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One particularity of hydraulic construction on most rivers of the U S~ is the necessity of passing ice through the structures. The requirements of safe passages of ice through the structure~ on rivers with significant spring ice runs predetermine to a large extent the type of basic structures of thehydraulic complexes, the stages and planning of their construction, and the required dimensions of the spillways, and this is reflected also in the economics of the constructions.Several ice passage systems were tested while constructing the Krasnoyarsk hydroelectric plant, some of which could be used again at other hydraulic complexes. During the springs of the 1960-1962 period the ice passage was obtained through a right-bank contraction, during the 1963 spring through an overflow weir having its crest at the level of the river bottom, during the 1964 spring through the spans of an overflow weir with its crest above the bottom and partially through the bottom outlets of Stage I with the invert at the level of the river bottom, during the springs of the 1065-1066 period through the bottom outlets of Stage I, during the 1963 spring through the bottom outlets of Stage II, and starting with the 1968 spring all the ice was retained upstream of the structures.The conditions and characteristics of ice passage through the structure of the Krasnoyarsk hydroelectric plant were described in a series of papers [i-I0]. Thispaper gives the basic results of the generalization of the experience with the retention and passage of ice during the construction of the Krasnoyarsk hydroelectric plant on the basis of the investigations carried out at the S. Ya. Zhuk Gidroproekt and the Siberian Branch of the B, E, Vedeneev

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Ice-jam formation is a characteristic process during the opening of rivers after the breakup of ice, in the USSR. large hydraulic developments practically eliminate the need for preventing ice jams within the limits of the reservoirs; however, small low-head hydraulic developments on rivers with stable ice covers aggravate the ice difficulties in the spring within the range of their influence. At such hydraulic developments, ice-jam formation is possible even immediately upstream from the structures, where it may complicate considerably passage of the ice.An example of these difficulties is provided by a hydraulic development near a thermoelectric plant in Siberia. The reservoir at this hydraulic development is characterized by the presence in front of the structures of water areas free from ice at the time of ice breakup in the river, whereas in the remaining reservoir portion, 180-250 m wide and about 7 km long, the ice cover remains and after river breakup causes difficulties in the passage of ice through the dam. At this reservoir, various preventive measures have been applied over many years in attempts to break and weaken the ice cover and to accelerate its opening prior to the arrival of broken ice from upstream.In 1969, the ice cover within the reservoir limits was blackened by coal dust dropped from an AN-2 airplane. The blackened strips were 40-45-m wide. the specific quantity of coal dust used was 300 B/rn 2, and the total quarttit), was 70 tons. The total cost of the blackening operation was 4500 rubles. The total solar radiation on the ground surface during April in the region under consideration varies from 8 to 14.5 kcal/cm2; during April 1969, it came to 9.7 kcal/cm z. For this reason, a substantial acceleration of the melting process was not observed. In comparison with the nonblackened portions, melting of the snow-ice cover in the blackened zones reached a depth of only 15 cm, which was not decisive in accelerating the opening of the ice cover within the reservoir limits. The relation between the blackening effect and the weather conditions during the spring reduces significantly the reliability of this method. For the conditions at the reservoir being considered, the blackening method can be used in combination with other well-known methods of preventing ice-jam formation [1,2]. During many years, the ice was shattered by blasting in order to prevent ice jams. However. the considerable labor involved in the blasting operations, organizational difficulties, and damage caused by the blasts to fishing industries did not permit carrying out the work in the required volume. Hence. only partial improvement in the opening of the ice cover was observed. The total annual cost of shattering the ice within the reservoir limits by the blasting method was 30.000-40,000 rubles.The search for more reliable and economical means for preventing ice-jam formation and accelerating the opening of the ice cover within the reservoir limits, in order to cope with the arrival of ice at the hydraulic development, led t...