Dredging Management Disasters in a Fictional World

Map of the dredging project at the city of Loof in the Country of Distan (Credit: CEDA 2017)

Albert Einstein made his greatest breakthroughs in the ‘Theory of Relativity’ in thought experiments. It provided him the opportunity to contemplate the extreme extends of a simple question: ‘What do I see, when I sit on a beam of light?’ How much more new insight does it generate, when a group of 200 experts in the dredging industry comes together to meditate on a thought experiment of a fictional dredging project in an imaginary country? Sure, the cases presented were very familiar, but that enabled the audience to engage in the action immediately.

Discussions at the interactive session at the CEDA Dredging Days (Credit: CEDA 2017)

In this imaginary world, there was a client, a consultant and a contractor. The client wanted a new quay wall which had to be filled with material from the river and entrance. The consultant drew up a plan and the contractor had to execute it. All three started out with good intentions, but during the project, they fell apart and got entangled in an inextricable knot of legal battles. The back fill material was not right, the dredging equipment was not adequate, the situation in the harbour was different and as problems stacked up to unsurmountable heights, several bad management decisions were taken, bringing the project further in dire straits. Apparently, the parties did not consult the CEDA’s Checklist for Successful Dredging Management!
It was up to the audience to recognise the management pitfalls and discuss the associated problems and solutions. Mike van der Vijver was there to moderate the discussions between the participants and the expert panel. The available expert panel from the CEDA Dredging Management Commission1 was able to provide background information or an alternative viewpoint on the case.

Expert panel of the interactive session at the CEDA Dredging Days: Johny Van Acker, André van Hassent, Kathleen de Wit, Charles Wilsoncroft, moderator: Mike van der Vijver. (Credit: CEDA 2017)

Considering the lively discussion, the concept really drew the audience into the thought experiment and the positive reviews proved they remembered the event long after, hopefully bringing their experience into future dredging projects. The positive effect of the Interactive Session, was that this is one of the few occasions where there is a representative selection of the dredging industry. This enabled some parties, that normally never meet each other in a project, to understand what effects of decisions in the beginning will have further down the timeline. Or the other way around: understand how some stupid contractual clauses were written in the contract, although in hindsight those were bad agreements. My personal opinion is, that the parties shouldn’t have agreed to the contract in the first place.
The Interactive Session was initiated by the CEDA Dredging Management Commission to introduce themselves and the concept of the ‘Checklist for Successful Dredging Management’2. This checklist was introduced the previous day and currently available in a paper version. However, the list will never be complete and is intended to grow and adapt as lessons are learned. So, even on this occasion there were some new issues that might be incorporated. In order to capture the discussion, there was an artist present, who made a graphic recording of the session. Most of the arguments in the audience revolved around the practical and legal side of the case, but I think, somewhere some people in the fictional case should have had the wisdom and courage to say: ‘NO!’

Graphic recording of the interactive session at the CEDA Dredging Days (Credit: CEDA 2017)



CEDA’s Checklist for Successful Dredging Management
Note: The Checklist will be available to CEDA members from this page.
Remember, first you have to sign in to access the full document.

See also

Mike van der Vijver


When does your pump suck?

Regular pump inspection

One of the key process indicators for the performance of your dredge pump, is the capability to work with low suction pressure. The parameter involved is called ‘Required Net Positive Suction Head’. Which translates more or less to: ‘the head value at a specific point required to keep the fluid from cavitating.1’ Effectively, this is the extra pressure above the vapour pressure. From the pump inlet to the blade, there still is a pressure drop. And the geometry and the form of the blade influence this pressure drop. The operator will notice this as when the blade wears down, the pressure drop becomes greater and the required suction pressure goes up. Resulting in less performance and less production. Regular inspection of the pump will warn the operator of prospective deterioration.

