Surface Water
Potential of Cyclonic Storms in Bay of Bengal
Dr. J. V. M. Naidu
(Lecture at the International Conference on
Storms (Brisbane 5 – 9 July 2004) being organized by World Meteorological
Organization and the Australian Meteorological Services.)
Cyclonic
storms are the wide synoptic systems, which give extensive rainfall in a few
days time in the maritime states. The run off is the maximum in the Post
monsoon cyclonic storms. Occurrence of the Cyclonic storms during the post
monsoon season helps in mitigating drought and heat wave deaths during the
subsequent summer. However in spite of these advantages little efforts are made
to manage this high quantity of surface water in view of the high variability
in rainfall distribution. Followed by southwest monsoon during June to
September months the soil is complete charged with moisture to give maximum
surface flood flows, which can be diverted to fill the reservoirs or tanks.
In South Indian plateau from the catchments of the rivers
like Mahanadi, Godavari, Krishna and Cauvery the thousands of cubic meter of
water is discharged into Bay of Bengal as surplus flows. In 1987, the country experienced a massive
drought with a record deficiency of country’s seasonal rainfall of southwest
monsoon season by 19%. During this period coastal Andhra Pradesh experienced a
severe deficit of 30% rainfall. However, followed by this in October and
November three cyclonic storms crossed coastal Andhra Pradesh giving extensive
rainfall. Similarly, there had been few more years like 1996, 1998, and 2003
with cyclonic storms or depressions crossing coastal Andhra Pradesh giving
extensive rainfalls.
A study of Cyclones and Depressions, which crossed east
coast of India below 20O N latitude for the period 1976 to 2003, is carried out. The system normally
gives more than 50 TMC of rainwater but depends on the duration of the storm
movement, the arial distribution of the convective activity and the track of
the storm. When the systems move parallel to the coast several districts get
intense rainfalls which when properly managed can be stored and used for the
agriculture. The highest rainfalls during 1990 cyclone that crossed near
Machilipatnam had given an estimated water of 900 TMC over coastal Andhra
Pradesh. Even for a low intensity cyclone or a depression an average of about
100 TMC can be obtained as rain. Assuming a loss of 50% due to several losses
including percolation and evaporation, the balance water can be properly stored
in reservoirs. In the light of each TMC of water capable to give a crop worth
of US $ 3 million these flood flows which occur in a few days time can be
properly harnessed by building the reservoirs across the coastal rivers for
optimum utilization of disastrous flood flows of the cyclone and for taking up
flood mitigation measures. Some of these features are discussed so as to plan
for the optimum utilization water resources.
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