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

¡VAMOS! mining concept for submerged inland mining on any continent

¡VAMOS! equipment on trial at Lee Moor, Devon, UK

Today, the WEDA Dredging Summit and Expo 2018 starts1. Tomorrow, Olivier Marcus is going to present a paper on the ¡VAMOS! project2, I assisted co-authoring. The message we wanted to convey is the applicability of the ¡VAMOS! system we’ve developed in a European Research and Development consortium3. By now we were well acquainted with the European Situation, but as this was going to be presented in the United States I had to do some research all over, for the American market situation. It turned out that ¡VAMOS! concept could be used their as anywhere else.

Schematic of typical vertical ore body in an opencast or submerged setting (Credit: ¡VAMOS!)

First of all, some explanation what the ¡VAMOS! project is about. We’ve noticed that here in Europe mineral resources are heavily depleted or located at locations that are not accessible due to their economic or environmental value. One solution would be to dig deeper, but in open cast mining, you’ll run into an enormous overburden removal and drainage problems. The other is to tunnel mining, but that is very expensive and dangerous. The ¡VAMOS! concept opens up a new approach: submerged mining.

Diagram of the original ¡VAMOS! concept (Credit:¡VAMOS!)

Instead of pumping the water out, we use it to transport the mineral to the plant. And this is very familiar for us in the dredging industry. So, we’ve found another location where we can discover dredging! Usually dredging involves transporting huge volumes of sediment, but the fraction of the ore, that is really paying for the operation tends to be very small. In mining terms it is the ore grade. Depending on the ore grade, the operation can be economically feasible or not. As this is a very fine line, mining economics have already done a lot of research on this and they call it the ‘Exergy Cost’. In short: an operation for low grade ore may be more expensive when the mineral is expensive. In fact, when one is mining sand, the ore grade is 100% and the price will be low, so the profit has to come from its volume.

Exergy cost (kWh) needed for producing a given mineral from bare rock to market. (Credit: Valero)

This model is basically applicable in both the European and the American market. Although the local business mentality will result in different underlying economic calculations. In Europe we were working with a report on the critical resources that are on the agenda of the European Commission4. It turns out, that now the United States has their own list of critical minerals5, just signed into executive order6. The list differs somewhat, but is certainly recognisable. This is a good indication, that the ¡VAMOS! mining concept can be evaluated equally to the other options for the American market.

Medium-Term (2015–2025) Criticality Matrix (Credit: US DOE)

So, who knows, maybe there is an innovative entrepreneur in Olivier’s audience at the WEDA and the first real production model might be put to work in an American mine. At least, when delivering a product like this, we would not have to worry about the Jones Act.

MV handling on LARV at Lee Moor test site in Devon, UK

References

  1. Dredging Summit and Expo 2018, WEDA
  2. WEDA Dredging Summit & Expo, Damen
  3. ¡VAMOS!
  4. EIP on Raw Materials, European Commission
  5. Interior Seeks Public Comment on Draft List of 35 Minerals Deemed Critical to U.S. National Security and the Economy, US Department of the Interior
  6. A Federal Strategy To Ensure Secure and Reliable Supplies of Critical Minerals, Executive Order 13817 of December 20, 2017

See also

How DOP Pumps Developed and Entered the Digital Age

First application of a DOP pump

Recently, my daughter asked me: ‘Dad, what good is it to know your history?’ And I answered: ‘Dear, if you don’t know your past, you will not understand the world around you.’ And the world around us is changing rapidly. The most recent change in our dredging world is the launch of the DOP web shop1. The ultimate entrance into the digital age of a well proven pump. For those young people that only know how to order online (or others interested in dredging history): long before webshops were around, customers and suppliers had a direct relationship with each other.

In the early ‘90s, when Ballast Nedam received the contract to build the railway tunnel near Schiphol Airport2, they had a real tough challenge. The ground water level near Schiphol is very high. Any hole there, fills up rapidly. Using sump pumps to remove the water from a building pit would be useless. To prevent collapse of the sides, there was already sheet piling in place, supported by braces to carry the side load. The space between the braces was too small for a long reach excavator. And the area under the braces too low to work from pontoons. Moreover, the foundation pilings where already in place and they should not get damaged by the excavation with a crab crane.

Construction site of the railway tunnel at Schiphol Airport

At this point, Ballast Nedam contacted their supplier De Groot Nijkerk for a smart solution. Ballast Nedam wanted a small self-contained dredging machine, that would fit between the braces and remove the sediment hydraulically. In a real Gyro Gearloose fashion, De Groot Nijkerk managed to patch together a contraption to prove the concept: ‘the first DOP pump’ (of some sort). It consisted of a normal dredge pump and a submerged jet pump in the same frame.

Proof of concept for a DOP

The tests were successful and the prototype was turned into a production model. The main difference being that the bearing and the dredge pump were designed with a mechanical seal to remove the gland water installation. This mechanical seal required some development on itself, as standard mechanical seals were too fragile. The newly developed seal was of real dredging proof quality. The product was successfully used and word spread around the Dutch contractors about this nifty little dredging machine. As a result, the new DOP was introduced in 1991 and started a career of its own.

Introduction of the first standard DOP on the market

As customers were very original in creating their own solutions for their specific problems, this single product slowly evolved in a whole line of products and options3. For as long as I remember, there was this picture in the product leaflets, that the customer could use to configure their own tool. Hence the slogan: ‘Your job, our tools.’

Typical selection diagram of DOP options

Over time, the range has been reengineered and thoroughly standardised. Due to this standardisation, the sales could also be standardised. Thus, the natural consequence: the webshop. Here you can experience online convenience with personal service.

Real DOP’s on display. Buy them at https://dopshop.damen.com/

References

  1. Damen DOP shop
  2. Schiphol Airport expansion, Wikipedia (Dutch)
  3. The DOP® submersible dredge pump and the possibilities for the contractor, DPC December 1998

See also