WATERSHED CHARACTERISTICS AND GEOMORPHICALLY DOMINANT FLOWS IN LEHMAN CREEK, GREAT BASIN NATIONAL PARK, NEVADA

We have conducted a GIS-based analysis of the Lehman Creek watershed to support an ongoing study of effective discharge in Nevada's Snake Range. Effective discharge is defined as the streamflow that transports the most sediment over time and is therefore the flow that controls channel shape. We present results for effective discharge and bankfull discharge (streamflow that fills the channel to the active floodplain level) at two sites along Lehman Creek, an alpine stream in Great Basin National Park, Nevada. Pressure transducers and stream gages were installed at an upstream and downstream site in Lehman Creek on October 10, 1999 to begin long-term water level monitoring. To correlate water level with discharge we made numerous streamflow measurements at each site using a Swoffer Current velocity meter. We also measured sediment transport with a Helley-Smith bedload collector and obtained historic discharge data from the United States Geological Survey (USGS). Cross-sections and longitudinal profiles at each site were surveyed several times to determine whether system morphology changed during the course of the study. As part of this project we performed a GIS analysis of watershed characteristics for the upstream and downstream basins. Within ArcView 3.2, we created a single digital elevation model (DEM) of terrain from the four USGS 7.5 minute DEM's that make up the southern Snake Range. From this base map, we then determined landform characteristics such as slope, aspect, and relief for the contributing watersheds at each site. Comparison of these and other watershed characteristics has proved useful in explaining downstream changes in streamflow, sediment transport, and effective discharge. Ultimately sediment transport models will be created to aid in responsible water use for municipalities that rely on alpine watersheds.