We have demonstrated that very high resolution, (~20cm), airborne thermal remote sensing can be used to quantify both hyporheic exchange and baseflow contribution to streams. During warm summer months, particularly during the afternoon, stream temperature is significantly warmer than the groundwater temperature, which is similar to the mean annual air temperature. Therefore, inflowing groundwater tends to have a cooling effect in stream reaches that are strongly gaining. Hyporheic fluxes buffer stream temperature fluctuations resulting in lower daily maximum stream temperature, higher daily minimum stream temperature, and delayed occurrence of these temperature extremes. Stream temperature is simulated using an energy budget model approach and a one-dimensional model of heat transport in the stream. Spatially distributed baseflow and hyporheic exchange are determined by varying these quantities until agreement (root mean square difference = 1.1 ºC) is found between the simulated stream temperature and both the remotely sensed profiles of stream temperature (0.6 ºC accuracy) and the recorded in situ temperature histories (0.1 ºC accuracy).
This is the first time baseflow and hyporheic exchange have been quantified using remotely sensed temperatures. For small watersheds with significant baseflow components, this technique provides a means to evaluate the spatial distribution of baseflow to an extent not practical or possible with commonly available methods. This technique showed both increased baseflow and hyporheic exchange in streams running through a restored subreach during late spring. This finding supports the hypothesis that restoration improves fish habitat in the stream by creating a more hospitable temperature regime. (powerpoint: Thermal Remote Sensing: Detection of Groundwater Discharge to Streams, GSA 2007)