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Towards more effective floodplain management

Effective floodplain management, like watershed management, is an iterative process of identifying and assessing alternative ways of reducing the impact of floods (particularly of catastrophic events) in flood-prone areas. Decision-making in floodplain management involves compromises between the costs and benefits of alternative actions. It also requires that upper catchment areas be considered part of the solution and not as the ‘source’ of the problem.

What is floodplain management?

Floodplain management refers to all the actions society can take to responsibly, sustainably, and equitably manage the areas where floods occur and which serve to meet many different social, economic, natural resource and ecological needs. Since this includes reducing the hazard and suffering caused by floods, floodplain and flood management consist of many common activities. However, floodplain management recognises explicitly that other factors of a social, economic, natural resource management and ecological nature also have to be taken into account in "managing" floods.

From: Mekong River Commission, 2001

In the past, structural responses (e.g., dams, levees, dikes, etc.) were emphasised and, indeed, in the early- to mid-20th century engineers prevailed in debates over the best means to tame the awesome power of floodwaters. With ‘flood control’ as their explicit objective, engineers around the world spent decades (and billions of dollars) building dams, embankments and levees to prevent floodwaters from inundating floodplains. These structures were often combined with dredging to straighten and deepen stream channels. According to the World Commission on Dams (WCD 2000), some 13 per cent of all large dams, or over 3,000 worldwide, were built with a specific flood-mitigation function.

Most flood defences were built as individual local schemes, with little consideration of their impacts across the wider river catchment, their impacts on the aquatic and coastal environments or, indeed, even their broad economic impacts. The fact that embankments and other engineering structures were most effective only for small- to medium-sized flood events was often not recognised. Also, river, road and other embankments sometimes inhibited the discharge of rainwater from water-logged areas into the river system (particularly where the number of sluices in the embankments is insufficient) and accordingly increased the dimension of flooding.

Can floods be controlled?

"Flood control" is a common expression... But one cannot control floods; at best one can manage their detrimental effects. The words "flood control" are therefore not used in this report.

From: Mekong River Commission, 2001

The available water storage of a typical reservoir is generally much less than the volume of a major flood surge. Moreover, structural solutions often have spill-over effects, shifting problems from one location to the next. For example, emergency releases of water during periods of high rainfall can dramatically and dangerously increase water levels immediately downstream of dams.

Experiences with embankments in Bangladesh

The Brahmaputra embankments channel the flood waters of the river, preventing the river from overflowing. In 1987, however, this had serious consequences for the left, unembanked side of the river: The water spread out and inundated large areas, and erosion on the left river bank increased dramatically.

From: Hofer and Messerli 1997

It should be evident that individual flood alleviation schemes cannot be considered in isolation and that a solution in one part of a river basin may be detrimental for other areas further downstream. Recently, numerous restoration projects have been implemented to reverse the impacts of earlier engineering works such as the Rhine Action Plan on Flood Defence adopted in 1998 after major floods in 1993 and 1995 (Leentvaar 1999). Increasingly, management of flood risks is moving away from structural engineering solutions toward programmes that work with natural processes. The impetus for this shift came from a number of major destructive events over the last 50 years, including:

The new approach weighs alternative actions in floodplain management in the context of whether overall flood effects are positive or negative. Although attention is usually focused on the negative effects of floods, there are highly important positive effects that warrant recognition and consideration. Flooding in many low-lying areas in Asia is a vital element of the culture and economy of the people. Annual floods along many rivers carry fine sediments and nutrients that renew the fertility of the land and aquatic habitats, and the continuous flow of silt-bearing irrigation water helps control diseases in many areas. In a region where agriculture and fishing remain vitally important, the loss of these beneficial effects could potentially lead to unacceptable economic and social disruption. However, what is beneficial to some may inflict heavy economic costs upon others. The challenge is to balance costs and benefits.

The positive effects of flooding

During a normal flood [in Bangladesh] the fields are inundated and alluvial organic matter is deposited. Normal floods are necessary for important monsoon crops.

From: Hofer and Messerli 1997

New flood management approaches are steadily introducing or expanding the role of non-structural measures within integrated floodplain management programs. Key measures include the identification of natural storage areas, such as swamps and wetlands, where excess water can be directed and temporarily stored during periods of flooding. The World Commission on Dams (WCD 2000) categorises the components of an integrated approach to floodplain management according to those which reduce the scale of floods, those which isolate the threat of floods and those which increase people’s capacity to cope with floods (Table 2).

A similar approach is also evident in the Mekong River Commission’s (MRC 2001) promotion of ‘Integrated Floodplain Management’, which comprises a mix of four types of management measures. These reflect the flooding, flood risk and flood hazard characteristics of a particular floodplain, the specific social and economic needs of flood-prone communities, and the environmental and resource management policies for the floodplain.

Table 2: Complementary approaches of integrated flood management

Reducing the scale of floods

Isolating the threat of floods

Increasing people's coping capacity

Better catchment management
Controlling runoff
Detention basins
Protecting wetlands

Flood embankments
Flood proofing
Limiting floodplain development

Support traditional strategies
Emergency planning

Source: World Commission on Dams (2000)

Integrated Floodplain Management on the Mekong River

Land-use planning measures are aimed at "keeping people away from the floodwaters." Land-use measures on the floodplain aim to ensure that the vulnerability of a particular land-use activity is consistent with the flood hazard on that area of land.

Structural measures are aimed at "keeping floodwaters away from the people." Typical structural measures include flood mitigation dams, embankments and flood detention basins.

Flood preparedness measures recognize that - no matter how effective the above types of management measures are - an overwhelming flood will eventually occur. These measures embody flood forecasting, flood warning, and raising the general flood awareness of the potentially affected population groups. In a number of cases, flood preparedness and emergency measures may be the only type of management that is feasible or economically justified.

Flood emergency measures deal with the aftermath of major events by "helping affected people to cope with floods." Flood emergency management, like floodplain management, is a process that typically encompasses preparation, response and recovery. The process embodies evacuation planning and training, emergency accommodation planning, flood cleanup, restitution of essential services, and other social and financial recovery measures.

From: Mekong River Commission, 2001

The importance of regional co-operation has also been stressed by the South Asian Floods Project (SAF) of the International Centre for Integrated Mountain Development. The project facilitates information exchange in the Hindu Kush-Himalayan region ( It stresses that one of the most cost-effective means of reducing the impact of floods is the nonstructural approach of providing people with sufficient advance warning for them to escape from approaching disasters. It further points out the importance of timely and reliable information on weather and river flows, and the open exchange of information among countries. Priority needs to be given to the development of such information gathering and dissemination networks in countries where no such systems currently exist.

Finally, there is a clear need to develop improved capacities for river systems to respond to flooding in both rural and urban environments, and by balancing land use more carefully. Agricultural and forestry policies, practices and incentive schemes need to be redirected towards reduction of flood risks and the restoration of the roles of formerly undeveloped floodplains for storing water and reducing peak flows downstream. Indeed, flood storage could become a recognised land use in development plans, which should be encouraged and compensated through government incentives. For example, over 25,000 homes have been relocated from the Mississippi floodplain since 1993, and thousands of hectares of marginally productive low-lying areas have been reconverted from agriculture to natural areas (Galloway, Jr. 1999).

Reversing the past

In the future, drainage design should reverse the past 200 years of engineering practice. Storage should be maximized and conveyance minimized. Post-modern drainage design should mimic the form and performance of the pre-settlement drainage system.

From: Hey 2001

Urban flood in Bangkok, Thailand (courtesy of the Royal Irrigation Department of Thailand through Water Resources Section, UNESCAP)

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