On-site observations of hydrological and meteorological parameters of regions with harsh climatic conditions after the creation of hydro developments [i, 2] showed that in the winter extended stretches of rivers with an open water surface form downstream of hydrostations, which are the cause of occurrence of heavy advection-radiation fog (steam fogs).In the presence of air temperatures below -12 to -15~ moderate winds (up to 12 m/sec), and sufficiently high humidity, a cold air mass flows onto the warm water surface having a temperature above 0~which promotes the formation of steam fog, which changes the conditions of heat exchange of the water with air, affects both the length of the polynya and climate of the region, possibility of occurrence of smog, icing of cables, and creates difficulties in the operation of air and water transport.A reduction of steam fog over the open water surface in the winter would solve to a considerable extent the problem of the negative effect of a hydrostation on the environment.When working on this problem it is necessary:i. To calculate the size and configuration of the zone of steam fog over the polynya in relation to the water temperature and meteorological factors and to evaluate the effect of the steaming process on the intensity of heat exchange of water with air.2. To determine how steaming affects the ice and thermal conditions of the lower pool and in what stretches the precipitation of steam fog is most effective.3. To recommend ecologically clean methods which can be used for this purpose.To solve the stated problems by mathematical modeling methods, it is necessary to examine a system taking into account the interaction of the thermal regime of the river and atmospheric boundary layer. However, since the thermal regime of a river is considerably more inertial than the atmosphere, as a first approximation the given problem can be solved separately and the mutual effect of the water and air can be taken into account by means of an iterative procedure.Heretofore the ice and thermal regime in the lower pool of hydro developments was calculated for constant meteorological characteristics, which were taken on the basis of a statistical analysis of long-term series of observations at weather stations.In this case, transformation of the air flow over the open water surface and the effect of steam fog on the intensity of heat exchange of the water with air were not taken into account.Steam fog forming in the winter over a nonfreezing polynya is supercooled (to between -15 and -20~ is liquid, is in a metastable state, and can crystallize under an artificial action.The effect of artificial crystallization of fog on the ice conditions of the flow in the lower pool is examined in this work.Two mathematical models were used for this purpose.The first model for calculating disturbances of the microclimate as a result of natural evolution and artifical crystallization of low clouds and fogs was developed at the Central Aerological Observatory (TsAO) [3][4][5]. The second model of the...

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...

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The construction of hydroelectric plants modifies the natural ice regimen of rivers since, in addiuon to the usual physicogeographical factors, the ice conditions are determined by the flow and temperature of the water leaving the reservoir. As a rule, under flow-regulation conditions the winter flows are increased over the natural regime. Because of this, the passage of increased flows under the ice cover, which is attended by an increase in channel resistance, causes a substantial rise in the water level. Of still greater significance is the magnitude of the outflows during the winter and spring periods, when the ice cover is formed on the river, as well as during the process of opening of the river (after breakup of the ice). Of special interest in this connection is an examination of the ice conditions observed at the downstream side of the Bratsk hydroelectric plant, from the viewpoint of regulation of the ice regimen in the region oft~enext downstream plant in the system--the Ust'-Ilim hydroelectric plant.Ordinarily, during the different construction stages the river channel is substantially constricted by the structures being constructed, and the passage of large ice floes becomes a serious problem [1]. Thus, at several hydroelectric plants now constructed the ratio of the ~ddth of the ice-passing front to the ~,-idth of the river upstream from the spillway crest during construction was as follows: at the Ust'-Kamenogorsk plant, 0.20; at the Bukhtarma plant, 0.28; at the Novosibirsk plant, 0.18; at the 8ratsk plant, 0.16; at the Mamakan plant,0.5-0.08; at the Krasnoyarsk plant 0.19-0.077; and at the Ust'-Ilim plant, 0.11.A substantial reduction in the width of the ice-passing front over the natural width affects passage of the ice through the structures under construction and leads to an increase in the probability of formation of large ice obstructions and accumulations.The hydraulic conditions and indices of passage of ice through the crest of the Ust'-Ilim hydroelectric plant are presented in Table 1.Under operating conditions during the ~,inter, water at a positive temperature passes from the reservoir to the downstream side of the Bratsk hydroelectric plant. During the initial operation period the water temperature dropped to 1.02*C at the beginning of April. Subsequently, the mean 10-day water temperatures in the Angara River at the downstream side of the Bratsk plant were in the range 1.65-4.58"C from November to May. Such water temperatures determine the maintenarice of a polynia (unfrozen patch of water in the ice) during the winter, the dimensions of which vary according to the meteorological and hydraulic conditions. As is known, ice formation in the downstream polynia takes place below the zero-temperature profile. The analytical positions of maximum approach of the zero-temperature profile to the dam at the downstream side of the Bratsk hydroelectric plant, obtained by the heat balance method [2], are presented in Fig. 1. It should be noted that the values of the air temperature presented in T...