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Where there's a will there's a Willow..

Trees are quite remarkable, and we're only really starting to venture into how they can resolve problems that we've grown used to throwing concrete or plastic at (often making the situation worse in the long run. Sometimes where there's a will to try something new, the answers can come from updating something old - traditional techniques that, with our expertise and experience now, we can use to make significant positive change. 

Our Trustee, Bob Vaughan, isn't just incredibly experienced in the theory, knowledge and policy behind water, landscapes and trees. He gets out there and demonstrates it in practice. I'm delighted he's able to share this blog about a fantastic, simple, yet incredibly effective river restoration project he set up this winter, using the wonderful Willow tree and a practice called Spiling. 



A tributary of the River Trothy in the Wye Catchment was eroding its bank adjacent to a property.  Recent changes in flows and turbidity worried the owners and they were increasingly concerned that erosion could threaten their garden and home.  Neighbours had already installed gabions (wire mesh cages filled with stone), but access here was difficult, and gabions require in-river work, including digging out the bank.  This would affect the stream and reduce the already small garden.  Gabions are also harsh structures which is out of keeping with the sites’ rural nature.  A quote to install them came in at £500 a linear metre.

On hearing their concerns, I suggested they discard an engineered approach and consider a natural solution.  For the twenty-five metres of riverbank forty willow posts, ten centimetres (4 inches) in diameter, and over 2 metres long could be hammered into the stream edge as deep as possible (at least half a metre).  Then long flexible willow whips are woven around the posts with the bottom of the whips pushed in to the bank to encourage rooting.  The posts and whips would not only absorb the energy of the stream and protect the bank from erosion, but the willow would also root into the bank creating a lattice which stabilises the soil.  And of course, the entire wall would be a living green hedge.

All willow species easily root and for this job they should establish quickly and provide the protection required.

The best time to install willow is in winter when the plants are dormant.  As you are planting alongside water and access into the stream/river is needed it is best to install either early on in late autumn or at the end of winter.  This should reduce the likelihood of high river flows which makes installation difficult or even dangerous.  More about what happened later!  If entering water ensure you use appropriate clothing, footwear, and safety equipment.

The householders were persuaded to give it a try.  A delivery of posts and whips arrived from Wye Willows in March 2024 and laid out on the bank.  The posts were set between 60cm and 75cm apart with the shorter distance reserved for the outer bends and where the stream bed slope was steepest and water velocity greatest.  A pilot hole was driven into the stream bed with a metal bar close to the bank.  The willow posts were then inserted and hammered in.  At first the posts were not rigid but would become so once the whips were installed.  Heavy rain overnight had raised the stream level and sediment had turned the stream akin to tomato soup.  This made it difficult to align the posts and pilot holes.  However, we were fortunate that the stream bed was not too stony, and the posts went in with a little persuasion.  We used a fencing maul to drive the forty posts from above, taking care on the bank to prevent collapse.  A few posts started to split but, in these cases, we swapped to a Post Rammer.

Once all the posts were inserted it was time for the whips.  Starting downstream the bottom of the whips were inserted into the bank and then, like a hazel hurdle, woven around the posts.  About 5 to 8 whips were used for each weave level, with the next few whips woven in the opposite way.  Special care was taken at either end to tie the weave into the bank to prevent water eroding behind the weave.  The post stood well above the slope and as the weave gradually worked up the posts the whip ends needed to be set further back into the bank.  Weaving the whips is very therapeutic.  The sounds of the flowing water, the gathering of handfuls of whips and weaving them around the posts is remarkably pleasing.  Soon our wall emerged upwards and by close of play on the second day a decent height of whips had been installed over the entire twenty-five metres.

As mentioned earlier, planting during March should reduce the risk of high flows.  How wrong I was; the first few months of 2024 turned out to be the wettest for years.  Overnight torrential rain saw the stream rise quickly up to, and in some cases above, the level of whips installed the day before.  Fortunately, the work was already robust enough to survive the barrage.  A late start was advised, and once flows dropped further whips were installed until the required height was achieved.  The bank behind the new structure was dug over and the gap between the bank and willow filled in.  Further material will be added over time to provide a flat area of the same height as the willow.  This will enhance the garden and enable safer access for maintenance of the willow.  Even higher stream flows occurred over following days and the wall has remained secure.

With such work there is a risk that high flows can erode around the base before the willow has rooted.  The above average flows had already made placing the whips below the water level difficult.  So, when flows receded stone was placed around some of the posts and where velocities were higher, I installed 4 two-metre-long hazel bundles pegged to the stream bed and tied to the posts.  These need only to remain in place for the first year whilst the willow established.

So, over a long weekend twenty-five metres of willow spiling was installed despite two high flow events.  The cost came out at about £60 a linear metre.  As soon as the work finished neighbours arrived with a general agreement on how artistic this work looked.  I doubt this would have happened had a gabion or concrete wall been installed.  Four weeks later and the willow is growing and looking even better.  In coming years, the growth can be treated akin to any hedge; kept at ground level on the garden side or allowed to grow upwards to create a short barrier.  The growth can also be rewoven back into the fabric of the wall.  As for the householders, they are thrilled with the result.  It is very natural, effective, and much cheaper than other alternatives.  So why has this approach fallen out of favour?  Perhaps a little promotion is needed.

By Bob Vaughan


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