Groundwater-Surface Water Interaction and Its Mechanism in a Piedmont Fluvial-Alluvial Fan of an Alpine Watershed

Conventional methods such as differential flow gauging, one-dimensional heat transport equations, and environmental isotopic and geochemical tracers are often used to study the interaction mechanism between groundwater and surface water in alpine watersheds. However, they can not accurately describe this mechanism on a small scale, such as the complex stream stretches of a piedmont fluvial-alluvial fan. Therefore, the piedmont fluvial-alluvial fan in the Hulugou Valley in the headwaters of the Heihe River was chosen as our study site. Discrete zones of groundwater discharge along the stream stretches from the east tributary to the mainstream were identified on the basis of variations in streambed temperature using a distributed temperature sensor (DTS). The DTS gives measurements of the spatial (±1 m) and temporal (10 min) variation of streambed temperature over a much larger reach of stream (~883 m) than previous methods. Results show that focused groundwater discharge has been identified in twelve points along the east tributary, and groundwater discharge in the mainstream has been dominated by diffuse flow. Combining the hydrogeology of this catchment, we build the conceptual model of interactions between groundwater and surface water in a piedmont fluvial-alluvial fan. The heterogeneity of fluvial-alluvial aquifers in the alpine watershed controls and impacts groundwater flow and its interaction with surface water. Furthermore, the impact's space-time scope will gradually increase with climate warming.