HYDROLOGICAL REGIME OF WATER STREAMS AND THE PROBLEMS OF PUBLIC WATER SUPPLY IN THE REPUBLIC OF KALMYKIA

Abstract

The constant shortage of fresh water for drinking and municipal use in the Republic of Kalmykia has become critically acute recently. Both natural factors, i.e. increasing climate aridity, limited reserves of fresh surface and groundwater, lack of sufficiently long sections of large rivers with constant flow, and the deterioration of hydraulic structures are the reasons. The exploitation of groundwater in existing deposits has led to their depletion and deterioration, while large deposits of fresh and slightly brackish groundwater in the southern Caspian region cannot be used because the content of pollutants in them is rather high. Recovery of old and construction of new water pipelines from the Volga River requires permanent significant financial investments at the federal level. Therefore, recently a new way to increase the supply of fresh water suitable for drinking purposes, i.e. an artificial groundwater recharge (AGR), has been actively discussed. The article provides an actual assessment of water resources of the littlestudied surface runoff of the rivers of Kalmykia, considers the possibility and feasibility of creating infiltration basins to replenish groundwater reserves, and calculates the parameters and operating mode of five planned basins. The main source of fresh surface water in Kalmykia is the rivers of the Ergeni Upland. The average long-term flow from its eastern slope is estimated at 0,120 km3/year, from the western slope at 0,105 km3/year and from the southern slope at 0,045 km3/year. Trends in modern modification of the hydrological regime of rivers under the influence of climate change have been revealed, namely a decrease in annual runoff and its intra-annual redistribution with a reduction of spring floods, a slight increase in winter runoff and a leveling of summer low-water periods. Calculation of the operating mode of planned infiltration basins allowed us to draw the following conclusions: the maximum possible volume of total infiltration will be about 220 thousand m3/year, which is 36 times less than the presentday water intake from the Troitsk and Bayarninsky fields for public water supply; sufficiently efficient operation of pools is only possible with annual cleaning of accumulated silt deposits, otherwise the soil filtration coefficient will come down each year, resulting in the reduction of infiltration supply by dozens times. Thus, the AGR can only be a temporary measure to compensate for the subsidence of groundwater level until the reconstruction and construction of new water pipelines from the Volga River to supply the city of Elista and the surrounding area with drinking water of acceptable quality