The Role of the Clast Layer of Desert Pavement in Rainfall-Runoff Processes

Desert pavement is a surficial feature widespread throughout arid lands in the world. Whenever found, it can play an important dynamic role in geomorphic, hydrologic, and ecologic processes in desert environments. The hydrological properties, especially the clast layer impact on hydrological processes, are still not clear to the academic community. Anecdotal evidences and empirical observations have reported rapid runoff generation process which implied low permeability of the pavement with the clast layer. Quantitative result, however, has not yet been reported. An experimental study has been carried out in Mojave National Preserve near Providence Mountain to investigate the hydraulic properties of the clast layer. Rainfall simulations were conducted with a pair of portable rainfall simulators. Each group of experiment includes two parallel runs on two adjacent plots, one with intact clast layer and one with clast layer removed. Soil moistures time series were measured with Water Content Reflectometers (WCR). Runoff was collected at the downstream side of each plot. Experimental results of both runoff and soil moisture did not show significant difference between two types of plots, which implied the clast layer at the experiment site is not a restrictive layer for infiltration and rainfall-runoff processes. In addition, the measured soil moisture curves were used to develop an optimization method for Green-Ampt infiltration parameters, which can produce a useful tool of direct estimation of G-A parameters for practical applications.