Groundwater/Surface-Water Interactions in the Loup River Basin

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Streams in the Loup River basin are sensitive to groundwater withdrawals because of the close hydrologic connection between groundwater and surface water. Pumping from aquifers that are hydrologically connected to surface-water bodies can have a significant effect on the streams by reducing the groundwater discharge to surface water. An evaluation of any groundwater management strategy needs to involve consideration of the impact on surface-water resources.

Streams in the Loup River Basin are known to receive a combination of focused discharge (groundwater discharge as springs) and diffuse discharge. Four stream reaches, totaling approximately 320 river miles, have been identified by the Upper and Lower Loup Natural Resources Districts as priority streams where additional groundwater/surface-water interaction information is needed to properly manage their water resources. The USGS, in cooperation with the Upper and Lower Loup Natural Resources Districts, received a grant from the Nebraska Environmental Trust to study and address these water supply concerns.

To map focused groundwater discharge points, aerial thermal-infrared imagery was collected over two stream reaches prior to onset of ice cover in late 2015, when warm thermal anomalies in stream-surface temperatures indicated areas of focused groundwater discharge. Zones of focused groundwater discharge were detected along the upper South Loup, North Fork of South Loup, and Dismal Rivers.  A series of focused groundwater discharge points was detected along the upper South Loup River where the river has incised into Pliocene-age gravel deposits. Stream surface temperatures from the aerial thermal-infrared imagery were plotted against distance downstream. Results indicated a substantial increase in the groundwater component of streamflow upstream from mapped springs which originated from diffuse groundwater discharge.

We are investigating and describing the spatial characteristics of groundwater/surface-water interaction for selected stream reaches in the Loup River Basin by:

  1. Examining the effectiveness of thermal airborne infrared imagery in identifying zones of focused and diffuse discharge.
  2. Evaluating spatial trends across various physical and geologic settings in the Loup River Basin with interpreted airborne thermal infrared data.
  3. Creating maps of focused discharge zones and inferred diffuse groundwater discharge areas within selected reaches in the Loup River Basin.

Additional information about this study, including a map of coupled groundwater/surface-water gages, is available from the Groundwater/Surface-Water Interactions in the Loup River Basin web site.

USGS scientist taking water temperature measurement in the North Loup River, NE