DIGITAL ELEVATION ANALYSIS FOR DISTRIBUTED HYDROLOGICAL MODELING - REDUCING SCALE DEPENDENCE IN EFFECTIVE HYDRAULIC CONDUCTIVITY VALUES

The recent widespread availability of digital terrain data has made au tomatic procedures for topographic analyses popular. Previous studies have shown that hydrological models and their effective parameter valu es are dependent on the resolution of the elevation grid. This paper e xamines the analysis of raster elevation data within the topography-ba sed model, TOPMODEL, framework. It is demonstrated that the algorithm used in processing channel pixels in calculating the topographic index kappa = ln(a/tan beta) can have a dramatic effect on the sensitivity of effective parameter values to the grid size. Suggestions are made f or calculating the topographic index of channel pixels, consistent wit h the TOPMODEL assumptions, that strongly decrease the sensitivity of the calibrated effective hydraulic conductivity values to grid size.