Estimating the Depth of Deposition (Erosion) at Slope Transitions on Alluvial Fans

A typical flood mitigation structure on an alluvial fan consists of a dike∕channel system that deflects the flow away from the area requiring protection. Such a structure results in a change in channel slope from steep to mild when the flow first encounters the structure and from mild to steep when the flow is released at the downstream end of the structure. These slope changes result in sediment deposition at the point where the flow encounters the structure and erosion at the point of release. In designing the structure, the length and maximum depth of deposition (erosion) are critical variables that must be estimated. A simple model to estimate these variables is proposed and developed. The hypothesized model has been used to estimate the length and depth of deposition (erosion) on several projects in southern Nevada.