GEOLOGICAL CONTROLS ON THE CHARACTERISTICS AND SPATIAL DISTRIBUTION OF STREAMBED SEEPAGE IN A GREAT BASIN STREAM, SOUTHERN SNAKE RANGE, NEVADA

In the driest state in the nation, groundwater recharge is of critical importance to Nevada’s water resource management. Whereas a large fraction of this recharge typically occurs as infiltration where mountain streams cross permeable alluvial fans, the specific spatial distribution and dynamics of these processes can vary widely depending on local conditions and, importantly, geology. Snake Creek is a small, mountain stream (with average discharge from 0.03 to 0.5 m³/s) that runs from crystalline and metamorphic core rocks high in the southern Snake Range (Great Basin National Park, Nevada), crosses the Southern Snake Range décollement, and continues East into Utah, passing through a structurally complex region containing limestone, quartzite, and cemented alluvial materials. We instrumented a geologically heterogeneous reach of Snake Creek with streambed piezometers (containing temperature loggers at multiple depths and pressure transducers) and fiber-optic cable for Distributed Temperature Sensing (DTS) in order to characterize the spatial distribution of streambed seepage. Initial assessment of the data indicates that there are both gaining and losing stretches, that each has a unique thermal signature, and that these stretches correspond to areas with differing geologic controls on seepage. Permeable streambed sediments with hydraulic conductivities ranging from K = 10^-5 to K = 10^-4 m/s are not sufficient to assure groundwater recharge; rather, this must be combined with a suitable geologic substrate.