Estimating flow and flux of ground water discharge using water temperature and velocity

The nature of ground water discharge to a stream has important implications for nearby ground water flow, especially with respect to contaminant transport and well-head protection. Measurements of ground water discharge were accomplished in this study using (1) differences between current meter measurements, (2) stream temperature surveys combined with streamflow estimates, and (3) heat transport modeling of measured temperature gradients below the streambed. The first two techniques produced an area-averaged estimate of ground water flow, while the last produced a point estimate of ground water flux. Point measurements differed from area-averaged methods by 1 or 2 orders of magnitude. We hypothesize that discharge to the study creek is spatially heterogeneous, and is dominated by springs and seeps. Thermal gradient measurement did not quantify these local sources of stream inflow. Point measurements of inflow from temperature gradients or seepage meters, therefore, may not represent ground water inflow in some streams. Stream temperature and streamflow surveys were combined using a simple heat-balance to yield a higher-resolution estimate of streamflow than could have practically been obtained with current meters alone. This approach has potential as a cost-effective method of quantifying ground water discharge in streams where stream inflow is highly heterogeneous.