Hydraulic effectiveness and ecological reliability of lined canals

Abstract

1. The hydraulic reliability of lined canals depends on the permeability of the linings and the carrying capacity of the canals on what, in turn, the quality of lining construction and the operating conditions of the canals will influence. In this case, the hydraulic reliability of canals exerts an influence on the ecological situation in a reclamation system. A rise in the water table as a result of seepage and the vigorous development of algae within the limits of the free cross section is noted during the summer for canals with a low hydraulic reliability; this results in deterioration of the reclaimed state of lands under irrigation and to a reduction in flow rates and carrying capacity of the channel. All this requires objective evaluation of the hydraulic reliability of lined canals on the basis of complex investigation of all fundamental factors affecting the ecological situation. 2. The proposed computational relationships for estimating the hydraulic and ecological reliability of lined canals take into account the probabilistic variability of random factors and make it possible to determine the permeability of linings, which is required by the efficiency, carrying capacity, and minimum design flow rate, which precludes silting and overgrowth of the channel by submerged hydrophylic vegetation (algae). 3. It was established as a result of full-scale hydraulic investigations conducted on lined canals operated by the Bagaevsko-Sadkovsk experimental station that the roughness coefficient of the canal linings ranged from 0.015 to 0.043 and depends not only on the surface condition of the lining, but also on the operating conditions of the canals (degree of silting and overgrowth of the free cross section by algae). In the case where the channel is silted and partially overgrown with algae, the roughness coefficients are increased significantly by a factor of 2–3 as opposed to standard values; this, correspondingly, leads to a reduction in the flow rates, and the carrying capacity of the canal is more than two times greater as compared with normal operating conditions. To create unfavorable conditions for algae development, it is necessary to ensure a silt-free channel over the entire length of the lined canal and an average flow rate of no less than 0.50 m/sec.