Hillslope characteristics and particle size composition of surficial armoring on a semiarid watershed in the southwestern United States

Distributed process-based hydrologic models have been used to describe and predict the movement of sediment on small watersheds. However, to parameter ize these models requires an understanding of the spatial variability of er osion processes and the particle sizes of the sediment being moved. In this study, a high resolution digital elevation model (DEM) and detailed sedime nt particle sampling allowed a comparison of hillslope characteristics and particle sizes of surficial armoring in a semiarid watershed. Individual pa rticle size classes on hillslopes are correlated with the underlying sedime nt type, local slope, aspect, and area draining through a grid element. The strongest correlations are between the underlying sediment and overlying s ediment. However, the distribution of the particle size classes is consiste nt with a hydrodynamic explanation for sorting. In particular, increased ar ea draining through a grid node and increased slope are correlated with hig her concentrations of the 16-64-mm particle size class. Both the coarsest a nd finest particle size classes are significantly correlated with the aspec t of flow from a grid cell, with increased coarse particles and decreased f ines on east-facing slopes. These spatial differences with aspect are attri buted to dry season prevailing winds. These observations about process and spatial distribution are useful in predicting the spatial distribution of p articles on the watershed for applications such as distributed hydrologic m odels. (C) 2001 Elsevier Science B.V. All rights reserved.