YOJANA, July 2016
(Ministry of Information & Broadcasting )
Flood Management: Need for Storage Dams.
M.S.Menon.
India which has 16% of the world’s population, has roughly 4 % of the world’s
water resources and 2.45% of the world’s
land area. Even in the distribution of the available fresh water
resources in the country there are great variations in space and time ie.,
between different parts of the country and in different periods in a year. The
challenges faced by the water sector in the country are many, such as – the challenge to feed a
growing population; challenge to meet their growing aspirations for a better
life; challenge to control the floods and droughts occurring every year
devastating lives and habitats; and the challenge to ensure sustainable growth
process balancing a delicate environmental and ecological system.
Problems of floods and droughts.
The Indian land mass receives on an average about
4000billion cubic metres (BCM) of precipitation and the average annual flow in
the rivers is estimated as 1953 BCM, the balance being lost to immediate
evaporation and soil moisture. Two thirds of the water resources is contributed
by the Ganga-Brahmaputhra-Meghna (GBM) rivers basin covering one third of the
geographical area of the country. Consequently, the remaining parts have to be
satisfied with the balance resource. Also,over 80to 90% of the run-off in the
Indian rivers occur in the 4 monsoon months of June to September resulting in
creating regions of harmful abundance of water during the monsoons and acute
scarcity in summer. With such a wayward and changing nature, we have to adapt
or compensate for these changes to survive. Since a few months account for most
of the year’s rainfall and consequent water availability, the ability to hold
water in reservoirs and spread out its release over the year can mean the
difference between devastating floods and droughts.
Due to its vastness, diverse relief features and
geographical locations, different regions of the country have varied climates
and rainfall patterns. It is not therefore uncommon to find one part of the
country under the grip of severe floods while another part suffering under the
effects of drought. Many a times it so happens that even in the same year in a state, some areas
have excessive rains and consequent floods while some other areas suffer due to
poor rainfall and consequent drought. Thus, the main characteristic of India’s
water resources is its uneven distribution in space and time leading to endemic
and sporadic problems of water shortages and excesses.
Further, the problems
during floods get compounded due to human interventions in the river basins.
Consequently, the upper catchments of a river are getting degraded bringing more sediments down causing
greater severity of floods and the activities of those encroached and settled
in the flood plains downstream result in the loss of lives and property of
inhabitants there.
Frequent occurrence of floods and droughts is a reflection
of our failure to develop and manage our water resources. Needless to say
that water, a key element in our
ecosystem, is not getting enough attention except when droughts stalk the
country side and floods devastate large tracts of land and habitats. Even then
, instead of learning from the failures
and taking recourse to obvious and available solutions, the issues are
forgotten after providing some relief to
the affected people till the next year when the problems again arise.
Past attempts in flood control and management.
The need for flood management was felt in the early fiftees
and a National Flood Management Programme was launched in 1954(1).The area
provided with flood protection then was about 3 million hectares(Mha), with a
total length of embankments of around 6000kms. As per the policy statement made
in 1954, the objective set before
the Nation was to rid the country from
the menace of floods by containing and managing the floods. However, it was
realised later that absolute immunity from flood damage was not physically possible because of
the unpredictability of several events which occur along with worsening
situations rendered by manmade activities. Hence it was decided then to provide
reasonable protection measures which were found technically feasible and
economically justifiable and to lay greater stress on flood forecasting, flood
warning etc. along with flood management.
A number of National and State level committees were set up
subsequently to study the issues and ultimately in 1976 a Rashtreeya Barh Ayog
(RBA) was set up(2) by the Government of India to review and evaluate the flood protection
measures undertaken since1954 and to evolve a comprehensive approach to the
problem of floods as a part of optimum and multipurpose utilisation of water
resources and suggest improvements wherever necessary. Area liable to floods
was assessed at 34Mha. at the time of RBA when reasonable protection was
already provided to an area of 10 Mha. The major concentration of the flood
prone areas was found to be in the Ganga-Brahmaputhra-Meghna rivers basin and
in the coastal deltas of the Peninsular rivers. Major recommendations made by
RBA include flood plain zoning and management to regulate man made activities
since periodic displacement and rehabilitation of people from the flood plains
during floods had become a common feature
Subsequently, the Centre had set up Regional Task Forces in 1996 to review the
impact of the recommendations of the RBA and to suggest short term and long
term measures etc. Their recommendations included (3) ,among other
administrative measures, construction of large flood moderation projects,
particularly in the North-East and following up the Enactment of Flood Plain
Zoning Act so as to tackle encroachment
by people in the flood plains.
