Breach of Dike Helps Make Maasvlakte 2 Accessible to Shipping (The Netherlands)
To make Maasvlakte 2 accessible to shipping, the PUMA contracting consortium (Boskalis and Van Oord) has started excavation of the temporary dam between the Yangtzehaven and the Maasvlakte 2 ports.
The contractor will leverage the water’s force for the very last part. This coming weekend the dam between the Yangtzehaven and Maasvlakte 2 will be lowered at low tide. When the flood tide returns, the rising waters will flow across the dam into the Maasvlakte 2. The expectation is that the flooding waters will wash away a great deal of sand and will ultimately breach the dam. This will speed up the rate at which the breach develops and the rates of flow will eventually decrease.
Providing access to the Maasvlakte 2 is one of the construction of the Maasvlakte 2 sub-projects that stirs the imagination. A planned ‘dike breach’ is a seldom occurrence. In accordance with the schedule, the PUMA contracting consortium will have completed all of its activities by the second quarter of 2013. The sub-projects that remain at that point primarily involve the construction of the road and the railway line for which the Port of Rotterdam Authority has selected different contractors. The construction of the Maasvlakte 2 is still on schedule and within budget estimates.
Breach at Yangtzehaven
By closing the seawall on 11 July 2012 an interior lake was created on the Maasvlakte 2 with a surface area of approximately 800 hectares. There is no low and high tide here, while the difference in the tides in the Yangtzehaven is in the order of two metres. As soon as a first breach has been made, the Maasvlakte 2’s current interior lake will once again be subject to tides. This means that during each tide approximately 16 million m3 of water will try to force its way through the breach. Especially when the breach is still relatively small, this will result in significant rates of flow. Thorough work planning has therefore taken place in preparation for breaching the temporary dam that separates the interior lake from the Yangtzehaven.
Similar to the closing of the seawall in July, the breach will occur during slack water. This is when the difference between high and low tide is smallest and permits the rate of flow in the opening to be as controlled as possible. During the period between flood and ebb, on Sunday, the dam will be excavated to approximately 50 cm above the New Amsterdam Water Level (NAP), the level of the interior lake. Once the water in the Yangtzehaven begins to rise again, it will overflow the dam at some point. Due to the increasing difference in levels, the water’s rate of flow will increase and will wash increasing amounts of sand away from the dam. This will create an opening in the dam that will become increasingly wider and deeper. In addition, the Edax and Zeeland II cutter suction dredgers will be dredging on both sides of the opening. This also increases the size of the opening. The water will continue to pour into the Maasvlakte 2 ports for approximately three hours. The flow will then revert itself. Because the opening in the dam will become increasingly larger, the rates of flow will revert to normal values over time.
Because the rising water will wash away the dam, the tidal flow will carry the sand along into the Maasvlakte 2. Here it can be used to raise the last terrains. Computer simulations indicate that the water will reach high rates of flow. The two cutter suction dredgers will be well anchored to ensure that they are not carried along by the flowing water.
Over the coming months, the Yangtzehaven will be widened to 600 metres and deepened to approx. 20 metres, so that large ocean-going ships can sail to the RWG and APMT terminals. According to the schedule, the Maasvlakte 2 will be accessible to ocean-going ships by the end of the first quarter of 2013.
Source: portofrotterdam, November 23, 2012