Hydrostratigraphic Characterization in South-Eastern Coastal Aquifer of
Bangladesh using Lithological Data and Step-drawdown Test
Abstract
The hydrogeological investigation of south-eastern coastal aquifer of
Bangladesh has been performed for the evaluation of well performance in
the aquifer based on well logs and step-drawdown tests. The consequences
from four single-well of step-drawdown tests have conductd in two recent
boreholes through Jacob and Rorabaugh’s methods. From lithological data
analysis it is observed that the aquifer of studied area is in Early
Miocene age which consists of Upper and Middle Boka Bil formation. The
values of step-drawdown test results have indicated well losses ranges
between 17% and 19.8% and loss of aquifer on two well ranges between
82.6 % and 80.2% which reflected higher efficiencies of two wells. The
values of specific capacity have varied from two wells in totally 18.13
m3/day/m to 23.79 m3/day/m, respectively whereas the values of well
efficiency varied from 95.3% to 98.5% which indicate that the wells
are properly developed and designed. The estimation of aquifer
transmissivity ranges from 271.24 (m2/day) to 263.3 (m2/day) and these
values have evaluated the wells indicating the higher production with
its water accessibility from the wells. Therefore, it is indicated the
laminar flow of the aquifer/well-face (negligible part of turbulent
flow). As a result, the water-bearing zone is effective for high amount
of water production per day. The total approaches of litholog and
pumping tests determine the effective application of the single-well on
step-drawdown tests and it has identified the safe and sustainable well
growth for the extraction of groundwater in future.