The National Commission for Water Resources, in 1999 (4),
had also observed that storage dams and embankments provided effective
protection to large flood prone areas. The Commission had also suggested the
urgent need to enact Flood Plain Zoning Act to prevent human interventions in
the flood plains.
In 2004,unprecedented floods in the Ganga and Brahmaputhra
rivers necessitated the Centre to constitute a Task Force(TF) to suggest
remedial measures. The Task Force had
recommended more involvement by the Centre to make flood management efforts
effective. The Working Group of the Planning Commission then had also
emphasised the need for Central involvement
and for setting up a Central Flood Management Organisation.
The National Water Policy , 2012, (5) had suggested that reservoir operation procedures should be
evolved and implemented in such a manner so as to have flood cushion and to
reduce trapping of sediments during flood season. It has also suggested to
incorporate coping strategies for possible climate changes, such as increasing
water storage capacity in dams.
Flood damage mitigation works.
Damage due to floods is mainly caused by the spilling of the river over its banks
and inundating the marginal areas along the rivers. For reducing the
damage, protective measures to be taken
include structural measures such as storage dams to absorb and regulate the
flood flows; and construction of embankments to confine the flows thereby
preventing spilling. Channel improvement works and works for improving the
drainage conditions in the area are also required to be carried out to address
flood conditions caused by such situations. Wherever construction of embankment
is not desirable due to acute drainage problems that would arise, schemes for
raising such villages and connecting them to the nearby roads are also being
implemented.
Flood control measures were taken up in a big way after the
National Flood Control Programme was launched
in 1954. Since then, more than 35000 kms. of embankments have been constructed
and more than39000kms. of drainage channels improved. Also over 7000 villages have
been raised and protected and likewise protection works extended to more
than2700 towns/villages. A number of storage reservoirs have also been
constructed during this period which have a total live capacity of about 250
BCM. (6).
Flood control and moderation by storage dams.
In the case of storage dams planned for flood control, the
planning would be to maintain a low reservoir level during high flow months and
use the storage capacity to absorb the incoming flood peaks. Soon after a peak
passes down, the reservoir is brought down at a controlled rate to the low level to be ready to face the next flood.
However, such projects only meant for
serving flood moderation would not be usually economically justifiable.
On the other hand, multipurpose projects for irrigation and power benefits could be
planned to also include flood moderation benefits as well. If irrigation and
power alone were the primary objectives, the endeavour would be to ensure a
full reservoir level by the end of the filling period (September). In the case
of projects planned for multiple benefits which include flood moderation, the
attempt would be to seek the optimum combination of possible benefits through
the planned operation of the reservoir, keeping in mind the declared purposes
and intended benefits.. Hence a rational economic solution to the problem of
floods during monsoons is to link it
with the water demands for irrigation,
power and other uses during the non -monsoon months. Thus ,a n irrigation and
hydropower scheme could be made to provide flood moderation during the high
flow period and meet various needs by drawing upon the stored water till the
onset of the next monsoon .
When a multipurpose project reservoir is called upon to serve
the flood moderation aspect, planned or unplanned, the operating authority is
often faced with a difficult choice, particularly when the incoming flood peak occurs towards the end of the
filling season. If the high reservoir level is
brought down based on inflow forecasts and best judgment, the authority
could be still criticised if the reservoir did not fill up later, leading to
short falls in meeting the needs. The authority risks equal criticism if the
reservoir level is not sufficiently
lowered to absorb the incoming peak
which would result in flood damages lower down .Self appointed activists
against large dams could then quote such instances as man made floods to attack
the water professionals. There have been
many such cases where the authorities were called upon to explain such situations in the dam projects.
Major projects providing flood control benefits.
Flood control measures were taken up in a big way after the
National Flood Control Programme was launched in 1954. Since then, apart from
construction of embankments, improvement of river channels etc., many storage
reservoirs were also constructed which could absorb and regulate peak floods
when necessary. However, as of now, we have been able to hold back only a
little more than 10% of the annually
available monsoon flows. Due to many issues, environmental, socio-economic and
others coming in the way of executing water resources development projects, the
progress in constructing storage projects has been slow in the country since
last few decades with the result that we are still facing the water woes
resulting from floods and droughts.
