The fifth dredging sector
Dams and Damen DOP pumps
When we think about dredging, the most common images that come to our minds involve large scale removal, transportation and deposition of sediments. We divide the sector into four different areas: capital dredging (the Suez and Panama canals), land reclamation (the Dutch ‘Maasvlakte’ harbour expansion project or Palm Island, Dubai), maintenance dredging (maintaining the draught of a port or harbour) and mineral mining.
Over the last few years, however, a new field of dredging has emerged: one that will have an impact on the water and electricity resources of many countries around the world. This fifth sector involves dredging the reservoirs directly upriver from hydroelectric dams.
“With around 40,000 hydroelectric dams worldwide, this is a considerable market,” says Dredging Product Director Olivier Marcus. “The majority of these were built in the 1960s and 70s, and many require urgent maintenance. An example: more than 50% of the dams in Northern Africa are not operating at full capacity. This has direct implications on supplies of water for human consumption and agricultural irrigation purposes. And of course affects the electricity generating capacity of the hydroelectric turbines in the dam itself.”
Analysing the problem…
“What happens is that, with time, sediment builds up near the dam – leading to the eventual blocking of the hydroelectric turbines. Of course, there is also a lot of other material that needs to be removed. Like trees and other vegetation.”
In handling this situation there are a number of factors involved, all of which make the job of dredging the area all the more challenging. “By definition these reservoirs are located in mountainous regions which are quite remote,” explains Mr Marcus. “So the challenges include accessibility and fuel supply – getting a vessel and its fuel to the area in question. Sometimes the location is so high – up to 3,000 metres – that even the air is too thin for diesel engines to run smoothly. Once on site, the matter of getting the vessel into the water is also an issue, because of the lack of infrastructure.”
The challenges continue once the dredging vessel is launched and ready to get to work. A reservoir behind a hydroelectric dam can be up to 60 metres deep. “These depths are necessary to achieve the height differences required for optimum hydroelectric power generation,” he continues. Dredging at such depths requires ingenuity and experience – such smart solutions are Damen’s forte.
The vessel and all its components – the motors, piping and winches – can fit into standard containers. So you can load everything in trucks and drive to the site
…to discover the solution
The answer lies in Damen’s DOP pumps. “These submersible dredge pumps are extremely versatile – operators can use different heads depending on the situation and material to be dredged. For example: Harder compacted materials are dredged with a cutter head. If the reservoir has a lot of silt deposits, water jets are used to loosen the sediment, then a suction head to remove the material. This is a very multifunctional solution – especially as the various heads are easily changed. It’s a simple plug-and-play operation.”
With the DOP submersible dredge pump taking care of the dredging aspect, the next solution concerns the vessel itself. These are often modular pontoons which, demonstrating another clever move by Damen’s design teams, can be completely containerised. “The vessel and all its components – the motors, piping and winches – can fit into standard containers. So you can load everything in trucks and drive to the site. The low weight involved means that transportation and assembly is relatively straightforward. This is important because lifting capacity in these remote locations is often limited.”
The modular aspect also has positive implications on the depths to which can be dredged. “It means that you can dredge, in principle, as deep as you like. We can increase the length of the dredging ladder and if that is not deep enough, we can lower the DOP pump on a wire to the required depth.”
In solving the problem of fuel supply logistics, it could be said that Damen’s response was blindingly obvious. “We often make all the equipment electric-powered. Why? Because when you’re working next to a hydroelectric dam, there is enough electricity available.” Moreover, unlike diesel-powered engines, an electrically-driven vessel will not be adversely affected by the low levels of oxygen present in the high mountainous air.
Given the fact that there are around 40,000 hydroelectric dams in the world, the scope of operations for the fifth dredging sector is substantial. What’s more, the human impact – in terms of water and energy supply – has immense potential.