LAUSR

Abstract Investments that make use of renewable resources of flowing waters must be based on the absolute necessity of protection of the water environment and that dependent on water. In practice, it means the obligation of leaving environmental flow in the river bed in the cross section below the place of water abstraction. The places of surface water abstraction for drinking and industrial purposes are thus limited with the volume of water obligatorily left in the flow for water organisms. In case of hydropower plants located directly in the watercourse, the environmental flow value corresponds approximately with the volume of water run in the fish pass obligatorily provided to maintain patency of the watercourse, in particular in the aspect of migration of diadromous fishes. Environmental flow is ineffective in investment terms, but highly important from the point of view of environmental protection. Thus, the proper calculation of the environmental flow value should be the compromise between the protection of the environment and the economics of the investment. No unanimous methodology in this respect has been applied in Poland for many years, and calculations were done with one of subjectively selected methods functioning in the literature. This work presents the methodology of environmental flow calculations broken down into water regions. Calculation path has been presented along with the possible inconveniences resulting from the effective legal regulations in Poland as regards the possibilities of carrying out projects that take advantage of flowing surface waters.