Flood Management

In South Bengal:

There are certain distinctive features of drainage condition which give rise to flood situation in south Bengal. The flood in this zone becomes voluminous because of the shape of the catchment area, its steep slope starting from a high-level plateau area and sloping sharply down to a flat terrain near the outfall of limited capacity. This feature is again adversely affected by tidal conditions as is generally noticed in the month of September, the likely month of occurrence of flood.

Basin-wise there are quite a number of river systems on the right bank of the river Bhagirathi-Hooghly like Pagla-Bansloi, Dwarka-Brahmani, Mayurakshi Babla and Ajoy. These rivers together drain out flood water from an area of 18,177 sq. km, spread over the State of Jharkhand (i.e., Chotanagpur Plateau) and the districts of Birbhum, western part of Murshidabad, Purba & Paschim Bardhaman, and finally outfall into river Bhagirathi. Carrying capacity of the river Bhagirathi is only 25% of the combined peak flood discharges generated from these basins because of simultaneous heavy rainfall, as it occurred during the flood of September 2000. In this vast tract of land there is one major reservoir, that is, Massanjore Dam over river Mayurakshi which interferes the flood discharge of only 11% of aforesaid combined catchments.

On the left bank of the Bhagirathi River system the Bhairab-Jalangi Sealmari group of rivers originate from Ganga-Padma at Akherigunj in Murshidabad district and meet the Bhagirathi at Swarupgunj in Nadia District. This system of rivers between them drains a total area of 2,537 sq. km. of Murshidabad and Nadia districts. Generally, this area suffers from flood because of three reasons – (i) high intensity rainfall in the basin area itself (ii) inflow of flood water from Ganga-Padma at its high spate and (iii) drainage congestion at its outfall because of high stage of river Bhagirathi during high tide.

In the Damodar-Barakar River system, the rivers originate at Chotanagpur plateau of Jharkhand and flows down the plains of West Bengal to outfall into the Rupnarayan-Hooghly system through two channels namely Mundeswari and Amta Channel. The catchment area up to Durgapur Barrage is 18,026 sq. km. as against total catchment of 24,341 sq. km. In this catchment area there are only 4 (four) reservoirs having a storage capacity of 1.21 BCM. The original concept of flood storage was to have an area reserved for storing a volume of 3.58 BCM. Thus, with this limited flood storage capacity the storage dams at present can modify only the peak flood discharge. Any discharge above 70,000 cusecs downstream of Durgapur barrage may cause flood depending on the outfall condition of the Mundeswari at Harinkhola.

The Shilabati-Darakeswar and Kangsabati-Kaliaghai river systems which have combined catchment areas of 16,938 sq. km spread out in the districts of Purulia, Bankura, Jhargram, Paschim and Purba Medinipur outfall into river Rupnarayan and Haldi respectively which finally meet river Hooghly. The Kangsabati-Kumari dam at Mukutmanipur, Bankura intercepts flood discharge of only 22% of the aforesaid combined catchment area. In this basin spillway discharge from Kangsabati dam above 50,000 cusecs may cause flood at lower reaches downstream of Mohanpur Anicut near Midnapore Town depending on tidal condition of the outfall and rainfall in the uncontrolled catchment downstream of Kangsabati dam.

The Mathabhanga-Churni-Ichamati system of rivers originate at the Mathabhanga off-taking from Ganga-Padma downstream of Farakka Barrage in Bangladesh and on reaching West Bengal at Majdia in Nadia district, bifurcates in two branches (i) the Churni flowing on South-Westerly direction meeting the Bhagirathi at Ranaghat and (ii) the other branch namely, the Ichamati flowing on South-Easterly direction to meet Bay of Bengal through the creek of Raimangal. The main flood situation in this area arises because of inflow from Ganga-Padma (when it rules high), rainfall in the own catchment area and also tide lockage. In 2000 flood, a very unusual situation arose where the Bhagirathi transferred a large volume of its floodwater to this basin area by breaching its embankments at several places.

Index map of river system in North Bengal and South Bengal is presented below. The inventories of rivers, tributaries, branch channels within the sub basins have been presented in Annexure-I.

Flood Management Programmes

In view of its geographical location at the tail end of the Ganga Basin and several other Himalayan rivers, the problem of flood management and drainage in the State is quite acute. Several committees have examined the problem and suggested the remedial measures at different times. These are being implemented in stages since the year 1954. The measures generally implemented are the embankments and river training works, improvement of drainage systems, providing flood storage in reservoirs, construction of multi-purpose reservoirs etc.

The State had taken measures mentioned above which resulted in providing a reasonable degree of protection to an area of 2.077 m.ha. out of a total flood prone area of 3.816 m.ha. the important storage projects which are giving benefits by virtue of flood storage specifically provided in the dams, are the D.V.C. system of reservoirs and in a limited way the Kangshabati reservoir. The flood storage is not fully available for moderation as the acquisition of land between the FRL & MWL in the Panchet and Maithon Reservoirs of the DVC system has not been made due to various factors. A committee was set up to examine this aspect and it submitted its report. Inspite of this lacuna, the flood cushion available in the two reservoirs has helped in reducing the effect of flood intensity in the lower reaches in most of the years in the past.