Infiltration and Surface Geometry Features of a Swelling Soil following Successive Simulated Rainstorms

rangement and distribution of the cracks. Moreover, White (1972) explained the energy implications that The theory of water movement in high shrink/swell soils has expericause the cracks to reappear in the same position from enced consistent revision since Haines first presented the topic in 1923. Several aspects of the infiltration process in cracking soils have event to event. Johnston and Hill (1944) observed that proven to be difficult to measure; seal/crust formation and properties, cracks develop between crop rows where the water concrack network patterns, preferential flow zones and contributions, tent was higher (due to less uptake by plants) and, thus, and soil moisture determinations within the profile (near crack and the strength of the soil was lower. Since dry clay soils near center of prismatic column) to name a few. Here, we used simutend to moisten more rapidly to a greater depth along lated rainstorms, laser measurements of surface elevation, needlea crack than at a distance from a crack, cracks transmit penetrometer measurements, and mass measurements of infiltrating more water deeper under heavy precipitation events, water over a 206and 145-d period to examine water movement and making the soil wetter in this area. cracking patterns in a large sample box filled with a swelling clay soil. Other authors have looked at cracking soils in the Water movement was restricted to the neighborhood of the crack field. Dasog et al. (1988), using methods outlined by El zone, since the formation of a surface seal/crust prohibited infiltration into the surface of the prismatic columns of soil between cracks. Also, Abedine and Robinson (1971), measured field crack the location of cracks was observed to alternate between rainstorms. networks and reported that moisture and swelling poThe alternating crack pattern led to more uniform wetting with depth tential coupled with vegetation and management activias time increased and the number of rainstorms increased, thereby ties influence cracking. Waller and Wallender (1993) reducing the extent of preferential flow. used image analysis of soil surface photographs to quantify prismatic column surface geometry, and noted that after irrigation the major cracks reformed in the same M of our understanding of infiltration and relocation. Chertkov and Ravina (1998) and Chertkov distribution of water in soils comes from experi(2000) used the similarity between cracks in rocks and ments with ‘ideal’ soils and models that depict the solid swelling clay soils to model crack network geometries part of the soil as a rigid medium through which water in swelling clay soils. Bronswijk (1991) linked water passes. This may be an accurate assumption for stable content changes and easily measured physical properties uniformly structured soils with low clay content, but for of soil aggregates with shrinkage prediction and dismany soils, the physical changes that take place (such cussed a second normal shrinkage phase. as swelling, sealing, shrinkage, and cracking) during and In addition to swelling and cracking, clay soils form after the rainstorm greatly affect the movement of water a surface seal, which also greatly affects infiltration. in the soil. In particular, in vertisols where large cracks Surface sealing occurs due to the impact of raindrops form after drying, the cracks are zones of preferential on the surface of the soil, causing compaction, and settransmission for water. Smiles (1974), drawing from tling of fine-grained detached material on the surface of Philip (1969), found that infiltration in swelling soils is the soil, effectively clogging the micropores. The surface very different from infiltration in rigid soils. Smiles seal is thin, in comparison to the bulk material; however, (1974) found that infiltration was primarily a sorption the surface seal and bulk material exhibit very different phenomenon. Infiltration through the cracks leads to a infiltration characteristics. Tackett and Pearson (1965) non-uniform profile of water content, which affects the used resistance methods to examine crust strength at subsequent swelling and cracking of the soil. The intervarious stages of simulated rainfall and concluded that relationship between these two processes is not catered resistance increased rapidly with small additions of clay. for by traditional oneor two-dimensional models. Mualem and Assouline (1989) presented a conceptual model of soil sealing, which described the seal as a nonUsing field observations, White (1970, 1972, 2001) uniform disturbed layer defined by minor differences presented a holistic model of how cracking soils develop in soil structure. Parlange et al. (1984), Baumhardt et and water infiltrates from one event to the next. He al. (1990), Philip (1998), and Smith et al. (1999) dispointed to a moisture dependency that defines the arcussed the theoretical aspects of infiltration into soils with a surface crust. R.R. Wells, D.A. DiCarlo, and M.J.M. Römkens, USDA-ARS NaMost of the studies that have been performed in swelltional Sedimentation Lab., Oxford, MS 38655; T.S. Steenhuis, and ing soils have focused on crack pattern formation, surJ.-Y. Parlange, Dep. of Biological and Environmental Engineering, face seals, or infiltration; very few studies have looked Cornell Univ., Ithaca, NY 14853; S.N. Prasad, Dep. of Civil Engiat the interrelationships between these processes. The neering, Univ. of Mississippi, Oxford, MS 38677. Received 30 May 2002. *Corresponding author ([email protected]). objective of this research was to study the processes that govern the relationship between cracks, surface Published in Soil Sci. Soc. Am. J. 67:1344–1351 (2003). seals, and infiltration in a highly swelling soil. We mea Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA sured total infiltration and surface runoff in a packed