Welcome to the Hydrophiles, the HR Wallingford Podcast. I'm Sally Jackson, and today I'm joined by three of our dredging experts to talk about nature positive solutions for dredging. Dredging has traditionally been seen as a rather dirty industry, blamed for all kinds of things, but actually there are so many interesting things we can do with dredging to create biodiversity solutions and nature positive solutions. So we brought three of our experts today together to talk about
those. The first is Mark Lee. Mark's one of the grandees of our industry. He's on expert panels for PIANC, CEDA, IADC and BSI, and he actually wrote a chapter in 'Dredging for Sustainable Infrastructure', and was part of the editorial panel. He's also been responsible for British Standards on Dredging and Land Reclamation. So lots of interesting things to come from Mark, I'm sure. Giulia Sforzi is a Principal Engineer in our
dredging group. She's worked on all kinds of projects for major international port developments, from concept to delivery. The last contributor to our podcast today is Dr Jez Spearman, who's one of our technical directors, and he's an expert in sediment transport and morphology of estuarine waters and in the development and application of dispersion models. So really he looks at a lot of our computer modeling and works out how people can best use their
sediment. So I talked a little bit about already why dredging has been seen as a problem, but how can dredging be a solution? Mark, what is the history of this area, and how are we going to take dredging from being something that people see as a problem to something that people see as a solution.
I think one of the key opportunities relating to nature based solutions and dredging comes from the fact that actually sediment is primarily a resource and not a waste. And I think people often get this idea, as you said, that it's a waste material. But actually, there are lots of important uses for sediment. Also important is the fact that dredged material is primarily a clean and usable product, and people often think about dredged sediment as being contaminated. In most cases, it
isn't. So if you think about your weekend trip to the DIY store, the money that you pay for a bag of sand and gravel to build that patio, or whatever it happens to be, then it's very clear that sediment has a value and is an important resource. Often we have projects where there's a requirement to maintain or deepen a navigational channel for access to a port, that obviously involves the removal of sediment. That sediment has a potential value and a potential
use. Those materials can be used for things like creating new habitats or contributing to coastal defense functions on beaches. The sediment has potential to be used in nature based solutions. We've worked on a number of projects which have involved nature based solutions, and one that we're involved in at the moment is aiming to use dredged sediments helping to stabilize and improve eroding salt marshes in coastal environments.
And just to be clear offshore disposal sites, it's when the sediment is taken out to sea to be disposed of away from the shore, is that right?
Yes, that's what usually happens. The material is taken offshore by ship and disposed of. But of course, what we're looking to do is to reuse that material, to recognise it as a resource and to use it in forms of coastal defence or beneficial reuse in coastal environments closer to the shore.
And I assume that if you're not taking the sediment offshore, you're actually reducing carbon emissions because the ship is not going out to sea.
Absolutely, you're reducing the carbon emissions from the vessel, but also you're reducing the duration, potentially, of the project, and also potentially you're reducing the cost.
So by creating new habitat or reusing it,it's not just a nature positive solution. It's actually a climate positive solution.
Absolutely, yes.
So Giulia, you'd like to come in on this.
So, yeah, imagine, for example, that you could use dredged sediments to renourish a beach, and you can bring a lot of benefits to that system reusing dredged material. For example, if the beach is in a state of erosion, you can raise the level and create sea defence, and it is particularly relevant with climate change due to sea level rise, but also you are enhancing a beach system that then can provide a lot of benefits, including financial ones.
That's really interesting, because often people think of environmental projects as being expensive. How can it provide financial benefits, Mark?
I think one of the key things is, how do you actually value nature based solutions? And it's quite a difficult thing to do, because it's not always the case that the benefits are just purely expressed in financial terms. So for example, if you create a new habitat, and there is a potentially a recreational use for that habitat, how do you value that recreational use in financial terms? And this is where the concept of ecosystem services comes along and can be useful.
Ecosystem services are essentially all of the benefits to humans provided by the natural environment and healthy ecosystems.
Jez, I know you've been working on some interesting work at Harwich, perhaps you could outline what's happening there.
Ok so one of the things that is inevitable really is that many of the ports and harbours that are in the UK and around the world are juxtaposed right next to some very valuable coastal habitats. And so those port authorities and coastal managers regulators are trying to negotiate this tension between these two demands of making ports more efficient, digging bigger channels to enable to have bigger ships, and, on the other hand, to preserve those coastal habitats
that Mark talked about. Now, when you deepen a channel to get your bigger vessel in, inevitably, you're digging a bigger hole, so you get more and more sediment falling in. And there's a understanding, as Mark said, that you've got more and more of this dredged material that you could do something with, but if only you could find a way of using that really well to benefit the coastline.
