Major contributing factors to flood in North Bengal regions
are the run-off because of heavy local rainfall, discharge of upper basin areas and also
outfall condition in the neighbouring countries. The Mahananda and most of the rivers of
Uttar and Dakshin Dinajpur districts get stagnated when the Ganga upstream and downstream
of Farakka Barrage rules high thereby not allowing drainage of flood discharge during that
period.In other sub-basin areas of the Bhagirathi-Hooghly there are
certain distinctive features of drainage condition which give rise to flood situation.
| +++
---------------------------------------------------------------------------------------------------------- |
 |
|
|
| +++
---------------------------------------------------------------------------------------------------------- |
Basin-wise there are quite a number of rivers on the
West bank of the Bhagirathi-Hooghly, these are Pagla-Bansloi, the Dwarka-Bramhani,
the Mayurakshi-Babla-Uttarasan, the Bakreswar-Kuye and
also the Ajoy. These rivers between them drain an area of 17,684 sq. km,
spread over the state of Jharkhand (the old Bihar Plateau), and districts of Birbhum, part
of Murshidabad (west of Bhagirathi) and Burdwan. They generate flood because of high
rainfall in these basins and limited carrying capacity of the river Bhagirathi between the
towns of Jangipur to Kalna. In this reach the Bhagirathi has discharge carrying capacity
of maximum 1.1 lakh cusec. All these rivers if receive rainfall simultaneously in their
catchment areas can generate run-off volume of any amount between 4 to 6 lakh cusecs at
their outfall at the Bhagirathi, as it occurred during the flood of September 2000. In
this vast tract of land there is one structure which interferes with the natural flow of
flood water i.e. the Massanjore Dam. This dam, constructed for irrigation, intercepts
about 36.4% of the Sidheswari-NoonBeel-Mayurakshi basin area of 5109 sq. km. It can
discharge / generate only 16% of run-off that is likely to be generated in case of
simultaneous rainfall in these basins, west of the Bhagirathi, from the Pagla-Bansloi to
the Ajoy (including catchment of Ajoy). 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 condition as is generally noticed in the
month of September, the likely month of occurrence of flood. As it happens, the
contribution of dam discharge to the total flood volume is not much. The Massenjore Dam
cannot control any flood.
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 drain a total area of 4,300 sq. km of Murshidabad and Nadia districts. Generally this
area suffers from flood because of three reasons – (1) high intensity rainfall in the
basin area itself, (2) inflow of flood water from Ganga-Padma at its high spate and (3)
drainage congestion at its outfall because of high stage of the Bhagirathi.
In the Damodar-Barakar Basin System, the rivers
originate at Chotonagpur plateau and flows down the planes of West Bengal to meet the
Bhagirathi. The catchment area upto Durgapur Barrage is 18,026 sq. km as against total
catchment of 22,015 sq. km. In this catchment area there are only 4 (four) reservoirs
having a storage capacity of 1.21 lakh ha.m. The original concept of flood storage was to
have an area reserved for storing a volume of 3.58 lakh ha.m. 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 down stream of Durgapur Barrage may cause flood depending on
the outfall condition of the Mundeswari at Harinkhola.
In the Kangsabati River System which also meets the
Hooghly, the total basin area is 8,369 sq. km and it has 3,625 sq. km at the upstream of
the Kangsabati dam. The dam has a limited flood storage capacity of 29,170 ha.m. which is
very nominal. In this basin spillway discharge from Kangsabati dam above 50,000 cusecs may
cause flood at lower reaches downstream of Midnapur Town (anicut at Mohanpur) depending on
tide and downstream rainfall.
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 Majhdia, in Nadia district, bifurcates in two
branches – (1) the Churni flowing on South-Westerly direction meeting the Bhagirathi
at Ranaghat and (2) the other branch viz. 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 flood 2000 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.
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.
