**Why K**_{fs}** is a pain**

Saturated hydraulic conductivity, or the ability of soil to absorb water, has traditionally been a complex measurement for scientists to make. Inaccurate field saturated hydraulic conductivity (K_{fs}) measurements are common due to errors in soil-specific alpha estimation and inadequate three-dimensional flow buffering. Three-dimensional flow means water infiltrates the soil in three dimensions; it spreads laterally, as well as downward. The problem is, the value which represents saturated hydraulic conductivity, K_{fs}, is a one-dimensional value. Researchers use K_{fs} in modeling as the basis of their decision making, but to get that value, they must first remove the effects of three-dimensional flow.

**Estimation—a risky proposition**

The traditional method for removing the effects of three-dimensional flow is to look at a table of alpha values or the soil macroscopic capillary length. But since alpha is only an *estimate* of the sorptivity effect, or how much the soil is going to pull the water laterally, the risk of inaccuracy is high. And if a researcher or engineer chooses the wrong alpha value, their estimate could be significantly off.

To get around this problem, researchers sometimes measure K_{fs }with a double-ring infiltrometer (Figure 2), a simple method where the outer ring is intended to limit the lateral spread of water after infiltration and buffer three-dimensional flow. However, a double-ring infiltrometer does not buffer three-dimensional flow perfectly (Swartzendruber D. and T.C. Olson 1961a). So if researchers operate on the assumption that they’re getting one-dimensional flow in the center ring, they may overestimate their field saturated conductivity values. This can be disastrous, particularly when working with a soil that has been engineered to have a very low permeability. If K_{fs} is overestimated, a researcher or engineer could incorrectly assume a landfill cover (for example) is ineffective (K_{s} is over 10^{-5} cm s^{-1}), when in reality, they’ve overestimated K_{fs}, and the cover is actually compliant.

**K**_{fs}**—solved**

The SATURO eliminates the estimation/assumption problem by automating the well-established *dual head *method. It ponds water on top of the soil and uses air pressure to create two different pressure heads. Measuring infiltration at these two different pressure heads avoids the need for estimating the alpha factor, enabling researchers to determine field saturated hydraulic conductivity without making any assumptions. Additionally, the SATURO uses *much* less water because it doesn’t require a large outer ring like a double ring infiltrometer. This automated approach saves time and reduces error in the hydraulic conductivity assessment. The following theory section explains in detail why this is possible.

See how SATURO readings compare with double-ring infiltrometer readings—>