ESTIMATION OF SOIL PARAMETERS FOR ASSESSING POTENTIAL WETNESS - COMPARISON OF MODEL RESPONSES THROUGH GIS

A geographic information system (GIS) is utilized to model wetness pot ential for a portion of Uwharrie National Forest, North Carolina. The wetness index is derived from TOPMODEL, a hillslope-scale runoff simul ation model. The wetness index is a distributed-parameter model, with the input parameters obtained from a digital elevation model (DEM) and Soil Conservation Service (SCS) soils data. The primary objectives of the research are to: (1) compare methods of estimating soil parameter s for input into the wetness potential model; and (2) determine how th e model outputs vary spatially as a consequence of different methods o f estimating soil parameters. Three methods of estimating soil paramet ers are used: (a) assuming uniform soil properties; (b) using SCS data presented as ranges; and (c) using alternative literature-based estim ates of soil parameters. Results indicate that the wetness model respo nds similarly regardless of how the soil parameters are estimated, but differences in the spatial variability of the wetness potentials occu r as a result of estimating soil parameters through alternative approa ches. Correlation, pair-wise regression and analysis of regression res iduals are used to compare model responses within a GIS environment.