Since early March 2020, Boskalis Nederland has been working on maintaining the depth of the western section of the port of Rotterdam. ‘In effect, we are continuing the maintenance work we have been doing here in recent years but the contract conditions have changed,’ explain Coastal and Seaports coordinator Martijn Zwakhals and project leader Dirk Bogaard.
The work is being conducted for the Port of Rotterdam Authority and Rijkswaterstaat (the Dutch Directorate General for Public Works and Water Management). ‘The aim of our maintenance work is to guarantee safe access for all vessels to the Maas Entrance, the Maasgeul channel and the western port basins of the port of Rotterdam,’ says Martijn. ‘The initial contract is for a period of three years, with the possibility of three additional years for which we will submit a proposal soon for making the dredging work even more sustainable. The main focus here is on reducing emissions of substances such as CO2 and NOx. Then there is an option for extending the contract twice by one year.’
Looking for sustainable opportunities
‘This is one of the first major Dutch dredging contracts with a sustainability component,’ says Martijn. ‘As part of their sustainability policy, air quality is an important priority for our clients. There is an assessment criterion for monitoring emission volumes: the Environmental Cost Indicator. It has financial consequences. Not to put too fine a point on it, this is a sort of emissions tax.’ The 4,500 m3 trailing suction hopper dredgers Strandway, Causeway, Freeway and Shoalway are highly efficient vessels that can usually complete the work in the standard way. ‘These vessels allow us to comply with the environmental requirements and contract conditions,’ says Dirk, who is responsible for operations as the project leader. ‘That doesn’t alter the fact that we will be working hard in the time to come on reducing emissions even further. For example by installing certain filter systems and using biofuels.’
Boskalis maintains water depth in port of Rotterdam.
‘The maintenance work in the port is always slightly unpredictable,’ explains Dirk. ‘Levels of sedimentation always vary. A short period with strong winds from the sea can result in a sharp rise of sedimentation in the fairways. In addition, a lot of river sediment can flow in from the hinterland in the spring. The most important condition in our contract is that we have to guarantee a minimum sailing depth in the port area at all times. In some places, that is 23.65 meters; it can even be as deep as 24.80 meters in other locations.’ Martijn adds: ‘The clients conduct surveys every month and the results are sent to Dirk’s team. We have contractual agreements about the response time for the deployment of our dredging equipment if sedimentation exceeds, for example, thirty centimeters. We know that we need to move quickly after severe storms. So we always have to have a dredging vessel available at very short notice. We take that into account in our planning, of course.’
Dirk and Martijn expect to dredge a volume of approximately 27 million cubic meters over the next hree years. The dredged material is deposited on the ‘verdiepte loswal’ (a submerged deposit area on the North Sea), half an hour’s sailing time from the Maas Entrance. ‘Depending on the weather, a cycle takes about two and a half hours,’ says Dirk. ‘We work day and night seven days a week, and so we complete an average of ten trips a day. We take the dredged material outside the port, and then sail a little bit further and pick up sand from an adjacent section. We deposit that in an underwater depot belonging to the Port Authority: the Scheurput. From there, it is transported by inland vessels to the hinterland, where it is used by the sand trade, for example for road construction,’ says Dirk. ‘So we never sail without a cargo and, in that way, we use our capacity as efficiently as possible.’