How does soil structure affect K values? How are they related?
Soil structure and aggregate stability will have a large impact on the hydraulic conductivity values. Depending on the type of soil structure that is formed and the strength of that structure you will see a larger development of macropores within the soil which will have the ability to transmit more water than if the soil had poor structure or no structure. Learn more about this here.
How would you measure horizontal hydraulic conductivity in field conditions? How would you disaggregate the horizontal component of hydraulic conductivity from the vertical one?
This depends on whether you are measuring saturated or unsaturated hydraulic conductivity. It can be difficult to try and do this for saturated hydraulic conductivity in the field. In theory, if you took a sample from the field and measured this in the lab, horizontal vs. vertical should be the same in terms of hydraulic conductivity. Hydraulic conductivity is independent of whether the flows are vertical or horizontal because these components are corrected for. If you want to measure unsaturated hydraulic conductivity in the field and look at how it changes in the horizontal vs. vertical position, this could potentially be done with tensiometers and water content sensors positioned in a grid to look at the movement of water and change in water potential. Find more information on how to measure hydraulic conductivity here.
Lab Ks measurements move from the bottom to the top. Is Ks similar if water goes from the top to the bottom of a sample?
As long as the calculations are done correctly there shouldn’t be a difference if water is percolated from the bottom or the top of the sample.
Soil with rock fragments is a common soil type but difficult to measure with traditional methods. What do you suggest?
Rock fragments can make things difficult when trying to measure hydraulic conductivity. If it is possible to avoid the rocks, that is the best approach. This will depend on the size of the rock fragments. If you are measuring in a gravelly site, you can still use traditional methods, but you will likely need to repair the ring edges more regularly as they will get bent and dinged frequently. If you have very large fragments, avoid the large rocks by measuring in a smaller area or by trying to encompass the large rocks within the infiltrometer. In some cases, a borehole approach might work better for these situations.
In preparing for an infiltrometer test, I'm thinking of statistical significance so would like multiple sites. How far apart should my test holes be?
Some of this depends on the soil variability at the site. Typically, we take measurements in triplicate at a single site. We then try to cover the expected variability at the site. This could mean somewhere around 3 to 12 measurement sites within a location. One way to approach this is to start with three sites and see what the variability looks like.
How could one determine the change in hydraulic conductivity at a soil spoil interface?
There are two approaches you could take. You could measure the two materials independently and see which one is going to be most limiting. Typically, hydraulic conductivity is governed by the most limiting layer. You could also just make the measurement in the field and see the interaction between the two layers. Again this rate will be governed by the most limiting layer.
When do we need a 10 cm ring?
As a rule, the 5 cm ring should work in most soils. The 10 cm ring is useful for disturbed or structureless soils. Use the 10 cm insertion ring in soils with high infiltration rates or if the 5 cm ring appears to be leaking to the surface.
How long will the SATURO last?
The lifetime of the SATURO depends on its components. The insertion ring will wear over time, depending on soil conditions. It will need to be filed down to keep the inside of it smooth. Eventually, it may need to be replaced. The pumps typically need to be serviced at 500 hours of run time. This is tracked in the diagnostics screen of the SATURO. The lead-acid battery will likely need to be replaced every couple of years, depending on how many charge cycles it goes through. This would be apparent when the battery will no longer fully charge. All other components should last for many years with proper use.
What might cause a water level error?
There are a few things that can cause a water level error. Check that there is no debris on the black seal before clamping the chamber to the insertion ring and that the seal isn’t damaged. When clamping the chamber down, make sure it isn’t too tight as this can cause leaks around the ring. If the ring is installed on a slope, make sure the water level sensor is in the middle of the slope to get the average water level. For soils with very high infiltration rates, higher than the water pump is able to keep up (>115 cm/hr), a water level error will occur. In this case, try to soak the soil longer, or use a 10 cm insertion ring.
How does the SATURO measurement compare to a double-ring infiltrometer measurement?
The SATURO and double-ring infiltrometer are both ring infiltrometers that measure the infiltration of water into the soil. The main difference is how the model corrects for three-dimensional flow. With the double-ring infiltrometer you have to make corrections in post-processing that require an estimation of the soil type. The SATURO uses a multiple pressure head analysis approach to directly estimate the effect of sorptivity, and this allows for the automation of the three-dimensional flow correction and more accurate Kfsestimation. For more details, read the full app note.
What is the maximum measurable infiltration rate of the DualHead Infiltrometer (SATURO)?
The SATURO can measure a maximum field saturated hydraulic conductivity (Kfs) of 115 cm/hr.
Can I measure directly into an area with grasses, or do I have to remove the grass and then do the calculations?
Short grasses are not a problem. You should be able to place the pressure chamber over the grass and run the sensor with no problems. The issues arise when the grasses are long enough to get in between the infiltrometer head seal and the insertion ring. If this happens, there is a high likelihood of leaking between that seal and the insertion ring. When grasses get longer (more than 2-3 inches), we recommend trimming the grass around the ring to prevent leaks.
Can measurements after a rain event be done? Are their issues due to soil pores being filled with water?
Running the SATURO right after a rain event is not a problem at all. The SATURO measures saturated hydraulic conductivity, so the first step in the measurement process is to completely saturate the soil in the insertion ring, which is the measurement area. If the area recently had a large rain event, or is near saturation already, then you can shorten the initial soak time of the test during setup.