What would happen if the Ukai dam collapsed?

Prepare for worse

The greenhouse effect will lead to more frequent and larger floods that will threaten more people than ever. Conventional approaches to flood control are likely to exacerbate the problem because they are insufficient for unusually large floods. What is certain is that there will be floods again and again. Humanity must therefore learn to live with them instead of trying to prevent them. [By Patrick McCully and Himanshu Thakkar]

Floods are among the most destructive, common and costly natural disasters - and they keep getting worse. In the second half of the year, rain floods in Equatorial Africa inundated 14 countries. Uganda and Ghana were particularly hard hit, each with 400,000 people injured. The summer monsoons in Asia hit 25 million people and killed 2,500 in India alone. Bangladesh, China and Pakistan were also badly hit.

Other countries were not spared in 2007: Britain experienced the worst floods in 50 years. Australia, Canada and the United States saw exceptionally heavy rainfall, causing significant damage and killing large numbers of people.

Although floods are part of human history and even though billions of dollars have been spent on protective measures, the number and cost of life-threatening flood disasters have risen sharply in recent decades. The causes are, on the one hand, global warming, which causes stronger storms, and, on the other hand, the increasing development of floodplain areas. Houses and company buildings are now where there used to be agricultural land.

But there is another reason: today's technologies for flood control, primarily dams and dykes, often turn out to be counterproductive. They amplify tidal waves and give those who are supposedly protected a false sense of security: they trust dykes that will give way sooner or later. Traditional or “hard” flood protection systems can prevent most normal floods, but in the long term they tend to increase the risk of particularly large floods - and climate change will dramatically increase the extent and frequency of such events.
A different approach to flooding is therefore urgently required. This other path is known as the "soft path" of flood management. It aims to understand the forces of nature, to adapt to them and ultimately to use them for one's own purposes.

Instead of wasting billions of dollars on futile attempts to prevent floods, we should recognize that they cannot be avoided and that we must live with them as best we can. That means we have to
- Find ways to reduce the speed and extent of flooding by restoring meanders and floodplains;
- Build houses on hills or stakes and use (well-maintained) dikes only to protect areas that have already been built on
- Develop early warning systems and evacuation programs to avoid approaching floods.

It's a tough problem

Conventional “hard” flood protection relies on dams and dykes. This approach has three key weaknesses:
- No complex technical system is immune from human and technical failure.
- Protection all too often relies on an incomplete understanding of the characteristics of rivers and coasts.
- It promotes the intensive development of flood-prone areas, while investments in flood protection and preparation for evacuations are neglected.

The city of Surat in Gujarat, India fell victim to a technical system prone to human error last year. The heavy and early monsoon rains of 2006 had filled the 100 meter high Ukai dam by the end of July. Actually, the reservoir should have been half empty before the heavy rains - instead it was almost completely full in the first week of August. On August 8, the New York Times reported that the dam operators had "opened the dam's 21 lock gates. The water did what water always does. It rushed downstream. ”Surat went under, at least 120 people died.

Investigations into the incident came to the conclusion that the dam operators had allowed the reservoir to overcrowd and had not factored in the outstanding monsoons. In addition, sediment deposits on the dam had reduced the storage capacity of the reservoir.

Other nations have experienced similar catastrophes: In Ghana at the end of August at least 20 people were killed in floods. 20,000 houses were destroyed. Reports suggest that the situation was exacerbated by the operators of the Bagre Dam in eastern Burkina Faso, who opened a lock gate and released a tidal wave in the White Volta towards Ghana. Burkina Faso informed the Ghanaian government, but it is not clear whether this warning also reached the people living on the river.

In 1992, the operators of Pakistan's Mangla Dam opened the overflow gates without warning - 500 people drowned. In 2005, at least 62 people died in India in a tidal wave caused by the Indira Sagar Dam. The operators had opened the overflow gates without notice as many Hindu pilgrims were preparing for a festival on the banks of the holy Narmada River.

Then there are the dams that do not hold up: In 2002, two dams broke in one day in Mexico. 21 people were killed and 3,000 had to flee. In 2004 a makeshift coffer dam broke in China due to heavy rainfall, killing 18 people. In the same year, the Camará Dam in Brazil burst, killing five people and leaving 800 homeless. In 2005 five dams collapsed in Pakistan - one of them over 30 meters high - after torrential rain. 80 people died, many more were injured and 4,000 were left homeless. In the same year, heavy rains destroyed the Band-e-Sultan Dam in Afghanistan. Eight people drowned and thousands of hectares of land were flooded.

