Combined removal of sediments from the Chiryurt reservoir

Abstract

The Chiryurt reservoir on the Sulak River, put into operation in 1961, had an original total storage of 98 and useful of 9 million m 3. During the next 7 years it was subjected to considerable silting, as a result of which its storage decreased to 1.5 million m 3. After conducting a series of hydraulic flnshings [1, 2], it was possible to partially remove the deposited sediments. With the construction of the Chirkey and then the Miatla hydro developments in 1978 and 1988, the Chiryurt reservoir began to receive clarified water, the process of intense siltation stopped. Subsequent observations showed that within the 2-m drawdown storage the regulating storage changes little and presently amounts to 7-8 million m 3.Considerable siltation causes difficulties in operating the reservoir by the water users, including the power industry. For example, the Miatla hydrostation at maximum load releases a 2.5 times greater discharge than the diversion works located below the Chiryurt hydrostation can take in. Owing to the lack of the regulating storage of the reservoir the possibilities of the operation of the cascade are limited in a number of gases, sometimes idle discharges of water occur, which, naturally, leads to losses in the generation of electricity.Since 1985 the sediments have been being removed by means of a ZGM-1-350-A dredge with a sediment capacity of 145 m3/h along with hydraulic flushing. The operating plan of cleaning, drawn up by the Baku branch of the All-Union Planning, Surveying, and Scientific-Research Institute (Bakgidroproekt), called for excavating the sediments in two stretches: on the left bank near the irrigation intake on an area of 150 x 600 m with a volume of 260,000 m 3 and on the right bank near the intake on an area of 150 • 300 m with a volume of 130,000 m3; the estimated cost of the work was 387,000 rubles. The rather high cost of the works limited the use of hydraulieking to local zones near the intake works and in comparatively small volumes.At the same time, hydraulicking has the advantage that it is possible to remove the sediments by the dredge to preassigned regions of the reservoir, thereby excavating deposits of the necessary profile and depth. This cannot be achieved by hydraulic flushing. The sediments are removed mainly from the channel part of the reservoir, affecting little or not at all the deposits along the banks and especially where they have become compacted and overgrown by reeds. Furthermore, scouring of sediments can occur at low elevations and thus a part of them will be removed not from the zone of the regulating storage but from the zone below the dead storage level.To increase the effectiveness of removing sediments, the management of the cascade of Sulak hydroelectric stations and the Industrial Association for the Organization and Improvement of the Technology of Operating Electric Power Stations and Networks (Soyuztekh6nergo) developed and tested a method of combined removal --the use of a dredge and hydraulic flushing [3]. In this case, the purpose was to unit...