Naturalization of the flow rate downstream from the Vesdre reservoir

Abstract

Dams are used worldwide for the purpose of water management. In this thesis we naturalized the discharge of the Vesdre (Belgium) at the location of the dam in order to quantify the storage effect of the Vesdre reservoir. This research does not study the influence of the water flow diversion from the river Helle towards the dam, its contribution is still included in the naturalized discharge. First, we compute the total inflow into the reservoir for which the contributing parts are the Helle tunnel, the Getzbach river, the upstream of the Vesdre river, and the portion of the reservoir water catchment that is drained but ungauged. This total inflow discharge is considered the natural discharge of the Vesdre. Then the outflow discharge from the Vesdre dam is computed based on a mass balance equation. These discharges were computed for the period of January 1995 to April 2022. 18 flood events were distinguished from the total inflow time series. For these 18 events, the inflow and outflow discharge were compared. The main findings are: that the dam reduces the peak head discharge by 14 to 85\%, the dam is able to shift the peak discharge by 5 to 69 hours, the dam is able to reduce the flood volume by 2 to 83\%. A flood frequency analysis was also applied on these data, and shows that the dam reduces the magnitude of flood peaks by a factor of two. This last result does not apply when the reservoir is saturated due to extreme flood events. The extreme flood event of July 2021 was not studied due to the unreliability of the data.