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Institut für Wasser- und Umweltsystemmodellierung - IWS



"The use of natural heat as a tracer to quantify groundwater surface water interactions: Maules Creek, New South Wales, Australia"

Water management in New South Wales (Australia) does not currently consider the connection between groundwater and surface water. Using water resources impacts on interactions between both sources, which are important factors contributing to unique ecological niches in the aquatic environment. The basic connectivity was described and an outline of the significance was given. Connecting flows must be estimated in order to adequately manage water balances. These are difficult to quantify especially when the traditional Darcy method is used. Natural heat promises to be an excellent alternative as it can be used to trace water movement through the shallow surface water sediment. Publications are reviewed and the theory for the two most suitable methods is extracted and explained: temperature forward modelling and the use of temperature fluctuations. Furthermore, multi-level temperature arrays and water level measurements were designed and jointly deployed in three different surface water pools in the Maules Creek subcatchment. Results are inspected, processed and compared to the level measurements. Spectral analysis reveals the presence of atmospheric tides which causes significant level fluctuations. This demonstrates that these ponds are windows to the groundwater table. Both heat methods produces accurate vertical velocities for the location Elfin Crossing which are between -0.2 and -0.7 m/d, indicating that there is streambed water loss to the subsurface. Additionally, recorded water levels decreased consistently during the same time period. The other locations illustrate similar but biased results caused by restricted boundary conditions to the heat transport theory such as one-dimensionality. A numerical model verifies that heat dispersion is a significant mechanism to be considered and that horizontal flow impacts on the result of both methods. Thus, horizontal flow can be detected but quantification remains difficult because solutions diverge. It is suggested that advective flow driven by gradients in the alluvial aquifer is responsible for level decline.