Test arrangement NPSHr

Normally, the measurement of the NPSHr requires a valve in the suction pipe and a valve in the discharge pipe to control the flow. Every time you want a data point, you have to adjust both valves and iteratively return to the same flow conditions, albeit with a different suction pressure. This usually takes a lot of time and one hour per data point is not uncommon. Klaas Slager presented an alternative method at the CEDA Dredging Days2. His method is more suitable for testing the NPSHr as installed in a dredge. It does not involve the dredge valves and is quicker to execute. It is optimised to check if the NPSHr wanders off nominal and thus will yield an indication on the condition of the pump. If the internal pressure drop increases, there is less differential pressure available in the suction pipe for the dredging process. Less concentration or less capacity, or less in the combination of the two: less production.

NPSHr measurement processing

Instead of varying the flow conditions, he proposes to vary the pump speed. This will influence both flow and suction pressure at the same time. However, by cleverly applying the affinity laws and presenting the operating conditions in a dimensionless scale, the cavition is immediately visible. A quick post processing will reveal any wandering of the NPSHr conditions. As this can be implemented in the PLC and executed during start-up every day, the operator will receive a daily update on the suction condition of his pump and can plan actions accordingly. This will prevent unnecessary delays and downtime.

Worn down suction side of a dredge pump deteriorates NPSHr

This concludes my scheduled series of posts about the CEDA Dredging Days. There was much more to discover. The interactive session was fun. There were a couple of interesting presentations. And I’ve seen some innovations at the exhibition. So, I will write some more reports, although at a more leisurely pace of about once a week. Later on, the other promised topics will be covered3. I’ll keep you posted.


  1. NPSH
  2. Presentation Klaas Slager
  3. Discover Dredging: A new personal website for dredging enthusiasts

See also

CEDA Dredging Days

CEDA DMC Checklist to start thinking

CEDA Checklist logo (Credit: CEDA 2017)

Oops!…I did it again. Nobody ever made money exclaiming that phrase. Unless you are a famous pop idol. If only you could be that wise and make mistakes only once. Even better: don’t make the mistake in the first place. But who would be so wise to never make a mistake? Well I am not one of those people. But I do try to prevent other people from making the same mistake again. So, that is why I participated in the CEDA Dredging Management Commission.

In the commission we are discussing how we can help people in the dredging industry to efficiently and safely manage dredging projects. One of the items that came up was a list with all the failures and problems in managing a dredging project. This could at least categorise the problems. It also provided a framework to advise people. i.e. It became the CEDA’s Checklist for Successful Dredging Management1. Today, this checklist was presented by Kathleen de Wit at the CEDA Dredging Days2.

CEDA’s checklist for successful dredging management (Credit: CEDA 2017)

The checklist tries to capture various problems, that mostly have multiple aspects. This is immediately the problem of making a comprehensive list. It was decided, to discern problems to topics involved and stages in the project, with an addition of affected parties. It is a long list and let this not intimidate you. Mostly, you will just check out the section you are working on. Just be sure, there is somebody in the project, that checks, that everybody checked their part.

The checklist is not intended to be another contract template. There are enough examples of those. e.g. FIDIC, NEC. It might be more of a starting point for a risk assessment. Or an initial resource planning estimate. Eventually you will have to do the work yourself, this list will only make you start thinking about everything that could go wrong in your project. You will have to provide the solution for it. And that is where your expertise and creativity comes in.

When I was a young innocent and inexperienced graduate student, I had an assignment on an auger dredge. The dredge was not performing well and the operator, contractor and the project owner were battling each other over the contract. It turned out, they had chosen a contract, that had no incentive for the operator to have a high production and the project owner had no way to put a penalty on the delay. No wonder the management of the project was underperforming with the dredge. If only they could have consulted such a checklist, cost and time overruns would have been minimised. On the other hand, I wouldn’t have had such a great graduation project.

Auger dredge ‘Detritus’, Schakt och Transport


  1. CEDA’s Checklist for Successful Dredging Management
  2. Presentation of the checklist at the conference

Note: The Checklist will be available to CEDA members from this page.
Remember, first you have to sign in to access the full document.

See also

CEDA Dredging Management Commission