A linear source method for soil infiltrability measurement and model representations

Abstract

Soil infiltrability determines the fraction of applied irrigation and/or rainfall water transferred into the soil and the surface runoff. A new method is advanced to measure soil infiltrability with linear distributed water flow on hill-slope. The experimental procedures were outlined for this purpose. Algorithms for estimating infiltrability from the experimental data were also formulated. An experimental system was developed, including a Mariotte bottle for water supply, a special outlet unit for linear distribution of water flow at the soil surface and a scaled flume. A digital camera was used to record the increase in wetted soil surface area as a function of time. Mathematical models were derived to compute the soil infiltrability-time function from the recorded changes in wetted soil surface area. Laboratory experiments using an air-dry loam were conducted with in flow rate of 4.4 l/h and slopes of 5° and 15° in 3 replicates. The infiltrability results of the new method were compared with the double-ring results obtained on the similar soil. The experimental results showed that the advances in wetted areas as function of time were well fitted with a given function, with determination coefficients ( R 2 ) greater than 0.89. Some existing infiltration models were also applied to the measured infiltration rates to illustrate how the model parameters were determined and how well the measured infiltrability curves were represented by the models. These models, including Philip’s, Kostiakov’s and several modified Kostiakovs’ with different constant infiltration rates, agreed well with the measured data, with determination coefficients ( R 2 ) equal or greater than 0.95. The dynamics of the infiltration curve represented the infiltrability of a soil conceptually. Very little water is needed to make a measurement of a complete infiltrability curve. Comparison of the cumulative infiltrated water with the total supplied water indicated that the relative estimation errors were 17.3–7.51% for this new method, demonstrating a very high accuracy of the method. The results validate the rationale of this new method, the computational models and the experimental procedures. This method is convenient for fast field determination of soil infiltrability with much less water required than in conventional methods.