Flood Management

Hard and Soft engineering: which is the better option?

Hard engineering strategies involve the use of technology in order to control rivers, while soft engineering, adopts a less intrusive form of management, seeking to work alongside natural processes. Hard engineering approaches tend to give immediate results and the river but are expensive. However, in the future, they may make problems worse or create unforeseen ones. Soft engineering is much cheaper and offers a more sustainable option as it does not interfere directly with the river’s flow.

What’s more important?

In the aftermath of the 2009 Cumbrian floods, local people were angry that more hadn’t been done to prevent them. They accused the authorities of ‘putting salmon before people’ after their earlier request to lower the river bed by 3 metres in Cockermouth had been turned down because it might harm fish stocks.

The cost of protection

Professor Samuels advises the government on managing rivers. He said ‘It is technically possible to defend places like Cockermouth against extreme events, but only by building huge walls and embankments along the river, which would cost billions and alter the character of the town. For most people, that would be unacceptable as the floods.’

Flood defence on the River Waal –

River management the River Mississippi –

Hard Engineering

Hard engineering involves building structures to defend places from floodwater. Dams and reservoirs exert a huge degree of control over a river. The natural flow of water is prevented by a dam (often a concrete barrier across the valley), water fills the area behind it and is released or held depending on circumstances such as current and expected rainfall. Dams and reservoirs are normally constructed as part of a multi-purpose project rather than with just a single aim in mind.
Hard engineering: The Three Gorges Dam, China
The Three Gorges dam was constructed at Yichang on the River Yangtse. The capacity of the reservoir should reduce the risk of flooding downstream from a 1-in-10-year event to a 1-in-100-year event. Not only will this benefit over 15 million people living in high-risk flood areas, it will als protect over 25,000ha of farmland. The dam is already having a positive impact on flood control, navigation and power generation, but it has caused problems. The Yangtse used to carry over 500 million tonnes of silt every year. Up to 50% of this is now deposited behind the
dam, which could quickly reduce the storage capacity of the reservoir. The water in the reservoir is becoming heavily polluted from shipping and waste discharged from cities. For example, Chongquig pumps in over 1 billion tonnes of untreated sewage per year. Toxic substances from factories, mines and waste tips submerged by the reservoir are also being released into the reservoir.
Most controversially, at least 1.4 million people were forcibly moved from their homes to accommodate the dam, reservoir and power stations. These displaced people were promised compensation for their losses, plus new homes and jobs. Many have not yet received this, and newspaper articles in China have admitted that so far over $30 million of the funds set aside for has been taken by corrupt local officials.
Soft engineering
Soft engineering involves adapting to flood risks, and allowing natural processes to deal with the rainwater. It is a strategy that accepts the
natural processes of the river and seeks to work with it to reduce the effects of folding rather than attempting to gain control of it. A conscious decision can be made to ‘do nothing’ but simply to allow natural events to happen, even if this involves the risk of flooding. In some poorer areas of the world, this is a necessary approach. In richer areas, it could mean money is set aside in years when flooding does not occur to provide relief after the event. However, there are many more positive approaches that can be adopted to reduce the risk of flooding without exerting a major force over the river and its processes.