What UZ depths do measurements need to come from?
Evidence from field (e.g. Nixon and Lawless, 1960) and theoretical analyses (Gardner, 1964) indicate that water content fluctuations typically damp out below a depth of a few meters. In some cases, however, fluctuations have been detected at depths of tens of meters (e.g. Jones, 1978). In order to establish confidence that flow is steady, matric potential or water content should be measured for a period of a year or more, though this is often impractical. Often the distribution of water or uniformity of matric potential with depth at one point in time is used as an indication of depth to steadiness. If subsurface properties can be adequately represented, computer simulations using a variable saturation flow model, such as VS2DT, may be used with known boundary conditions to evaluate steadiness of flow at depth. • Can K be estimated rather than measured? Because unstaurated hydraulic conductivity is costly and time consuming to measure it is often estimated based on more easily measured
