Hyporheic exchange and residence time distribution in the Petit Buëch river in France

Abstract

Hyporheic exchange and residence times are important for the response and prediction of hydrologic systems for both natural and human-induced changes. Understanding residence times of particles in the hyporheic zone is important for understanding the consequences of e.g. climate change, industrial pollution, and fertilizers for agriculture, aquatic life, and human water supply. The main challenge in understanding contaminant migration is characterisation of hyporheic zone water flow paths that differ in length and duration. Data that were collected for modeling of hyporheic exchange were: hydraulic heads, digital elevations, Darcy velocities, porosities, travel times, and the thickness of the water-bearing layer. Modeling of hyporheic flow and particle tracking was done with Modflow and PmPath. The program ArcGIS was used for the visualisation of data. The fluctuation of the river discharge and water level resulted in variable locations of river water infiltration locations and rates. A small river discharge resulted in large quantities of river water infiltration which could be more than 50% of the total river discharge. Furthermore, the variation in residence times and hyporheic exchange rates were due to the varying morphology of the point bar. As a result of long residence times, the hyporheic zone was able to retain large quantities of solutes from stream water. Therefore, chemical signals due to e.g. precipitation, industrial pollution, or agriculture may be delayed or even attenuated by hyporheic zone exchange.