Investigating the Temporal and Spatial Characteristics of Groundwater Discharge in the Loup River Basin

Streams in the Loup River basin are sensitive to groundwater withdrawals because of the close hydrologic connection between groundwater and surface water. Groundwater discharge constitutes over 90 percent of streamflow in the Loup River basin in the Nebraska Sand Hills. The Upper and Lower Loup Natural Resources Districts, in cooperation with the U.S. Geological Survey, recently initiated a study to investigate the temporal and spatial characteristics of surface-water/groundwater interaction within the Loup River basin. Four stream reaches, totaling approximately 320 river miles, have been identified by the Upper and Lower Loup Natural Resources Districts as priority reaches where additional information is needed to protect stream flows. Currently, groundwater discharge is estimated from seepage runs completed in 2006, where streamflow was measured at various points along a stream’s reach, often up to 15 miles apart. Within the four stream reaches, a network of six coupled surface-water/groundwater gages will be installed, each consisting of a stream gage coupled with an observation well screened below the elevation of the streambed and instrumented with a groundwater-level recorder. Information from the network of monitoring stations will provide scientists and water managers with information about temporal and spatial changes in streamflow and groundwater discharge. Additionally, airborne thermal imagery will be collected over the four stream reaches to identify thermal anomalies in stream-surface temperatures, which may be indicative of focused groundwater discharge. Airborne thermal imagery will be verified with continuous water-temperature data from stream gages and self-logging thermistors. Mapped thermal anomalies will be further investigated using a variety of techniques, including water and streambed temperature surveys and potentiomanometer measurements.