Book Review: Mannen Van Sliedrecht

This year is coming to an end. Two weeks of holiday for me. My favourite pastime is reading. So, I thought to recommend you something to read on your holiday, also. Mmh, what kind of book should I suggest? It should be entertaining, maybe educating and for all: about dredging. And the first book that springs to my mind is ‘Mannen van Sliedrecht’ by the author K. Norel.

Opening page of ‘Mannen van Sliedrecht’

Jan Baan is the hero of the book. As a young, intelligent  and energetic boy, he is withdrawn from school, to earn some money digging peat in the Biesbosch. There he uses his intellect to organise his work and improve the equipment. From there, he works his way up through a brilliant career, ending as one of the most influential captains of dredging industry. Although Jan Baan is the protagonist, the story unfolds through the life of Dirk Punt. He is the average really hard working crewmember on the dredges. No frills, no aspiration, only loyal, honest maybe even devout and modest. Sliedrecht had thousands of those men in their workforce and in combination with the innovations by people like Jan Baan, Sliedrecht became the biggest village in the world.
Whereas Dirk Punt is modelled after a non-descript Anybody, Jan Baan is mainly based on the historical person Adriaan Volker1. He really was an innovative engineer, threading new paths in the dredging business and managing his people effectively. He became the founder of one of those big dredging companies from Sliedrecht, eventually incorporated in Koninklijke Volker Wessels Stevin2.

Adriaan Volker (Credit: Nationaal Baggermuseum)

K. Norel was not the first to write about this subject. Herman de Man started out to collect data by interviewing people that were part of that era. Alas, the second World War came along and all the collected documents were lost and Herman de Man had other priorities after losing his family. K. Norel took over and had to start from scratch again3. So, even the story behind the book is interesting. It is out of print, but over the course of time, had several reprints. You will find it in most second hand book stores and markets. You will even find copies online4.
I do have my own copy, but am reluctant to lend it out, as I am very attached to it. It was handed to me personally by my grandmother. As a twelve year old girl, she was the nanny at the Volker family to take care of Adriaan’s descendants in the mansion that is now the National Dredging Museum. She received this picture for her services. So, there you have it: my personal connection to one of my hero’s in the dredging industry.

Happy reading! Enjoy your holiday. Best wishes for the new year.

Volker children (Credit: Henk Swijnenburg)


  1. Adriaan Volker
  2. Koninklijke Volker Wessels Stevin
  3. Geschiedenis van Mannen van Sliedrecht
  4. Mannen van Sliedrecht online for sale

See also

Nationaal Baggermuseum

CEDA Dredging Days 2017 Technical Visit Prinses Beatrix Locks

New and old basins Prinses Beatrix Locks

Today was a trip down memory lane. I went on the Technical Visit of the CEDA Dredging Days1 to the extension of the Prinses Beatrix Locks in Nieuwegein2. As a small boy, we sometimes drove to the locks to see the ships being raised or lowered according to the water level in the river. Mostly, the locks handle merchant traffic. However, in the summer, lots of pleasure boats come through and that is when the fun starts. Usually the crew on these small boats is not very experienced and funny mistakes and amusing near accidents happen all the time.

Actually, there is a lot more history about the locks3, than my own little stories. The locks were built in 1932 in a time, where such functional constructions were allowed to be beautiful. One of the most prominent features of the old locks are the monumental lock gate lifting constructions. They are really like big portal buildings signifying the transition from the ‘natural’ Lek River to the civilised environment of the Amsterdam-Rhine-Canal. As this is a ‘historical horizon element’ the new lock is designed to have the lowest possible impact on the scenery.

Lock gate buildings Prinses Beatrix Locks

The new doors will be rolling to stay out of sight. The doors are also double executed. One reason is for redundancy, in case the other is damaged or in maintenance. As the contractor is also responsible for the operation later on, any delays will be penalised. Therefore the most reliable solution was chosen. However, there is another reason. When both outer doors are used, the lock basin is long enough to transit two 135m long inland vessels. The so called XL operation. The construction of the lock recesses are in full swing. The floors are already poured.

