Spatial Variability and Measurement Scale of Infiltration Rate on an Agricultural Landscape
- Nathan W. Hawsad,
- Bingwu Liube,
- C. W. Boastc,
- P. S. C. Rao *a,
- E. J. Kladivkob and
- D. P. Franzmeierb
- a School of Civil Engineering, Purdue Univ., West Lafayette, IN 47907-2051
d Currently at Dep. of Geography and Environmental Engineering, Johns Hopkins Univ., Baltimore, MD 21218-2686
b Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907
e Currently at National Lab of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil & Water Conservation, Chinese Academy of Sciences, Yangling, Shaanxi 712100, China
c Dep. of Natural Resources and Environmental Sciences, Univ. of Illinois, Urbana, IL 61801
Determining representative infiltration rate parameters for use in modeling field-scale flow and transport processes is difficult because of the spatial variability of soil properties. To determine how steady-state infiltration rate variability is affected by support scale, steady-state infiltration rates (Is) were measured at three spatial scales (local, hillslope, and landscape) along a 710-m transect on a swell–swale landscape in Indiana. Spatial variability at the local scale was studied using measurements in a 1 × 1 m2 array of 100 ring infiltrometers (7.2-cm diam.) for three soils at three horizons each. Studies were conducted at the hillslope and landscape scales using three nested infiltrometers of sizes 20 × 20, 60 × 60, and 100 × 100 cm2 Geostatistical analyses show a decrease in the sample variance of the Is values and an increase in spatial correlation of Is with depth. They also suggest that an area >10, 7.2-cm diam. rings (i.e., approximately >400 cm2) is needed to provide a representative measurement area (RMA; i.e., area needed to filter out smaller-scale heterogeneities) at the local scale. Hillslope- and landscape-scale tests indicate that Is measurements with infiltrometers require an infiltrometer with a support area greater than the local-scale RMA to show the spatial correlation of the larger scales. In addition, these infiltrometer measurements may not provide appropriate effective Is estimates at these greater scales unless they are averaged over a domain that extends across the landscape's range of variability, estimated from the computed semivariograms to be 120 to 200 m for this study.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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