Interview with Luca Sittoni: Dredged sediment is the new gold

Sustainability means acting in a way that is not harmful to the planet, preserving natural resources, and thus supporting long-term ecological balance.

By adhering to principles of sustainability for dredging and dredged material management by using natural systems to integrate these actions, the dredging industry believes that the goals of environmental quality and economic prosperity can both be achieved.

Regarding this, and many other related topics, we caught up with Mr. Luca Sittoni to find out more about the latest developments in these processes.

DT: Can you tell our readers about your academic and professional background and experience, current project you are involved in?

Mr. Sittoni: I am Program Manager Sustainability at Deltares, an independent institute for applied research in the field of water and subsurface. Within the Sustainability Program, we focus on developing and mainstreaming sustainable solutions for deltaic environments, with focus on Nature-based Solutions and circularity of natural resources.

At Deltares, I especially focus on managing research and development projects and develop new opportunities related to Nature-based Solutions and beneficial use of sediment, like: sustainable dredging, wetland development, dike reinforcement or contaminated site restoration and remediation.

These projects are generally multi-disciplinary and multi-stakeholder, developed and executed in co-creation with public and private parties.

I also take an active role in the EcoShape – Building with Nature consortium, where I am part of the management team and responsible for a portfolio of pilot projects that focus on beneficial sediment use.

In the new EcoShape format, which just started at the beginning of 2021, I lead the Beneficial Use Table and participate in the Strategy Team.

DT: Do you believe that dredging industry can make a difference in improving the environment’s quality, and what is your opinion on this?

Mr. Sittoni: Let me start with a bold, but in my opinion, very important statement: we need to consider dredged sediment (mud, sand, all dredged material) as a new gold!

Sediments are a very important natural resource. We simply need to learn how to use it in a sustainable way within its natural cycle. If we don’t use it in the right way, we can easily create unsustainable situations.

For example: when we build dams, all the sediment stays behind them. Downstream the dam, we have erosion of the riverbed, often till the sea.

When we build harbours, sediment settles inside the harbor basin. This creates issues for navigation, so we need to dredge. Often the sediment is disposed at sea, while a few kilometers downstream we may have a situation of sediment starvation with coastal erosion or wetland retreat.

The global need for economic expansion along the coast, for navigation, port development, residential or recreational uses, etc. is putting big pressure on natural systems everywhere.

Yet, natural systems – for example wetlands – are key habitats with unique species of flora and fauna, with great biodiversity. Plants and animals trap and hold sediment, creating protection against erosion and flooding of nearby communities. They also help sequestering green house therefore contributing to climate mitigation.

Also, there is a great opportunity for the dredging industry to make its know-how experience and technology available to understand, mimic and proactively use these natural processes, using dredged sediment as a key resource to favour human and ecosystem development and restoration at the same time.

It is thus clear that the dredging industry is a key player in our ambitions towards sustainable development. Sediment is the foundation for climate adaptive dykes, healthy and biodiverse coastlines, livable (coastal) cities, and primary resource to counteract subsidence.

DT: A dyke made of the clay from the clay ripeners (Kleirijperij) near Delfzijl was tested in the Delta Flume of Deltares recently. A full-size cross-section of the dike has been constructed in the flume and is being subjected to the conditions of a superstorm. Our readers would love to find out more about this very interesting project?

Mr. Sittoni: In the North of the Netherlands, the Eems-Dollard estuary is too turbid, likely because of recent human interventions. These high turbidity levels cause low productivity and poor water quality status. At the same time, the Water Authority Hunze en Aa’s needs clay to strengthen the dike that bounds this estuary, because of climate change and sea level rise projections.

There is thus an opportunity to use the sediment from the estuary by taking dredging sediment from the Delfzijl harbor channel, let it ripen (for three to five years) and use the resulting clay to strengthen the dyke. In simple terms, this is the concept.

In general, we try to answer to the question whether we can build the dykes with natural available sediments. This is what the Dutch used to do a few decades back. But there is a catch: following the current Dutch regulation, clay to build a dyke needs to have specific characteristics. We can not just use any clay for these purposes.

It turns out that the sediment we are ripening into clay has too much salt and organic matter, and this takes longer than expected to decrease.

The Delta Flume tests, together with other smaller scale research activities, are designed to test and prove that, even if this clay has too much salt and organic matter, it can be used safely to build a dyke which will withstand a big storm. Also, these experiments test whether we can build a dike with smaller slope.

In this project, different partners are involved. The Dutch Flood Safety Program (HWBP) is the main sponsor of this research, under the responsibility of the Water Authority Hunze en Aa’s. EcoShape partners van Oord, Boskalis and Deltares carry out the research, but also invest in-kind. The central government participates too, through the subsidy TKI Delta Technology.

With the knowledge of this research trajectory, the water authority can improve the design of the demonstration project Broad Green Dyke, assuring its safety. This demonstration project will be a short reach of the Eems-Dollard dike built with the clay produced by ripening Eems-Dollard dredge sediments.

If the demonstration project proves to be successful, Hunze en Aa’s will build the entire 11 km stretch of dike with locally produced clay. The results of this research and of the demonstration project will also be of general application to increase the predictability and applicability of locally extracted dyke material in the entire Netherlands and likely abroad.

The Delta Flume tests will be completed in 2021, the research trajectory in 2022. The construction and monitoring of the demonstration Broad Green Dike project will start in 2022 and continue through 2024.

DT: Sustainability now comes in many forms, and as a scientist, you have knowledge, data and expertise to make a positive difference. What are your priorities when it comes to protecting and restoring coastal ecosystems?

Mr. Sittoni: First, I’d like to clarify that sustainability goes beyond green. There is still a bit of confusion when it comes to green, sustainability and environment. Sustainability includes three important pillars: environment indeed, but also economics and society. We cannot have sustainable solutions that only focus on one or two of these three items. Green is thus important, but it is not all.

For example, when we wish to transport dredge sediment from a harbor basin to a starving wetland a bit further away or to reuse it as clay to build a dike, dredging activities will likely be more expensive, impacting a larger number of stakeholders (like community, city, tourist industry, nature areas).

The only way to make these solutions truly sustainable is to create stakeholder engagement and financial models which support these activities. Luckily, sustainable (like nature-based and beneficial sediment use) solutions are perfect for this because they offer a wide range of benefits which are valuable for a broad range of stakeholders.

For example, city and tourist industry will benefit by a wetland park near the industrial harbor. Also, local authority will be happy to use clay that is made by ripening dredge material in her dikes.

The State and the European Union will support biodiversity enhancement, climate mitigation and adaptive solutions. Interested in the outcome and to enjoy these benefits, these stakeholders will likely agree to pitch in the project, investing in these solutions. Therefore, when able to leverage upon and accounting for all benefits, sustainable solutions often happen to be cheaper (in relation to the benefits offered).

Also, they are generally supported by a wider range of financial resources – usually coupling private, public and subsidies. This proves that environment (green) intrinsically goes hand in hand with social (stakeholders) and economics (cost and financing).

My priorities are to protecting and restoring coastal ecosystem, but really, to go beyond these truly sustainable solutions and to:

• Think and act in “system” terms, understanding and accounting for the physical, ecological but also social and financial dynamics of the broader system (for example beyond the single infrastructures). We need to move from an objective-based asset management to a system-based asset management, or a landscape vision;

• Proactively embrace natural dynamics, focusing on building with nature (not against nature) and beneficial sediment use;

• Develop a policy ecosystem that synergizes human and nature development, where governance as well as fiscal and financial policies privilege long-term sustainable solutions and multi-party multi-sector collaboration.