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Journal of Environmental Hydrology
ISSN 1058-3912 |
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Electronic Journal of the International Association for
Environmental Hydrology
JEH Volume 15 (2007), Paper 21 Posted September 17, 2007 INFLUENCE OF SPATIAL STRUCTURE OF SOIL HYDRAULIC PROPERTIES ON SURFACE RUNOFF PROCESSES IN WEST AFRICA
Ayodele E. Ajayi1,2,4 2Department of Agricultural Engineering, Federal University of Technology, Akure, Nigeria 3Department of Meteorology, Federal University of Technology, Akure, Nigeria 4Center for Development Research (ZEF), Bonn University, Germany ABSTRACT The effect of spatial variations of soil hydraulic properties on runoff response at plot scales was investigated in this study using a combination of results from field observation and numerical simulation experiments. Field observations were from two sets of scaled runoff plots during twenty-four (24) runoff events. Simulation experiments on four scenarios of hydraulic conductivity (K) distribution in a 2 m x 6 m runoff plot was implemented with a two dimensional hydrodynamic model developed and validated for tropical watersheds. In scenario A - "expanding", K values were increased linearly from 30 mm h-1 to 172 mm h-1 at regular grids downslope. In scenario B-"shrinking", K values were decreased downslope (inverse of scenario A). For scenario C - "measured" field measured K values were used on all the grid points; and in scenario D - "homogeneous" an average K value of the K distribution in scenarios A and B, 81.5 mm h-1, was used on all the grids. Two typical rainfall events; high and low intensity, were selected from field data of 2002 for model simulations. The results clearly demonstrate the role of spatial variability of K in runoff processes during storm events. Scenario A produced lowest runoff volume, due to increasing infiltration opportunity, whereas the homogeneous distribution (scenario D) yielded the highest runoff volume for both low and high intensity events. Scenarios B and C showed similar results possibly due to their decreasing infiltration capacity downslope. For proper interpretations of runoff processes such as scale dependency, runoff coefficient, etc., this study showed that there is the need to consider temporal dynamics associated with surface runoff travel from point of initiation to discharge, spatial distribution and orientation, as well as the temporal pattern and intensity of rainfall events. Further discussions on the field observed runoff response to variability in hydraulic conductivity and plot sizes are included. Reference: Ajayi, A.E., P.G. Oguntunde, B.J. Abiodun, and I.D. Horta. 2007. Influence of spatial structure of soil hydraulic properties on surface runoff processes in West Africa. Journal of Environmental Hydrology, Vol. 15, Paper 21. CONTACT: Ayodele E. Ajayi Universidade Federal de Lavras-UFLA/DCF Caixa Postal 3037 37200-000 Lavras MG Brazil E-mail: ayodele.ajayi@yahoo.com |
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