English

Abstract

A model of soil erosion and sediment transport on hillslopes is used to illustrate the role of process understanding in determining dominant processes as a function of spatial scale. Erosion and sediment yield from hillslopes are primarily determined by surface runoff, topography, vegetative canopy cover, ground surface cover, soil erodibility, and sediment properties. In areas where winter processes (snow, snowmelt, soil frost, etc.) are important, erosion and sediment yield also determined by these factors. The Hillslope Erosion Model (HEM) incorporates these factors in simulating erosion and sediment yield. The world's largest rainfall simulator database for arid and semiarid areas and data from small hillslope-scale watersheds are used to calibrate and validate the spatially distributed, processed-based HEM. Spatially distributed estimates of sediment transport and yield along hillslopes from the HEM are used with an understanding of dominant processes as a function of spatial scale as the scientific basis to determine stability of slopes at plot to hillslope scales. Interrill processes of raindrop splash and thin sheetflow transport are diffusive. Concentrated flow (rill erosion) processes are advective. Spatial loci of transition from diffusive to advective processes are inherently zones of landscape instability and channel formation. The HEM is used to define these areas of instability on hillslopes. Stability criteria for hillslopes are in turn used as criteria for geomorphic designs. Field data taken on a mine rehabilitation site in Queensland, Australia and at the Yakima Training Center in Washington State were used to extend the erosion model to disturbed site rehabilitation problems. These example applications from natural and designed slopes are used to illustrate model predictions and their applications in scaling and geomorphic designs.