IDENTIFYING NONCONTRIBUTING AREAS OF WATERSHEDS BY UTILIZING SOIL INFORMATION: A NEW AND REPEATABLE APPROACH

A new approach for delineating noncontributing areas of watersheds is presented. The procedure is based on existing methods of watershed delineation with the additional use of soil maps to locate where water ponds instead of flowing directly to a stream network. This method offers improvements over methods of manually delineating noncontributing areas by being more time efficient and consistent. This method also offers improvements over proposed methods that use only digital elevation models by not needing prior estimation of the noncontributing area or arbitrary settings of thresholds for each watershed. Maps of soil properties offer indicators of subtle landscape features and hydrologic functions. Our approach is to identify soil map units that reflect upland ponding and then define the sum of their watersheds as the noncontributing area. This new method for delineating noncontributing areas will be described in detail and demonstrated through the delineation of noncontributing areas in some watersheds of Iowa and Texas. The decrease in time required to delineate noncontributing areas with a GIS method makes it practical to perform regional scale analysis of non-contributing areas.