Forestry: Silt Sump and the seven-minute solution to silt management

ON any forestry site where intensive work is being undertaken – such as harvesting or road construction – silt is likely to be an issue. 

Disruption of soil can lead to sediment being washed into nearby streams, rivers, or lakes, where it can degrade water quality, affecting both human and ecological health.

Excessive silt can smother fish eggs, clog gills and destroy habitats for organisms that depend on clear water for feeding and breeding, as well as polluting drinking water.

Water flows into a newly installed Silt Sump. (Image: FJ/JM)

Silt erosion can also result in the loss of fertile topsoil, making the land less productive for future forest growth and affecting the long-term health of the forest ecosystem.

As such, foresters are expected to take a proactive approach to silt management on site, but existing practices can leave much to be desired.

It’s a serious problem, but one that’s unlikely to keep many forestry professionals awake at night.

The exception is Drew Gall, who has been fascinated by the problem of silt mitigation – and how to improve it – for years. His enterprising work in the field has now led to the creation of his own company, RDK Environmental, and the launch of its first product, Silt Sump.

The sump in action. (Image: FJ/JM)

A quarry manager working with Forestry and Land Scotland, Drew had long been frustrated with existing approaches to managing silt runoff.

His dream was to develop an environmentally sustainable, recyclable and cost-effective solution which could replace more expensive, environmentally harmful materials and reduce the need for ongoing maintenance. That dream finally crystallised in 2023 when he won the Emerald Challenge, run by the Institute of Quarrying, which offered a £5,000 grant for innovative ideas to support the industry’s net-zero carbon and sustainability ambitions.

Silt collects in the trap and can be removed, quantified and documented. (Image: FJ/JM)

“The concept was born out of frustration,” Drew explained. “Working over 10 years in forestry, I got sick of seeing ineffective approaches to silt management. On too many sites you’ll see some silt netting and a bale of straw in a ditch and that will be it. Go back a year later and it’ll still be there, clogging up the ditch, doing nothing for watercourses.

“The idea for Silt Sump started off as a thousand-word essay for the Emerald Challenge and I didn’t think it would get through, but eventually I was told I was joint winner.

“All I had at that point was the concept. But winning the challenge inspired me to put pen to paper and start designing it.”

Drew has spent most of his time since then deep in product development, producing prototypes in different sizes, designs and materials, and calling on the help of friends in the industry to conduct extensive trials on site.

Drew Gall of RDK Environmental, creator of Silt Sump. A former Royal Engineer, he was informed soon after Forestry Journal’s visit that he has been shortlisted for ‘Innovator of the year’ at the Scottish Ex-Forces in Business Awards. (Image: FJ/JM)

“The design has come a long way from where it originally started,” he said. “I tried so many different materials, searching for something that was environmentally friendly, recyclable and reusable. I actually started with hessian, which from an environmental perspective would have been great, but it just rots in the water.

“There’s been so much back and forth with materials, all different grades. A lot of people look at it and think it’s just a one-tonne bag. But a huge amount of development went into this to make sure it actually works.”

The finished product is made out of a woven polypropylene (PP) plastic which is 30-per-cent recycled and can be reused multiple times.

There are three different sizes: 450 mm, suited for small roadside ditching requirements; 800 mm, ideal for forest road construction; and 1,000 mm, designed for large-scale utility upgrades and windfarm construction projects.

When placed in a ditch, Silt Sump’s design allows for water to enter at one end and gradually fill the bag, before pouring out the other end. The process interrupts the flow of water, allowing silt to settle and be captured in the trap.

When full, the Silt Sump can easily be removed from the ditch, the silt tipped out, and then put back to work.

If it looks simple, that’s because it is, and Drew has devoted a huge amount of time and energy to making it so. 

Lightweight and durable, the solution has been praised not only for its performance and reusability but also for its simple installation – something that has been one of Drew’s top priorities from inception, with the name RDK Environmental standing for ‘Rapid Deployment Kit’. 

Forestry Journal met up with him at Clachan Quarry, Cairndow, where numerous Silt Sumps have been in place for months. 

Demonstrating just how rapidly the kit can be deployed, he said: “A big advantage is it’s very self-contained, so lightweight. You can have five of these sitting behind the seat in the work van, in case you come across a need for them on site.

“The idea is that one person can put them out, on their own, quickly. I’ve got it down to seven minutes, from start to finish installation. It’s really that simple.”

A tour of the roadside ditches at Clachan Quarry revealed the impact Silt Sump has when multiple traps are installed in a daisy-chain sequence, slowing the flow of water and giving silt a chance to settle.

Every Silt Sump installed along the chain offers another opportunity for filtration, leaving the water cleaner.

“In the forestry industry, we’re not just dealing with foresters and civil engineers, but with SSE, Scottish Water, SEPA and other stakeholders who all want to see evidence that this issue is being taken seriously,” said Drew.

“With previous systems, there’s no way to document how much silt is being prevented from reaching rivers. But as soon as you put it in a bag you can quantify it.

“By deploying Silt Sump, you can go back to the likes of SEPA and show you’re going a little bit further than putting a bale of straw in a ditch. More than that, you can actually quantify exactly how much silt is being removed from the watercourse.

“Say I put out 10 Silt Sumps around a site. One, when full, holds roughly 70 kilos of silt. So when they’re all full I can prove I’ve taken out 700 kilos of silt which otherwise would be flowing down into the river.

“Once the job’s finished, you can extract, document and actually tell people how much silt you’ve taken out of the watercourses. Then take them to the next site, where they can be reused. I’ve made them robust enough that they can be reused over and over again.”

Earlier this year, Drew left FLS to join road construction specialist A&L McCrae (an early supporter of Silt Sump) as silt mitigation specialist.

This has allowed him to expand trials of Silt Sump across A&L McCrae’s sites and demonstrate the product’s effectiveness to visitors from different sectors.

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Drew said: “Interest has come from a range of industries – quarrying, utilities and forestry – from as far north as the Shetlands and as far south as Cornwall. People recognise the need for change. The days of just throwing a bale of straw in a ditch and calling it silt management are definitely out the window.

“With Silt Sump there is now something on the market that is bespoke, created and tested by people from within the industry, and designed to do the job.”

Now attracting interest from forestry specialists, civil engineers and ecologists involved in windfarm and other infrastructure projects, hopes are high that Silt Sump could soon become an essential tool across multiple industries and form part of standard working practice on forestry sites.

“The beauty of Silt Sump is it’s low cost, easy to install or remove and can be reused again and again,” said Drew.

“It creates a capture point that you can see. You can document how much silt is being removed and it looks good. It’s another weapon in the armoury which offers accountability and actually proves you’re taking your responsibilities to the environment seriously.”

For more information on Silt Sump email Drew on info@siltsump.co.uk or visit www.siltsump.co.uk.

Keep an eye on the Forestry Journal YouTube channel for a step-by-step installation tutorial.