Design Charts of Optimal Canal Section for Minimum Water Loss

Abstract

Seepage and evaporation are the most serious forms of water losses in an irrigation canal network. Seepage loss depends on the channel geometry, whereas evaporation loss is proportional to the area of the free surface. In this investigation, a methodology has been devised which describes the optimal canal dimensions to convey a particular discharge. The objective nonlinear water loss function, for the canal, which comprises seepage and evaporation losses, is developed. Two constrains, 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 are obtained which give the least water loss. Using a random search method, a simple computer program was developed to carry out design calculation and provide the optimal canal dimensions. A set of design charts has been prepared by plotting the results. The proposed charts facilitate easy design of the optimal canal dimensions guarantying minimum water loss and computation of water loss from the canal section without going through the conventional and cumbersome trial and error method. A design example with sensitivity analysis has been included to demonstrate the simplicity and practicability of the proposed method.