ESTIMATING HYDRAULIC CONDUCTIVITY USING GRAIN SIZE DISTRIBUTION IN AN ALLUVIAL SYSTEM IN MATLAB, BANGLADESH
Several empirical equations to calculate hydraulic conductivity using grain size distribution of unconsolidated aquifer materials from Matlab, Bangladesh, have been evaluated in this study. About 60 sediment samples of different depth from 10 test wells were analyzed (i.e. grain size) to estimate the hydraulic conductivity Based on grading analyses of soil samples extracted from test holes during groundwater investigations and particle size distribution characteristics, hydraulic conductivities were computed. Results showed that all seven empirical formulae used reliably estimated hydraulic conductivities of the various soil samples within known ranges. The Kozeny-Carman formula proved to be the best estimator of most samples analyzed. By using the USRB and Kozeny-Carman formulae from grain size analysis, it is shown that in shallow aquifers (50-60m), hydraulic conductivities are 55-190 m/day and 20-200 m/day, respectively, which are similar to the historical pumping test data (18 -181.44m/day) of the same region.
From the comparison of grain size analysis and pumping test result, it is evident that grain size analysis can be an effective method to estimate hydraulic conductivity.