AFON
Willow Spiling: A Natural Solution to Flooding
One cold November morning, a group of young Yorkshire Wildlife Trust volunteers found themselves crammed into a van on their way to begin work on a natural flood management project in Leeds. Our goal was to reinforce the banks of the river Aire through the process of willow spiling.
Me carrying out willow spiling
We began at Esholt Hall, a waste-treatment site where willows had been planted to combat possible future spillage events. With the rain closing in the hard work began. After hacking through a sea of brambles we spent the morning coppicing willow to be used the next day for spiling. Autumn and winter are the best times for this as the willow has the highest amount of energy stored in its stem for regrowth. Wet and aching we finally headed back to the van for lunch and a hot cup of tea, preparing us for our next task – sorting the cut willow into piles and attaching them to the trailer.
The next morning the sun was out for our first day in the river and, after a show from a local kingfisher, the fun began! We fought our way into our rubbery waders and braved the fast-moving, icy water, knocking in live willow posts along a line about a metre in front of the bank. Once the posts were in position we could start spiling. Rods of bendy willow were weaved between the posts in both directions to create a robust structure. The species of willow used was a fast-growing hybrid that would mature to be small and bushy, leaving space for other plants to grow in between and further strengthen the bank.
After the willow had been weaved to the height of the bank, we began to fill in the gap between the bank and the fence. The gap was filled with bundles of the shorter branchy sections of willow and then covered with a thin layer of soil. The bundles catch loose sediment in the water, preventing it from building up downstream and causing floods.
Willow spiling is typically done far upstream where the risk of flooding is lower than it is downstream. Flooding occurs due to a large influx of water into the river, this can be more damaging downstream as the river channel is wider and flatter due to the deposition of sediment by the water. A large influx of water causes the water levels to rise and where a steep channel reduces the flood risk upstream, a flatter channel downstream means that flooding is more likely.
After a day of fun working in the water our efforts had paid off and the spiling had successfully been completed. If we were to come back in a year, the bank would be covered in shoots, the willow’s root system would be starting to strengthen the river bank and the river would flow much slower and cleaner.
The removal of trees and other vegetation in Yorkshire’s uplands had reduced the land’s natural ability to retain water and prevent surface run-off, when water runs straight over the ground into the river, causing a sudden rise in the water levels. This, along with the increase in extreme weather events due to climate change, has led to a heightened risk of flooding in the more densely populated lowlands. Natural flood management strategies, such as willow spiling, offer a cost-effective and reliable solution to this problem and are therefore becoming increasingly popular in the region.