Accurate measurement of flow in the San Joaquin River at Vernalis, California, is vital to a wide range of Federal and State agencies, environmental interests, and water contractors. The USGS (U.S. Geological Survey) uses conventional stage-discharge rating techniques to gage flows at Vernalis. These techniques, however, are poorly suited to the gaging of extremely unstable alluvial channels due to the frequent migration of bed forms and the scour and fill of the channel. The channel at Vernalis has scoured and filled as much as 20 feet in some sections since the flood of January 1997. These processes alter the relation between river stage and flow, diminish the accuracy and reliability of the resulting flow records,...