J. A. Yeakley, G. M. Hornberger, W. T. Swank, P. V. Bolstad and J. M. Vose. 2000. Soil Moisture Modeling in Humid Mountainous Landscapes. In: J.C. Wilson and J.C. Gallant, eds. Terrain Analysis: Principles and Applications, John Wiley & Sons, pp 205-224.

A method of modeling hillslope soil moisture was implemented and assessed for a multi-year period in a 12.3-ha watershed (WS2) at the Coweeta Hydrologic Laboratory in the southern Appalachian mountains. The modeling framework consists of three modules: (1) contour-based terrain analysis (TAPES-C); (2) above-ground canopy interception; and (3) a hillslope hydrology model (IHDM4) using a 2D Richard’s equation of subsurface moisture dynamics. Terrain analysis was conducted to identify hillslope planes in the watershed. The canopy interception module was calibrated based on 14 years of hourly climate data and extensive interception and throughfall measurements in the Coweeta Basin. The hillslope hydrology module was calibrated for stream flow using both wet and dry antecedent storm events and for soil moisture using time domain reflectometry measurements of soil moisture on a lower hillslope plane in WS2, over a period spanning a severe autumn drought through winter precipitation recharge. The accuracy of this modeling approach was examined using monthly soil-moisture measurements from Oct 94 to Oct 96 on another, more extensive hillslope plane in the watershed. The model predicted mean monthly soil moisture for the hillslope plane with errors ranging from 1% to 23% in dry months and up to 45% in wet months. During wet months, the model predicted soil moisture along the hillslope better near the ridge and stream than on the midslope. During dry months, the model predicted soil moisture more accurately on the midslope. Two issues need to be addressed in future model development: incorporation of lateral variation in soil hydraulic properties and more accurate representation of soil-moisture content near seepage faces. Ongoing research is being conducted to address both of these issues in several watersheds in the Coweeta Basin.