Last week we posted a blog about our working washland near Plumpton. One week on and our working washland is complete. The weather has obliged us by raining heavily for a few days, filling it with water, so that we can show you exactly how it works.
When you look at the site, you would never imagine that such a small, innocuous valley could make such a huge contribution to reducing flooding locally, and to biodiversity. But witnessing just one of these projects in action makes you realise just how easy it would be to capture and store millions more litres of water in our countryside, in flood storage that would benefit people and wildlife.
At the final count, the additional flood water storage water that the site creates is a whopping 350,000 litres (350 tonnes) of water, and that’s BEFORE the site floods! Once it floods, the flood storage in the valley could be anything from around 350,000 litres to 1,350,000 litres of extra flood storage, depending on the height of the flood. This flood water is slowed down and spread out across the land, allowing silt and other debris to drop out of the water, making it a much less dangerous flood peak, benefitting soil fertility and reducing pollution and siltation in our rivers.
When we started this project, we thought that the majority of the water flowing into the site would be flood overflow from an adjacent stream. What has happened instead is that it has filled up rapidly from rainfall running off the surrounding grassland slopes. This is particularly interesting. In a natural meadow like this, it is widely accepted that the rough grassland will slow
down rainfall enough to enable most of it to filter into the soil and away into aquifers rather than flowing over the land surface. However, the intensity of the rainfall meant that instead, there was very obviously a lot of overland surface water flooding filling up the new washland, way before any actual river flooding took place. The soil on the site is some of the best I’ve seen, so it is not soil compaction creating this flood run off, it is simply the volume of water falling onto the slope in a short space of time.
So our new washland is helping to store both river and ‘land’ flooding, and in doing so is creating some really nice restored wetland habitat. Seeing so much water appear in the washland overnight was fantastic. I can’t wait to see what wildlife shows up next spring.
What does Natural Flood Management look like on the ground? There are all sorts of things we can do to slow and store water in our landscapes – planting trees and hedgerows, digging ponds, putting natural wood back in streams and more. We can also restore natural washlands – but what are they?
Washlands are areas of land where water can spread out, slow down and be stored temporarily, whilst it’s flooding. Some of the biggest potential for storing excess flood water when it’s raining hard is in our smaller stream floodplains. These are often where the land use is less intensive, and where there is space for water to come and go periodically without adversely affecting people and farming.
Water follows the line of least resistance. If we can create those lines of least resistance in the right places, then suddenly water is flowing into all the areas we want it to, rather than into our houses. At the same time, we can provide climate regulation, water purification, pollination, wildlife habitat, better green spaces for people and much more.
This week we spent a couple of days with an obliging landowner and a digger, restoring the relict course of an old chalk stream. Diverted decades ago to feed a local mill, the old stream bed only really gets wet now when it floods. The local landowner saw the potential to make the stream a more active flood relief channel, and we went to work.
It’s been fantastic watching it take shape. All we needed to do was to make it easier for the flood water to find the old stream channel, and the water and natural gravity will do the rest. We’re only half way through the project, and already we have created around 100 tonnes of extra flood water storage, as well as a fantastic area of habitat for wetland wildlife.
... now we just need some rain to check that it works !!