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 stepdrawdown 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.

Analisis Potensi Debit Air Tanah Melalui Pumping Test Metode Step Draw Down pada Sumur Bor Irigasi di Desa Bonto Rannu, Kecamatan Kajang, Kabupaten Bulukumba, Sulawesi Selatan

“…Setelah pemompaan pada sumur 1, permukaan air sumur dapat kembali dengan cepat seperti semula bahkan melebihi elevasi awal [14]. Sedangkan untuk sumur 2, debit optimum (Qopt) sebesar 0,00318 m 3 /s atau 11,45 m 3 /jam dengan Sw optimum 2,100 m. Data tersebut menunjukkan terdapat cadangan air tanah yang terbatas [17].…”