Sediment transfer and storage in dryland headwater streams

This study describes the dynamics of sediment transfer and storage in three headwater channels of the Walnut Gulch Watershed in the Chihuahuan Desert, southeastern Arizona, USA. Spatially distributed information on volumes of stream-bed scour and fill and the resultant net changes in sediment storage was collected from three channel reaches using dense arrays of scour chains. Reach-averaged estimates of volumetric scour for individual events ranged between 0.001 and 0.11 m3 m− 2. Scour volumes combine with relatively little scatter when rated against peak unit stream power demonstrating that flood magnitude accounts for much of the variance. As a result of locally compensating scour and fill, net changes in sediment storage during individual events were small. Because aggradation and degradation fluctuated with no persistent temporal trend over the study period, sediment transfers through the reaches were not significantly affected by movement of sediment into or out of storage. Measurements of the volume of sediment trapped in a stock-pond downstream of the study sites suggest that scoured bed material travelled several hundred m year− 1 with a virtual velocity of about 350 m h− 1.