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Infiltrometer data are utilized to test a fitting procedure for the Green and Ampt infiltration equation parameters. The spatial variation of the estimated parameters is averaged to give lumped parameter values for watershed modeling. An appropriate scale for parameter averaging is discussed, which transforms parameter values to normal deviates. A sensitivity analysis for the equation parameters is performed for both infiltration estimates and runoff hydrograph volume and peak rates. The capillary pressure parameter shows least sensitivity; however, variation in the fillable porosity and effective conductivity parameters has a major influence on infiltration and runoff amounts and rates.

The surface runoff hydrograph at the outlet of a watershed is the result of distributed inputs being modified by flowing through the watershed surface drainage networks. In this study a model is proposed by which an outflow hydrograph is synthesized by routing input through a simulated drainage system. The simulated flow system is developed from a flow net. Overland flow is routed through stream tubes formed by pairs of stream lines constructed normal to the contour lines (equipotentials) of the watershed to an intersection with an appropriate surface channel. Channel flood routing is then performed down to the outlet, with the calculated overland flow from each stream tube as lateral input. Optimization of the system parameters is studied with respect to factors calculated from hydrograph moments. By comparison with visual judgments the hydrograph lag and shape factor were found to be possible criteria for optimization. (