Flood Modelling Report

Flood modelling has been used over several years, to assess the River Thames Scheme's (RTS) impact on fluvial flood risk. Fluvial flooding is flooding that originates from high flows in the River Thames and its tributaries.

Specialist expertise and computer software has been used to generate flood levels from predicted river flows and tidal levels combined with topographic data. The flood model has been used to test hundreds of variants of the Scheme design. This is to help the Scheme work more efficiently and reduce construction costs. The flood modelling is vital, to make sure the Scheme functions as intended and to maximise flood risk reductions.

The flood modelling shows that the River Thames Scheme will reduce fluvial flood risk from Windsor to Teddington, although the reduction in flood levels from the Scheme varys by location and flood magnitude.

The greatest reduction in flood levels is in the Egham Hythe and Penton Hook area, near the upstream end of the Runnymede channel, where flood levels reduce by up to 0.9 metres.

The reduction parallel to the Spelthorne channel is similar and up to 0.8 metres.

There is a reduction in flood levels upstream of the flood channel through Staines and beyond. This is due to the drawdown effect of the Runnymede channel diverting flow out of the Thames further downstream.

In Staines, the reduction in flood levels can be up to 0.5 metres, but this impact diminishes moving upstream so that by Datchet and Windsor the benefit provided by the RTS is very small at 0.1 metres or less.

Downstream of Shepperton flood level reductions are up to 0.2 metres. Flood levels are reduced in this area by the bed lowering downstream of the Desborough Cut; and the additional gates at Sunbury, Molesey and Teddington weirs.

Downstream of Teddington the flood level reductions are very small at 0.03 metres or less; effectively there is no change in flood risk.

There is no increase in flood risk predicted at any location in any flood conditions. The RTS will not make flooding worse for anyone.

Our flood modelling work is ongoing as we are still testing further refinements to the Scheme design, such as changes to the landscaping. Once complete, reporting of the additional flood modelling will be included in future updates to this Flood Modelling Non-Technical Summary Report.

If you're interested in reading the Flood Modelling Non-Technical Summary Report (PDF), this is available to download.

The full version of the flood modelling report is available on request. Please email enquiries@riverthamesscheme.org.uk.