River dynamics and flood hazard with special reference to the Kosi River

IHRR Research Brief No 1

Report: Workshop on ‘River dynamics and flood hazard assessment with special reference to the Kosi River’ 23 March 2011, Patna, India Published by the Institute of Hazard, Risk and Resilience, Durham University 2011

Background and Objective A major project on river dynamics and hazard assessment has been funded by UKIERI (UK-India Education and Research Initiative) and is being executed by IIT Kanpur and Durham University. One of the major objectives of this project has been to understand the causative factors of widespread flooding in the Gangetic plains, and as part of this we have chosen to study the Kosi River draining parts of north Bihar and Nepal. The Kosi River in the north Bihar plains is a major tributary to the Ganga River system and has long been considered as a problematic river due to recurrent and extensive flooding and frequent changes in its course. The year 2008 witnessed one of the greatest river disasters in recent history when the Kosi River shifted by ~120 kilometers eastward, triggered by the breach of the eastern afflux bund at Kusaha in southern Nepal. This breach resulted in flooding of a very large area in Nepal and north Bihar and more than 3 million people were affected by this disaster.

Our UKIERI-funded research has specifically examined the role of sediment flux on flood risk in the Kosi River. The Kosi carries a very high sediment load and the construction of embankments and barrages had resulted in the rise of river bed level, so that the river has been flowing in a ‘super-elevated’ condition at several reaches – in other words, the bed elevation is higher than the elevation of the surrounding plains. As such, the river was close to its avulsion threshold at several places and this, combined with poor maintenance of the embankments, led eventually to the disaster of August 2008. Flood management strategies in the Kosi River have largely focused on embankments, and the controls of geomorphology and sediment flux have not been suitably incorporated in such programmes.

A workshop on ‘River dynamics and flood hazard assessment with special reference to the Kosi River’ was organized on 23 March 2011 in Patna as a part of the UKIERI project. The objective was to impress upon river management authorities and stakeholders the need to incorporate geomorphic considerations in designing long-term solutions for river management, and to educate the local communities towards adaptive strategies for river management. A list of participants in the workshop and the programme are provided in Annexure I and II respectively.

Workshop proceedings The inaugural session of the workshop was presided over by Mr Anil Sinha, Vice-Chairman of

the Bihar State Disaster Management Authority (BSDMA), and Mr Prataya Amrit, Secretary of Road Construction, Government of Bihar, Prof. Rajiv Sinha (IIT Kanpur) and Dr Alexander Densmore (Durham University, UK) provided the overview of the research project and a summary of the important issues related to river dynamics and flooding of the Kosi River. Mr. Anil Sinha summarized the activities of BSDMA which is currently focusing on reducing the impact of disasters on the people of Bihar and developing strategies for better disaster risk reduction.

Subsequent efforts will focus on the causal factors of disasters and better techniques for their management.

Mr. Prataya Amrit emphasized the need for integrating infrastructure development with river management in such as way that development does not become a disaster in the long run.

The other participants in the workshop included Mr. R.C. Jha (Member, RM, Central Water Commission), Prof. A. S. Arya (former professor at IIT Roorkee), Mr. J.R.K. Rao (Commissioner, Kosi Commission), Mr. A. K. Ganju (Chairman, Ganga Flood Control Commission), Prof.

Malay Mukul (IIT Bombay), Dr. Vikrant Jain (Delhi University) and several leading persons from academia, NGOs and the public sector such as USAID. Throughout the workshop, it was emphasized that the problem of Kosi flooding is a problem of sediment. Any solution which can deal with the sediment that the river supplies to the plains of Bihar will also address the issue of unexpected and catastrophic shifts in the river, as occurred in 2008. This means that hard engineering solutions, such as the barrage and embankment scheme, are doomed to fail in the face of such a geomorphically active and dynamic river system. Participants in the workshop emphasized the need to work with the river to allow some degree of dynamic behaviour, but in a way that does not compromise the people and communities on the fan.

The group proposed a low-cost and sustainable approach that has been developed together with NGOs and flood activists and researchers in Bihar. They called for breaches to be made and maintained in the embankments that line the river, so that controlled flows of water and sediment can be released down old channels on the Kosi River fan – channels that are past river courses of the Kosi, and which are thus already capable of carrying large flows. By allowing controlled releases of sediment and water during high flows of the Kosi, at levels which can be adequately conveyed by each of the old channels, the uncontrolled and catastrophic shift of the river system could be avoided. This approach would also decrease pressure on the existing flood defenses, which must be maintained and rebuilt almost yearly at great cost, and this expenditure, the flood defences have not prevented breaching and widespread flooding since their construction in 1953. The group also noted that NGO and community groups have long argued against the existing flood defense scheme and have asked for greater access to water resources, which would be provided by the proposed controlled releases.

Recommendations The specific recommendations that emerged from the discussion are as follows: 1. Workshop participants felt that the intentions of the Kosi project for water management and flood control may have been good, but that it is time for a socio-economic audit of the project to assess the long-term benefits accrued against the costs and adverse impacts. It is important to recognize the flaws in design and implementation strategy and the changed boundary conditions to evaluate the present utility of the project.

2. The embankments are not a sustainable long-term solution to Kosi River flood control due to their inherent disturbance of the natural equilibrium of the river system and the high costs of maintenance. The high sediment flux of the Kosi has resulted in a rise of the river bed over the years and repeated failures of the embankments during the last 3-4 decades, indicating that the embankment strategy have not proved to be effective.

3. At the same time, the current embankments cannot be demolished because a large population now lives close to the embankments and a number of later infrastructure projects are reliant on their existence. However, they need to be maintained properly and a pilot channel away from the embankment must also be maintained. Furthermore, the construction of new embankments for flood control/management must be completely avoided and alternative solutions must be sought.

4. It must be recognized that the embankments along with rail-road network in the Kosi region have also caused severe drainage congestion resulting in a much longer period of inundation and extensive waterlogging. Immediate steps must be taken to (1) identify the extent of the worst-affected areas and (2) work directly with the Government of Bihar on reinstatement of drainage pathways to clear flood waters.

5. Alternative approaches to flood management must be based on technical knowledge which should be translated into an action plan.

6. The paleochannels on the Kosi fan area may provide an effective solution to dissipate and distribute the excess discharge during high flows. If these paleochannels can be reactivated by connecting them to the main channel using regulation structures and can be maintained as natural channels, this will allow both water and sediments to be distributed across a large area and would reduce the flood risk as well as the siltation of the Kosi river. Some research and surveying will be necessary to identify the potential paleochannels for this purpose and to compute the flows which they can carry.

7. Use of modern technologies such as remote sensing and GIS, GPS-based surveys and echo sounding for river bed and floodplain mapping must be adopted on a routine basis and the database should be continuously updated.

8. The structure of BSDMA and district level disaster management offices must be strengthened and exploited more fully for flood management in Bihar and Kosi in particular. The BSDMA should work towards flood risk evaluation and risk reduction in partnership with academic institutions and governmental agencies, as well as with existing local and regional NGOs. 9. The role of community participation in evolving flood management schemes was strongly emphasized. The voices of people for whom the schemes are designed must be heard. It would be useful to involve the Gram Panchayats in this process which are the most organized and democratically elected bodies at village level.

10. It is also important to focus on developing resilience to floods at individual, community, district and state levels, following the age-old concept of ‘living with floods’. Most policy makers around the world have now realized that floods cannot be fully controlled and in fact low intensity, regular floods provide more advantages than damages.