In connection with reconstruction of the North Donets-Donbass canal to increase its capacity, it was necessary to obtain exhaustive information on the roughness coefficients of characteristic reaches. Therefore, the Ukrainian branch of the All-Union Planning, Surveying, and Scientific-Research Institute (Ukrgidroproekt) between 1970 and 1974 carded out full-scale investigations of the roughness coefficients of reaches of the canal with different slope coverings, established the effect of overgrowth of the canal by algae during different periods of their vegetation, and determined the roughness coefficient of the ice cover and siphons.The initial data for calculating the roughness coefficients and the canal capacity were the discharges measured simultaneously by five current meters during a steady regime with observations of the water level at the gauging station and on slope gauges every 5 rain. The time for one discharge measurement was 12-15 rain, during which the hydraulic regime changed insignificantly. As a rule. the discharges were measured as series of five. To increase the reliability of determining the slope of the water surface (and consequently the calculations of the roughness coefficients), the water levels were observed with an accuracy of 1 ram, for which we used staff gauges with dampers whose elevations were determined by leveling with high accuracy. The surface slopes were determined in reaches within which the revetment of the slopes and bottom of the canal were the same.The roughness coefficients of the channel reaches of the canal were calculated by the Chezy--Manning formula n = (o:,R 2/s It/2), Q, CL)where Q is the measured rate of flows; w is the cross-sectional area of the water, mr; R is the hydraulic radius, m; J is the slope of the water surface.To calculate the roughness coefficients of the lower surface of ice, we used N. N. Pavlovskii's formula [2]where n i is the roughness coefficient of the lower surface of the ice; n c is the roughness coefficient of the slopes and bottom of the channel (under summer conditions); nre is the reduced roughness coefficient of the channel and lower surface of the ice; a = •215 is the ratio of the wetted perimeters of the ice cover and channel; in this casewhere R w is the hydraulic radius, m; w w is the cxoss-sectional area of the water, mZ; Jw is the slope; Qw is the measured rate of flow. The quantifies with the subsetipt "w" were measured in full-scale investigations under winter conditions.Twelve reaches were used for determining the roughness coefficients. In these reaches 36 series of full-scale observations were carried out. The average value of the coefficients for each series of measurements was calculated as the arithmetic mean. The results of the calculations ate presented in Table i (observations made during an unsteady hydraulic tegh-ne ate not included in the table). It follows from these data that:Translated from Gidrotekhnicheskoe Stxoitel'stvo, No. 7, pp. 25-27, Iuly, 1976. 678
The bermless damming of the Dnepr near Kanev * was completed on September 25, 1972. The Dnepr at the site of the Kanevsk hydroelectric station, now under comtruction, has a well-formed channel in a stratum of fine-grained sands composing the valley. Side branches and oxbow lakes are located in the river valley.Before start of construction of the Kanev station, the Dnepr at the dam site flowed in the main channel located in the right half of the valley and in the Starik and Ruda branches. During construction the Ruda branch, which is the extreme left channel adjacent to a broad floodplain, was dammed. Its flow was directed to the Starik branch. In 1971 the Starik branch was connected by a cut with the main river channel, which permitted it to flow into the main channel in the region of the headrace. Thiscut should have facilitated diversion of the flow from the Starik branch into the temporary headrace during damming. This headrace, supplying water to the structures, and the tailrace straightened the bend formed by the natural channel of the Dnepr in the construction region (see Fig. I). The new tailrace was ready by the start of damming, and linking of the headrace with the main channel of the Dnepr minimized additional flow resistance.Owing to the high spring flood of t970, when the floodplain had already been dammed, the Dnepr channel at the site of the station was scoured considerably; the lowest water levels reached 65 m. They lasted until the spring of 1972, when preparation for damming began. The 1972 spring flood was exceptionally low: the maximum water level did not exceed 82 m, and in the last third of May the low-water stage began with water levels of the order of 81 m. At the end of the flood and during the low-water period the water levels were affected by the regulating effect of the Kanevsk station. The backwater from the Kremenchug hydroelectric station and the winddriven rise and fall of the water level on its reservoir also had' an effect during the low-water stage. During August and September the water levels gradually dropped due to drawdown of the Kremenchug reservoir.
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