EVALUATION OF TOPOGRAPHIC WETNESS INDEX AND CATCHMENT CHARACTERISTICS ON SPATIALLY AND TEMPORALLY VARIABLE STREAMS ACROSS AN ELEVATION GRADIENT

Topography can be used to delineate streams and quantify the topographic control on hydrological processes of a watershed because geomorphologic processes have shaped the topography and streams of a catchment over time. Topographic Wetness index (TWI) is a common index used for delineating stream networks by predicting location of saturation excess overland flow, but is also used for other physical attributes of a watershed such as soil moisture, groundwater level, and vegetation patterns. TWI works well for large rivers and streams; however, TWI has less accuracy for small spatially and temporally variable streams (nonperennial) partly due to fickle discharge and drying out. Also as discharge becomes lower more factors such as geology, elevation, upslope soil, and upslope vegetation create unpredictable locations of streamflow in the watershed. This study evaluates the relationships between the active drainage network of four headwater watersheds at various elevations in the Colorado Front Range to topography, geology, climate, soils and vegetation in attempt to determine the controls on streamflow location and duration. The objectives are to 1) digitize the active stream networks in four watersheds across an elevation gradient and document temporal and spatial variation 3) evaluate how well TWI works across a elevation gradient and 3) determine relationships between stream network and topography, geology, climate, soils, vegetation and elevation.