Assessing the effect of flood restoration on surface–subsurface interactions in Rohrschollen Island (Upper Rhine river – France) using integrated hydrological modeling and thermal infrared imaging

Abstract

Rohrschollen Island is an artificial island of the large Upper Rhine river whose geometry and hydrological dynamics are the result of engineering works during the 19th and 20th centuries. Before its channelization, the Rhine river was characterized by an intense hydromorphological activity which maintained a high level of biodiversity along the fluvial corridor. This functionality considerably decreased during the two last centuries. In 2012, a restoration project was launched to reactivate typical alluvial processes, including bedload transport, lateral channel dynamics, and surface–subsurface water exchanges. An integrated hydrological model has been applied to the area of Rohrschollen Island to assess the efficiency of the restoration regarding surface and subsurface flows. This model is calibrated using measured piezometric heads. Simulated patterns of water exchanges between the surface and subsurface compartments of the island are checked against the information derived from thermal infrared (TIR) imaging. The simulated results are then used to better understand the evolutions of the infiltration–exfiltration zones over time and space and to determine the physical controls of surface–subsurface interactions on the hydrographic network of Rohrschollen Island. The use of integrated hydrological modeling has proven to be an efficient approach to assess the efficiency of restoration actions regarding surface and subsurface flows.