Flood alleviation

The Hoe Valley Scheme (HVS) is driven by two major issues. The flooding to the Westfield area and the landfill site - Former Westfield Tip. The two issues are linked as the tip is actually located within the flood plain of the Hoe Stream. By completing the HVS, Thameswey Developments Ltd aims to reduce the risk of flooding to the area.

This is to be done in two ways.

1) Remediate the former tip (removing contamination and leaving it as normal inert soil) and also lower the tip ground level on the site as this will increase the capacity of the flood plain and remove the possibility of future contamination to the water course.

2) Provide flood bunds, new bridges, flood walls and compensation ponds along the length of the Hoe Stream from just north of the Leisure Centre to Westfield School.

The flood protection works by removing the existing bottle necks at Bonsey Lane footbridge, Elm Bridge and the park access bridge which presently cause flood water to back up and overtop the banks. This is done by raising the deck height of the bridges and widening the tunnels under them. The flood water is then further contained by flood bunds and walls.

However, if the obstructions were just removed and the flood water was contained within walls all that would happen would be the flood surge would move faster down the water course and move the flood further down the stream. Therefore, an important part of the scheme is the introduction of flood compensation ponds and wet land which baffle the contained flood water and slow it down. This means that the flow is regulated and there is no increased risk to either up or down stream of the flood protection. This is an important point as it is a requirement of the Environment Agency permission to do any flood protection work that it does not make the situation worse in any other part of the stream.

In this case, while the flood protection work is designed to benefit the area of stream from Westfield School to the Leisure Centre the removal of Westfield Tip will provide a slight benefit to the whole stream by significantly increasing the size of the flood plain.

The original flood modelling documents (Volume 1 and Volume 2) which informed this scheme are attached to this web page if people would like to read about the science behind the flood model. The model has been changed slightly since the documents' production in 2006 to make it slightly better and improve its ability to be built, however the detail behind the scheme remains the same.