I read a string of articles on how to control flood. I also read a lot of articles on benefits of flooding and the ecosystem sustained by it. It seems that a debate is required in the beginning of each and every flood control project to determine the cost-benefit return of the project. The reason is counter-intuitive : Flood has both risks and benefits. I would like to quote from World Commission of Dams report in my article to articulate my position.
Each year flood events result in significant loss of property, life and livelihood in many countries. But on a small scale floods can be beneficial in providing groundwater recharge, silt deposits, floodplain fisheries and so on. Floodplains have played and continue to play an important role in the economies of many countries.
Physical flood protection infrastructure in the form of embankments and storage reservoirs cannot always provide full protection, and their effectiveness change with changes in river morphology and sedimentation. Additional management effort is required involving non-structural interventions such as flood forecasting, land use zoning, flood proofing, disaster preparedness, flood insurance and so on, either in parallel or independently from structural forms of protection.
As developing countries urbanize and industrialize, the financial consequences of flood damage will increase, and the demand for flood protection will intensify, leading to the need to construct more dams. At the same time such investment in flood protection often encourages settlements in floodplains, a rise in property values and pressure to provide more flood protection. Consequently it is likely that there will be a significant increase in flood physical protection structures, particularly dams, in the coming decades, to counteract the effects of climate change as well as to meet the needs of growing urbanization.
Risks of Flood Control
Flood is a part of ecosystem. Controlling flood will remove one part of the ecosystem – causing irreparable damage. To understand the damage, one needs to understand how the floodplain ecosystem works.
Floodplain Ecosystem
Floodplain rivers in their natural form are in a constant state of change, roaming about across unrestricted floodplains, creating and destroying side channels, backwaters, oxbow lakes, and a variety of other habitats. In this process, over long time periods, rivers maintain a relative balance between these various habitats a situation called “Dynamic Equilibrium”. The floodplain serves as an important part of the river itself, acting as a check valve to absorb high flows or flood pulses, as a kidney to cleanse runoff waters, as a mechanism of energy exchange, and as temporary and seasonal habitats for its biological components. In fact the presence of a periodic flood pulse is a key factor in maintaining a healthy river ecosystem.
The typical damages done once flood is artificially controlled -
- Damage to shallow floodplain aquifers and subsequent damage to plants and animals dependent on it
- Impact on migratory species
- Loss to direct silt and nutrient replenishment leading to gradual loss of fertility
Mitigation : Managed Floods
The WCD Knowledge Base includes a number of cases where artificial floods have been released from large dams to regenerate the natural resource base of downstream floodplains for local livelihoods (for example Manantali dam in Mali and Senegal and the Pongolapoort dam in South Africa). Managed floods generate economic benefits when downstream communities depend on natural, flood-maintained resources such as grazing, flood-recession agriculture and fishing (see Chapter 4). For example, on the Tana River, Kenya, a released flood from the planned Grand Falls scheme would have a net present value of at least $50 million for the downstream floodplain economy. Managed floods also entail an opportunity cost which may be greater or lesser depending on the value of the released flood waters to the dam for irrigation, hydro-power or other uses. A set of preliminary studies show that in some cases there are clear net economic benefits to these releases and in other cases the opportunity costs exceed the
value of downstream benefits that were identified, quantified and valued in economic terms. The potential for managed floods is often constrained by the design of the sluice-gates, sedimentation in the reservoir and in downstream
channels and the development of infrastructure on areas previously prone to flooding. Another constraint may be the political will to support traditional means of livelihood at the expense of benefits from the dam.
How to Manage Flood
Reducing the scale of floods - It includes better catchment management (afforestation), Controlling runoff (by creating reservoirs), Detention basins (to bypass excess water), Dams (to control flow), Protecting wetlands. Example – Large dams in Japan have dramatically reduced the sudden arrival of floods in populated areas where the rivers are exceptionally steep and short, and susceptible to flash floods.
Isolating the threat of floods - It includes Flood embankments (dykes and other structures to enable better drainage), Flood proofing (waterproofing walls; fitting openings with permanent or temporary doors, gates, or other closure devices; fitting one-way valves on sewer lines), limiting floodplain development (not to build any major infrastructures in floodplains).
Increasing people’s coping capacities - Emergency planning, Forecasting, Warnings, Evacuation, Compensation, Insurance. The last option is really interesting one as it avoids most of the observed shortcomings of the earlier ones. It includes :
- integrated catchment and coastal zone management, and wise planning and use of floodplains and coastal zones;
- empowering local communities to make choices about land development and flood alleviation;
- reducing the impacts of humans on the environment by promoting flood disaster resilience;
- valuing and preserving the best of indigenous adaptations and improving local capacities to respond;
- addressing problems of equity (for example alleviating poverty and lack of access to resources as a means of addressing
- flood vulnerability)
Emergency planning and management has three phases: preparedness, response and recovery. The capacity of individuals, households, groups, and communities to cope with flooding depends upon
- their knowledge, resources, organization and power
- their knowledge about how to identify that a flood threatens, how to mitigate effects of floods, what to do before, during and after a flood, the causes of flooding and appropriate mitigation measures;
- the resources at their command, including their skills and physical assets, and the support of others that they can call upon;
- the extent of their organization, including within households, within neighborhood groups, and within whole communities, as a way of pooling knowledge, skills, resources, and planning and coordinating activities to achieve optimum use and power in relation to other groups in society.
