What is the Slope-Area Computation (SAC)?

The Slope-Area Computation (SAC) is a solver used to compute peak flood discharges from measurements of high-water marks along a stream reach. The original approach was developed by T. Dalrymple and M. Benson of the U.S. Geological Survey (USGS) in the 1960s and subsequently modified and coded by a long list of USGS employees, including Janice Fulford. The solver was further improved and prepared for installation in iRIC by Keisuke Inoue of Mizuho Instrumentation and Research with direction from Jonathan Nelson, Bob Holmes and many other users at the USGS. The solver uses a general version of the slope-area method to estimate flows based on high-water marks and prescribed roughness values.