Sensitivity of methods for calculating environmental flows based on hydrological characteristics of watercourses regarding the hydropower potential of rivers

Abstract

The paper analyses selected problems with the estimation of environmental flows (EF) in the aspect of hydroelectric potential of rivers. The study was conducted for mountain catchments located in the upper Vistula catchment in Poland: Mszanka, Poroniec, Grajcarek, Ochotnica, and Kamienica Nawojowska. The data for calculations, in the form of observational series of daily flows in the years 1985-2014, were obtained from the Institute of Meteorology and Water Management of the National Research Institute in Warsaw. Based on the data, environmental flows were calculated as 25% Mean Annual Flow (MAF), 70% Median Flow, Q90, 7Q10, 7Q2, and additionally with the Eflows Management Framework and Upscaling method (EMFU). The calculations made it possible to indicate the main problems related to the calculation of environmental flows using hydrological methods: selection of the appropriate characteristic flow, the method of determining guaranteed flows, selection of appropriate statistical distributions or sensitivity of environmental flows to the length of the observation series for which they are esteemed. In addition, the paper showed that the choice of method for calculating the environmental flow influences the volume of electricity production in hydroelectric plants. For watercourses not covered by specific forms of protection, the compromise between environmental protection and investment economics seems to be calculating the EF value by 25% MAF or Q90. It was also found that it is optimal to maintain the value of EF (from the point of view of caring caring for the aquatic environment) along with choosing the economically justified options.