Hydrostratigraphy and aquifer piezometry of Dhaka city

Abstract

Dha!<",the capital of Bangladesh, has one of the f"lest uroatl growth rat•• amoog the dcveloping countries. Groundwat.r of Dhaka city occurs in lhe Dupi Tila 'atId~' aquifer of Plio-Plebtocene age atId alm",l only source of potable wat.r in lhe city. Abstraction by water wells is the main disch.rge and causing dewatering of the aquifer. The research is aimed to understand the nydro,tmtigmph, and piewmetry oflh. dopleled aquifer. Prest!l1t srudy has u"d lithological and geophysical re,,,tivity 1"g infonnation to build hydro,tratigraphy of the area. Dhaka WIISII ground"ater abstraction and well design iufonnation, and BWDB Groundwater le\'el data ha" been ",ed to reconstruot the piezometry of th. aquifer. A thick oolumn of unconsolidated sedimen!., comp"'ed of sands, sillS and clays build [~c hydrostr"'igraphy of the region and pmvi;ionally subdivided into 7 UnilSup to a depth of 450m. lbese unil' organized into three aquifers system separ••••d by day-,ill dominared hori7<)Ils.The average thickness of the fir;! aquifer rang.s ITom IOO-150mwhile ,econd aquifer range. from 50.IOOm.A thick day lay.". of 37_128mi. rollowed by the seeond aqnifer and capping d,e third aquifer "funiform lhiLknc•.•(-40m). Third aquifer i, liased by another day dominJled layer. L"ng tenn hydTIlb""ph, /Tom the dilferent pan., or the city specify the inc"''',ing t",nd of drop in waler level throughout Lbe city (R'~O 75.(1.94, n-12). Groundwa!er abstractioEt in the eity has increased more dian 1200"/0from 1970 to 2003.Tbis increased abstraclion causing sbarp drop "f "aler level throughout the dty and exce"i •• high rate of production In the south-central and '''uth'wes!em region formc-dmne;, or d"ptC"ion Tho Hydrostratigraphy and piezornetry of lhe firsl aquifer indicale hig.hervulnerability ur gmund".ter in tb" centTalcit)' area. InfolTTJotionon qualt\) and quantity of waler 10lhe lower aquife" (second and third aquifer) are still inadequate. Ro,ource ",sessmont or the lowor aquife" require adequate hydmgculogical data to e'tablish s)"tem geometty and continuity, aquifer transmiosiyily, and areas and ra1eof annual recharge 10con;idIT the lower aqu;fer><> a, potent;al b'fOundwatersource. 1 0 mooL the presem crisis of potable "alL'! ahstraction has to be und.r t.k.TI from the peripheral region or the city. For long.t.nn sustainable solmion peri.uman well_field, have [0 be e<tablisb.d .nd conjunctive usc of gruundwater .nd stuface water should bc .doptcd.