Numerical simulations of runoff generation with surface water-groundwater interactions in the Alzette river alluvial plain (Luxembourg)

Detailed field measurements of water table levels and river stages operated on the Alzette river basin in Luxembourg have pointed out that the runoff response of the catchment to rainfall is strongly dependent on the groundwater level behaviour and on the water storage of the catchment. This dependency becomes even more pronounced for the topographic configuration of the Alzette basin that is characterized by narrowing valleys that hamper the downstream progression of alluvial groundwater. Modelling the hydrologic response of the Alzette catchment with a physically based approach requires the selection of a model that allows the simulation of an interaction between groundwater and surface water in the alluvial plain. For this reason a hydrological model based on the representative elementary watershed (REW) approach has been selected. The approach consists in discretizing a watershed in sub-watersheds or REWs, each subdivided into five zones according to dominant hydrological processes. Balance laws are averaged within each zone and hydrologic relations are derived directly at the REW scale. Each REW is considered as a spatial unit, represented by averaged watershed scale parameters and variables. The approach enables an interaction between saturated zone and channel reaches, which plays an essential role in the runoff generation in the Alzette floodplain. For this study a sub-catchment of the Alzette basin is selected that is located upstream of Luxembourg City. Results show that the model conceptualization is appropriate to describe the catchment dynamics in the alluvial plain, while the same cannot be assured for other regions of the study area. The model has been calibrated on channel flow data and piezometric observations provided by the Public Research Center-Gabriel Lippmann of Luxembourg. (C) 2005 Elsevier Ltd. All rights reserved.