How often should I clean the HYDROS 21 sensor?
The cleaning schedule for the CTD (HYDROS 21) will depend primarily on the environment it is being installed in. Installations in sites with the potential for higher biofouling will need more regular cleaning (every two weeks to one month). These sites are typically estuaries, tidal marshes, or areas with higher nutrient loading. Sites with lower biofouling can probably be on a three-month cleaning schedule. These are typically freshwater sites like streams, lakes, etc.
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.
What influence do high soil temperature associated with forest fires have on short term unsaturated conductivity?
Because of the hydrophobicity effect from the high temperatures associated with forest fires, I expect you would see a significant impact on the unsaturated hydraulic conductivity of the soil. There are experts who have done work in this area. Researchers at the US Forest Service would be a great sounding board for this question. Pete Robichaud, in particular, might have some thoughts on this topic. We’ve highlighted his forest fire research 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 soul 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.
Is the CTD-10 (HYDROS 21) electrical conductivity measurement temperature corrected?
Yes, the bulk electrical conductivity (EC) value is already temperature corrected within the sensor using the temperature correction outlined by the US Salinity labs Handbook 60. Values for EC in tap water can range from 100 to 800 microS/cm (0.1 to 0.8 mS/cm).

The CTD (now called HYDROS 21) uses the temperature to adjust the EC measurements to their 25 ◦C default value and provides the temperature output for the data stream.
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.
Can the CTD-10 (HYDROS 21) survive the winter?
Possibly. If the sensor is in water, it must not be allowed to experience temperature below freezing (0 °C or 32 °F). If water freezes in the CTD sensor pressure transducer cavity, then ice formation will ruin the pressure transducer.
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.
How do I convert from mL of drainage collected to cm of drainage for my G3 Drain Gauge?
Since you already know the volume of drainage that was collected, the conversion is based purely on the cross-sectional surface area of the divergence control tube (DCT). The DCT area is 506.7 cm2.

Dividing your volume by the cross-sectional surface area yields the one-dimensional drainage. For example, 1000 mL of leachate volume is 1.41 cm of drainage.
Why did the HYDROS 21 housing change to plastic? Is the housing supposed to be moveable? They all can be slid about 5mm.
The housing has always been plastic, though it may look a little different than before. The sleeve is meant to slide off to make cleaning easier. In the latest model, the sealing is much better around the transducer, and it is more durable.


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