Aquifer Characterization of the Raya Valley Based on Pumping Test and Geophysical Data Analysis
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Date
2010-06
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Addis Ababa University
Abstract
This work has focused on the quantitative characterization of aquifer hydraulic parameters of the raya valley by establishing a relationship between aquifer properties (specific capacity and BH yield data with transitivity and between aquifer hydraulic parameters and aquifer electrical properties i.e. Transitivity and transverse resistance aiming to extrapolate measured aquifer hydraulic parameters to an area with no pumping test data using the established relationships between T and Sc, T and BH yield and between T and R. Beforeestablishing relationships between aquifer hydraulic parameters and aquifer hydraulic and
electric properties a huge volume of raw data set are analyzed using different softwares. 135raw pumping test data are analyzed to determine T & K from constant and recovery. 49wells tapping unconfined aquifers are corrected for decreasing saturated thickness using Jacob correction method and 64 wells whose pumping rate exceeding 36 l/sec are corrected for well loss using step draw down test data by employing the Han tush- Herschel well loss solution method. Three methods are applied to determine a relationship between T and Scand one method between aquifer hydraulic and electric properties. By using the three approaches of estimating T from Sc i.e. analytical, empirical and statistical regressed relationship between the parameters (T & Sc) for each approach is established with R2 value>0.95 and interpolated map of transitivity and hydraulic conductivity are created through
statistical approach by using cooking and rigging techniques for T from Sc and K from K respectively. The results of analytical and empirical techniques are compared based on their mean error and mean absolute error and it is found that the mean absolute error and mean error for transitivity estimated using the analytic approach are 0.21 and -0.21respectively. A mean absolute error of 0.21 means on average, the estimated value of T is within a factor of 1.6 of the measured value. The mean absolute error and mean error for T estimated using the empirical approach are 0.073 and 0.00021 respectively. A mean absolute error of 0.073 indicates that, on average, the estimated value of T is within a factor of 1.18of the measured value. The established relationship between T and BH yield data also shows BH yield can also be a fair estimator of T in areas with only BH yield data. This has goodness of fit above 0.8. The T and R of the aquifer are also linearly related with R2>0.95using an empirical relation and this can be used to extrapolate PT data to an area.
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Hydrology