A flood management strategy will need to cover flood warnings, flood mitigation, any necessary evacuation and post-flood recovery. A clear commitment by national or federal governments to the emergency planning and management process will enhance its effectiveness.
Conclusion
Flood Damage Cycle
If we compare between method 1,2 and 3 for managing (the third one does not actually ‘control’ but let flood to occur) flood the third one has almost no impact on the environment and ecosystem since flood is not stemmed. It is the most eco-friendly approach towards managing flood. So, why don’t people adopt it always?
The answer to it could be obtained by the countries those successfully adopted first two options. The Netherlands and Japan built their flood management system broadly based on structural measures – the Netherlands built dams, embankments and artificial drainage, while Japan built a series of reservoir dams to stem the flash flood. They both sacrificed a significant amount of bio-diversity and ecosystem to build up their industrial infrastructure. The third option to let the flood continue can not work with modern day infrastructures. That is the biggest drawback of that method.
I believe all these three could be used together with an appropriate mix to obtain the best result. To decide on the ration in the mix the floodplain ecosystem needs to be studied, the losses need to be appropriated and corresponding benefits should be evaluated. A debate on cost-benefit will help all of the interested parties to come to a correct conclusion.
Source
1. World Commission of Dams report – chapter 2, 3 and 5
2. Flood plain ecosystem by Jerry L. Rasmussen, U.S. Fish & Wildlife Service
Further Studies
1. Rhine river ecosystem restoration (The Netherlands, Germany, France)
“stretches of the originally freely flowing Rhine and its numerous tributaries, such as the Mosel, Main and Neckar, have been turned into a series of impoundments. Numerous engineering measures along the main channel of the Rhine and of almost all its tributaries have fundamentally changed the hydrological and morphological conditions. More than 85 percent of the floodplains have been cut off from the Upper and Lower Rhine leading to a considerable loss of habitat and of animal and plant species typical of the river.”
2. The Land Reclamation in the Netherlands – the other face of the story
The loss of estuarine environments in the deltas of the Rhine, Meuse and Scheldt is a good example of the effects of excluding natural environments in decision making processes (Saeijs, 1999). Of the original 8,660 km2 of estuaries in this delta in 1900, there remain only 3,930 km2 in 2000: more than 54% of estuarine environment (4,730 km²) has disappeared within one century. When Costanza’s key figures (1997) are applied to these estuaries and the new systems, the Gross National Nature Product of the estuaries in 1900 is estimated to have been ca. $4 16 billion per-annum. These water-systems would presently represent a capital value of ca. $ 336 billion. Of course, the figures are not absolute, but indicative. However, the message the figures convey is clear. Taking in account the gains of the new land and lakes, the loss in national nature product amounts to $ 8.8 billion per-annum while the net production loss can be estimated at $ 6.6 billion. The net loss in capital is estimated $ 138 billion. These costs of estuarine destruction have never been included in decision making tools like cost-benefit analyzes during projects like the so-called Zuyderzee project and the Delta project. …….. For example, the cause of ever increasing water levels in The Netherlands is a result of 500 years of land reclamation in the floodplain and un-sustainable use of the rivers’ resources.
3. How Japan damaged their ecosystem and how they are trying to recover
“Human impacts such as river engineering, agricultural development, invasion by nonnative species, and urban development have degraded aquatic ecosystems throughout Japan (Yoshimura et al. 2005). Since 1868, wetland area has decreased by approximately 60% (GSI 2001). Recently, the appearance of once common species such as medaka (Oryzias latipes, or Japanese rice fish) in the Red Data Book of Japan has shocked the public (MOE 2003). Today the conservation of aquatic ecosystems is of great importance in Japan, and many countermeasures have been implemented to slow or reverse the degradation of river habitat (MLIT 2001, ESJ 2002). In 2004, for example, the Invasive Alien Species Act was implemented to eradicate certain invasive species and to regulate their import, dispersal, and spread.”
4. Environmental Aspects of Integrated Flood Management
5. Bigger, Better, Bolder (Netherlands land reclaimation)
“Marsh areas that depended on the right balance of salt and fresh water are slowly dying as fresh water takes over. Where shrimp, mussels and oysters once thrived, invasive freshwater zebra mussels the same species that plague U.S. waterways have taken up residence. … Scientists are hoping to try this approach on a larger scale. The new philosophy calls for reversing the whole trend line of Dutch history: Giving up some reclaimed land and letting water reclaim it. The general idea is that if water has more space, it is less likely to flood inhabited areas.”
6. The Eastern Scheldt barrier: Environmentally friendly engineering? by HUIB DE VRIEND
7. Fisheries was destroyed in Isahaya Bay, Japan by Stanley
“Moreover, other economic consequences are making themselves apparent. Tairagi (pen shell in English) is another species symbolic of the Ariake Sea, and since the closure of the dike, the number harvested has plummeted and catches of various species of fish off the Shimabara peninsula are dropping. It seems that the sacrificed tideland was a nursery for the young of various species and the smaller creatures that make up the base of the Ariake’s food chain. The cosmetic compromise of opening the narrow gates for a limited period of time cannot restore the intricate mosaic of life in Isahaya Bay or the Ariake Sea as a whole. We are witnesses to the death of a wetland of vast importance.”
8. How Fisheries were affected by Dutch Delta-works
“The salmon case clearly shows that one-sided promotion of navigation and hydropower interests harmed the ecosystem and fishery interest despite a treaty on salmon preservation.”
Salmon Catch over years in Rhine
