Geomorphologic and Soil Hydraulic Parameters for Watershed Environmental Hydrology (WEHY) Model

Abstract

The upscaled hydrologic conservation equations in the Watershed Environmental Hydrology (WEHY) model are capable of taking into account the effect of heterogeneity within natural watersheds. Model parameters that are capable of describing the heterogeneity of the flow domains also need to be estimated. The parameters of the WEHY model are related to the physical properties of the watershed, and they can be estimated from readily available information on topography, soils, and vegetation/land cover conditions. The fundamental assumption of the parameter estimation methodology in this study is that the heterogeneities of land characteristics over a model computational unit (MCU), representing an individual hillslope, are spatially stationary. Consequently, the parameters of the WEHY model that represent the statistical moments of point-location parameter values (such as the variance of log saturated hydraulic conductivity) do not vary over different transects of an MCU. The geomorphologic parameters that describe the rilled surface geometry of MCUs are derived directly from the digital elevation model map of the watershed by using Arc/Info tools or ArcView. The soil hydraulic parameters of the WEHY model require a soil texture classification database and/or field investigations. In this paper, a detailed methodology on the estimation of the geomorphologic and soil hydraulic parameters of the WEHY model is described. Applications of the methodology to the Upper Cosumnes River watershed in California and the Shiobara-Dam watershed in Japan are also presented in order to illustrate how to utilize the available geographic information system database and field survey data for the estimation of the parameters of the WEHY model.