RESERVOIR SEDIMENTATION EFFECT ON WATER SUPPLY UNDER CONDITIONS OF CLIMATE CHANGE

Reservoir sedimentation is the gradual accumulation of the incoming sediment load from a river. With the increasing inappropriate usage of agricultural land, the amount of sediment is becoming larger due to erosion. This undesired outcome is supported by changing hydrological and climatological conditions within a river basin. Climate change has wide effects on all processes within the water cycle, which directly affects water resources. Water management in the future must be adapted for oncoming extremes accompanying climate change, such as floods or droughts. Therefore, sediment accumulation is a serious problem with severe consequences for water management, flood control and the production of energy. Unfortunately, sedimentation will be always a problem until anthropogenic activities (which are accompanied by topsoil erosion), such as overgrazing or deforestation, are strictly controlled. We analysed the effect of sedimentation on two reservoirs � Vranov and Znojmo � which are in the Czech Republic, near the border with Austria. The new measurement of each reservoir�s bottom was carried out in 2021 and 2022. Using ArcMap software, two digital models of the reservoir bottoms were developed. One model used the original measured data, and the other the new data from 2021. The storage-area-elevation curves were evaluated for both models and then compared. There was a storage loss of 7.7% for reservoir Vranov and 16.2% for reservoir Znojmo for the maximum operating water level. Since both reservoirs are water supply reservoirs and in cascade, their management has a large impact on the whole system of reservoirs. This impact was tested using a reservoir system model created in HEC-ResSim software, where the change in long-term mean streamflow was observed. The effect of reservoir storage loss was also analysed under conditions of climate change, where three different RCP scenarios were used to simulate climate change during the period from 2021 to 2060. Storage loss for both reservoirs had added an average 1.95% decrease in long-term mean streamflow to another decrease of 28.0% caused by climate change.