The Horsbere Brook flood alleviation scheme is now complete. The scheme is operational and reduces flood risk downstream in Gloucester to over 350 homes. We have now started preparing the flood storage area for seeding, tree planting and fencing to create a 50 acre environmental amenity area.
Flooding from the Horsbere Brook
In June 2007 approximately 100 properties in the Longlevens area, predominantly in Cypress Gardens, were flooded. Some properties reported to have flooded to a depth of over one metre.
Then again on Friday 20 July areas of Longford, Longlevens, Elmbridge, Hucclecote and Brockworth experienced flooding from the Horsbere Brook. In total some 300 properties were affected.
Flooding of this area is frequent and potentially severe when the river breaks out of its banks. This happened at least three times in 2008, requiring over-pumping by the fire service to avert flooding.
The completed flood risk management scheme
The completed scheme provides a flood storage area to the east of the A417/A40 at Barnwood, which provides capacity to store over 170,000 cubic metres of water, In normal conditions the vast majority of it will be empty, but when flowsincrease above the capacity of the flow control structure water will spill into the flood storage area. It will remain there until river flows have reduced.
The flood storage area has been created by excavating approximately 120,000 cubic metres of earth.
The majority of this earth has been used to profile the existing hillside to the North and the South to create a natural looking landscape.
The best of the quality clay, which was excavated to create the flood storage area, was then used to form a flood embankment along the Western edge of the site. This provides further flood protection to the A40 carriageway, residential areas and businesses to the West.
The availability of good quality soil within the site, and the detailed planning and design of the scheme, allowed the reuse of this material and kept the construction costs down.
A control structure located in the brook takes the form of a bridge/culvert over the brook and acts to throttle flow in the river at times of high flow. The size of this throttle has been carefully determined. This is to ensure the flow that passes downstream does not exceed the capacity of the brook during floods on a similar scale to that of July 2007. The flow control structure causes water to back up in the brook upstream, overtop the right bank and flow into the new flood storage area.
What protection it will offer?
The scheme is designed to provide protection from flooding with a 1 in 100 chance of occurring in this location in any one year (1 per cent chance) plus an allowance for climate change (20 per cent increase in flows).
We are working with our partners, including Gloucester City Council, to plan landscaping that will provide an environmental amenity area with over 15 hectares of biodiversity habitat.
The bowl of the flood storage area provides ponds which, with planting and over time, will establish. Wetlands will then form.
The 20 hectare flood storage area has been designed to benefit the environment and the wider community. We aim to plant a community orchard, hazel coppice, native woodland, meadows and wet grassland. We hope to work with the City Council in the future to share maintenance of the flood alleviation structures and environmental amenity space.
We will be holding an official opening ceremony of the scheme on Monday 12 Decemeber 2011 at 10:00am to mark completion of works. Richard Benyon MP, and Parliamentary Under-Secretary for Natural Environment and Fisheries will perform the official opening. All are welcome to join us.
Toby Willis, project manager said: I am so pleased that we are now able to better manage flood risk to so many homes in Gloucester who suffered terribly in 2007, and who have been living with this worry ever since. I hope that residents are also able to make use of what will become a lovely environmental amenity area