Maasvlakte 2: Seawall Closure Set for July (The Netherlands)

On 11 July, the high point in the construction of Maasvlakte 2 will occur.

Then, at slack water, when the current is at its weakest, the gap in the 11 km long seawall will be closed. From that moment, the Dutch coastline will be changed forever and the new land will be well protected from the sea. Her Majesty the Queen will give the starting signal for the closure on 11 July. The construction of Maasvlakte 2 is on schedule and within the estimated budget. The schedule that was agreed with building consortium PUMA (Boskalis and Van Oord) when they were contracted in 2007 is still being adhered to.

One or two things have taken more time, such as the construction of the hard seawall, but to counteract this other elements were completed early, such as the bathing beach. Also, the Port Authority, PUMA and other contractors are managing to keep construction costs for the first phase within the estimated budget of € 1.9 billion. The total investment for Maasvlakte 2 is € 2.9 billion (2006 price level).

Seawall

Up to now, around 215 million cubic metres of sand have been sprayed on. That is to say that about 90% of all the sand needed in this phase of the project is now in the right place. The seawall is complete, apart from the closure gap. To the north and north-west lies the 3.5 km long hard seawall, consisting of a stony dune and a block dam. This was finished in February 2012. The structure is unique in the Netherlands, due to the combination of stony dune and block dam, for which almost 20,000 blocks of concrete from the seawall of the existing Maasvlakte were recycled.

The soft seawall in the west and south-west is 7.5 km long and consists of a beach with 14 metre high dunes. In 2011, the whole length of the dunes was planted with marram grass. On the south side, the beach has been made 100 m wider, so that beachgoers also have a nice wide beach when the tide is in. This bathing beach was opened to the public during Whitsun weekend. There are over 1500 parking spaces and a permanent building for the life guards on top of the dunes.

Closure

Since mid-June, the trailing suction dredgers Prins der Nederlanden and Vox Máxima and the suction cutter dredger Edax, owned by the PUMA consortium, have been transporting the last 10 million cubic metres of sand to the missing piece of seawall between the sandy and stony dunes.

The closure is planned for 11 July, at slack water: then, the three suction dredgers will work together to link the northern and southern sections of the outer contour with each other. This first major sand closure since the construction of the Philips Dam 25 years ago is quite a feat by hydraulic engineers Boskalis and Van Oord, united in PUMA (Project organisation for the expansion of the Maasvlakte).

On 31 March of this year, there was a trial closure of the compartmentalisation dam, which closes off part of the inland lake of Maasvlakte 2 (the future Alexiahaven). This reduces the flow in the closure gap, making the closure easier. After the gap has been closed, this temporary dam will be opened again. The main factor that needs to be taken into account with the closure is the loss of sand due to erosion, which is the result of current caused by the tidal differences. PUMA’s Engineering department is using various mathematical models to calculate the expected sand losses.

During the closure on 31 March, the Survey department of PUMA deployed a small survey vessel on Maasvlakte 2, which performed continuous depth and flow measurements. The purpose of this was to analyse if the mathematical models coincided with reality. This experience is now being used with the closure of the outer contour.

The closure is taking place in phases. In May, the trailing suction dredger Prins der Nederlanden began rainbowing operations near to the closure gap. Bulldozers, cranes and shovels are being used to get the sand into the right profile. On the northern side of the closure gap, on the outer side of the seawall, the trailing suction dredger Vox Máxima has sprayed on a ‘sand cone’. This mass of sand will form part of the seawall, but by applying this already the current will be reduced for the dredgers during the closure operations.

In the gap in the outer contour, a bar will then be applied crosswise at – 8 m New Amsterdam Water Level (NAP). The opening in the seawall will then be reduced by widening the bar and raising it to -1.5 m NAP, and applying sand on both the north and south side.

If the seawall is closed around the time of slack water, one trailing suction dredger and the suction cutter dredger Edax, which is temporarily ‘trapped’ in Maasvlakte 2, will continue to apply sand in the planned dune profile. The whole seawall will be at the right height and width by mid-August.

NB: On 10 July, 24 hours beforehand, the final decision will be made about starting the closure process, based on the weather forecast. If the wind force is higher than 6-7 on the Beaufort scale (depending on the wind direction), the closure will be postponed.

Infrastructure along the seawall

On both sides of the closure gap, a road, railway line, cycle path and cables and pipes for utilities have already been constructed. After the summer, sub-contractor BAVO will connect these together. That work should be completed by the end of October and the road behind the seawall will then be opened. From that moment on, the businesses to the north of the Maasvlakte (Maasvlakte Oil Terminal, GATE gas terminal and Euromax container terminal) will be accessible via Maasvlakte 2 and their current access road by the Yangtzehaven will be closed. The Yangtzehaven will then be extended to the Maasvlakte 2 inland lake, so that ships will be able to sail from the Yangtzehaven to Maasvlakte 2 in the spring of 2013.

Connecting infrastructure

At the moment, a lot of work is going into the infrastructure which will have to connect the new land seamlessly with the existing port area. For instance, as an extension of the N15 immediately to the north of the Slufter, an overpass has been built for road and (in the future) rail. In November, work will start on converting the Europaweg/Coloradoweg junction (in the N15, by the ECT terminal) into an overpass that can handle the container flows between the current terminals and the new ones on Maasvlakte 2.

Cooling water

Currently, the cooling water from the E.ON power plant is discharged into the inland lake on Maasvlakte 2. As long as there is an open connection between this and the sea, there is no problem but, unless measures are taken, the inland lake would become too hot and the water level too high in the period between 11 July and the extension of the Yangtzehaven. For this reason, the cooling water will be channelled towards the Yangtzehaven via a temporary canal in the coming nine months.

[mappress]

Dredging Today Staff, June 29, 2012; Image: portofrotterdam