So we've been working with Harwich Haven Authority over many years to develop ways of using dredged sediment in a better way. Harwich Haven Authority is the conservator. That's the official title, or guardian, if you like, of the Stour and Orwell estuary system in the south east of the UK. And that's where the port of Felixstowe is located, which is one of the busiest ports in Europe. It's also where there's a lot of environmentally sensitive coastal habitat, or to you and me, mudflat and salt
marsh. Harwich Haven Authority are responsible for maintaining all of this, including the dredging of the navigation channels to Felixstowe, as well as all the other smaller berths and walls. Since about 1998 Harwich Haven Authority have been using some of their muddy dredged sediment and releasing it carefully so that it is taken up into the Stour and Orwell estuary on the
flood tide. And the intention is to increase the amount of mud present in those estuaries, so increasing the deposition of this sediment on the mud flats, and therefore making those mud flats more resilient to erosion. This approach has a name. In the UK, it's called sediment recycling. Our US cousins across the water call it strategic placement. It's the same thing. Sediment recycling with muddy sediment is less
widely practiced. It's not like you have a big load of sand that you can put next to a mudflat to protect it. It's basically where you introduce mud into the water column, into the water and you let the currents take it away. And the idea is to let the currents take it away so that it deposits on mudflats. But the effects, the benefits you get, are actually quite small. They're really important, but they're actually quite small and really hard to measure. They might be centimeters, perhaps
even less sometimes. And so it's always been quite difficult to demonstrate how successful this sediment recycling is. So one of the problems has been for Harwich Haven Authority that they've never really known how well this has been doing. So at HR Wallingford, we addressed the problem by developing a really, really detailed numerical model of the way sediment enters and moves around within the estuary
system. We spent a lot of time comparing this model with observations of the movement of water and sediment and to the changes in bed level in the estuary system. Once the model was working really well, we reproduced the changes in the estuary, both with and without the sediment recycling, and we were able to identify what happens to the sediment that is released in the sediment recycling. And it's the first time anybody's been able to robustly evaluate the benefits
of the use of this method. Now we found that about 20% of the sediment released found its way onto the intertidal or very shallow sub-tidal areas, and this sedimentation clearly explained the features observed in the bathymetric surveys. We were able to compute that the sediment recycling contributed nearly two hectares of extra mudflat per year.
Ok, so just to clear up a couple of things there. The idea of resuspending this sediment is reproducing a kind of natural phenomena, if you like. Normally, you have sediment in a river, and it deposits as a mudflat. So if you put it in at the right point, then you would hope thatnatural process will be replicated.
That's absolutely the way to think about it. Yeah, it's trying to get back to the situation where, if you like, the dredging is not there. We're just helping the sediment to go along its way to where it always ought to be.
But that's hard to measure, so we've developed this method to measure the benefits of that and shown that it actually grows.
Yeah, absolutely.
Tell me, Jez, it sounds like an excellent project. You know, we've created more habitats. We've given more feeding grounds for birds. We're able to measure it, we've replicated natural processes. Why would Harwich do this? Is it regulatory? Has it saved money? How does it help them, or do they just want to do it because they're an organization that wants to do good?
Well, interesting, the reason that they started with the sediment recycling was regulatory, and it was a part of the consent process from the deepening that happened between 1998 and 2000. But now they've got the bit between their teeth, and they've realized that this sediment recycling is pretty good. It's contributing extra money for that, but actually it's still not as good as it
could be. One of the problems is there's only still a small amount of this mud material that they're dredging and using for sediment recycling. Most of the sediment is still going offshore, and they've realized that most of their dredgers are still spending most of the time transporting this material offshore and coming back. Because of that, Harwich Haven Authority have been looking at ways to improve their dredging further, and they've developed a new type of dredger, which
they've called the Tiamat. This dredger is pretty small. It's cheap to run, and importantly, instead of taking sediment a long way offshore, it releases the sediment into the water column, into the water above it, for the currents to either transport it away or to bring it further into the estuary. The new type of dredger provides the possibility of similar benefits to the sediment recycling, because you are allowing all this segment to go into the water, to be taken upstream on
the flood tide. But it's cheaper and it's got a lower carbon footprint, so it's bringing back all the things that Mark was talking about. Now we've been working with Harwich Haven Authority to evaluate how good this new dredger is, because there's no point having a new dredger if it doesn't actually perform very well at dredging.
So we looked at how good it was at removing sediment, and we were able to use our detailed numerical model that I spoke about in order to evaluate how good the dredger is at providing muddy sediment. And we found that the small dredger was actually as good as a much larger, expensive dredger at removing sediment, basically because it can spend its time dredging, not transporting the
material offshore and back. We also found that the dredger gave many of the benefits of the sediment recycling, but now you have to be clever in the way you dredge. So you have to dredge the parts of your maintaining areas which are mostly furthest landward on the flood tide, and that means you maximize the amount of sediment that is taken upstream. And of course, on the ebb tide, you want to be dredging all those areas which are furthest away, near the entrance.
