ICOLD Bulletin 156: Integrated Flood Risk Management
Floods are a potentially devastating natural hazard. The introduction to this International Commission of Large Dams (ICOLD) Bulletin describes how increasing wealth and population growth is putting pressure on floodplains for continual development. It further sets out how this, combined with an apparent trend for more frequent and intense rainfall events, makes it a complex and growing global issue.
The aim of integrated flood risk management (IFRM) is stated to take a balanced approach of accepting and mitigating flood risk while maximising the positive impacts of flooding on the floodplains. A relatively recent concept as a specific application of water resources management, it has mainly been applied in developed countries. The Bulletin discusses that while structural measures can be an efficient way of flood control, they are not always financially viable and may have environmental and societal impacts that need to be considered. Non-structural methods are described as ways in which society learns to live with the risk of flooding and should form part of a holistic flood management solution. Examples given include control of development, insurance, flood forecasting and evacuation plans.
This ICOLD Bulletin describes the fundamental knowledge needed for IFRM and gives guidance on the implementation strategy and design.
Chapter 2 describes the available methods to evaluate the magnitude of large floods and their characteristics. The need to take into account historical floods is emphasised.
Chapter 3 describes impacts and benefits of floods and gives an example of an economic analysis.
Chapter 4 describes current IFRM practices, introducing the concept of a stepwise approach to implementation. The five key steps are identified and discussed including understanding the current place within the risk management cycle.
The Bulletin further gives some useful case studies where the applicability of different methods to specific river basin characteristics have been studied.
The Kitakami River in Japan where five major dams were constructed as part of a solution following the devastating floods of 1947–1948. Asset values increased by more than four-fold from 1976 as area categorisation changed to non-inundation.
The Al Whada dam in Morocco (commissioned in 1996) where the need for multipurpose dams was explored (also provided irrigation, drinking water and electricity). This boosted social and economic development, greatly improving the safety in an area previously affected by devastating floods.
Minerve project in Switzerland synchronises the operation of existing dams with a sophisticated real-time system with hydrological and meteorological inputs to reduce flooding in the Rhone valley. This is a complex system involving artificial lowering of reservoirs and political and legal agreement from all owners. The modelled benefits are significant, reducing peak flood discharges by up to 34% (most effective for flood return periods that may vary between 50 and 100 years). Now implemented, early results compare well with modelled predictions.
The Bulletin provides useful insight into the current state of knowledge of IFRM. While a balance has to be found between structural and non-structural methods, there is clearly a role for dams as part of an integrated solution to flood management. The degree to which we need to learn to live with the impact of flooding will depend on a multitude of factors as is demonstrated with the diametrically opposed approaches of the Netherlands (exclude) and Bangladesh (adapt). The Bulletin also highlights the difficulties in managing public perceptions by looking at Saxony in Germany. There are limits to the size of a flood where effective mitigation is achievable, with small floods being reduced more than large ones.
Maximising the use of existing infrastructure through real-time monitoring and control systems is clearly an efficient method, but one that requires a sophisticated system and complex management arrangements. Implementation across international watersheds can also make agreement of multiple stakeholders difficult. When designing new structures, should future proofing be incorporated to increase flood resilience by considering the level of automation and capacity of drawdown facilities? The impact of rapid drawdown, which could otherwise be a limiting factor, could also be considered at an early stage.
