Laboratory Study of Short Term Response of Alluvial Fans to Changes in Input Water Flow and Sediment Supply Under Lateral Confinement

Abstract

In this chapter, the autogenic process of alluvial fan under various discharges and sediment feed rates were studied. Meanwhile, the discharge and sediment feed rate were suddenly changed during some experiments to analyze alluvial fan’s delayed response to external disturbances. The results demonstrate that progradation processes both slow down when water discharge or sediment feed rate is halved separately. When reducing both water discharge and sediment feed rate simultaneously, progradation process become even slower. Widening process of alluvial fan is less sensitive to change of discharge and sediment concentration than progradation process. When sediment feed rate is reduced by half, alluvial fan aggradation processes along flow path slows down obviously. When water discharge is reduced by half, upstream aggradation processes accelerate while downstream aggradation processes decelerate. The alluvial fan fluvial cycle and the channel morphology react to discharge reduction differently with sediment concentration reduction. The rate law can be employed to describe the actual response process of the deposition thickness. Calculated results demonstrate that the response rate of the upper-fan siltation layer is higher than that of the mid-fan and lower-fan. The response rate of the fine-sand alluvial fan is higher than that of coarse-sand. The response of the deposition layer to discharge increase is faster than that of discharge decrease. Alluvial fan development is influenced by both fan reaction mode and the status of fan development.