Lock gate recess canal side third basin

One of the first items finished in the project is the new high water dike to protect the polders behind. The material for the construction is mostly reused from the old dikes and other parts of the approach channel. Now, the new approach channel is excavated, making the river side a 120m wider. It also provides extra waiting jetties. Although the third lock should minimise the waiting time to a bare minimum.

Finished dike river side Prinses Beatrix Lock

Most of the work in the project is related to the construction of the new lock and the dredging of the approaches. But, one part of the project is to renovate the old locks. Once the new lock is in place, the contractor has a ten week time slot to renew everything but the buildings. All the mechanical and electrical installations have to be made up to date. To my opinion this is a loss. When you see all the beautiful shafts, gears and sheaves. And they have been working already for more than 80 years. I guess they should have proven their reliability by now. Well, maybe it is just my sentimental heart.

Lifting machinery gate building Prinses Beatrix Locks canal side

One thing, that we luckily not have to be sentimental about, are the three bunkers of the Hollandic Water Line4, a military defence system, that is now defunct. The bunkers are being relocated and taken up into a display about the darker side of history. They even made a colouring page to make even children aware of what it was for and how they were transported. They were distributed during the monthly public visits, which you can do yourself also.

Colouring page bunker transport Hollandic Water Line


  1. Technical Visit of the CEDA Dredging Days
  2. Expansion of the Prinses Beatrix Locks
  3. Prinses Beatrixsluizen (Dutch)
  4. Hollandic Water Line

See also


How to dress your dredge pump for success

C. de Groot Double walled dredge pump, 1970

Sometimes, we are just reinventing the wheel. In 1970, when we were still this company ‘C. de Groot’, we delivered a dry soil transfer pumping station ‘GP6’ to Volker Stevin. Special requirement of the client, was to have a double walled dredge pump installed. Because of the pressurised outer cover, the cast inner pump wall had less stress and lasted longer. Even more, in case the inner wall became damaged, it leaked into the gap between inner and outer wall. No mixture spilled into the pump room. Double walled pumps were already around in the ‘60s, but always in cast material. C. de Groot was the first to build one from steel plates. In effect, we were the inventor of the double walled dredge pump. Since 1970, a lot of high performance or safety demanding pumps have been built this way. Not only by us, but later by many other manufacturers1 also.

Now, we might upturn history again, as we developed a new outer cover for dredge pumps2. This time, the outer cover can be literally tailored to your pump. It is of woven flexible material, that can be zipped around any new or existing pump. Well, it involves some modifications of the steel pump doors, but it should fit on any size or design. It will withstand the pressures occurring during a pump burst, when the cast casing is worn through.

We went through several interesting design and test cycles, before we finally had a solution, that ticked all the marks:

  • Light weight
  • Easy access
  • Water tight
  • Safe and reliable
  • Durable
  • Retrofit

Added advantages are: less weight on the dredge pump is more cargo in the hopper. And as fabric can be slid through the gap between lowest point of the pump and the bottom plate of the hull, the pump will stay at the lowest possible location, favouring a good NPSHa.

Ewout van Duursen will explain more about how we achieved confidence in this concept, on the CEDA Dredging Days3. We did a lot of practical tests and thereby gained operational experience on handling a real life DynaCover. We discovered that the handling is much easier than a steel cover, indeed. As for the experiments: stay tuned, because the presentation will involve some Mythbuster style research, rather than academic experiments. In a way, fitting between the other interesting more scientific presentations of the Friday morning session of 11:00.

In line with the practical nature of this research, we have a sample of a DynaCover with us, for you to judge yourself4. It will provide you a tangible glimpse of the future, where double walled dredge pumps look like this:

Damen DynaCover double walled dredge pump, 2017


  1. Double walled dredge pump for longer life, Ports & Dredging #73, p13, IHC, 1971
  2. Innovative outer pump cover zipped on
  3. Presentation session Ewout van Duursen
  4. Damen booth

See also

CEDA Dredging Days