Hydrodynamics of Surface Irrigation—Advanced Phase

The Saint-Venant equations governing gradually varied, unsteady flow in an open channel with seepage are put into characteristic form and solved numerically in finite steps along the irregular network formed by the characteristic lines using a simple predictor-corrector scheme. The infiltration into the soil is assumed to depend solely upon contact time between water and soil. In the regions of substantial curvature of the characteristic lines, step size is reduced to preserve accuracy. Near the very front of the advancing stream, where the forward and backward characteristics curve extremely sharply and merge with their envelope, the wave-front trajectory, the numerical approximations to the characteristic equations break down and are replaced by the assumption that water velocity is independent of the distance coordinate and equals front-propagation speed.