Floods are often exacerbated by the fact that floodplains, open bodies of water and swamps, which used to hold excess floodwater, are made available for settlement and agriculture. For example, the Ganga Brahmaputra flood area in India shrank by more than two million hectares until the early 1990s due to irrigation, drainage and flood protection measures.

Dams and levees profoundly alter the flow of water and sediments through watersheds. They increase flood damage because they increase sediment deposits and reduce the flow capacity of canals. Sediments that are deposited in reservoirs do not reach the estuaries. This contributes to coastal erosion and subsidence of river deltas. Protective dikes restrict the flow of rivers. When rivers are straightened, made shorter and narrower, they flow faster. Their water levels are higher and the risk of flooding increases.

The “hard” flood protection is also based on the assumption of a constant climate. Engineers use fictional static climate values ​​to calculate the greatest possible flood tide a particular dam or levee will have to withstand. But on a warming planet, flood protection calculated in this way will probably lead to incorrect and dangerous results.

A soft solution

“Soft” flood risk management, on the other hand, is adaptable and flexible. It aims to keep the destructive power of large floods small and responds to the hydrological consequences of changes in land use and changes in river courses.

Such risk management is based on the assumption that floods cannot always be prevented, that all flood protection can fail and that such failure must be included in the models. Such strategies also assume that floods are not bad per se, but that some floods are necessary for the health of river ecosystems.

Five key elements characterize successful flood management in a changing climate. Many of these measures, albeit limited, need to be expanded.

Slowing the tide: Strategies to reduce the speed and size of the tide include moving dykes away from the rivers into the hinterland, restoring floodplains, floodplains and meanders, and countering urban sprawl. Many countries are now pursuing such strategies. In China, almost 21,000 km² of floodplain landscape on the central Yangtze is being restored. In Florida, USA, the Kissimmee River Restoration Project is expected to revive approximately 10,000 acres of river and floodplain ecosystems that were destroyed by a flood protection project in the 1960s. In Northern California, a ten-year $ 220 million flood reduction project on the Napa River will restore a tidal bog, remove some buildings in the flood plain, and relocate dams.

Improve emergency response measures: The most important life-saving measures are likely to be improved flood forecasting, warning and evacuation procedures. In the Ganga Brahmaputra Meghna Basin, for example, a citizen flood watch has been working successfully for three years, in which 1,000 people take part via telephone and e-mail. In addition, it is necessary to prepare aid strategies so that households and communities can survive floods and deal with damage.

Avoiding destruction: In order to limit damage, especially in less densely populated areas, it is important to prevent people from settling in endangered areas. The management of floodplain areas includes preventing new development and creating financial incentives for people to move to higher areas. After the catastrophic Mississippi flood of 1993 in the United States, 10,000 homes and businesses were relocated from the flooded area.

Protect High Risk Buildings and Areas: Flood risk management includes structural measures such as securing buildings by building on stilts or mounds, as is common practice in many traditional communities. Other precautions are the construction of containment and diversion systems in poorly or undeveloped areas and the well-thought-out use of well-maintained dykes to protect endangered cities.

Improving dam management: In many countries, dams that overflow, collapse or are poorly operated increase the damage caused by floods. The rules for the operation of dams should be developed with public participation. And they should be published and strictly enforced. Safety reports on existing dams are also important; unsafe dams should be removed quickly.

While there is growing acceptance that mitigation rather than prevention is the most realistic flood policy, powerful institutions, including the World Bank and the Indian water establishment, remain loyal to the outdated "tough" flood protection. An “iron triangle” made up of politicians, bureaucrats and dam builders is even promising flood-affected communities that they will be rescued through dykes and dams, even though dykes and dams have aggravated or even caused many floods.

We can and must get better. If we want to better manage floods in current and future climatic conditions, then we have to adopt the smarter “soft” management techniques. In doing so, we not only reduce the extent of death and destruction, but also give rivers, wetlands and other valuable ecosystems back to nature.