Using Heat Tracer to Estimate River Water and Groundwater Interactions in Alpine and Cold Regions: A Case Study of Hulugou Watershed in Upper Reach of Heihe River

The quantitative research on the interaction between surface water and groundwater in alpine and cold regions is of essential significance for the evaluation and management of the water resources. However, there are relatively few quantitative researches carried out on the interaction between surface water and groundwater in alpine and cold region. Taking Hulugou watershed in upper reach of the Heihe River with permafrost distributed as the study site, monitored temperature time series were used to identify the interactions between river and groundwater, and the utility of heat tracers is also evaluated in this paper. Temperatures of groundwater riverbed sediments at different depths, river stage and groundwater level were monitored at the site. Then, the vertical flow velocities of river water infiltration to groundwater at 3 points along river channel were calculated through the Hatch analytical solutions with the monitored data. The results indicate that river stage was higher than groundwater level, suggesting the recharge of the river water to the groundwater. Temperatures of riverbed sediments were higher in July in comparison with those in September. The river infiltration velocity was between 2×10^-6-5×10^-5 m/s in the monitoring period. The analyses show that exchange between river and groundwater can be estimated by heat tracers in alpine and cold regions. However, the other recharge sources to groundwater should be investigated by other methods such as isotopic method and numerical modeling. Exchange between river and groundwater is mainly controlled by the relationship between river stage and groundwater level, hydraulic conductivity and heat capacity of riverbed sediments.