Quantifying the efficiency of river regulation

Dam-affected hydrologic time series give rise to uncertainties when they are used for calibrating large-scale hydrologic models or for analysing runoff records. It is therefore necessary to identify and to quantify the impact of impoundments on runoff time series. Two different approaches were employed. The first, classic approach compares the volume of the dams that are located upstream from a station with the annual discharge. The catchment areas of the stations are calculated and then related to geo-referenced dam attributes. The paper introduces a data set of geo-referenced dams linked with 677 gauging stations in Europe. Second, the intensity of the impoundment impact on runoff times series can be quantified more exactly and directly when long-term runoff records are available. Dams cause a change in the variability of flow regimes. This effect can be measured using the model of linear single storage. The dam-caused storage change 1S can be assessed through the volume of the emptying process between two flow regimes. As an example, the storage change 1S is calculated for regulated long-term series of the Luleälven in northern Sweden.