Slowing the flow with Leaky Dams
- Natural Flood Prevention
- Holds Runoff
- Increases Water Penetration into Soil
- Self Regenerating Structure
For a variety of reasons, Run Off from higher ground and Flooding are becoming more common, year on year, often with devastating consequences for land and infrastructure alike.
Some of the solutions must necessarily be at the societal scale but others are more accessible to communities and individual landowners.
A natural & sustainable solution, that is relatively accessible and affordable at any scale, is the installation of “leaky dams” to slow the flow.
Watercourse
The first type is designed to be installed across existing streams.
Natural or processed wood is laid perpendicular to the stream flow and fixed in place on both sides of the stream bank.
Typically a gap is left to allow the free flow of water beneath the dam during normal flow periods.
This allows for the free passage of fish and other aquatic life during normal flow periods.
In periods of high rainfall, when the stream fills with fast flowing water, the dams come into effect causing the water to back up and create temporary pools, thereby slowing the flow of water from higher ground.
Surface Runoff
The second type is designed to intercept and slow the flow of surface run off water before reaching the streams.
It is this surface run off water that is so damaging to soils, often scouring the soil and organic matter en route.
They are used to slow down the flow of surface water before it can gather pace & volume further down the slope scooping up valuable top soil along the way.
A physical barrier is created – up to 60cm high – that slows the flow of water forcing it to back up behind the dams allowing any soil & organic matter to settle out of the water rather than being dumped into streams or rivers or even roads or properties further down the valley. This slowing of the flow also allows more time for the water to penetrate into the soil, particularly where there are plant roots present.
It is this ability of plant roots to create fine channels in the soil facilitating water penetration that makes Living Willow particularly useful in this context. Fast growing shrub willows are renowned for their rapid growth producing extensive & fibrous root systems that are known to stabilise soil & maximise water penetration. You could say that the presence of an extensive willow root system “turbo charges” the soils ability to absorb and store water. This in turn helps to restore the natural water cycle whereby the water is enabled to penetrate deep underground, recharging deep aquifers and enhancing long term water security.
Self Regenerating
Any timber used in a leaky dam will create a physical barrier that will slow the flow, but will ultimately rot and need to be replaced in time.
One big advantage of using Live Willow Vertical Stakes is that they do not decay AND they will also produce an abundance of living material that can be cut with secateurs/loppers and used to top up the horizontal bundles or brash.
This will eliminate the onerous job of bringing in replacement material from off-site.
In effect they are self regenerating.
Hardy
They are tough, resilient, fast growing and adaptable to a wide range of growing conditions including exposed sites, high altitudes, poor soil, flooding in the winter and dryer conditions in the summer many of which are typical of sites where leaky dams are most useful.
BioDiversity
Willows are known to host a large diversity and abundance of insects which creates a strong foundation for building bio-diversity and resilience further up the food chain. Producing abundant catkins early in the spring when little else is available willow is particularly good for bees and other pollinating insects.
Carbon Capture
Willow is very fast growing, meaning it captures a relatively large amount of carbon compared to other tree/shrub species over a similar timescale.
Soil Fertility
Willow produces an abundance of leaf litter which adds valuable organic matter to soil improving the soil habitat and therefore the abundance and diversity of biological life in the soil. This process is part of what makes willow such a good pioneer plant in the wild as it improves the quality of the soil enabling other less resilient species to colonise as conditions improve.
