A Damming project: dam building and dam busting

One of the most vital engineering spheres of work is dam building. It fits right alongside such disciplines as water engineering, civil engineering, hydro-electric and geotechnical engineering. Dam engineering revolves around everything related to the design and construction of dams – and the importance of dams in a water-scarce world cannot be emphasized enough. Water is critical for food production and generally the survival of all living things on our delicately balanced planet.

What is involved in building a dam?

  • Constructing a dam is a complex task that requires sophisticated modern technology and technical expertise, along with ingenious planning, design and construction.
  • Dams help in producing hydro-electric power; the reservoir thus created is also invaluable for storing fresh water for use during water shortages.
  • Various aspects such as stresses on the environment, water storage capacity, and the strength of the structure of the wall itself with regard to fractures and durability, are all responsibilities of the dam and structural engineering.
  • Dam engineers will evaluate a proposed site for dam construction, taking into consideration: hydrologic balance; geotechnical and seismological studies; safety monitoring; the design of pumped-storage power plants; soil conservation; and watershed management.
  • Various advanced computer programs are used for analysing water and soil samples from the site and investigating the subsurface conditions for potential fault existence and future leakages.
  • Structural and hydraulic design analysis in dam engineering involves evaluating the behaviour of earth and rock fill under various loading conditions. Seismic analysis is important in evaluating the risk to the dam from earthquakes.
  • During the construction process sophisticated instrumentation systems are used to monitor the process.
  • In a nutshell, dam engineers apply their professional knowledge and engineering experience with modern engineering technology and computing analysis technology to identify and analyse risks and potential threats, and determine countermeasures.

But then, sometimes, we break them down

While dams can represent real value and convenience to a population, they may also in certain times and under certain conditions, present danger. Making sure dams are safe is a full-time occupation for engineers. However, no matter how well they may have planned the security of any one dam, they may never predict the severity of an earthquake or catastrophic flooding – or even that a direct bomb attack could be so successful that the dam wall would collapse.

Just such an attack took place in Germany in 1942 during WWII. At the time, the British hoped the destruction of German dams would cause massive disruption to the German war production effort.

The design of the bomb was genius. British engineer Barnes Wallis, began working on plans for a bomb that could skip across water. He developed the idea by experimenting with bouncing marbles across a water tub in his back garden. But the real brilliance lay in the fact that the bomb had to spin backwards across the surface of the water before reaching the dam. Residual spin would then drive the bomb down the wall of the dam before exploding at its base, thus ensuring the collapse of the wall.

Experiments carried out by the RAF revealed that the drum-shaped bomb needed to be dropped from a height of 60 feet at a groundspeed of 232mph. The obvious plane choice was the famous Lancaster bomber, which had to be modified to carry the bomb.

Three main targets were chosen – the Möhne, the Eder and the Sorpe dams. The Möhne dam was a curved ‘gravity’ dam and was 40m high and 650m long. It was surrounded by trees, but any attacking aircraft would be exposed as it approached.

The Eder dam was of similar construction, but its winding reservoir was bordered by steep hills. This meant that any attacking plane could only approach from the north. The Sorpe was a different type of dam and had a watertight concrete core 10m wide. Land rose steeply at each end of the reservoir, and to add to the difficulties, there was also a church spire in the path of the attacking aircraft.

After many months of planning, the mission was launched on 16 May. Nineteen Lancasters took off in three waves to bomb the dams. It took five aircraft to drop their bombs before the Möhne dam was breached. The Eder finally collapsed at 1.52am. Unfortunately, the Sorpe was repeatedly attacked but remained intact. Of the nineteen bombers launched on the mission, only 11 returned. Many lives were lost, but the Dam Busters, as they became known, are still revered as the perpetrators of one of the bravest missions of WWII.

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To find out more, visit: www.outeng.co.za

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