Detecting ground water - surface water interaction in streams with DTS

Groundwater-surface water (GW-SW) flux measurement techniques, such as reach mass-balance, seepage meters, Darcian flux and temperature sensing can be applied simultaneously to provide multiple lines of evidence (e.g., Gonzalez et al. 2015, Schmadel et al. 2014, Kennedy et al. 2009, Gilmore et al. 2016b), but challenges remain for directly linking results from different spatial and temporal scales of measurement. For smaller streams where groundwater discharge is a significant percentage of stream discharge into the reach (typically ≥10%), the integrated groundwater flux from point measurements can be compared to a larger-scale (i.e. 10^2-10^3 m reach length) approach to confirm results. But for reaches in larger stream (river) systems, the stream-groundwater discharge ratio is usually much too large to use reach mass balance as a direct point of comparison (Gilmore et al. 2016b, Schmadel et al. 2010, Jain, 2000). A promising approach for linking point measurements and testing interpolation techniques in large river systems is fiber-optic distributed temperature sensing (FO-DTS) (Briggs et al. 2012a, Briggs et al. 2012b, Tyler et al. 2009). FO-DTS uses a fiber-optic cable to detect groundwater discharge through the streambed along the length of the cable (typically ≤1km). This may be an effective way to “connect the dots” between point measurements of groundwater discharge in large systems (Krause et al. 2012), when other techniques like reach mass balance, are not feasible. The overall goal of this research is to develop an optimal approach to link point measurements of groundwater-surface water fluxes in large river systems. The specific objectives are to: (1) test the combined DTS and point-measurement approach in a small stream, where interpolated results can be confirmed using a reach mass-balance approach, and (2) apply the technique in larger river systems to characterize spatial distributions and temporal variability of groundwater fluxes at existing groundwater-surface water monitoring stations on larger rivers. This project will improve techniques for multi-scale measurement of groundwater-surface water interactions, give critical insight into temporal and spatial variability of water fluxes in larger river systems, and improve our understanding of the value of existing groundwater-surface water monitoring stations.

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