Simulation of flood reduction by natural river rehabilitation using a distributed hydrological model

Abstract. The effects of river rehabilitation on flood reduction in the Steinsel sub-basin of the Alzette River basin, Grand-Duchy of Luxembourg, are discussed; the rehabilitation measures include planting and changing riparian and in-stream vegetation, and re-meandering of channelised reaches, etc. in the headwater streams. To simulate flood reduction by river rehabilitation, the streams have been classified into different orders and by assessing the response of the stream channels to the resistance or obstruction of flows. Based on this assessment, the roughness to the flow in the first and second order streams is adjusted in line with the river rehabilitation while the roughness of higher order channels downstream is unchanged. The hydrological analysis utilises the WetSpa distributed model based on spatial information on topography, soil type and land use. The increased channel roughness in the headwater channels delays the flows, so that peak discharges at the outlet of the basin are reduced. The simulation indicates that, after river naturalisation, the reduction in peak flow can be as much as 14% and the time of concentration may be delayed by as much as two hours. Also, an impact analysis has assessed the possible flood reduction for a changed climate scenario.

Keywords: river rehabilitation, flood reduction, distributed hydrological modelling, WetSpa