FEATURES OF HYDRAULIC CONDITIONS OF LARGE CANALS OPERATION
Objective: a calculated assessment of the roughness coefficients of earthen, concrete and partially lined channels of large canals. Materials and Methods: the materials of field studies of canals in the earthen channel and in the concrete lining channel by the example of the Donskoy main canal, Proletarsky, Tersko-Kumsky, Bolshoi Stavropol’sky, Nevinnomyssky, Gissar and other canals are the basis of the work. The current issues of large canals operation related to their work features, including the formation of ice sheet in winter at pressure and free flow of water, the formation of deformations in beds of dynamic stability, as well as in cases with a rolling bottom relief in the form of ripples, dunes or ridges are described. Results: based on generalized studies of large canals, the criteria and conditions for their efficiency in terms of carrying capacity, permissible velocities, bed formation flow rate, roughness coefficients, relative canal width, efficiency and permissible canal seepage loss are given. Based on the results of field data processing distribution histograms of roughness coefficients of earthen and concrete channel beds were compiled and their average values were obtained (for the earth channel n = 0.0227, for the concrete channel n = 0.0169). Conclusions: according to the research, when using the authors' field data on 25 canals, the values of the carrying capacity reduction coefficient α′ = 0.958 and decrease in efficiency β′ = 0.935 were obtained, that indicates an average decrease in carrying capacity by 4.2 % and efficiency by 6.5 % . For partially lined channel beds, calculated dependencies for determining the given roughness coefficients along the length with uniform and unsteady flow are recommended.