INCREASED UNDERSTANDING OF WATERSHED DYNAMICS THROUGH THE ADDITION OF STREAM AND GROUNDWATER TEMPERATURE MONITORING AT USGS GROUNDWATER STREAMGAGES

Temporal and spatial variations of streamflow, stream temperature, groundwater recharge/discharge areas, and groundwater temperature are primarily controlled by localized climatic conditions within watersheds. Many watershed components, including stream/groundwater exchanges, can be tracked using temperature patterns, and due to the hydrologic information gained through the use of temperature monitoring, the USGS has increasingly included continuous (15 minute) stream temperature data along with continuous stream stage (elevation) at many streamgages nationwide over the past 25 years. To advance the localized understanding of recharge and discharge patterns near streams, the use of continuous water-temperature monitoring was extended to include the groundwater component of hydrologic systems with the development of USGS Groundwater Streamgage (Eddy-Miller et al., 2012, USGS Fact Sheet 2012-3054). The necessary and sufficient parameters of a basic USGS Groundwater Streamgage are: stream stage, stream temperature, groundwater elevation and groundwater temperature (http://wy-mt.water.usgs.gov/projects/ogw/index.htm), with availability for add-on parameters (e.g., electrical conductivity) as appropriate. The ability to evaluate stream and groundwater hydrographs simultaneously with their thermographs permits detailed analysis of continuous stream exchanges with nearby groundwater, and for example, if a specific stream reach is a groundwater discharge or recharge area on a given day or over a season or on a decadal scale. There are numerous case-specific advantages available using this four-parameter approach in watersheds; for example, determination whether a rise in the water table is induced by increases in overpressure or rather by groundwater recharge may be determined by analyzing whether the corresponding groundwater temperature changes, which indicates groundwater recharge. Several visual examples are provided to detail methods in which USGS Groundwater Streamgages utilize stream and groundwater temperature in tandem with stream and groundwater elevation to enhance our hydrologic understanding in watersheds, with a clear potential for analyzing impacts of land-use change or climate change on the hydrology of watersheds.