Throughout their long history, ports have been at the centre of changing trading patterns and global economic trends, adapting their design and operations to accommodate evolving trends in transportation and cargoes. As the world increasingly seeks lower carbon solutions, ports are already starting to respond, refining their own operations, and adapting to meet their customers’ needs.
There are multiple low carbon options and eco-friendly measures that ports can (and in some cases do already) implement, including: optimising dredging operations, and, where possible, using dredged material to the benefit of the environment; designing port infrastructure to keep construction materials to a minimum; introducing biodiversity into existing and new structures; taking full advantage of port locations to generate renewable energy on site; offering services to the offshore wind industry; and adapting to support evolving ship design as the industry moves to lower and zero carbon fuels.
Cutting emissions by refining dredging practices and techniques is one of the most obvious areas for ports and harbours to make carbon savings, and this can result in significantly lower costs and can sometimes provide ecological benefits too.
To reduce the volume dredged, understanding exactly how ships move in port and the access channel is key. Navigation simulations can be used to model the manoeuvring of the design vessel to more tightly define the area requiring dredging. We recently used this approach to help a client significantly reduce their maintenance dredge requirement (and associated carbon release), which also saved the customer $4 million in expenditure for dredging (and will continue to save them significant sums as they do maintenance dredging into the future).
Capital and maintenance dredging can also be minimised by designing the port and access channel so that its location, shape and orientation make the most of natural features. Reductions can also be achieved by being precise about underkeel clearance, or deciding to adopt a navigable depth approach where operations are adapted to allow ships to navigate through soft muddy layers present in the port area.
In terms of transporting the dredged material, ports can make carbon and monetary savings by relocating it the shortest practical distance from where it was removed. Harwich Haven Authority, for example, calculated that it could save 1,000 tonnes of CO2 per year by moving its disposal site five miles closer to the harbour.
The ideal situation of course is to not have to transport the material from where it was excavated at all, and that is exactly the approach employed by water injection dredging and agitation dredging, where the material dredged is released into the water directly where it is excavated and dispersed by currents and gradients on the seabed. Modelling techniques can be used to predict where the material will come to rest. HR Wallingford has recently assisted a major international port in adopting just such an approach for a major maintenance dredging campaign – none of the more routine dredging techniques were adopted, purely agitation dredging. The campaign was successful and resulted in a significant carbon and cost saving over the alternative which would have involved many trips to an offshore disposal site. A further benefit was that the sediment was kept in the local sediment transport system, thereby reducing the risk of erosion and potentially costly remediation in the long-term.
Water injection dredging was used during the construction of the Liverpool2 terminal on the River Mersey. HR Wallingford used numerical modelling of sediment plumes, sediment quality and water quality (contaminants) to demonstrate that the technique could be used effectively and to the satisfaction of regulators, thereby unlocking the potential carbon and cost savings available to the project. The modelling showed that the majority of the dredged material released from the water injection dredging would be carried offshore, with most of the material ending up spread thinly over a wide area outside the mouth of the estuary.
Dredged material has the potential for use to benefit and restore habitats. Sand and mud from dredging can be used to restore and create habitats, as well as to provide offsetting for habitat losses from new infrastructure. As well as benefitting wildlife, intertidal habitats may also help store carbon from the atmosphere.