Winterbourne Flood Alleviation

The scheme comprised of the realignment of the Winterbourne Stream and the construction of a 300m long, 2.4m high flood defence bund on the land to the north of Winterbourne village. The project also included the construction of associated control structures to form a flood storage reservoir with a capacity of approximately 22,000m³. The aim of the scheme was to intercept fluvial and pluvial flows, and store and release them in a controlled manner.
This was achieved through the installation of a number of hydraulic control structures consisting of an inlet and outlet structure and 0.9m diameter culvert. In addition, a pair of 7m wide spillways convey the 10,000 year flow safely without overtopping the bund. On completion of the works, the site was completed with extensive landscaping works.
The design of the project used site won material to construct the bund. Early into the project it became apparent that the material available on site would not be suitable for much of the bund construction. By locally sourcing an alternative material from another project underway in the vicinity of the works, Dyer & Butler mitigated programme delays and minimised costs.

The design of the bund to key into the existing chalk was also re-designed by our project team to minimise both excavation and the volume of imported bund material.

The Winterbourne Stream is an extremely important Chalk Stream tributary, which flows into the River Lambourn. The underlying bedrock is chalk, with overlying river gravels that house a diverse range of aquatic life that support some of the most productive fisheries and natural fish populations in the UK.

The Winterbourne Stream is an environmentally designated SSSI and a SPA protected site and required close liaison and consent agreements with the EA as well as West Berkshire Council, where all our working methods and temporary works required approval.

A key challenge of the project was to reduce the impact of the higher than anticipated ground water which was struck just a few hundred millimetres below the existing ground level. Dyer & Butler employed well point dewatering technology as well as 24/7 pumping via silt buster tanks to reduce the groundwater levels below construction formation levels. We also drove the re-design mitigation measures with the Principal Designer and Panel Engineer to raise the bund foundation levels to minimise the programme impact of the groundwater issues.

The scheme was constructed predominantly to protect the local residents and farms from flooding. Stakeholder engagement was key to the success of the project. Stakeholders were kept informed throughout via letter drops from WBC and an open-door policy on site by Dyer & Butler. This resulted in full support from the local community throughout the construction process culminating in a grand opening ceremony with local Stakeholders, MP’s and press all in attendance to celebrate a successfully delivered project.