Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2003
Publication Date: February 28, 2005
Citation: Arnold, J.G., Potter, K.N., King, K.W., Allen, P.M. 2005. Estimation of soil cracking and the effect on surface runoff in a Texas blackland prairie watershed. Hydrological Processes. 19(3):589-603. Interpretive Summary: It is estimated that 320 million hectares of the world¿s land area is covered with expansive soils and up to 20 percent of the United States may be mantled with soils subject to shrink-swell behavior. In agriculture, soil shrinkage cracking allows rapid transport of water, nutrients and pesticides to the subsoil where they are both inaccessible to shallow rooting plants and can pollute the local groundwater system. In addition, seasonal cracking of the soil results in poor estimates of runoff and infiltration due to the changing soil storage conditions. In this study, soil cracking was measured at the ARS experimental watershed in Riesel, Texas. Using the data, a model was developed to estimate the impact of cracking on surface runoff. The crack model was tested against measured runoff from the Riesel watershed and found to improve model predictions. The results of this study will provide more realistic models for the transport of water, nutrients and pesticides in cracking clay soils.
Technical Abstract: Seasonal cracking of the soil matrix results in poor estimates of runoff and infiltration by simulation models due to the changing soil storage conditions. In this study, soil surface elevation changes were measured every two weeks and soil crack volume was calculated for a two-year period at the USDA-Agricultural Research Service, Riesel Y-2 watershed in central Texas. Soil anchors were placed in triplicate at depths of 0.15, 0.45, 0.90, 1.50, and 2.5 m and relative movement from a monument at 4.5 m was measured. Soil movement was translated into crack volume assuming isotrophic shrinkage. A crack flow model was developed for this study that computes crack volume from crack potential, soil depth and soil moisture. Simulated crack volume followed the seasonal trends found in the measured crack volume and was in general agreement with a regression R**2 = 0.84. The crack model was incorporated into SWAT (Soil and Water Assessment Tool), a comprehensive hydrologic model. Regression analysis was performed on measured and simulated daily surface runoff with an R**2 = 0.87 indicating good agreement. The model was able to simulate surface runoff accurately in winter months when cracks were swelled closed and in the fall recharge events of 1998 when crack volume went from 70 to 10 mm. The relationships between measured crack volume and hydrologic variables simulated by the model were also examined and discussed.