Design and analysis of a canal section for minimum water loss

Seepage and evaporation are the most serious forms of water loss in an irrigation canal network. Seepage loss depends on the channel geometry, while evaporation loss is proportional to the area of free surface. In this paper, a methodology to determine the optimal canal dimensions for a particular discharge is developed. The nonlinear water loss function, for the canal, which comprises seepage and evaporation loss, was derived. Two constraints (minimum permissible velocity as a limit for sedimentation and maximum permissible velocity as a limit for erosion of canal) have been taken into consideration in the canal design procedure. Using Lagrange's method of undetermined multipliers, the optimal canal dimensions were obtained for minimum water loss. A computer program was developed to carry out design calculation for the optimal canal dimensions. The results are plotted in form of a set of design charts. The proposed charts facilitate easy design of the optimal canal dimensions guaranteeing minimum water loss. Water loss from the canal section can be estimated from these charts without going through the conventional and cumbersome trial and error method. Sensitivity analysis had been included to demonstrate the impact of important parameters.