Integrated Methodology of Instream Flow Assessment : Study of a Belgian River, the Crupet

English. peer reviewed

English. Pumping stations and dams generate modifications of rivers’ state flow. In this work, we propose to implement and compare the results of three instream flow assessments. We are studying a Belgian river called Crupet, which has some pumping stations on its catchment. The Crupet medial flow is 0.56 m3/s at the point of discharge of the catchment. The three methods are : the Range of Variability Approach, the Instream Flow Incremental Methodology and the Wetted Perimeter Method. The aim of the first method is to find an instream flow so that the river conserves as much as possible its natural behaviour after pumping. This method is usually based on twenty years of flow data, before and after the construction of the pumping stations. In our case, the data were not available, especially because there are no stage gauging stations. So we had to generate hydrologic data based on some approximations and hypotheses (estimation of the quantity of water pumped on the catchment, method of regionalisation). Next, we used the IHA software to analyse the alteration of thirty-three hydrologic parameters, and we formulated an equation that calculates how much water could be pumped to minimize the alteration of the parameters. The second method is based on hydrological, morphological, and biological (fish habitat) data to assess the minimum flow in a river at low water. The third method, the Wetted Perimeter Method, is used to find the minimum flow knowing the morphology of the transect (relation between wetted perimeter and flow). For the last two methods, we found the minimum flow for the studied section being equal to 1.5 m3/s. The RVA methodology recommends, however, a higher minimum flow and imposes to reduce the pumping, at least if all our hypotheses are correct.