Managing flood risk in development and building works

These are a few examples of how we reduced the flood risk in new developments or redevelopment projects in the borough.

Hogsmill Sewage Treatment Works

As well as environmental improvements, this project featured several flood risk measures, all which restored the river to its natural, wildlife-friendly state.

• realigning the river and altering river flow processes to handle high water levels
• constructing groynes in the river to maintain low water speed
• removing earth mounds at the river edge and reducing riverbank gradients to open the river corridor

Chessington Nurseries 

The recent redevelopment of the nurseries identified opportunities to store and recycle rainwater, reducing net flood risk as a result. Flood risk measures included:

• surface water drainage via the drainage network and source control measures
• on site storage in the form of a reed-bed to offset the increase in roof area
• collecting and recycling rainwater for plant irrigation

Bishops Palace House 

This redevelopment featured specialised sustainable urban drainage systems (SUDS), which can reduce the net flood risk despite an increased footprint which otherwise would reduce storage and increase water runoff.

Flood risk measures included:

• use of SUDS
• ‘green’ roofs and walls to help drainage
• installation of a flood vent grille to let floodwater flow through the building
• connects as much surface water drainage to existing river outfall as possible