The floods of West Bengal have exceptional peculiarity. Though heavy rainfall in this state cause flood, yet these areas are mainly lying outside this state. The West Bengal is flooded by water from adjoining states or countries.
Northern region of the states are mainly affected due to heavy rainfall, discharge of upper basic areas and also outfall condition in the neighboring countries. North and South Dinajpur area including Malda are affected by the stagnated condition of the Mahananda river due to the Ganges upstream and downstream of Farakka Barrage rules where it’s not allowing draining of flood discharge during monsoon. The Ganges, forming the southern boundary of the district, brings flood water from eleven states and Nepal. The Districts affected by flood in northern region of the state are Cooch Behar, Jalpaiguri, North Dinajpur, South Dinajpur, Malda and relatively affected Darjeeling.
The area of Bhagirathi-Hoogly basin is getting flood affected due to high rainfall and limited carrying capacity of the river Bhagirathi. In this vast tract of land there is only the Massanjore dam to interfere with the natural flow of flood water. Delay in drainage causes more accumulation resulting in spread of flood in the upstream of the river system in the west and beyond Berhampur.
The basin of river Damodar has about 70% of its basin just upstream of Durgapur town. This upper catchments of Jharkhand plateau, above Durgapur, generates heavy run-off during high rainfall and is carried to Durgapur in a short time. Any major discharge along the downstream of Durgapur Barrage may cause flood depending upon the outfall condition of the Mundeswari at Harinkhola. In Kangsabati river system, the Kangsabati Dam has a limited flood storage capacity which is very nominal. Any major spillway discharge from Kangsabati Dam may cause flood at lower areas downstream of Midnapore town depending on tide and downstream rainfall.
The district affected in southern region of the state are Nadia, Howrah, Murshidabad, North 24 Parganas, South 24 Parganas, Hooghly, Burdwan, Birbhum, West Midnapore, East Midnapore and relatively affect Purilia and Bankura.