HYDRO 2018 Gdansk: Selecting A Dredge For Your Reservoir Maintenance

Barrage du Ksob, M’Sila, Algeria with a DOP dredge 350

This week, I am here in Gdansk for a presentation on the HYDRO 2018 Conference1 and assist at the Damen booth at the corresponding exhibition. The paper and the presentation are already prepared and I am very excited to do the presentation, but I can’t wait till tomorrow and I like to share the story now, already. So, you, as my favourite audience, will have my personal spoiler after so many teasers have been floating around2,3,4.

General modes of siltation at the usual location in a reservoir

The thing is, dam maintenance and reservoir restoration is something already long on my attention list. Back already in 2008, I wrote a paper on this subject for the CEDA Dredging Days5. Over and over we’ve conveyed the message on various platforms, that dredging might be a viable solution for sedimentation problems in reservoirs. Usually, the solution by dam owners and operators is to flush, sluice or store the sediment. This looks horrible from a dredging perspective, but it is also to the environment. You either smother or starve the downstream river with sediment. As a right minded dredge enthusiast, you see many possibilities to dredge such a project. Immediately we can identify what dredge to use on which location for which purpose.

Selection of applicable dredges for reservoir dredging

If you are very close to the dam and the length of the discharge line allows it, you might even not need a dredge pump. (No wear parts!) It is a so called siphon dredge. But as soon as there is some further transport involved, either distance or uphill, you need a dredge like a cutter suction dredge or a DOP dredge. For even further discharge, you might employ a booster for increased discharge pressure. If the distance becomes very far, you might have to resort to grabs and barges.

Water injection dredging principle and example (this example would be too big for a common reservoir)

As an intermediate solution you might even consider using a water injection dredge. Usually the reservoir is in the mountains and a bottom gradient will be present, enabling the required gravity flow. The actual dredge should have created a silt trap where it can collect the inflowing material from the water injection dredge. Than it can handle the material as usual.

Alternative uses for the dredged sediment a) silt farming as fertile additive b) gravel extraction for concrete

Off course, the dredged sediment belongs to the river and the best thing would be to gradually release the sediment after the dam. But there might be conditions, where it is beneficial to extract the valuable fraction of the sediment and use it for agriculture or as aggregate in the construction industry.

Dredge selection diagram for reservoirs

We noticed, that it is often difficult to convey to dam owners and operators which dredge to select for which job. Sediment is seen as a liability and not as an asset and they rather neglect issues associated with the sediment. So, I made an attempt to have a plain and simple selection diagram. That is the core of my manuscript. But my objective is, that we will see many beautiful dredges contributing to a sustainable and viable operation of hydropower dams and reservoirs.

New DOP dredge family

References

  1. HYDRO 2018: Progress through partnerships, Hydropower and Dams
  2. LinkedIn Teaser, Saskia den Herder
  3. Damen: Spotlight on Hydro Power Dam Maintenance
  4. LinkedIn Teaser, Olivier Marcus
  5. Multi Functional Small Dredging Solution For Maintenance Of Deep Irrigation Reservoirs And Hydro Power Dams, CEDA

See also

Dredging Exhibits At The National Maritime Museum Gdansk

Overview of the National Maritime Museum in Gdansk, Poland

Currently I am in Gdansk, Poland. Last week I had a CEDA event1 and next week I am at the Hydro 2018 Conference and Exhibition2. On both events I will report later. My colleague Saskia den Herder wrote a teaser for you3. Now, here, I had the weekend for myself and what better to do, than be a tourist, visit a maritime museum and write a blog about it. So, I will report you about interesting dredging exhibits I discovered at the National Maritime Museum in Gdansk4.

The National Maritime Museum comprises three major venues: the museum building itself5, the ‘SS Sołdek’6 and the old city ‘Crane’7. All equally interesting in their own way. Buy a combined ticket and you get the ferry between them for free. As general maritime museums go, they mainly focus on the history of shipping, shipbuilding and the interaction with the development of the city or country. Gdansk in itself has a very long history in shipbuilding, as the country was well forested for providing the building material for ships. In modern times, one might have heard of the ‘Lenin Shipyard’8, the birthplace of the free labour union ‘Solidarity’, which brought Poland out of the socialist led economy. And of course, where there is water, there are ships and where there are ships, there is Damen9,10.

Horse powered scoop ladder dredge

Between the many models and pictures I found some about dredges indeed. This one seems to be a very first attempt at mechanical dredging. The power was provided by two real horses. There were some sort of scoops or blades drawn over a chute. The wooden blades excavated the soil from the bottom. Water was expelled through holes in the blades. The drained material could be loaded in barges for further transportation. Only after translation later on, I learned that in fact this was an example of a Dutch dredge!

