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hypothetical ponding depth imposed is similar to a physical situation under which an infiltrometer operates after a brief intake of irrigated water to the saturation point. hypothetical immediate.ponding rain infiltration problem with the rainfall intensity (r) of 200 cm/hr and the assumed ponding depth (h) of 4 em after ponding, using various space-step (Az) size, The infIl- tration decay curves are plotted on log-log paper in order to assure a complete functional relationship between rand t with a broad range of both the infiltration rate and time scale, including especially the portion of the high infiltration rate shortly after ponding, The computed f before ponding and tp are nut shown in Figure 8 because the imposed ramfall intensity is so high that even with the first At tried, the boundary condition before ponding, Eq, 22, was never used in the computation. Three different Each of the possible factors which may affect the accuracy of the numerical model was tested and its computer results arc briefly discussed in the following, Effect of space-step size (6Z) The computed infiltration decay CUIVCS de- picted in Figure 8 arc the computer results of a 10 l 6 5 4 3 / -4- Saturation front depth - L - em f -A- Ponding depth - h - em E 2 u .c .c ~ ~ Z " ~ '" 5 bO 4 " ,~ '" 3 " 0 (l. 2 ~ 0 E 10-1 u , f ~ .-l .c 5 ~ 4 " ~ 3 '" ~ " 2 0 ~ ~ " 10-2 0 ,~ ~ 0 ~ 8 ~ .B 7 ~ 6 Ul 5 4 3 2 -3 10 -2 10 h J 1 ~ ,. ~ ~ ,I 2 3 4 56789 -I 2 3 4 5 7 9 2 3 4 5 789 10 1 10 Time - t - hours Figure 7. Saturation front depth (Lf) versus time (t) and ponding depth (h) versus time (t) relationships. 2S