Innovation can reduce costs and emissions in maintenance dredging

One of the key competitive advantages of the Port of Rotterdam is its navigable depth. This allows the biggest vessels (with a draught up to 22 m) to enter and berth in the port. Because of port sedimentation, the Port of Rotterdam and Rijkswaterstaat make a continuous effort to maintain this large navigable depth. This requires continuous maintenance dredging, which comes with high annual costs, environmental impacts (i.a. emissions) and hindrance for navigation and port operations. Therefore, the port and Rijkswaterstaat are continuously looking for innovations to reduce dredging efforts. This research shows that innovative gel barriers have the potential to reduce sedimentation in individual port basins by up to 17% and direct the sediment to more favorable locations. This could potentially reduce the sailing distance for dredging vessels and, hence, costs and emissions for maintenance dredging.

Gel Barriers
Gel barriers are biodegradable obstacles that are intended to reduce the spreading of sediments and concentrate sedimentation at easily accessible locations in channels and port basins. In this way, gel barriers can help to reduce costs and emissions for maintenance dredging. For example, by reducing sailing distances and limiting sedimentation at less accessible berths. The barriers are a combination of biological flocculating agents and mud particles (sediments). The image below is an example of a gel barrier on a laboratory scale. The basic idea about these “gels” is that they are sufficiently solid to block sediments and, at the same time, sufficiently liquid for a safe passage of ships.

Research

Gel barriers are not yet applied in practice. Therefore, the Port of Rotterdam, Rijkswaterstaat, Royal HaskoningDHV, Deltares, Delft University of Technology and SmartPort joined forces in this research project to better understand the stability and effectiveness of gel barriers. Can stable gel barriers be designed? How effective are they in reducing maintenance dredging? And is this a feasible alternative for maintenance dredging?

A stable gel recipe
The first challenge in this research was to find a promising recipe for such gels that is sufficiently stable, cost-effective and eco-friendly. A large variety of recipes with gel ingredients such as Xanthan Gum (XG), Carboxy Methyl Cellulose (CMC) or Kaumera Nereda® Gum was tested and evaluated on barrier stability and lifetime in the laboratories of Deltares and Delft University of Technology (Bampatzeliou et al. 2022). A stable gel that is strong enough to keep its shape but does not obstruct ship navigation has been found by using Xantham Gum. One of the key findings was that there is a trade-off between the lifetime of the barrier and the biodegradability rate. The most promising barrier recipe from this research has a lifetime of around 4 weeks. It is expected that the lifetime can be further optimized in follow-up studies.

Download the report ‘Design of a Gel Product for sedimentation control in the Rotterdam port area’ here.

Stability and effectiveness of gel barriers
The stability and effectiveness of the gel barriers with the most promising properties were evaluated using a numerical model for the Botlekhaven, Waalhaven and entrance to the Calandkanaal (Jaksic and De Wit 2022). The results show that, at these locations, the gel barrier can remain stable under ambient flow conditions. However, the barriers are likely to erode locally under the influence of the propeller jets of passing ships. The barriers are more effective in reducing maintenance dredging in stratified water bodies, with increasing barrier height and with larger under keel clearance (vertical distance between the bottom of the ship and the seabed). Therefore, the effectiveness differs highly between different port sections. For example, the results suggest that a 3-meter-high barrier is not effective at all in the Calandkanaal, but could reduce sedimentation up to 17% in the Botlek and 6% in de Waalhaven and steer this sediment towards other more favorable locations. This could potentially reduce the sailing distance for dredging vessels and, hence, costs and emissions.

Download the report ‘Gel barriers in the Port of Rotterdam’ here.

Next step
An important next step is to verify whether the results of this study can lead to a positive business case for the Port of Rotterdam and Rijkswaterstaat. Depending on the business case, future efforts could focus on reducing the costs of the gel barrier production, analyzing its stability under different failure mechanisms and increasing its lifetime. If the business case is positive, the gel barriers could be optimized and upscaled in large-scale lab trials and, finally, in a full-scale pilot in the port.

SmartPort
SmartPort will continue to stimulate ongoing research with this coalition to provide the scientific knowledge needed for further implementation and accelerate innovations for port sediment management in the port of Rotterdam.

More information
For more information, please contact Wiebe de Boer (project developer Future-proof Port Infrastructure at SmartPort) or Lynyrd de Wit (project leader Gel barrier project from Deltares).