The Delta Works

Holland's Delta Works has been on Geoff's list of things to see for a long time, so we headed down to Neeltjie Jans to see the works with friends of ours Justin and Bronwen Cross who now live in Rotterdam.

The Engineers: Justin and Geoff

On a cruise around the storm surge barriers

Upon setting up the building site, this skeleton of a Mammoth was excavated and now welcomes visitors to the centre 

They grow them big in the Netherlands..

Approximately half of the Netherlands lies below sea level and the sea has been kept at bay by a series of dykes for centuries.  In 1953 very high sea levels combined with a severe storm resulted in a number of dykes being breached and causing catastrophic flooding with 18,000 people dead and tens of thousands of head of livestock drowned.  In response the Delta Works project was launched to protect the low lying areas from flooding from the sea.  A series of new dykes and dams were proposed and built (the dams becoming fresh as water drained into them).  The government started this in the northern and inner areas which were 'simpler' to construct, hoping that by the time that they needed to build the more south easterly dykes and dam walls that closed the huge combined Rhine, Meuse and Scheldt Estuary that they would have gained the necessary experience and skills to tackle these difficult tasks.  All went according to plan until they started building the final dam wall in the Oosterschelde area.  By then the 1970's and huge protests broke out over the closing of the estuary - both from the environmental groups and from the local fisheries industry who grew and harvested shellfish from the estuary. The government was forced to go back to the drawing board and they came up with a series of storm surge barriers that would be closed if the sea level was expected to rise more than the spring high tide.  This compromise allowed the Oosterschelde to remain open to the sea and tides and at the same time protect the low lying areas from flooding in severe conditions.  It was one of the first times in the world that the impact on the environment became such an important issue, dividing the country, and where the preservation of the natural ecosystem influenced the approach taken to this engineering problem.

The storm surge barrier viewed from the water. It comprises of  three sections made up of 64 buttresses.

Windmills everywhere!

The design of the barriers involved compacting the seabed, then laying a rock mattress over it both to found the barrier on and to prevent erosion around the barrier. At Neeltjie Jans they cast the complicated and enormous concrete buttresses in a bunded dry dock area which was flooded once all 64 (plus one spare) buttresses were complete. The buttresses were then floated and towed out to the correct position where they were lowered to a tolerance of less than 10mm (often having to contend with tides! Huge concrete beams span between the buttresses holding a road and the service ducts.  They then built up the foundation material around the buttresses and hung the big storm surge barriers between the buttresses.  These are lowered to close the sea out when very high tides are predicted, which is approximately twice a year. The project has resulted in a reduction in the flood risk from 1 in 80 to 1 in 4000 years.  The project was completed in 1986.

Neeltje Jans is the artificial island that was built on a sandbank in the estuary to accommodate all the building infrastructure required for building the storm surge barriers.   It is now the site of the information centre, museum and visitor activities.  

The spare buttress now lies dormant in the flooded old construction area. It was designed such that if any of the other buttresses was lost or failed it could be used instead and not delay the project. It is now used for recreation. Spelunking trips course through its cavernous interior and climbing walls pickle its exterior. 

Looking across one of the barrier gates. The dark grey structure on the left is the heavily reinforced gate, the white pylons are the hydraulic rams that force it down and pull it up again. 

A model of the storm surge system from a front elevation.

We spent a full day at Neeltjie Jans and really enjoyed learning about the project.  Apart from the museum and the information centre, there is a section of the barrier that is open to the public and you can walk in under the road and out onto one of the pillars and see how it works.  We were there as the tide was coming in and it was amazing to see how fast the water was flowing in through the gaps between the pillars.  By modern standards the barrier could not claim to have "no impact on the natural ecosystem" and we're pretty sure they would need a more complicated solution now days, but it was pretty ground breaking for the 1970's/80's. 

The storm surge barriers from the shore.

The tide racing through at 4m/s. Note the enormous standing wave - though too shallow to be able to surf...?

We enjoyed the exhibition covering the events of the 1953 flood, through the planning and construction of the dams of the Delta works to the final section on the storm surge barriers and how they came about and were constructed.  There was also a movie shown summarising the events and highlighting Dutch humour.  We enjoyed the ferry ride which took us past some of the sites of the Delta Works, exploring the aquarium that they have there, experiencing the strength of hurricane force winds in the hurricane generator and doing the water slides.

One of the amazing hydraulic kids displays. This kid really enjoyed himself!

What happens when you merge Geoff and Lucy at high speed...? Gucy du Toit?

The Delta Works is a fascinating set up and well worth a visit if you're in the Netherlands.

You knew it was coming...