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Continuous Flow Method for Rapid Measurement of Soil Hydraulic Properties

I. Experimental Considerations

Department of Soil and Crop Sciences and Department of Mathematics, Colorado State University, Fort Collins, CO

View larger version (34K): [in a new window]   Fig. 1. Experimental set-up for continuous flow method.

View larger version (65K): [in a new window]   Fig. 2. Errors in the directly estimated hydraulic conductivity near saturation (h < -20 cm) in three hypothetical soils. Contours represent Kestimated/Kactual as a function of soil length (L) and the rate of lower boundary pressure change (P). The K() and (h) of the simulated soils were represented using van Genuchten forms (Eq. [2]).

View larger version (65K): [in a new window]   Fig. 3. Direct estimation of K(h) and (h) in three hypothetical soils. In each case, L = 3 cm and the lower boundary pressure change was -1 cm min-1. The K() and (h) of the simulated soils were represented using van Genuchten forms (Eq. [2]) with parameters in Table 1.

View larger version (17K): [in a new window]   Fig. 4. Inverse recovered (h) in a hypothetical silty clay loam (s = 0.43, r = 0.089, = 0.01 cm-1, n = 1.23, Ks = 0.001167 cm min-1, and = 0.5) with varying degrees of random error in the simulated data. No independent or K values were included in inverse data and all parameters were floated except as indicated.

View larger version (79K): [in a new window]   Fig. 5. The near saturation water pressure, air pressure, and water flow (downward negative) in (a) a structured sandy clay loam field sample, L = 3.2 cm; (b) a repacked silty clay loam, L = 2.7 cm; and (c) a repacked loam, L = 6 cm. Air pressure (gauge) was measured in an artificial cavity at z (cm) above the lower boundary as indicated.

View larger version (72K): [in a new window]   Fig. 6. The direct and inverse estimated draining (h) and K(h) in (a) a structured sandy clay loam field sample, L = 3.2 cm; (b) a repacked loam, L = 2.5 cm; and (c) a repacked fine sand, L = 2.5 cm. The open markers indicate direct estimates prior to air-entry. Solid triangle is independently measured s.

View larger version (25K): [in a new window]   Fig. 7. Effect of drainage rate on the estimated (h) for a nonstructured (repacked) silty clay loam and (b) a structured sandy clay loam. Parameter estimates for each soil and drainage rate are listed in Table 3.

View larger version (22K): [in a new window]   Fig. 8. The direct, inverse, and equilibrium draining (h) in a structured sandy clay loam field sample (L = 3.5 cm) and a structured clay loam field sample (L = 3.5 cm).

View larger version (22K): [in a new window]   Fig. 9. Effect of measurement range and inclusion of (1.5 MPa) on inverse estimation of (h) in a structured sandy clay loam field soil.

View larger version (77K): [in a new window]   Fig. 10. Effect of measurement range and model representation on inverse estimation of (h) and K(h) in a repacked silty clay loam (L = 2.7).