Measurement of hydraulic properties during constant flux infiltration: Field average

Accurate measurement of in situ soil hydraulic properties is important for developing, testing, and applying water and solute transport theory. ii met hod of measuring hydraulic conductivity (K), soil matric pressure head (psi ), and water content (theta) relationships is presented. The procedure uses a series of multipurpose time domain reflectometry (TDR) probes that measu re both theta and psi, The TDR probes are installed vertically and measure the rate of change of local soil water storage (q) along the probe during c onstant rate water application. The values of q are equal to local soil wat er nus, and assuming unit gradient, are set equal to K at the steady state theta and psi measured at long times. The measured values of K, theta, and psi from different water application rates are combined to obtain average K (theta) and theta(psi) functions. To test the procedure, multipurpose TDR p robes were installed vertically in a sandy soil every 0.15 m in a 7.5-m-lon g transect for a total of 50 probes per depth. This was repeated in paralle l transects 0.1 In apart for four depths (0.2 m, 0.4 m, 0.6 m, 0.8 m) and a total of 200 probes. Six different water application rates were applied wi th subsequent drainage. Average K(theta) and theta(psi) functions were obta ined and used in an analytical solution for constant rate infiltration. Tra nsient water storage changes were accurately predicted for all application rates.