Accurate Field Saturated Hydraulic Conductivity—Why is it so difficult?
Inaccurate saturated hydraulic conductivity (Kfs) measurements are common due to errors in soil specific alpha estimation and inadequate 3D-flow buffering. Leo Rivera, METER research scientist, explains why getting an accurate saturated hydraulic conductivity (Kfs) measurement is so difficult.
Water infiltrates the soil in three dimensions; it spreads laterally, as well as downward.
“Sorptivity, or the ability of soil to absorb water, has traditionally been a complex measurement for scientists to make. This is because water infiltrates the soil in three dimensions; it spreads laterally, as well as downward. The problem is, the value which represents sorptivity, Kfs, is a one-dimensional value. Scientists use Kfs in modeling as the basis of their decision-making, but they have to remove the effects of the three-dimensional flow to get that value.
“The traditional method for removing those effects is to look at a table of alphas or the soil macroscopic capillary length. But since alpha is an estimate of the sorptivity effect, or how much the soil is going to pull the water laterally, if you use the wrong value, your estimate is going to be significantly off.
“The other problem with making this measurement is that most researchers have found the double ring infiltrometer does not buffer three-dimensional flow perfectly. Thus, if you are operating on the assumption that you’re getting one-dimensional flow in the center ring, you will overestimate your field saturated conductivity (Kfs) values. This can be disastrous, particularly if you’re working with a soil that has been engineered to have a very low permeability. If you overestimate Kfs, you could incorrectly assume your cover is ineffective (Ks is over 10-5 cm s-1). But really, you’ve overestimated Kfs, and the cover may actually be compliant.”
Leo discusses solutions to these and other infiltrometer difficulties the webinar “Advances in Lysimeter Technology“.
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