Some such major
projects completed after the National Programme was launched in 1954 which
provided flood control benefits are the
dams of the Damaodar valley corporation (DVC), the Hirakud dam on the Mahanadi,
Ukai dam on the Tapi, and the Bhakra dam across the Sutlej. Some salient
features of these projects are discussed as under. Major flood flows could be
absorbed and discharges from the dams regulated by these projects to provide safety for the
downstream villages and towns. However, when major floods arrive infrequently ,
such as in a period of 1 in 25
years etc., flood damages did
occur inhuman settlements in encroached flood zones largely on the river banks and
sometimes even in the main river channel , due to release of regulated
discharges from the dam into the river
channel below, necessitated by dam safety considerations. Enactment of the
Flood Plain Zoning Act is the only way to control such situations .
Hirakud dam.
This is a major earth cum masonry dam constructed in 1957
across the Mahanadi river and has a live storage capacity of 5222 million cubic
metre(mcm). The full storage is used for moderating floods during the monsoon
and thereafter the stored waters are utilised for irrigation and generating
power. Prior to the construction of the dam, the Mahanadi delta used to be
ravaged by floods almost every year.
Dams under the Damodar Valley Corporation .
A series of 4 dams have been constructed on the Damodar and
Barkar rivers for the moderation of
floods and also for irrigation and power benefits . The four dams, namely,
Konar, Maithon, Panchet and Tilaiya have
a flood storage of 1603mcm.and have been in operation since 1958. These could
considerably moderate floods in the lower Damodar region, even though the
Maithon and Panchet dams are operating
at less than the designed cushion for flood control .
Ukai dam.
The Ukai dam on the Tapi, completed in 1977 has a live storage of 6615mcm. It has, to a great extent,
reduced the flood havoc in the lower reaches and has saved the Surat town from
flood ravages. The project confers other benefits also, such as irrigation and
power generation.
Bhakra dam
When Bhakra was planned on the Sutlej river, great emphasis
was laid on drought management in the region and thus irrigation benefit was
the main consideration while flood
issues were not important. However, the fairly large storage of 7190 mcm. was
always utilised in such a manner as to render flood moderation benefit for
downstream reaches. After the commissioning of the dam in 1963, floods in the
first few years of its operation were
absorbed in the reservoir. As 65%of the catchment of the river lies in Tibet
(China), often information about flash floods originating upstream does not
reach areas downstream till the flood itself arrives. The worst such flood
occurred in the year2000 when the water level of the Sutlej river rose by
15metres due to flash flood resulting from a cloud burst and temporary blockage
of river in Tibet. Though areas upstream of Bhakra dam were affected by the
flood, it was fully absorbed and evened
out when it impinged on the reservoir, thereby
preventing downstream devastation in Punjab plains.
In the recent past, major projects like the Tehri hydro
–project in the Bhagirathi (Ganga), could reduce the flood damages in Rishikesh
and Haridwar caused by flash floods in
the Uttarakhand region. The dam absorbed and regulated the unprecedented flood
flows of 2.5 lakh cusecs which hit the reservoir and released only less than 7%
of the flood flows into the downstream
river channel. Likewise, Sardar Sarovar Project on the Narmada river has also been able to
reduce the flood ravages downstream by
regulating the flood flows.
In this connection, the
Indian River Linking (IRL) project which envisages construction of
storage dams and a network of canal systems across the country to divert the
flood waters of the Brahmaputhra and
other major rivers to water deficit areas for equitable distribution and
optimum utilisation of water, is an important avilable option to reduce the
miseries of floods and droughts visiting the country frequently.
Conclusions.
To conclude, it is
feasible in most cases to provide a certain degree of protection against
floods in terms of reduced frequency and flood damages by having storage dams across major rivers
which would be able to absorb the peak floods and regulate the flows downstream
into river channels. The proposed IRL project would be an available option to
address the problems caused by devastating floods. However, there are no
universal solutions which can provide complete protection against floods. Hence
apart from storage dams, the country has also to focus its strategy to have
efficient management of flood plains, flood proofing including disaster
preparedness and response planning including flood forecasting and warning and
other non structural measures such as disaster relief, flood insurance etc. to
mitigate the miseries caused by floods.
Reading:
1.Dr.K.L.Rao : India’s Water Wealth- Orient longman limited,
1975.
2. Ministry of Water Resources: Report of the Rashtreeya
Barh Ayog, 1980.
3.Ministry of Water Resources: Reports of Task Forces on
Flood Management, 1997.
4.Ministry of Water Resources: Report of the National
Commission for Integrated Water Resources Development plan, 1999.
5.Ministry of Water Resources: National Water Policy, 2012.
6. Central Water Commission: Water Resources at a Glance,
2016.
