GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION DISTINGUISHED CAREER AWARD: EFFECTS OF SEDIMENT SUPPLY ON RIVER CHANNEL MIGRATION

Sediment supply is an important driver of river channel evolution within floodplains. However, its role is rarely studied in a systematic manner because of the difficulty of establishing long-term supply rates. Three approaches to systematic investigation of this effect are illustrated with varying degrees of resolution. Statistical analysis of channel migration rates in large Amazon River tributaries documents circumstantial evidence associating sediment supply with channel activity. A combination of measurements and hydrodynamic modeling in a simplified meandering reach of the Merced R., California explores the underlying mechanisms at a scale where processes can be monitored and predictions checked against measurements. A medium-resolution analysis of the interacting effects of sediment supply and bank erodibility on bend migration is possible for the Sacramento R., California.

The combined results indicate that increasing sediment supply enhances bar growth, bend curvature, and bed gradient, all of which favor bank erosion and channel migration. Bend growth and shoaling of pools enhance rates of channel cutoff, which then acts to maintain a relatively stable sinuosity over time. These results indicate that reduction of sediment supply through reservoir impoundment should reduce downstream rates of channel migration and cutoff, and thus the generation and re-surfacing of floodplain topography. Although difficult to achieve, estimating the long-term sediment supply to a river is probably as fundamental to the interpretation and prediction of river behavior as is the bankfull or other ‘characteristic’ discharge.