HYDROGRAPH SHAPE AND BORDER IRRIGATION EFFICIENCY

Sloping borders with free outflow were studied to determine the effect of inflow hydrograph shape on maximum application efficiency. A zero- inertia model describing the movement of water along the border run wi th infiltration was used to predict the maximum application efficiency for five inflow hydrograph shapes. The irrigation parameters consider ed were four infiltration families, three slopes, three roughness coef ficients, two field lengths, and three volumes. The maximum applicatio n efficiencies averaged over all combinations of the irrigation parame ters for the five hydrographs were as follows: constant, 68%; cutback, 77%; cablegation, 59%; modified cutback, 80%; and modified cablegatio n, 78%. Efficiencies for each hydrograph shape ranged from zero to 92% , with the low values occurring for high infiltration rates and roughn ess, small slopes, long fields, and low volumes of application. The in filtration family and its cross products with the other irrigation par ameters were the most important variables affecting the maximum applic ation efficiency for the five inflow hydrograph shapes.