This idea of keeping sediment in the system is one which is obviously important, not just at Harwich, but has been important on other estuaries, and certainly in the outer Thames, for example. There's been quite a lot of use of water injection dredgers along the berths on the northern side of the outer Thames, and that has a similar benefit in that the material is not taken out of the marine environment and transported offshore.
Instead, it is mobilized from the bed, and in this case, in the case of a water injection dredger, it forms a turbidity current, which basically runs along the bed to deeper areas where it then settles. It's similar to the Tiamat in some ways, but it isn't suspending sediment quite so far up into the water column to be transported as widely by currents. Instead, you got this density current which flows along the bed, down slopes into deeper areas and then settles there.
What I am hearing from Jez and from Mark, is that actually this could be cheaper and easier. Is that right, Jez?
That's the whole point. It can be easier and cheaper, and it's all about honing into those ways in which you can make it a win-win situation. Win for nature, win for the people maintaining those ports.
Another example - in the UK, is what has been done at Poole. So Poole Harbourhad to do maintenance dredging, and they used to bring the material that was removed from that campaign and be brought offshore to what we were discussing before these offshore disposal
sites. And then they realised that a nearby beach was actually under erosion, need of fresh sediment, and because of the material that was excavated was clean, it was found that there was the possibility to create one of these win-win solutions.
So we've talked quite a lot here about what's happening in the UK, and that's quite specific, and some of the habitats, but there are other things happening all around the world that are kind of contributing to showing that we can have win-win solutions for biodiversity and nature, positive solutions around the world. Giulia, perhaps you could enlighten us on a few of those.
Yeah, of course. For example, we were working on a project which is based in the Caribbean. The location of this project is an island which was used for mining purposes, which then has been reconverted into a marine reserve for juristic
reasons. When we were starting to be involved in this project, additional dredging had to be done to widen some of the navigation areas for various reasons, including safety and navigation, and we found that the material that was going to be excavated was actually of good quality, both for construction and, of course, in terms of being not polluted,
being untouched. So we are considering various options of how to maximize the benefits that we can gain with the use of this material, and, of course, the standard solution that you would have put in the past is what we have been discussing before. So displace the material and put it far away. So what we tend to call offshore placement
sites. But we are considering, for example, creating a submerged berth, both for island protection from wave activities, but also potentially for coral reimplantation and creating an artificial reef. We are also considering the option of using part of the sand component of the dredge campaign to renourish the beach of this island. But also another alternative that we are considering is to extend an existing little island to create both additional land for
juristic purposes. And then here I mentioned this because sometimes we think of an environmental benefit solution that they only bring cost but do not bring financial value. This would be an example where it will bring financial value, and this additional land, of course, could also encompass a space for creating, like a solar panel scheme. It would potentially create additional birding breed.
It could potentially create nesting areas for passing birds, as well as, of course, enhancing the benefits for touristic purposes.
So it sounds like ports have a lot to be positive about them.
Yes, and the main hurdle, I think, is that you need to think out of the box. Quite often, ports are in hurry, orI mean, let's say call them clients and project initiators. They are in hurry. They want to achieve their permit as soon as possible. And some of the solutions potentially might be requiring a slightly different type of studies, and therefore they might not want to consider them at first, just because they think that might make their
process longer. And so a lot of these benefits could be lost if there is not an intention in looking beyond the mere objective of your initial dredging campaign.
But this also comes back to the question of valuing the benefits properly that these sorts of projects can provide. So these nature positive solutions need to be looked at properly in terms of the value of the new habitats that they create, as well as the coastal defences and other aspects which are easier to put monetary
values on. So this question of valuing and properly valuing what these projects are capable of delivering will help us in terms of being able to deliver them and for clients to see the value. And also speaking to those stakeholders at an early stage to understand what they know about the system and the environment and what those benefits potentially mean to them.
Now what Mark just said is extremely important. It is highlighting the importance of thinking about these additional benefits the sooner as possible in the project phase, because that's when you will have the possibility to implement those changes. Once you are down into contracting arrangements, then
it might be too late. So even if you are able to identify some positive benefits, then you might not be able to actually implement them because they have not been part of the permitting, they've not been part of the contracting arrangements, and then those opportunities are lost.
Sounds like very sage advice, Giulia, and it also sounds like quite an exciting time to be in the dredging industry. Sounds like the kind of industry is changing its image, and hopefully, you know, in 10 years time, we might be in a very different place in terms of what that industry is providing. So really value your time today. Thanks so much for joining me.