USGS Recognizes "Protect Your Groundwater Day," September 6, 2016

Figure 1. Infrared image indicates water temperature, where warmer temperatures are represented as yellow and cooler temperatures as purple. The image presents an area where a relatively warm groundwater seep is discharging along the edge of a relatively cooler stream, and the water is mixing. The temperature range displayed is approximately 1 to 8 degrees Celsius. The area at the center of the image is about 2 meters across. Image: USGS/Martin Briggs.

Groundwater/Surface-water Interaction

Understanding the interaction of groundwater and surface water is essential to water managers and hydrologists for the development of effective water-resource policy, protection, and management. Groundwater/surface-water interactions include the exchange of fluids and solutes, which can affect water quality and water supply. Groundwater is a major source of water to streams, lakes, and wetlands; surface water can also recharge (replenish) groundwater supplies.

Traditional methods of collecting groundwater/surface-water exchange data can be labor intensive. The effects of groundwater/surface-water exchange can occur on a variety of spatial and temporal scales. Various methods of data collection apply to fundamentally different areas and time periods. Conditions at the local and regional scale are often characterized based on measurements made at a few individual points. However, useful predictions based on point measurements are difficult because the characteristics of groundwater/surface-water exchange can vary over time and across a site or region.

Figure 2. Thermal infrared image details multiscale groundwater discharge to surface water through macropores and peat pipes. First, a visible light photo is shown, with the approximate inset area covered by the thermal infrared data collection. Infrared image indicates water temperature, where warmer temperatures are represented as red and cooler temperatures as blue. Thermal image temperature range displayed is approximately 10 to 28 degrees Celsius. Source: Briggs and others, 2016.

Heat as a Tracer of Water Movement Near Streams

Temperature has long been recognized as an important water-quality parameter. Differences between temperatures in a stream and surrounding sediments can be analyzed to trace the movement of groundwater to and from streams and to better understand the magnitudes and mechanisms of stream/groundwater (hyporheic zone) exchanges. Figures 1 and 2 show how thermal imaging can be used to rapidly identify, visualize, and quantify differences in water temperature that may indicate groundwater discharging to the surface. To learn more about use of heat as a tracer, see "Heat as a tool for studying studying the movement of ground water near streams."

Handheld Thermal Imaging Cameras for Groundwater/Surface-water Interaction Studies

USGS Science Centers are using high-resolution handheld thermal imaging cameras (figs. 3 and 4) in groundwater/surface-water interaction studies and other investigations where thermal signatures are of interest. The cameras can be used to image streams, lakes, and adjacent structures (e.g., banks, bars, seeps, etc.) to quickly locate and characterize thermal anomalies in real time at a scale of centimeters to tens of meters. Variations in temperature can be used to track (or trace) the heat carried by flowing water, such as during groundwater discharge into a stream.

Although airborne and satellite thermal imaging for water-resources studies is common, the availability of robust handheld thermal imaging tools in support of USGS groundwater studies is relatively new. The cameras allow hydrologists to rapidly image real-time variations in temperature at high resolution in the field. The information can be used to

• identify localized groundwater discharge,
• help characterize local hydrogeologic conditions, and
• optimize sampling and monitoring locations.

The small size of the cameras makes them convenient tools for studies in dense urban settings as well as remote field sites. Potential field applications are being explored within the USGS Water Mission Area and in interdisciplinary work with other USGS Mission Areas.

Figure 3. Two thermal infrared imaging cameras in use, one full size camera and another attached to a computer tablet. Image: USGS/C.B. Dawson

Figure 4. Close up view of thermal infrared image of two scientists working in a stream. Infrared image indicates temperature, where warmer temperatures are represented as red and cooler temperatures as blue. The scientists appear red because they are relatively warmer than the stream water. Image: USGS/C.B. Dawson

Figure 5. Thermal infrared (TIR) image displayed as an inset of a true-color photograph taken in the field. TIR indicates water temperature, where warmer temperatures are represented as red and cooler temperatures as blue. The image presents an area where warmer groundwater (yellow) may be discharging into a cooler (purple) stream. Variations in temperature can be used to track (or trace) the heat carried by flowing water, such as during groundwater discharge into a stream. Image: USGS/Brian Clark.

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