Comparison of Measured and Estimated Unsaturated Hydraulic Conductivities during Snowmelt

1991

S. 243-259

5 Abb., 3 Tab., 38 Lit. Ang.

Unselbständiges Werk

200088110

Estimates of unsaturated flow often required an assessment of the relationship between unsaturated hydraulic conductivity (Ku) and moisture content (0). Measured Ku-0 relationships for a well-sorted sandy soil were obtained using the instantaneous profile method during snowmelt recharge. These values are compared with estimates from three approaches: the Campbell equation, a modified version of the Campbell model that considers residual water, and the rate of isotopic tracer displacement during infiltration. The modified Campbell model provided the best fit to the observed data, although all three methods overpredicted Ku. The isotopic tracer method overestimated observed Ku values by 2.6-4.5 times. This may reflect the role of macropores upon hydraulic conductivities during infiltration, since the tracer method is employed during recharge, while the instantaneous profile method is generally used during drainage periods when macropores are nonconductive. Whereas Ku estimates derived from empirical approaches such as the Campbell model may be valid during conditions of drainage, the isotopic tracer model appears to provide more realistic conductivity values during infiltration. The latter method also provides a direct means of estimating the immobile fraction of total soil water.