Upper versus lower Colorado River sub-basin streamflow: characteristics, runoff estimation and model simulation

Streamflow in the upper Colorado River in the western USA is always snowmelt dominated. whereas the lower river's perennial streamflows are snowmelt dominated only 50% of the it me. The magnitude and timing of peak flows is important for water resources management. In the upper basin the annual maximum daily discharge usually occurs in May or June, and in the lower basin this peak is observed to occur in any month except May or June. The timing of one-half of the specific runoff is used as a second measure of the variability in timing and magnitude of streamflows. For the upper basin, nine watersheds are used to illustrate streamflow trends, with the Yampa River used as a sample sub-basin. For the lower basin, five watersheds are used. of which Salt River is used as sample sub-basin. The differences in monthly flow variation over 20-year time periods (1920-1939, 1940-1959, 1960-1979, and 1980-1999) are substantial for the Salt River but not for the Yampa River. Three model types were used to estimate streamflow characteristics. An autocorrelation model was used to generate winter specific runoffs, which were more reasonable for the Yampa River than the Salt River. A regression between snow water equivalent (SWE) and winter specific runoff showed a good correlation for the two sub-basins. A weaker relationship exists between SWE and non-winter flows for the sample lower basin watershed. Streamflow was simulated relatively well using the Precipitation Runoff Modeling System hydrological model. Copyright (C) 2006 John Wiley & Sons, Ltd.