Flood mitigation measures in action
Littleborough flood plan stands up to Storm Christop test
As part of our new Stubley Meadows development in Littleborough, we are providing a sophisticated flood mitigation system that will help to boost the local area’s flood defence measures.
The system was subject to an early test of its effectiveness during the recent Storm Christoph (January 2021) which saw the Littleborough area given a Red Alert flood warning by the Environment Agency.
Happily, the system proved robust and worked exactly as designed, with flooding contained to the designated areas.
The Stubley Meadows development is a 8.19 hectare site, the southern boundary of which sits just 17 metres from the River Roch.
This southern part of the site, around a third of the land we acquired, has historically been flooded by the river following heavy rain.
It is designated Flood Zone 2 by the Environment Agency and is expected to flood as part of the local flood plain, as it did during Storm Christoph, and will have no homes built on it.
We have actually excavated and extended the flood zone to increase the volume of water which can be stored in this area in the event of a flood, thereby contributing towards the local flood mitigation measures.
This area will be grassed open space once the development is complete (see site plan), and it is likely to be waterlogged from time-to-time as flood waters recede naturally.
Part of this southern area will also be home to an Attenuation Pond, an engineered space designed to collect and hold rainwater draining from the development’s own roads and gardens.
It is likely to have water in it most of the time as it will release this water slowly into the River Roch.
The importance of this engineered solution is a critical part of Russell Homes’ support for the local flood defences. Historically there would be a surge of water draining back into the river following heavy rain which could cause flooding further downstream.
By installing the Attenuation Pond, any surface run-off (rainwater) collected from across the site will be diverted into the pond and discharged into the river in a managed way, preventing this volume from entering the river all at once.
This, together with the extension of the flood plain area, will provide large storage potential for the River Roch in Littleborough. It will keep both rain water and river flood water away from nearby properties in the immediate vicinity, and prevent a surge which would impact on land and properties further downstream.
Some areas in the upper part of the site have also historically been subject to localised flooding owing to the presence of an uncapped artesian well. This well enabled access to the aquifer, a fresh water source some 96m below the surface, but was left unmanaged and leaked water for a number of years.
It’s closure was one of the requirements of the Environment Agency when consulted during the planning process. When we arrived on site to begin works, the well was sealed with a temporary cap and no longer discharges water into the site. Our experienced engineering consultants are now progressing the permanent solution to cap the well line with the Environment Agency’s guidelines .
This is the part of the site on which we are building new homes which has been subject to a significant groundwork operation to install drainage and raise levels above the height of any potential flooding.
The works have been reviewed by the Environment Agency and local authority, neither of which raised an objection to the application. In its report, the Environment Agency said the finished development ‘will not be at an unacceptable risk of flooding or exacerbate flood risk elsewhere’. The agency has also redesignated the development platform as Flood Zone 1 which, like the majority of the local area, is the lowest risk.
During Storm Christoph, and despite the local Red Alert, the development platform did not flood, giving us a clear demonstration of the success of the flood plain and drainage works undertaken.
Our water management programme is not limited to river flooding mitigation, we are also working to prevent surface run-off from collecting on the site or pooling at the boundary.
Directing surface run-off to the attenuation pond is achieved with the use of drains and land drains throughout the development, including a ditch at its edge where water from neighbouring properties will also drain to the flood plain.
Some visible pockets of water on the development platform were shown to be where rainwater had pooled in holes excavated as part of the construction programme and should be no cause for concern.
Stubley Meadows Flood Mitigation Works
- Increased the size of the existing flood plain
- Installed an Attenuation Pond
- Extensive groundworks to re-level the site
- Capping the artesian well
- Provision of land and boundary drainage to divert surface run-off