Analysis of Time Compression Approximations

2 TCA, time compression approximation, is a practical and often quite accurate tool to predict 3 postponding infiltration for field applications. A modified approximation (MTCA) can be used 4 just as easily and, in general, will reduce the error by about 50%. This is based on two results: 5 1. After ponding, TCA and MTCA predict very close infiltration rates; and 6 2. MTCA, but not TCA, uses the actual cumulative infiltration up to the ponding time. 7 Thus, TCA has an additional error in its prediction of postponding infiltration. 8 Previously, those results, including the 50% reduction in error, were observed numerically for 9 linear and Burger’s soils. They are illustrated here numerically with an actual soil (a Grenoble 10 sand). More importantly, we developed a general analytical approximation for this problem and 11 showed that it can provide a very convenient predictive tool which can then be used for arbitrary 12 soil properties. 13