ABOUT HYDROLOGICAL BASES OF THE JOINT USAGE OF SURFACE AND GROUND WATER IN THE PAKHRA RIVER BASIN
The joint use of surface and ground water in the Pakhra river basin in low-water years for water supply of the Podolsk district of the Moscow region is considered. There are determined deficits of the guaranteed water yield, duration of deficits, maximum monthly deficits, months of deficit, ranges of changes in the depth of reduction of the guaranteed water yield for 1925/26-1992/93 in the usual regime of operation of the Podolsk water storage pond and under the joint use of surface and ground water. There are determined characteristics of water provision and reliability of water yield: provision according to a number of regular years, duration of regular periods, volume of the supplied water to the consumer. It is proposed to complete construction of the Podolsk water storage pond, to lay additional underground water intakes near the Pakhra river as well as to use the existing water intake units to replenish deficits of the guaranteed water yield of the Podolsk water storage pond. As the calculations show, the total volume of the operational groundwater reserves in the Podolsk district of the Moscow region -307426 m<sup>3</sup>/day (9.53 million m<sup>3</sup> per month) should be enough to cover the maximum monthly deficit equal to 8.42 million m<sup>3</sup> provided commissioning of additional wells. The joint use of surface and groundwater water for water supply increases the guaranteed water yield of the Podolsk water storage pond while maintaining the required indices of reliability and availability of the guaranteed water yield without increasing the regulatory volume of the reservoir.