Hello, my name is Leo Rivera. I’m the Director of Scientific Outreach at METER Group, and in this course, we’re going to talk about two methods for measuring hydraulic conductivity: SATURO versus the KSAT. These two instruments measure saturated hydraulic conductivity. The SATURO is for making those measurements in the field, and the KSAT is our device for making the measurements in the lab.
There are a few differences that you need to understand about the two instruments, and there are pros and cons to each. With both of these methods, you’re going to need a water supply. With the SATURO, the water supply is going to be connected to this external port. That’s going to the water supply. When using the KSAT, the water supply is going to be connected to a reservoir that’s feeding water to the device.
KSAT: Lab measurement
The KSAT is a really simple device: water from the reservoir infiltrates through the bottom of the sample. A pressure transducer measures the change in the pressure head and automates that measurement of the infiltration rate of the water through the sample. The water goes through the sample and then outflows over an exit port. The collar seals everything up, so we have no leakage.
After filling the reservoir with water, turn the knob, and then the device starts taking measurements. This is going to be connected to a computer running software that does all of the measurements. With this instrument, measurements typically take anywhere from a few minutes up to a few hours, depending on the soil type and how fast the water actually flows through the soil. You can easily run through many samples in a day. And what’s really nice about this approach is you can collect samples from the field and store them for measurements in the lab later on.
If you have a lot of measurements that you have to make, this really makes that easier, because you can collect those samples and then just have them stored and ready to start making those measurements.
SATURO: Field measurement
The SATURO is our field instrument. We insert this ring into the ground, and we’re going to drive it into the ground. The upper chamber is where we do some control. In this chamber, we have an air port, a water port, and a level sensor.
The level sensor monitors the water level. We’re trying to maintain a constant water level of five centimeters. We add water from the main control unit. The control unit does all of the calculations on board. This device pumps water into the chamber through the hose. The SATURO uses an air line to control the hydrostatic pressure above the water column. That allows us to infiltrate water at two different hydrostatic pressure heads.
In doing that, we are actually able to calculate the sorptivity of the soil. That allows us to simplify how we correct for three-dimensional flow from the device. When water is infiltrating through the ring, it’s not just going down vertically, it’s also going out laterally. We have to make that correction. Using that dual head approach simplifies how we make that correction.
Measurements with the SATURO typically take anywhere from an hour to two and a half hours, depending on how fast water is infiltrating and how long it takes to reach a steady state in the field. The time that it takes to complete a measurement is controlled by quite a few things, but one of the most important ones is the initial water content. If the soil is closer to field capacity initially, typically the measurements are a little bit faster, but also soil texture can play a role there as well. Finer textured soils, like clays, can tend to take a little bit longer to make a measurement and get to that steady state value. But what’s nice about this is when it’s done, it actually does all of the calculations on board to do the corrections for three-dimensional flow, giving you a final field saturated hydraulic conductivity.
Saturated hydraulic conductivity—field vs. lab
When I talk about the SATURO I use the term field saturated hydraulic conductivity, and when I talk about the KSAT, I use the term saturated hydraulic conductivity. And one of the reasons we do that is because in the field, it’s hard to actually get the soil to full saturation. Usually, we wind up within trapped air, so when we’re making these measurements we usually refer to those as field saturated hydraulic conductivity. In the lab, it’s much easier to actually fully saturate a sample and get to that saturated point, the Ksat.
Both the SATURO and the KSAT are great tools for making hydraulic conductivity measurements, but like we just discussed, there are differences between the methods that you need to take into account when trying to decide which one you’re going to use for your research and for your measurement goals.
