Estimating transmissivity using empirical and geostatistical methods in the volcanic aquifers of Upper Awash Basin, cent
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ORIGINAL ARTICLE
Estimating transmissivity using empirical and geostatistical methods in the volcanic aquifers of Upper Awash Basin, central Ethiopia Andarge Yitbarek Baye • Moumtaz Razack Tenalem Ayenew • Engida Zemedagegnehu
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Received: 28 June 2011 / Accepted: 17 September 2012 / Published online: 29 September 2012 Springer-Verlag Berlin Heidelberg 2012
Abstract Transmissivity (T) is a basic hydraulic parameter of an aquifer that is utilized in most groundwater flow equations to understand the flow dynamics and is generally estimated from pumping tests. However, the cost of performing a large number of aquifer tests is expensive and time consuming. The fact that specific capacity (Sc) is correlated with hydraulic flow properties of aquifers simplifies parameter estimation mainly because specific capacity values are more abundant in groundwater databases than values of transmissivity and they offer another approach to estimate hydraulic parameters of aquifers. In this study, an empirical relation is derived using 214 pairs of transmissivity and specific capacity values that are obtained from pumping tests conducted on water wells penetrating the complex volcanic aquifers of Upper Awash Basin, central Ethiopia. Linear and logarithmic regression functions have been performed and it is found that the
Electronic supplementary material The online version of this article (doi:10.1007/s12665-012-2011-6) contains supplementary material, which is available to authorized users. A. Y. Baye (&) Ministry of Natural Resources Operations, 5th Floor, 1044-5th Ave., Prince George, BC V2L 5G4, Canada e-mail: [email protected] M. Razack Department of Hydrogeology, University of Poitiers, 40 avenue du Recteur Pineau, 86022 Poitiers, France T. Ayenew Department of Earth Sciences, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia E. Zemedagegnehu Water Works Design and Supervision Enterprise, P.O. Box 2561, Addis Ababa, Ethiopia
logarithmic relationship predicting transmissivity from specific capacity data has a better correlation (R = 0.97) than the linear relationship (R = 0.79). The two parameters are log-normally distributed, in which the logarithmic relation is also better statistically justified than the linear relation. Geostatistical estimations of the transmissivity were made using different inputs and methods. Measured and supplemented transmissivity data obtained from estimates using the derived empirical relation were krigged and cokrigged, spherical and exponential models were fitted to the experimental variograms. The cross-validation results showed that the best estimation is provided using the kriging procedure, the transmissivity field represented by the measured transmissivity data and the experimental variogram fitted with the exponential model. Based on the geostatistical approach, the transmissivity map of the aquifer is produced, which will be used for groundwater flow modeling of the study area that will follow this analysis. Keywords Transmissivity Upper Awash Specific capacity Logno
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