Ice and thermal conditions of the pools at the Ust'-Ilim hydroelectric station

Abstract

Filling of the reservoir of the Ust'-llim hydroelectric station, located 303 km downstream of the Bratsk hydroelectric station, began in October, 1974. In December, 1974 the water level in the reservoir reached the start-up mark, and by the end of the year the first three units of the hydrostation were put into operation. By the end of 1977 all 15 units of the first phase were started up [i]. In 1978-1979 the last (16th) unit was put into operation, and in December, 1980 the Ust'-Ilim hydrostation was received into industrial production.The ice and thermal regimes of a river change substantially with the construction of hydrostations.This is due to a change in the discharges and temperature of the water in the lower pool. To study the character of the change in the ice and thermal regime of the pools of the Ust'-Ilim hydrostation and its effect on the region of construction of the fourth reach of the Angara cascade of hydrostations --the Boguchany --being constructed 386 km downstream of the Ust'-llim, the following observations are being conducted in the investigated region: in the upper pool --thermal observations of increased accuracy on a permanent vertical located 1600 m upstream of the dam and 1800 m from the left bank; transverse thermal sections along a section line located 1600 m upstream of the dam and passing through the permanent thermal vertical; and longitudinal thermal sectionsat a distance up to 40 km from the hydrostation; in the lower pool --measurements of the water temperature in the tailrace directly at the dam opposite each even unit with subsequent averaging of the data obtained; transverse thermal sections on thermal section lines located at a distance of 1.5, 4.5, Ii.0, and 15.5 km downstream of the hydrostation; longitudinal thermal sections at a distance of 40 km from the hydrostation; and observations of the position of the ice edge, water levels and discharges, and ice situation. The water temperature in the pools is measured with an accuracy to 0.OI~ The middle course of the Angara, where the Ust'-llimhydrostation is constructed, is located in a region with a markedly continental climate. The mean annual temperature at the nearest weather station, Nevon, is --3.9 ~ The normal temperature during the period October-May is --12.5 ~ .During the years of operation of the hydrostation from 1974 to 1980 the coldest fallwinter period was observed in 1976-1977 and the warmest in 1977-1978. Westerlies prevail in the region of the pools of the Ust'-llimhydrostation.The maximum wind speeds are observed mainly in the fall months, when the temperature regime of the reservoir, which to a considerable extent determines the variation of the water temperature under the ice in the upper pool and, consequently, the temperature of the water entering the lower pool, forms.After filling to the normal pool level (NPL) in May, 1976 the Ust'-llim reservoir represented a water body 303 km long and 90-92 m deep in the near-dampart.The annual thermal cycle of the reservoir includes thermal periods characteristic...