Bias in Ponded Infiltration Estimates Due to Sample Volume and Shape

Abstract

with estimates increasing as much as a factor of 20 when the scale of measurement increased from 0.1 to 2 m (e.g., Estimates of saturated and unsaturated water flow in soil are impor- Garbesi et al., 1996;Tidwell and Wilson, 1999). tant for predictions of infiltration, runoff, and solute transport. Previ-Measurement bias related to sample size has someous research indicates that ponded infiltration estimates are influenced by the volume or cross-sectional area of the measurement. Our study times been attributed to smaller samples having less probcompared quasi-steady infiltration measurements made using 20-, 30-, ability of encountering spatially infrequent, high magniand 45-cm-diameter cylinders driven 25 cm deep into 56 field plots tude portions of the soil (Iverson et al., 2001; Starr et al., under diverse agricultural management practices. Mean infiltration 1995). As pointed out by Sisson and Wierenga (1981), rate increased from 50, to 81, to 95 mm h Ϫ1 as diameter increased. however, this would be a violation of the central limit Standard deviation and range also increased with diameter. All three theorem, since the mean of randomly selected samples diameters produced lognormal data distributions. These results indishould be centered on the same value regardless of their cate that increasing the sample area is not equivalent to pooling of sample volume. If a sufficient number of small-volume many smaller samples, which would have produced the same mean but samples are used, the mean should be equivalent to that with a lower variance. Follow-up experiments with a double-ring configuration or a divider placed in the center of a 45-cm cylinder demon-of larger samples. In terms of the variance, large-volume strated that adding vertical barriers reduced infiltration even when samples should be equivalent to pooling small samples, the total infiltration area was unchanged. A pulse of dye introduced unless the measurement technique creates artifacts de-10 min before removing the ponded water showed an extensive netpendent on the volume or dimensions of the sample. To work of dyed flow pathways in all but the slowest infiltration situaaccount for the decrease in infiltration measured with tions. The pathways were not associated with visible macropores. smaller infiltration rings, Shouse et al. (1994) suggested Careful consideration should be given to the dimensions of samples that a stagnation zone (an artifact of the measurement used to estimate saturated and possibly unsaturated flow from infiltechnique) was introduced when partitions were driven tration experiments.

Cumulative effects of 20 years of fire, grazing and selective tree cutting on soil water infiltration in sudanian savanna-woodland ecosystem of West Africa

“…Further, measurements of steady infiltration rate were made after each measurement period in dividing the cumulative infiltration water depth for the period by the required times (Wuest, 2005).…”

Buffer Index Effects on Hydraulic Conductivity Measurements Using Numerical Simulations of Double‐Ring Infiltration

“…Measurement error due to lateral flow decreased as the outer ring size increased, and consequently the measured infiltration rates better approximated the one-dimensional vertical flow rates. More recently, Wuest (2005) investigated the influence of sample volume and shape on estimates of saturated flow in a cylinder infiltrometer and demonstrated that the mean infiltration rate increased as the diameter increased, while the standard deviation and range also increased with increasing diameter. Then Wuest (2005) concluded that these phenomena might be attributed to deep insertion of the cylinder and high antecedent soil moisture.…”

Tillage and no-tillage conservation effectiveness in the intermediate precipitation zone of the inland Pacific Northwest, United States

“…The hardpan classification is the result of a discontinuous silica layer developed between 1.0 to 1.5 m (3.3 to 4.9 ft) below the soil surface, less than 10 mm (0.4 in) thick and occupying less than 15% of the area. This feature does not adversely affect soil surface hydrologic properties; Wuest (2005) conducted four-hour ponded infiltration tests within 500 m (1,640 ft) of the plots reported on here. The infiltration rates did not change after four hours, indicating that deep, less pervious layers were not influential.…”

“…The inside circumference was tamped with a 4 mm (0.2 in) thick rod to seal any gaps between the cylinder and the soil. Water was maintained at a constant depth of 20 to 30 mm (0.8 to 1.2 in) with float valves for two hours (Wuest 2005). Two hours were sufficient to achieve near steady-state infiltration, which was usually approached within 30 to 60 min.…”

“…Bezdicek et al (2002) reported that particulate organic matter and light fraction organic matter can increase substantially in as few as three years in NT systems in the PNW higher intermediate and high precipitation zones. In general, surficial accumulations of soil organic matter contribute to well formed macroaggregates (Cambardella and Elliott 1993) and are associated with the development of superior soil hydrologic conditions (Williams 2004(Williams , 2008Wuest et al 2005). This relationship is well established (Bissett and O'Leary 1996;Six et al 2000;Wuest et al 2005;Kennedy and Schillinger 2006) and improvements in soil and water conservation when using NT have been observed in many areas of the world (McGregor and Greer 1982;Angle et al 1984;Dickey et al 1984;Edwards et al 1993;Shipitalo and Edwards 1998;Castro et al 1999).…”