Flood Management

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.