Assessment of possible water withdrawal by floodplain fish farms from the rivers of Belarusian Polesie using the example of the Bobrik river

The aim of this study was to scientifically substantiate the permissible redistribution of the river runoff in the Belarusian Polesie caused by the water withdrawal for the needs of floodplain fish farms at the present stage and in the future, using the example of the Bobrik River in the area of the Polesie fish farm. The determination of the calculated hydrological characteristics was carried out by applying analytical functions of the distribution of annual exceedance probabilities - the three-parameter Kritsky-Menkel gamma distribution. Calculations of the intra-annual distribution of the river runoff were made for water management years starting from the first month of the high-water season using the seasonal composition method. The method of security increasing was used to determine the environmental runoff taking into account the intra-annual distribution. The method of maximum likelihood was used to determine the parameters of the distribution function (three-parameter gamma distribution). The article presents the results of a comprehensive study of the permissible water withdrawal for the needs of the Polesie fish farm located in the floodplain of the Bobrik River. Calculations of hydrological characteristics were carried out for sections above and below the water withdrawal area, and transverse profiles were constructed. The minimum average monthly water flow of 95% probability of exceedance and environmental runoff were determined taking into account the intra-annual distribution of the flow with different security levels. Mathematical models for river sections were developed that allow to determine the flow rates and water consumption depending on the average water depth in the section, as well as the volumes of permissible water withdrawal from the river for the needs of the fish farm while ensuring the condition of maintaining environmental runoff in the river. Estimates of the water withdrawal by the fish farm impact on changes in the hydrological regime of the river were obtained based on operational hydraulic calculations. At the time of the survey in the summer of 2021, the river runoff under study was greater than the lowest critical environmental runoff. The level of impact of the Polesie fishery enterprise on the water regime of the Bobrik River with the existing volumes of surface water withdrawal is below its permissible values, so it is recommended to maintain the current level of impact without increasing it. Keywords: BELARUSIAN POLESIE, WATER CONTENT OF THE YEAR, MODEL, SECURITY, FLOODPLAIN, PROFILE, SECTION, RUNOFF, CONSUMPTION, FISH FARM, LEVEL, ENVIRONMENTAL RUNOFF