Atrai Basin a small physiographic unit occupying a low-lying area where mixed sediments from the atrai and ganges and from the barind tract overlie the down-warped southern edge of the Barind Tract. The landscape north of the Atrai is mainly smooth, but floodplain ridges and extensive basins occur south of the river.
Heavy clay soils predominate, but loamy soils occur on ridges in the south and the west. Drainage from this unit is blocked when high river levels in the jamuna burden the exit through the hurasagar. Seasonal flooding was formerly deep, and extensive areas in chalan beel used to remain wet throughout the year. The construction of polders since 1960s has improved drainage to some extent. However, deep flooding can still occur within polders as well as outside when there is heavy rainfall locally and when flash floods flow down the Atrai or off the adjoining Barind Tract, causing natural or manmade breaches of embankments. [Jabed Kalim]