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
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
SEE ALSO
wspro88(1) - A computer model for Water-Surface PROfile
computations