Soil-Water Properties Computed from Transient Flow Data
1967
Weeks, L. V. | Richards, S. J.
A method is given for calculating water conductivity (K) of unsaturated soil by the use of data obtained during transient changes of moisture content (θ) and suction head (h) along a horizontal soil column. A soil moisture characteristic curve was obtained from the data. Absolute values of the slopes of the latter curve, the differential water capacity (C), pertaining to the experimental values of h were then used to calculate soilwater diffusivity (D) from the equation, D = K/C. The experimental procedure does not involve boundary conditions that, in some procedures, are difficult to evaluate, nor are steady-state and equilibrium-flow conditions required. Data for most soils was obtained in from 8 to 12 days. A program was written in Fortran IV language for use with the IBM 7040 Data Processing System. The solution of the problem was reduced to a routine that saves several hours of hand calculations. Values of K, C, and D for field cores and laboratory compacted soil columns were measured over the range of 50 ≤ h ≤ 750 cm of water. Relative error values between measured values of K and those calculated from the equation K = ch⁻ᵈ were less than 50% in 83% of 288 measurements. Relative error values between measured values of D and those calculated from the equation D = α exp (βθ) were less than 50% in 74% of the 288 measurements. The constants, c, d, α, and β are empirical for a given soil. Water conductivity values were shown to be independent of hydraulic gradients over a wide range of gradient values.
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