Infiltration under ponded conditions: 4. An explicit predictive infiltration formula

An approximation to an implicit infiltration formula presented earlier in this series is developed. At worst, the relative error of the approximation is always less than 1%, and it is much better than that for most cases. The approximation becomes more accurate in both the short- and long-term Limits as it becomes exact in each case. Application of the new formula is demonstrated using both laboratory and numerical experiments.