Reducing the carbon footprint

Pressing the CO2 buttons

In order to significantly contribute to reducing the carbon footprint of marine engineering projects, a distinction can be made between five important emission factors, otherwise known as ‘CO2 buttons’:

1. The equipment deployed

2. Execution

3. The design

4. The sandpit

5. The ecosystem in which the project is located

Project designers usually ‘press’ on buttons 2, 3 and 4. Button 1 should be considered an autonomous trend in the dredging sector. Button 5 represents the natural system with which the project interacts and designers can also press on this button if they integrate nature as “building block”.

Equipment

This refers to the dredging sector’s efforts to develop more energy efficient vessels (which are of all equipment used in a project, the biggest emission source) and to use cleaner fuels in order to reduce CO2 emissions. This efficiency oriented effort is largely cost driven, since a substantial part of the costs associated with dredging projects relates to fuel use.

The average economic lifetime of a dredging vessel is 25 to 30 years, therefore, dredging vessels are not replaced frequently. So although older vessels are often upgraded and updated in certain ways, the latest generation of vessels represent a smaller carbon footprint. In recent years, the trend away from heavy fuel oil towards gas oil has been a response to the pressure exerted by international laws and regulations on the industry to switch to cleaner fuels.

Execution

This “button’” refers to the efficient (or more efficient) deployment of equipment and thus reduced fuel use. Dredging companies are already making this change ‘organically’ because it directly affects costs. For example, optimisation in execution is being sought, primarily in collaboration with customers, through measures such as reusing materials and reducing transport distances. These are solutions, which involve direct placement rather than pressurised sand delivery and make it possible to use larger vessels and use them much more efficiently.

Design

A project can be designed so that it requires less sand, perhaps by seeking a thorough balance between the construction and maintenance phases, between hard and soft elements and the reuse of materials within a project. Using so-called ‘Blue Carbon Ecosystems’ is a possibility for actively sequestering CO2. In this respect, consideration may be given to using natural systems, such as salt marshes, mangroves, as well as cultivating dunes and willow thickets. Thanks to clever design optimisations (leading to minimum sand in design and for maintenance), dredging companies have reduced the amount of sand needed for construction projects which has led to fewer trips between the project location and the sandpit, resulting in lower fuel consumption and lower carbon emissions.

Sandpit

At the outset, this button relates to the selection of the extraction area, the transport distance between the extraction area and the project site, and extracted material that is brought to the surface – emission factors that cannot be ignored. A sandpit, however, also creates a potential storage site for silt and organic substances, and thus for CO2 as well. Location, orientation, shape, and method of extraction from the sandpit all impact the quantity of silt that is captured, both during and after extraction.

Ecosystem

This button refers to the interaction between a project, execution, sandpit and the ecosystem where the project is located. Nutrients released by activities such as dredging stimulate the growth of algae that absorb atmospheric CO2. These algae are ultimately deposited with the silt in the salt marshes where the CO2 is then sequestered. A sand replenishment project can create a lee zone behind which a salt marsh can develop and, in turn, where CO2 can be sequestered. However, a substitution situation could also arise, silt that is deposited in a sandpit will no longer be available for the later development of a salt marsh.

Execution, the design and the sandpit are the CO2 buttons that marine engineering project designers can press. In this respect, it is important to realise that one of these buttons cannot be pressed without affecting the others. For example, execution is dependent on the amount of soil a project requires, but also on the equipment the contractor deploys. The combination of equipment deployment, design and sandpit impacts the environment, and vice versa.

A green case study

The Hondsbossche and Pettemer Sea Defence (HPSD) (Figure 1) is the weakest link in the sea defence of the North-Holland coastline, a structural eroding part of the Dutch coast (Figure 2). The project is part of the national High Water Protection Programme and comprises the construction and maintenance of a new sandy coastline.

The Van Oord – Boskalis joint venture, responsible for design, execution and maintenance, has just reached the stage of having deposited 36 million cubic metres of sand sourced from the sea. Executing the works with a minimum carbon footprint is one of the greatest challenges, as with any other marine development project.

The €140 million HPSD-project for Waterboard HHNK commenced in early 2014 and encompasses sand replenishment for the construction of a combined beach-dune system in front of the old dike, a sea defence of pitched stones. Also the connection with the adjacent dunes north and south of the dike is included. The new coastal area is designed so that it offers room for nature development, flora and fauna and recreation.

After completing the construction phase of the project on 31 December 2015, the Van Oord – Boskalis joint venture will be responsible for maintaining the coastline for another 20 years. The replenishment activities are carried out with four medium size and two jumbo size trailing suction hopper dredgers depositing 36 million cubic metres of sand sourced from sea.

The project was awarded with consideration of the fact that both Van Oord and Boskalis are certified on the highest level of the so-called CO2 Performance Ladder, which makes actively seeking to reduce the carbon footprint of the project one of the contract requirements. The CO2 Performance Ladder is meant to help clients, such as Waterboard HHNK, develop a sustainability policy. It also encourages contractors to become aware of their carbon footprint in their operational activities and in project execution. As a consequence, the joint venture must now do its utmost efforts to use materials efficiently, introduce energy saving measures and utilise renewable sources of energy.

In the HPSD-project, it can be concluded from analyses of emission data that the interaction between all of the above CO2 buttons has resulted up to now in a carbon footprint reduction of 5 to 10%, compared to the original estimation made during the tendering phase.

Getting even greener

Although the construction phase of the HPSD-project has not been finalised yet, the results already indicate that with a combination of smart design and (wet and dry) equipment deployment, more emission reduction can be achieved than with only focusing on the dredging vessels.

To examine this in greater depth and to be able to include the results in future projects, Van Oord and Boskalis joined forces with NGOs (The North Sea Foundation and Wetlands International), engineering and consulting firms (Arcadis, Royal HaskoningDHV and Witteveen+Bos) and Deltares, a Dutch institute for applied research in the field of water, subsurface and infrastructure.

The goal is to develop and construct marine engineering projects that leave a much smaller CO2 footprint over their entire lifecycle than they would have with conventional design and construction methods. Ultimately, the aim is to achieve at least a 20% smaller CO2 footprint over the lifecycle of maritime engineering projects constructed after 2020.