Full-scale investigations of the roughness coefficients of the North Donets-Donbass canal

Abstract

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