Picture and model of a steam powered bucket ladder dredge

I did find a picture and a model of a locally build dredge. It employs a German steam engine and was built on an oak hull. It already featured the classic iron buckets on a ladder. The development of the working principle did not change that much. The dredged material could be delivered to barges at the aft end for further transport.

Grab dredge ‘Homar’

Finally I came across this model. It is a grab dredge ‘Homar’11, built in 1971 and operated by PRCiP Sp.z o.o. (Dredging & Underwater Works Co Ltd) here in Gdansk12. OK, I don’t want to brag, but it looked vaguely similar to the one we saw when we were on a site visit with the CEDA to the Port of Gdansk13. We had a splendid view over the harbour from the port control tower. And there I already noticed they were doing some dredging works in the entrance channel. But for all what we could see, it could also have been its sister ship ‘Świdrak’. And that concludes a nice round up of dredging discoveries for the weekend.

Overview of the entrance channel as seen from the port control tower. Dredging works indicated.

References

  1. CEDA-MIG Joint Symposium on Advances in Dredging Technology 2018
  2. HYDRO 2018
  3. Dam maintenance – deep dredging, Saskia den Herder
  4. National Maritime Museum in Gdansk
  5. Granaries on Ołowianka Island, NMM
  6. Sołdek, NMM
  7. Crane, NMM
  8. Gdanks Shipyard (Lenin Shipyard), Wikipedia
  9. Damen Engineering Gdansk, Damen
  10. Damen Marine Components, Damen
  11. Homar, Dredgepoint
  12. PRCiP
  13. Port of Gdańsk

See also

Sunken Treasures From ¡VAMOS! At Silvermines

Overview of the ¡VAMOS! test operation in the Magcobar Pit, Silvermines, Ireland

Last week, I was at a test site for the ¡VAMOS! project. It was in the abandoned Magcobar Pit1. Well, only in ancient times, people have been digging for silver at this location. In 1963 the site was opened for a large scale operation to mine Baryte2. A mineral used in the oil industry. After the veins ran out in the open cast mine, they continued underground, extending the tunnels almost to the next mine in an adjacent area. Then they had to stop operation altogether and the pit got filled with water from a small river that now enters in an attractive waterfall. So far the historic perspective of this site. Currently the forgotten mine is bustling with activity. So many people and equipment was brought in from all corners from Europe, it looked like a circus has come to town.

The ¡VAMOS! road show on its way to Silvermines, Ireland

When I came there, the team had already set up camp and assembled the Launch and Recovery Vessel. The Mining Vehicle was ready to be deployed and we could commission and test the special drive we had provided for the project3. Another item we had to commission was the dewatering facility. Well, it is a fancy name for a dump area. Basically, it is a reclamation area, where we can collect the material that has been cut by the mining vehicle and was pumped through the discharge line to the shore. We had one pond for collecting the cuttings and one pond for containing the fines. Eventually all effluent water was skimmed trough an overflow box.

Overview of the dewatering facility

As there might still be some very fine material contained in the overflow water, we wanted to dispose the water at a lower level than where we were going to do the cutting tests with the mining vehicle. This would ensure clear visibility and an undisturbed background turbidity for the effects measurements. A submerged pipe line for dredging is a well-known component in the dredging industry. If e.g. a discharge line of a cutter suction dredge has to cross a busy fairway, the discharge line is submerged under water, so the traffic can pass without interruption.

Example layout of a submerged dredge line

There are several issues to pay attention to. Selecting the right diameter is the first to consider. You definitely don’t want to block the submerged dredge line. In order to reduce the critical velocity and increase the mixture velocity, the diameter of the submerged pipe is usually chosen a bit smaller than the rest of the pipe. Furthermore, you don’t want any air get trapped in the submerged line. Air inside the line will make the pipes float again, usually at the most inconvenient moment and probably damage the line. Positioning the submerged line can be done by actually having the air in the line slowly escape. The line will lose buoyancy and settle on the bottom. Injecting compressed air will float the line again.

Deployment of a submerged dredge line

The mining we are doing at the Magcobar Pit is solely for scientific purposes. The material we gather and sample will not be used. But, we hope our technology will revive some disused mines again to their former glory. At least get some people back at work. There are a lot of little villages that fully depended on the activity of the mine. The little town of Silvermines is still remembering those good old times with a little monument to commemorate a glorious past4.

Memorial for the mining industry in the town of Silvermines

References

  1. ¡VAMOS! preparing for second field tests in Ireland, ¡VAMOS!
  2. Baryte, Wikipedia
  3. Dual Stage Dredge Pump and Double Action Pump Drive for ¡VAMOS!, Discover Dredging
  4. Silvermines, Wikipedia

See also