Session FT 5.16

Role of dams and reservoirs in Integrated Flood Management

 

 

Conveners

• Spanish National Committee on Large Dams (SPANCOLD-ICOLD)

To mitigate the flood impacts it is necessary the implementation of local actions whit the participation of all stakeholders. These actions should be considered with a holistic vision and inside the framework of Integrated Water Management. The local actions should consider all the measures and possible and viable actions, coordinating and implementing structural and non-structural actions jointly, with an Integrated Flood Management (IFM). IFM moves from the concept of flood control to that of flood mitigation, pointing out that it is impossible to fully protect against extreme floods, and that the risk of floods can never be reduced to zero. We must therefore learn to live with floods, reducing their impacts as much as possible. In IFM it is essential to have public participation, and the broadest involvement of all stakeholders. In the international basins regional cooperation is indispensable. The IFM process requires the allocation of financial resources.
The real cases show that dams and reservoirs are an action that could mitigate in great way the impacts produced by floods, since they are able to store significant flood volumes, and thus to reduce the peak flows.

 

Lessons learned

 

1. Natural disasters are a serious threat to life on Earth and to mankind’s sustainable development. Amongst natural hazards, floods are one of the most important categories of natural disasters. Floods are responsible for 30% of the total number of natural disasters, 30% of all economic damages, and for 20% of fatalities caused by natural disasters. Between 1975 and 2000, each year on average there were some 95 significant floods, which caused about 11,000 fatalities, and affected around 150 M people per year.
2. Actions and measures to mitigate the impact of floods should be formulated inside the Integrated Flood Management (IFM). The IFM approach is more realistic, more critical and less optimistic. In flood management an integrated approach should be applied both at basin level and in deciding the type of actions and measures. When assessing alternatives in flood mitigation all possible and feasible alternatives must be considered and implemented jointly and co-ordinately, both structural and non-structural measures. IFM moves from the concept of flood control to that of flood mitigation, pointing out that it is impossible to fully protect against extreme floods, and that the risk of floods can never be reduced to zero. We must therefore learn to live with floods, reducing their impacts as much as possible. In IFM it is essential to have public participation, and the broadest involvement of all stakeholders. In the international basins regional cooperation is indispensable. The IFM process requires the allocation of financial resources.
3. Dams and reservoirs must be considered an effective alternative within the IFM framework, especially in those cases in which there are extensive settlements in the floodplains which make it difficult or impossible to apply some non-structural measures and to modify or restrict land use patterns. Dams and reservoirs constitute a very effective structural measure, since they are able to store large flood volumes, modify flood routing, and significantly reduce peak flows.

 

Key messages

 

1. The increase in the world population, economic growth and intense urban development in flood-prone areas has caused a major increase in the impacts and economic damage caused by floods. Current assessments estimate that one billion people live in the potential path of floods with a 100-year return period. Two billion people could be vulnerable to floods by 2050.
2. A holistic approach and integrated perspectives must urgently be applied, and effective Integrated Flood Management policies must be developed. In assessing flood mitigation options all the possible and feasible alternatives must be considered and implemented jointly and in a coordinated way, including structural and non-structural measures
   
3. Increasing investments in structural measures and non-structural is necessary to achieve “water security” i.e. coping with too much or too little water. The strategy should also incorporate non-structural measures, working with nature, and include coping with risks. Dams and reservoirs should be considered as one of the effective infrastructure elements in flood risk management, and must be developed in an economically, socially, and environmentally just and sustainable way.
4. The international development and financial institutions should focus more on disaster-risk reduction and move from response to preparedness to risks.
5. Some of the current problems and crises involving floods may be attributed to greater climate variability. It is likely that in the future, global warming will increase the intensity and frequency of flooding in most regions of the world, with a growing occurrence of extreme floods. Thus, new scenarios should be considered in the relationship between floods and dams. In general, it will be necessary to adapt to more frequent and severe floods, and in this context dams and reservoirs could play an important role in flood mitigation.

Orientations for action

 

1. The international community should agree on the global target “to halve the number of losses of human lives due to water related disaster by 2015”. They should likewise reduce the risk of floods for 50% of the people living in floodplains by 2015.
2. Governments should adopt Integrated Flood Management policies and strategies based on river basins, coordinating these with Integrated Water Resources Management policies.
3. Increasing investments in structural and non-structural measures is necessary to achieve “water security” The strategy should also incorporate the most effective non-structural measures, working with nature, and include coping with risks. Dams and reservoirs should be considered as one of the effective infrastructure elements in flood risk management, and must be developed in an economically, socially, and environmentally just and sustainable way.

 

Local Actions presented

Flood Management Plan in Segura River Basin.

M. URREA, Confederación Hidrográfica del Segura, Spain
 

Ya desde mediados del siglo XVI se conocen referencias sobre graves inundaciones en la cuenca del segura, que han continuado hasta fechas recientes. Inundaciones caracterizadas fundamentalmente por el carácter torrencial de las precipitaciones en el Mediterráneo, donde en escasamente 24 horas se producen precipitaciones que suponen un porcentaje muy elevado respecto al valor medio anual, ello hace que los caudales circulantes por los ríos y ramblas se incrementen enormemente en un corto espacio de tiempo. La defensa de las personas y los bienes han sido el objetivo directo de dicha acción. Por ello la Administración General del Estado ha acometido el denominado Plan de Defensa de Avenidas, que ha tenido que modularse a nivel de ejecución en función de las disponibilidades presupuestarias debiéndose realizar un ingente trabajo de ingeniería consistente en los estudios hidrológicos previos, redacción de los proyectos de recrecimiento de presas existentes, nuevas presas y encauzamientos de tramos del río Segura, actuaciones que han sido precisas según dichos estudios incluyendo ensayos en modelos reducidos. Socialmente ha habido aceptación ya que los beneficios sociales superan los costes sociales asociados.

 

Flood Management Strategy Study

X.CHENG,  China Institute of Water Resources and Hydropower Research, China

 

Flood management issues in China are getting more complex and difficult to undertake due to the huge population, the rapid process of urbanization, in harmonic economic development, vulnerable ecosystems, and increasing pressures on food and water supply. In order to ensure sustainable development in the 21st century, a series of difficulties and constraints should be coped with in establishing an advanced flood management system in China.