Algebraic Computation of Flow in Border Irrigation

Approximate advance and recession curves are obtained for a surface irrigation defined by the border characteristics— length, width, slope, Manning roughness, and infiltration parameters— and by the operation characteristics, inflowing discharge, and cut-off time. Thus, all the data necessary to compute the distribution of infiltrated water and water-application efficiency for that particular irrigation are obtained. The chief analytic tool is mass conservation: the volume applied as inflow is continuously accounted for. The volume infiltrated into the ground is related to infiltration time through a given infiltration formula. Surface volume is approximated by: (1)assuming a reasonable, simple shape for the surface-stream profile at any given time; and (2)assuming the depth at key points in the surface profile to be at normal depth for the particular discharge there. The solutions when compared to the results of complex mathematical models and laboratory and field experiments are found to yield results of useful quality.