-area method: U.S. Geological Survey Open-File Report 94-360, 31 p. RELATED DOCUMENTATION Dalrymple, T., and Benson, M.A., 1967, Measurement of peak discharges by the slope-area method: U.S. Geological Survey Techniques of Water-Resources Investigations, book 3, chap. A2. TRAINING Surface-Water Hydraulic Analysis (SW2009TC), offered annually at the USGS National Training Center. CONTACTS Operation: U.S. Geological Survey Office of Surface Water Janice M. Fulford Building 2101 Stennis Space Center, MS 39529 jfulford@usgs.gov Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the SAC software can be retrieved are, respectively: http://water.usgs.gov/software/sac.html --and-- /pub/software/surface_water/sac 7 Jul 1998 2 sac(1) U.S. Geological Survey (wrdapp) sac(1) SEE ALSO wspro88(1) - A computer model for Water-Surface PROfile computations 7 Jul 1998 3