Estimation of saturated hydraulic conductivity from double‐ring infiltrometer measurements

Abstract

SummaryThis research aims to determine soil vertical saturated hydraulic conductivity (Ks) in situ from the measured steady infiltration rate (I), initial soil properties and double‐ring infiltrometer (DRI) test data. Characterizing the effects of these variables on the measured steady infiltration rate will enable more accurate prediction of Ks. We measured the effects of the ring diameter, head of ponding, ring depth, initial effective saturation and soil macroscopic capillary length on measured steady infiltration rates. We did this by simulating 864 DRI tests with the finite element program HYDRUS‐2D and by conducting 39 full‐scale in situ DRI tests, 30 Mini‐Disk infiltrometer experiments and four Guelph Permeameter tests. The M5′ model trees and genetic programming (GP) methods were applied to the data to establish formulae to predict the Ks of sandy to sandy‐clay soils. The nine field DRI tests were used to verify the computer models. We determined the accuracy of the methods with 30% of the simulated DRI data to compare I/KS values of the finite element models with estimates from the suggested formulae. We also used the suggested formulae to predict the Ks values of 30 field DRI experiments and compared them with values measured by Guelph Permeameter tests. Compared with the GP method, the M5′ model was better at predicting KS, with a correlation coefficient of 0.862 and root mean square error (RMSE) of 0.282 cm s−1. In addition, the latter method estimated Ksvalues of the field experiments more accurately, with an RMSE of 0.00346 cm s−1.