Dredging in an environmentally friendly way

Millions of cubic meters of seabed material is dredged and pushed around every year for various purposes.

Disturbing the seabed constitutes a source of pollution and while dredging supports fundamental needs of societies, tough legislation is in place to protect the marine environment and keep pollution in check.

Environmental protection agencies around the world are constantly raising the bar, which puts innovation at the heart of the dredging industry to drive new green technologies.

So how can one ensure that dredging activities are carried out in an environmentally friendly way? The answer: by using modelling software!

Dr. Jacob Hjelmager Jensen, Head of Projects at DHI, answers following questions about the role of computer models in dredging today and shares his insight on how models will drive innovation going forward in this digital age.

Q1: What is dredging?

Dr. Jensen: Dredging is a massive business encompassing a wide range of activities on water. This could be nourishment of beaches to combat coastal erosion, creation of land reclamations, maintenance of river mouths for flood mitigation, maintenance of port access channels and port basins, trenching of pipelines and cables, sand mining, dredge spoil disposal, sand capping and so on. Common to these are that seabed material is relocated as part of an intervention.

Q2: Why should we be concerned about the effects of dredging?

Dr. Jensen: Dredging operations often create turbidity plumes. Excess turbidity in the water has the potential for triggering permanent and damaging impacts to our marine environment. It can be tricky as dredge plumes are not always visible from the surface of the sea. To understand the seriousness, try googling ‘dredging penalties’. Several examples of exorbitant fines for violating, for example, ocean dumping acts can be found. Awareness and strict enforcement are key to fencing the problem. Regulators and Environmental Protection agencies set the bar. Dredging, port and waterway engineering communities drive the innovation to comply, and it’s a constant source of admiration to me what this industry is achieving technically to keep up.

Q3: How is DHI contributing to this industry?

Dr. Jensen: DHI services the dredging industry by offering our expert advisory and trademark models both rooted in our detailed understanding of the complex processes associated with stirring of seabed sediments. I am very pleased that we have launched a pioneering web-based application this year which allows easy access to complex modelling, where dredge plumes can be emulated in full, seamlessly and coherently. This will definitely make life easier for our clients and hopefully boost the potential of computer models in driving innovation within the industry.

Q4: What are the benefits of using models?

Dr. Jensen: This is a nice one! For starters, models can be used to shape and test eco-friendly solutions, mitigation options and determine ‘environmental windows’ for limiting impacts of dredging. We commonly use models to optimise and validate dredge plans prior to dredging works (for example, at the initial Environmental Impact Assessment stage). Models are particularly useful for distinguishing dredge plumes from background concentrations, assess cumulative effects and impacts during extreme events; something otherwise difficult. There is a long list of possibilities within the operational space. For instance, we see a potential for using models as an integral part of the vessel control system to guide onboard decision in real-time.

Plume from disposing sediment contained in a 10-litre bucket. Imagine the plume from 1000 m3/DHI photo

Models have a lot to offer. If data is sparse, models can fill data gaps and de-risk projects. However, if supported by live onsite data stream and made web-accessible then traditional models will advance towards truly digital twins unlocking new possibilities.

Q5: Can you give an example of a solution where models made a difference?

Dr. Jensen: I always like to talk about feedback monitoring – a DHI specialty that is endorsed by PIANC– and how dredging can be proactively managed to minimise impacts. This is a lovely example of how models can be used intelligently to cap impacts and de-risk operations. In short, a plume model is set-up in operational mode, in principle for any given dredging works, continuously calibrated with various data and then used to forecast dredge plumes from dredge plans.

Forecasting of dredge plumes is used to identify risks of trigger level exceedances and thus allows for timely adjustments to the dredging works to comply with environmental targets. The adjustments being tested as well. Using models in operational mode has many upsides for both the environment but also for the dredging companies. At this stage, feedback monitoring is more suitable for larger infrastructural projects. Without doubt, it has broader potential and we are therefore developing methods that will push feedback monitoring beyond its current applicability. This we believe will contribute to the continuous innovation race.

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Photo: DHI

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