Between September and November 2022, we worked closely with a team of six Engineering Masters students from  Delft University of Technology in the Netherlands alongside our project partner Boskalis Westminster  to investigate the upscale potential of seagrass restoration in the Solent.  

Esmee Menting – MSc Mechanical Engineering, Delft University of Technology: 

Our aim was to (re)design the process or tools in order to increase capacity of reseeding seagrass meadows in the Solent by 300% within two years. We started by analysing the current restoration process applied in the Solent, as well as restoration techniques implemented in other seagrass restoration projects worldwide.  

When reviewing the available literature, it became clear that the success of restoration methods is extremely bound to the local ecosystem and conditions. This leads to an elaborate trial-and-error process that must take place for nearly all restoration projects to establish a fruitful process. Resulting restoration success can be quantified and evaluated by the germination rate; how many seedlings appear per planted seed, per deployment method. 

The reseeding process that is applied in the Solent can be split up into five phases; (1) the collection of spathes, (2) rotting out of plant material (releasing seagrass seeds), (3) filtering seeds from the plant material, (4) packaging the seeds and (5) deploying the seed pods or packages.  

As a team, we identified two critical points in the current process of the Solent restoration effort: 

• The filtration of viable seeds from the plant material is an incredibly time-consuming process step, due to its heavy reliance on manual processing. 

• The deployment of seed (packages) is labour-intensive and might strongly influence the germination rate and thus overall success of a restoration effort. 

After concluding on these focus areas, we created a number of conceptual designs to replace the current filtration and deployment systems. The designs were ranked and selected based on grading criteria such as degree of automation, the result of the separation (filtration), planting speed (deployment) and operating complexity. Eventually, five designs were worked out in detail: 

1. A funnel system that is to be integrated in the aquaria tanks where the ‘rotting out# process takes place, allowing for a first coarse filtration of the plant material and seeds based on buoyancy. 

2. A vortex mixer, which allows for an automated method to perform fine filtration between the seeds and remaining plant material based on buoyancy. 

3. A wheelbarrow mechanism for seed deployment that releases loose seeds into the sediment. 

4. A paperpot mechanism for seed deployment that places a strip of hessian fabric containing seed pockets into the mudflats. 

5. An adjustable mud cart that allows for easier manoeuvring on the mudflats. The wheelbarrow and paperpot deployment systems can be mounted to the mud cart, creating a semi-automated deployment system. 

Finally, we built prototypes of the Vortex filtration system and the Wheelbarrow deployment system. Early tests of the prototypes showed incredibly promising results, where the Vortex filtration system easily, quickly and cleanly separated rice seeds from plant material and dirt. A first-order estimation indicates that this could save over 200 hours on the current scale, which can be allocated to other steps in the process.

The Wheelbarrow system easily deposited rice grains through its deployment tube. The next step in the development of these mechanisms is testing in real operating conditions. We’ve therefore sent the prototypes to the HIWWT marine team to be tried out in the Solent restoration effort. 

We’re really excited to see how these systems hold up in real seed filtering and deployment conditions. The gained efficiency could enable a significant capacity increase of maximally 433% [estimated] when the vortex and wheelbarrow systems are both successfully implemented in the restoration process.