资源环境科技发展态势分析平台

The application of heat as a tracer for assessing river-aquifer exchanges has been mainly limited to vertical flow through the riverbed. Lateral river-aquifer exchanges become more important than vertical riverbed exchanges if the river is deeply incised into an aquifer. Few studies have examined lateral river-aquifer exchanges and the ability of heat to constrain such exchanges. This study aims to perform a robust assessment of the limits of heat as a tracer to quantify lateral river-aquifer exchanges. The study is based on a section of the Meuse River in Belgium, a river predominantly gaining in the studied area and becoming intermittently losing in the winter time. A calibrated transect model shows that river temperature can affect groundwater temperature up to 9 m into the aquifer. An accompanying synthetic modeling investigation using Monte Carlo simulation shows that heat data for distances between 4 and 9 m from the river can reduce the uncertainty of river-aquifer exchanges for conditions similar to those of the transect model. The ability of heat to reduce the river-aquifer exchange uncertainty improves with distance from the river because of the reduction in the number of acceptable model realizations. The optimal distance is 8 m from the river where the groundwater temperature is no longer affected by the river temperature. The synthetic modeling also indicates that heat alone cannot constrain river-aquifer exchanges better than the commonly used hydraulic head. However, when combined with hydraulic head, heat can significantly reduce the uncertainty of river-aquifer lateral exchanges under gaining conditions.