ESTIMATION OF SATURATED HYDRAULIC CONDUCTIVITY FOR DIFFERENT SOIL TYPES IN JIMMA ZONE, ETHIOPIA

Abstract

A saturated hydraulic conductivity (Ksat) is the utmost vital soil hydraulic parameter for flow with in the soil. The knowledge of it is vigorous for water resources applications. Numerous methods & models (field, laboratory and empirical formulae) are available for determination of it. However, all of them have their applications and limitations. But, most investigators prefer the usage of empirical formulae to direct measurements of Ksat (field / lab) as direct measurements are very challenging (sometimes impractical), necessitating testing, quantification, and decision; making it extremely difficult to use in hydrologic modeling. Thus, it is vital to effectively asses the illustrative Ksat values matching the cost and its reliability. This study therefore presents the laboratory estimation of the Ksat for different soil textures in Jimma zone (nearby Jimma, Serbo, GilgelGibe and Asendabo towns) in Ethiopia, by both constant head and falling head methods, which are the simplest and cost effective ones. In these procedures, we determined the Ksat values of the soil in the study region. The results indicated that its average values are (1) in between 0.00124 and 0.00173cm/s for sandy-loam soil, and (2) 0.000124cm/s for clay soil. The porosity of soil samples were also calculated and found out to be in the range of 41.25 % and 44.24 % (the average being 43.04%) for sandyloam soil and 43.54% for clay soil. We then compared the results with the corresponding values in the literature, and finally we concluded that the Ksat and porosity values obtained for the study region were found to be in a good agreement with the corresponding literature values.