Hydraulic efficiency of irrigation channels in the course of operation

Introduction. The co-authors have analyzed different reasons for the reduction of the hydraulic efficiency of irrigation channels comprising hydro-technical reclamation systems. The main factors include plant invasion, siltation and deformation of beds. The co-authors provide data describing changes in the values of bed roughness ratios and efficiency of main and distributary channels in the process of operation in the south of Russia. Materials and methods. The hydraulic efficiency of irrigation and drainage systems will be called the pro-vision of their high throughput, close to the design, with minimal losses. They are based on throughput capacity and efficiency values, acceptable flow rates and water losses due to the process of filtration. The criteria have been developed in furtherance of the analysis of operation of irrigation channels and previous studies. Results. Factors reducing throughput capacity and channel efficiency have been identified for normal operating conditions; dependences needed to identify other hydraulic efficiency factors are also provided. Based on the analysis of actual data, the efficiency of main canals in the earthen bed is 0,790, and for canals in the cladding — 0,870, which is significantly lower than the re-quirements of the norms. Computer assisted processing of the field data on roughness and channel efficiency ratios, obtained under normal conditions, was performed to obtain empirical dependences n = f(Q) and η = f(Q). The field data describing changes in the throughput capacity of linings and earth beds of irrigation channels exposed to significant plant invasions (vegetation and algae) are provided for comparison purposes. The influence of these factors is demonstrated in the photos and proven by the values of roughness ratios that are two to four times different from the design ones. Conclusions. Comparison of the roughness coefficients for 15 canals and sections with strong overgrowth with the design data indicates that for canals in the earthen channel their roughness increases by 2.5...4.0 times, and for canals in the lining — 1.7...2.5 times. Weedy bed roughness ratios were obtained by applying theoretical formulas and the field data, their comparison has demonstrated close convergence in respect of three channels, including Nizhne-Donskoy and Azovsky main channels, as well as distributary channel Bg-R-7.