The article develops and calculates the method of calculation, taking into account the change in the useful volume of the reservoir under the influence of turbid sediments, the hydrological regime of turbid sediments entering the reservoir. Field research was conducted at the South Surkhan Reservoir. Based on the data collected in the field studies, a map of the reservoir bowl was constructed and morphometric parameters were evaluated, taking into account the formation of turbid sediments in the reservoir. When the normative stagnant water level of the reservoir is 415 meters, the projected water surface area is 65 km2, with a total volume of 800 mln. m3, and according to the results of field research, the total volume of the reservoir at the normative stagnation water level is 491.2 mln. m3, the water surface was 72.45 km2. The full volume of the reservoir decreased by 38.6% compared to the projected volume during operation, and the water surface area increased by 7.45 km2. The results of the study allow us to assess the change in the useful volume of the reservoir under the influence of turbid sediments, which can be used in the development of hydraulic and mechanical cleaning measures in the reservoir.