Optimization of Main Canal Parameters in the Area of Hydraulically Most Advantageous Sections

The main canals of reclamation systems, along with the best economic performance, must also meet the requirements for connecting the conductive network in the vertical plane and the technology for the construction of the channel. 

Although the channels of the hydraulically most advantageous profile are the most economical un terms of excavation volume, often turn out to be too deep and of small width along the bottom, which does not meet the specified requirements.  All these factors can be taken into account by slightly reducing the water flow velocity u (compared to the velocity in the channel with the most hydraulically advantageous cross section u_h.a.), which leads to a significant decrease in the channel depth and, accordingly, an increase in the width of the channel along the bottom.  Such a decrease in velocity is economically justified (without a significant increase in the cross-sectional area) in the region of the most hydraulically advantageous sections, where the curve of the function h = f(u) sharply increases and asymptotically approaches the ordinate with the maximum possible velocity u_h.a. This area can be approximately characterized by the values of the velocity u = (0.95–1.0)u_h.a. For the convenience of calculation, the formula obtained earlier by the author for the channel depth of the hydraulically most advantageous profile has been converted to a simpler form. An analytical method is proposed for calculating the optimal parameters of the channel section, located in the area of the most hydraulically advantageous sections, which is characterized by the optimization coefficient K_opt = u/u_h.a, varying within K_opt. = 0.95–1.0. In this area, the cross section of the channel differs slightly from  the most hydraulically advantageous profile, and, at the same time, satisfies the requirements for conjugation of the conductive network in the vertical plane and the conditions of work. The proposed calculation method is less laborious and is applicable in a wide range of changes pertaining to exponent y in the formula of N. N. Pavlovsky to determine the Chezy’s coefficient. The calculation according to the proposed method is performed based on the use of dependencies to determine the characteristics of the most hydraulically advantageous section and the formulas of channel hydraulics (with a slight gradual decrease in the water flow rate u). Formulas are obtained for determining the depth and width of the channel along the bottom at various values of velocity.

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