Leaky Dams Are A Feature Of An Increasing Number Of UK Water Catchments, & Here Is Australia’s Answer To Erosion Control
In the West Country, we are well aware of how leaky dams can help control erosion, rainwater run off and inadvertant nutrient enrichment of water catchments. And we aren’t the only ones. In Australia they call leaky dams PCDs, Porous Check Dams. Later in the this text I explain the importance of leaky dams to gardeners and allotment tenants.
As the West Country Rivers Trust have demonstrated, used correctly the dams slow down the flow of rain water after heavy rain, and allow it to soak into the soil where it can replenish underground water reserves. This also prevents soil erosion as the water is slowed down and any sediment in it has time to fall out of the water column and be retained by the porous dams.
Water is then slowly released, in a more controlled way, to allow streams, books and rivers to flow for longer and with less ferocity.
And because the water is retained there are added biodiversity benefits. the ponding of the water creates temporary habitats for wildlife. Fish don’t get swept away and nor do the invertebrates that inhabit streams.
Another benefit, one which farmers appreciate, is that the water table rises and drought is often averted. Fields with adjacent streams controlled by leaky dams are less prone to dry out. Crops keep growing for longer and give higher yields.
Leaky dams, aka PCDs, are a win win for nature and crop yields. It demonstrates how farming and conservation can work together for a better, healthier and more resilient countryside.
In the UK we tend to create leaky dams solely using natural materials but in Australia they sometimes use wire mesh and other manufactured materials.
The two images are a local modification to the normal leaky dam design. They use locally available materials and are very effective at slowing down surges of water. The range of designs and uses of leaky dams is only limited by our imagination.
Leaky Dams, Gardeners and Allotments
So often I see posts online where allotment holders show photos of flooded allotments. Allotments where year after year water courses down a hill and floods the land where the allotment stands.
In some cases the flooding can be reduced by improved drainage, allowing the water to flow away. But in many other cases the answer is to control the water flow, to prevent it flooding downhill to the allotments below. The way to do this could be with leaky dams.
The Fitzroy Basin Association PCD (Leaky Dam) Video
As the following video shows ….
To halt and reverse gully erosion, a two-step approach is essential: resting the affected area and initiating efforts to restore and replant the eroded gullies. This brief video presentation outlines an uncomplicated and budget-friendly technique aimed at reducing the rate of water flow and commencing the restoration of gully bottoms by constructing Porous Check Dams (PCDs). PCDs stand out as an economically viable and low-risk solution for erosion control, an approach strongly endorsed by CSIRO in their comprehensive ‘Gully Toolbox’ toolkit.
For reference I’m adding the approximate text from the video underneath the video.
Today, our focus is on property building and addressing an essential aspect: Porous Check Dams (PCDs). PCDs are designed to regulate water flow, reduce sediment transport, and contribute to rebuilding gully floors effectively.
Two main types of PCDs have been employed in this project. Firstly, the mesh and post wedge-shaped design are implemented. Steel structures are placed across the gully, approximately 400 millimeters above the lowest point. Then, chicken mesh with a diameter of about 50 millimeters and a length of 900 millimeters is applied, with one end elevated 400 millimeters above the ground. The toe end of the mesh on the upstream side is securely pegged into the ground, ensuring that sediment and water cannot escape beneath it.
The second type of PCD consists of timber mesh and steel posts. Here, mesh is laid on the ground and filled with sticks, timber, leaves, and any available organic material. This bundle is tied at the top, forming a cylinder structure approximately 400 millimeters high. Steel posts are inserted to secure it in place.
The specific site chosen features a natural watercourse and a main road. This watercourse is funneled into a culvert underneath the road, causing a rapid water flow downstream, leading to erosion. PCDs are being constructed to reduce water velocity and capture sediment. The site’s suitability arises from the width of the stream and the natural slowing of water, which accumulates sediment.
In conclusion, PCDs are an essential tool in managing water flow and preventing erosion, particularly in areas with challenging landscape configurations like this one. They complement natural processes and help conserve resources while reducing the environmental impact of erosion.
Image credits: Vicky Whitworth
Tag: Leaky Dams
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