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- Title
Improved Calculation of Hydraulic Conductivity for Small Disk Tension Infiltrometers.
- Authors
Nimmo, John R.; Voss, Paige R.
- Abstract
Because tension infiltrometers apply water through a disk of finite size, the infiltrated water moves laterally as well as downward. Only the vertical component of this flow is indicative of the hydraulic conductivity K, so the algorithm for computing K must include a way of isolating that component from the total flow. Some commonly used formulas correct for the multidimensional effects by subtracting an estimate of the laterally spreading flow. For disks smaller than about 200 mm in diameter, however, lateral spreading constitutes so much of the total flow that these subtractive formulas lose considerable accuracy, and sometimes overcorrect so severely as to produce a negative number for K. Other methods rely on empiricisms that are not completely consistent with unsaturated‐flow theory and that require prior knowledge of certain soil properties. We developed a new formula that uses a multiplicative factor instead of a subtracted term to achieve the needed correction. For testing we conducted numerical experiments with synthetic data produced by solving the Richardson‐Richards equation using the code VS2DRTI, for diverse media and a range of disk sizes, including the widely used 45‐mm diameter. We compared K values calculated from our formula to the actual K used to generate the simulated data, as well as to results from other published formulas. This comparison shows that our method provides an algorithm based in unsaturated‐flow theory that produces more reliable values for small disks without requiring prior knowledge of soil properties. Plain Language Summary: Tension infiltrometers are much‐used devices for field measurement of the hydraulic conductivity of soil. Hydraulic conductivity is a measure of how easily water flows in the soil. If it is high, water at the soil surface can cause more infiltration and less runoff, and can move faster within the soil. Tension infiltrometers apply water over a circular area of the soil surface and measure the flow rate of the water being drawn into the soil. For small infiltrometers, a large fraction of the water spreads laterally within the soil, rather than straight down. Consequently, the amount of water flow measured by the infiltrometer is much greater than just the downward‐flowing portion needed to indicate hydraulic conductivity. This laterally flowing water must be corrected for in the formulas that calculate hydraulic conductivity from the measured data. If the diameter is less than about 200 mm, as it is for the great majority of infiltrometers, the needed correction is so large that large errors result from the approximate corrections applied by commonly used formulas. Our new method uses an estimate of the distance the water spreads laterally to give more accurate results. Key Points: Measurements from small diameter tension infiltrometers require a large correction to account for the lateral spreading of infiltrated waterThe use of a multiplicative, rather than subtractive, correction method provides greater accuracy when the correction is large, as needed for small disksOur proposed method provides a direct estimate of how much flow is going into lateral versus vertical components, thereby yielding additional information for interpretation as well as more accurate hydraulic conductivity results
- Subjects
INFILTROMETERS; HYDRAULIC measurements; HYDRAULIC conductivity; TENSION loads; SOLIFLUCTION; SOIL permeability; SOIL moisture
- Publication
Water Resources Research, 2023, Vol 59, Issue 3, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2022WR032475