Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Chowdhury Sarwar Jahan ¹, Quamrul Hasan Mazumder ¹, Shyamal Kumar Ghose ¹, M. Asaduzzaman ²

Affiliations
1 University of Rajshahi, BD
2 Barind Multipurpose Development Authority, BD

Abstract

Proper planning of groundwater exploitation policy in Barind area, Bangaladesh needs the knowledge about the specific yield of the aquifer, whose computed values vary from 8 to 32% with a general decreasing trend from north towards central portion but the southern portion has better specific yield value than the central portion. On the basis of specific yield variation the area is divided into: Zone-I: includes Dhamoirhat, Patnitola, Mohadevpur, Manda, eastern side of Tanore, southern side of Godagari and Nawabganj, Shibganj and Bholahat thanas (specific yield values > 15%); Zone-II: covers the area of Niamatpur thana and the rest part of Nawabganj thana (specific yield valle 10-15%) and Zone-III: includes Nachole thana and the rest of Gomastapur thana (specific yield values <10%).

Keywords

Groundwater, Hydrogeology, Barind Area, Bangladesh.

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Mrinal Kanti Roy ¹, Sudip Saha ¹, Syed Samsuddin Ahmed ¹, Quamrul Hasan Mazumder ¹

Affiliations
1 Department of Geology and Mining, University of Rajshahi, Rajshahi-6205, BD

Abstract

The present study on tide, morphology, lithofacies and evolution of the Meghna estuary is confined to its Hizla-Goshairhat-Damudhya-Burirhat( HGDB) branch which represents the relict main channel of the Meghna-Padma river system. Tide in this HGDB branch is semi-Diurnal showing daily, monthly and yearly time versus water level asymmetry. This branch is at present microtidal in nature having tidal range in between 0 41-1 78 m, though mean water level varies from 0 87-5 18 m above average mean sea level. Geomorphologically the study area is divided into estuarine plain in south and deltaic plain in north with estuarine channel in between the 3 m high bank cliff section of the 26 km long estuarine channel at 32 sites recognizes seven litho-Facies. The litho-Facies-Finely laminated sand and silt (facies A), finely laminated silt and clay (fac~ies B ), laminated sand-Clay (sub-Facies C₁), alternating clay and organic matter (facies D) and rippled laminated sand (facies G) are tide generated. Crudely laminated to masslive clay (facics E) and clay with ripple laminated silt and sand (facies F) are interdistributary bay/Swamp and deltaic plain deposits respectively. Sub-Facies C₂(massive sand) and some ripples within facies B and G are storm/Flood and wave influenced deposits respectively. The morphological straight-Meander-straight divisions of the HGDB estuarine reach can be zoned as funnel-Meander-Head on the basis of channel morphology, sedimentary structure, facies and sand+silt clay ratio of sedimentary succession. Rhythmic occurrence of sand-Silt, slit-Clay and clay-Organic matter with sedimentary structures of parallel-and wavy-Lamination along with occasional lenticular-, flaser-, and bi-Directional cross-Lamination and plained off ripples of facies A, B, D and sub-Facies C₁ are tide generated. Some ripples in facies B and G and sub-Facies C₂ are wave and storm/Flood generated. These laterally change to massive to crudely laminated clay with minor amount of rippled sand and silt embedded with soil peds and ischolar_main traces of delta originated facies E and F in headward direction and vertically up the succession. This is a well-Recognized geologically predictable spatial variation when estuary is linked up with delta in landward direction and when delta progrades down the estuary with time. The relative influence of tide(facies A, B, D and sub-Facies C₁), wave(part of facies B and G and sub-Facies C₂) and river (deltaic facies E and F) is well reflected in this zonation. The facies A, B, C and D were deposited in an estuarine environmental set up that was established in the study area immediately after the mid-Holocene 7000-5000 years BP marine transgression. The Ganges delta was shaped and started progradation towards southeast direction probably after the late Holocene sea level fall at around 3000 years BP when the Bhagirathi, now in West Bengal, shifted toward east through Mathabhang, Bhairab-Pushar, Garai-Madhumati-Haringhata, Arial Khan to Padma, the new main branch of the Ganges in Bangladesh. The Padma might have met the old Meghna at around 1110±90 years BP and facies E and F deposited in a deltaic environment at a later time when the Ganges delta prograded to the present position. Facies G is a tidal bar deposit within the present estuarine channel. The Ganges delta is still prograding southeastward, but at a much reduced rate due to present trend of global warming initiating a new sea level rise.

Keywords

Tide, Morphology, Facies, Zonation And Evolution, Meghna Estuary, Bangladesh.

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