The effect of microtopography on soil-water movement is a topic of interest for a range of disciplines, with experimental studies investigating the relationship between the two lacking. Laboratory experiments were conducted by simulating rainfall across packed soil surfaces to investigate the effect of microtopography on wetting front movement within experimental soil profiles. In small soil box experiments, the observed wetting fronts for soil profiles showed considerably deeper movement beneath a smooth surface than depressions for 12–60？min rainfalls. For large soil box experiments, the wetting front reached moisture sensors installed at 5 and 10？cm depths and corresponding to various rough and smooth surface features at significantly different times, with movement being most rapid beneath the smooth surface. Wetting front movement was “quicker” beneath surface peaks than depressions for the rough surface as attributed to 2D/3D unsaturated flow. This study provides valuable experimentally based insight into the effect of microtopography on soil-water movement. 1. Introduction Infiltration is controlled by a number of factors such as soil capillary suction, initial moisture content, hydraulic conductivity, and pore structure. For practical applications (such as unsaturated flow modeling), infiltration is generally considered homogeneous across a soil surface. In reality, infiltration rates often vary significantly and dynamically across a soil surface [1, 2]. Infiltration characteristics also strongly influence subsequent water percolation through the vadose zone. The factors that control spatial and temporal variations in infiltration and soil-water percolation can be divided into three categories: site characteristics, soil characteristics, meteorological characteristics [3]. Site characteristics include slope, microtopography, vegetative cover, grazing conditions, and subsurface conditions; soil characteristics include saturated and unsaturated hydraulic conductivity, degree of aggregation, bulk density, and the presence of macropores; and meteorological characteristics include rainfall intensity, duration, and spatial variations [3]. Soil moisture condition is an important site characteristic, which exerts a significant influence on water movement in soils [3–6]. Microtopography is a site characteristic that can affect spatial variations in infiltration and soil-water percolation directly and indirectly and is a research area in need of significantly more work [7]. Generally, increasing soil roughness will result in increased infiltration [8–10]
References
[1]
A. S. Tricker, “Spatial and temporal patterns of infiltration,” Journal of Hydrology, vol. 49, no. 3-4, pp. 261–277, 1981.
[2]
M. Sullivan, J. J. Warwick, and S. W. Tyler, “Quantifying and delineating spatial variations of surface infiltration in a small watershed,” Journal of Hydrology, vol. 181, no. 1–4, pp. 149–168, 1996.
[3]
B. E. Haggard, P. A. Moore Jr., and K. R. Brye, “Effect of slope on runoff from a small variable slope box-plot,” Journal of Environmental Hydrology, vol. 13, no. 25, pp. 1–8, 2005.
[4]
Y. Le Bissonnais, B. Renaux, and H. Delouche, “Interactions between soil properties and moisture content in crust formation, runoff and interrill erosion from tilled loess soils,” Catena, vol. 25, no. 1–4, pp. 33–46, 1995.
[5]
M. K. Magunda, W. E. Larson, D. R. Linden, and E. A. Nater, “Changes in microrelief and their effects on infiltration and erosion during simulated rainfall,” Soil Technology, vol. 10, no. 1, pp. 57–67, 1997.
[6]
L. Wei, B. Zhang, and M. Wang, “Effects of antecedent soil moisture on runoff and soil erosion in alley cropping systems,” Agricultural Water Management, vol. 94, no. 1–3, pp. 54–62, 2007.
[7]
G. Govers, I. Takken, and K. Helming, “Soil roughness and overland flow,” Agronomie, vol. 20, no. 2, pp. 131–146, 2000.
[8]
R. E. Burwell and W. E. Larson, “Infiltration as influenced by tillage-induced random roughness and pore space,” Proceedings of the Soil Science Society of America, vol. 33, pp. 449–452, 1969.
[9]
K. Helming, M. J. M. R？mkens, and S. N. Prasad, “Surface roughness related processes of runoff and soil loss: a flume study,” Soil Science Society of America Journal, vol. 62, no. 1, pp. 243–250, 1998.
[10]
J. A. Gómez and M. A. Nearing, “Runoff and sediment losses from rough and smooth soil surfaces in a laboratory experiment,” Catena, vol. 59, no. 3, pp. 253–266, 2005.
[11]
T. Dunne, W. Zhang, and B. F. Aubry, “Effects of rainfall, vegetation, and microtopography on infiltration and runoff,” Water Resources Research, vol. 27, no. 9, pp. 2271–2285, 1991.
[12]
J. K. Mitchell and B. A. Jones, “Micro-relief surface depression storage: analysis of models to describe the depth-storage function,” Water Resources Bulletin, vol. 12, no. 6, pp. 1205–1222, 1976.
[13]
C. A. Onstad, “Depressional storage on tilled soil surfaces,” Transactions of the American Society of Agricultural Engineers, vol. 27, no. 3, pp. 729–732, 1984.
[14]
F. Darboux, P. Davy, C. Gascuel-Odoux, and C. Huang, “Evolution of soil surface roughness and flowpath connectivity in overland flow experiments,” Catena, vol. 46, no. 2-3, pp. 125–139, 2002.
[15]
D. M. Fox, R. B. Bryan, and A. G. Price, “The influence of slope angle on final infiltration rate for interrill, conditions,” Geoderma, vol. 80, no. 1-2, pp. 181–194, 1997.
[16]
D. M. Fox, Y. Le Bissonnais, and A. Bruand, “The effect of ponding depth on infiltration in a crusted surface depression,” Catena, vol. 32, no. 2, pp. 87–100, 1998.
[17]
D. M. Fox, Y. Le Bissonnais, and P. Quétin, “The implications of spatial variability in surface seal hydraulic resistance for infiltration in a mound and depression microtopography,” Catena, vol. 32, no. 2, pp. 101–114, 1998.
[18]
S. Assouline and M. Ben-Hur, “Effects of rainfall intensity and slope gradient on the dynamics of interrill erosion during soil surface sealing,” Catena, vol. 66, no. 3, pp. 211–220, 2006.
[19]
S. Assouline, “Rainfall-induced soil surface sealing: a critical review of observations, conceptual models, and solutions,” Vadose Zone Journal, vol. 3, no. 2, pp. 570–591, 2004.
[20]
D. Hillel, Environmental Soil Physics, Academic Press, San Diego, Calif, USA, 1998.
[21]
L. Sande, X. Chu, and T. DeSutter, “A new method for replicating complex microtopographic surfaces in laboratory soil box experiments,” Applied Engineering in Agriculture, vol. 27, no. 4, pp. 615–620, 2011.
[22]
C.-H. Huang and J. M. Bradford, “Potable laser scanner for measuring soil surface roughness,” Soil Science Society of America Journal, vol. 54, no. 5, pp. 1402–1406, 1990.
[23]
F. Darboux and C. H. Huang, “An instantaneous-profile laser scanner to measure soil surface microtopography,” Soil Science Society of America Journal, vol. 67, no. 1, pp. 92–99, 2003.
[24]
L. D. Meyer and W. C. Harmon, “Multiple-intensity rainfall simulator for erosion research on row sideslopes,” Transactions American Society of Agricultural Engineers, vol. 22, no. 1, pp. 100–103, 1979.
[25]
L. D. Meyer, “Rainfall simulators for soil erosion research,” in Soil Erosion Research Methods, R. Lal, Ed., CRC Press, 2nd edition, 1994.
