Mainamati, Physical Setup
Mainamati, Physical Setup an isolated low, 18 km long and 2 km wide spur of a dimpled range of hills, dotted with more than 50 ancient Buddhist settlements of the 8th to 12th century AD, and known as the Mainamati-Lalmai range extended through the centre of the district of comilla. It lies between latitudes 23'20'N and 23'30'N and longitudes 91'05'E and 91'10'E. It is 8 km west of Comilla town. The Dhaka-Chittagong and the Comilla-Sylhet highways run along the northern part, while the southern portion of the hills can be reached by the Comilla-Chandpur road which runs parallel to its eastern side.
Climate mostly humid and temperate. Mean annual rainfall ranges from 1930 mm in the eastern plains and to more than 2540 mm in the highlands of the west. The cool and dry winter-December to February- is followed by a hot and shower premonsoon period-March to May- and then by the relatively cool but very wet monsoon season- June to September. Mainamati is rarely affected by cyclones. The maximum temperature ranges from 37'C to 39'C, whereas the minimum temperature varies from 7'C to 10'C.
Soil the soil is mostly composed of fine Madhupur clay, which cakes very hard in the dry season. These soils are acidic, low in plant nutrient and droughty. The loose and friable Recent and subrecent alluvial deposits laid down by the rivers dakatia, gumti and feni form the rest of the soils.
Agriculture very similar to mahasthangarh. At least 40% of the area are single cropped, 38% double cropped and10% triple cropped. Rice, mainly aus' [aush] and transplanted aman' [aman], is by far the most extensive crop. Homestead areas are mainly used for vegetables, bananas, fruit trees, pan (betel leaf) and seedbed for aman rice.
Topography and relief the area is characterised by low hills and broad valleys. The overall trend of the hill is NNW-SSE. The average height of the hills is about 12m but some peaks rise to about 40m or more. The western part of the hills abruptly changes to plainland while the eastern part merges gradually with the adjacent areas. There are numerous small hillocks scattered throughout the area. The hill range gradually widens from about 1 km in the north to about 3 km in the south. Some of the hilltops representing table surfaces are separated from each other by deeply incised valleys.
Drainage the lalmai hillS, surrounded by the Chandina deltaic plain, are drained by three major rivers-the Gumti, the Dakatia, and the little feni. Numerous rainfall channels, which characterised the area only, become active during the periods of heavy downpour. These have built up an overall dendritic geomorphic feature in the area. More of such channels occur in the central and southern parts than in the northern part. Jamura khal originates west of Salbanpur and flows eastward to meet the plainland at Gabtali. The Chandri khal originates north of Jamura khal and flows southeast up to Noapara. Because of the higher elevation of the western side, most of the rainfall channels flow east.
Landform units the area can be divided into three geomorphic units. From the east, they are: Lalmai deltaic plain, Chandina deltaic plain and Meghna floodplain. A deltaic plain is a level or nearly level plain surface composing the land ward part of a large delta.
Lalmai deltaic plain extends from Sahaji Bazar in the north to Dattasar in the south. It skirts the western slope of the Tripura Hills. It is mostly formed of Pleistocene (2 million years to 0.1 million years before present) Madhupur Clay that unconformably overlies the tilted Dupi Tila formation. The Madhupur clay consists of reddish brown and yellowish brown clay and sandy clay. In places, it contains ferruginous nodules. The formation is unconsolidated and flat. The pattern of drainage that has developed in the unit is dendritic.
Chandina deltaic plain generally level land that lies between the uplifted Lalmai deltaic plain and the Meghna floodplain. It is made up of silt, silty loam, silty clay and clay and has been named the Chandina formation. The sediments are similar to the recent Meghna floodplain deposits except for being comparatively more compact and oxidised. The drainage pattern is characterised by meander scars, meander scrolls, old levees, oxbow lakes, now mostly filled in. The Chandina deltaic plain was designated the tippera surface by Morgan and McIntire. Some authors believe it is a floodplain long abandoned by the flowing rivers. The original levee and basin landscapes have almost been smoothed out by erosion and deposition into a plain of very low relief.
Meghna floodplain the Meghna floodplain is the result of the present-day building process by the mighty meghna river and its tributaries. The Meghna mostly meanders but braids in places. The scenery is of a vast plain criss-crossed by the many streams of the Meghna, merging and branching and building out channel bars, meander bars and levees. The material laid is mostly silt, sand, and clay.
Geology the Lalmai-Mainamati hill range and its adjoining areas are situated on the western fringe of the folded flank of the Bengal Foredeep. The Lalmai-Mainamati anticline is delineated on the east by the Comilla syncline and the Tichna anticline, the Daudkandi and Kachua anticlines on the west, the Begumganj anticline on the south and the Rokhia anticline on the north. All these folds are at the sub-surface and they may be quieter expressions of the tremendous tectonic activity during the Himalayan movements.
The major structure in the Lalmai area is a doubly plunging asymmetrical anticline trending NNW-SSE. A significantly straight scarp on the western side of the hill range indicates the presence of a fault.
The Lalmai-Mainamati Hill range is mostly composed of poorly consolidated sandstone. A thin layer of reddish, highly oxidised, mottled clay acts as a capping. Occasionally clayey sand and sandy shale with subordinate gravel are present. The mottled clay layer is present only in the topographically higher places and is absent in the valleys. No fossil could be traced. M Abu Bakr divided the exposed sediments of the locality, in order of age, into the Chandina Formation (Recent), the Madhupur Clay Formation (Pleistocene) and the Dupi Tila Formation (Pliocene). [Sifatul Quader Chowdhury]