What is the scheme?

The Lower Mole Flood Alleviation Scheme (FAS) protects around 1,300 homes and businesses in the area from flooding. The enlarged river channel provides additional capacity for the high flows in the river during periods of prolonged and heavy rainfall.

The scheme covers the stretch of the River Mole as it makes its way northwards from Hersham up to the River Thames. This also includes the River Ember; the engineered channel created when the flood scheme was constructed during the 1980s, as well as the side channels at Royal Mills and the Ember Loop.

The original Lower Mole FAS was designed to reduce the risk of flooding in the lower reaches of the River Mole catchment, following a significant flood event in September 1968. The River Mole has a history of flooding, though the September 1968 event is still considered to be the largest and most severe recorded flood event along the River Mole. It has been estimated that several thousand properties in the lower reaches of the River Mole were flooded during that event.

Planning permission for the scheme was granted in 1974. The construction of the scheme took several years, with the works being completed during the 1980s.

How it operates

The enlarged river channel provides additional capacity for the high flows in the river during periods of prolonged and heavy rainfall. The sluice gates function to regulate water levels under normal circumstances, but must be opened during times of high river flows.

Why it needs updating

The scheme is now reaching the end of its design life and needs to be refurbished to maintain its standard of flood protection and to ensure it is the best scheme for the environment, people and wildlife.

There are six main water level control structures, sluice gates, and we need to make decisions on their future.

Updating the flood protection figures

In our correspondence about the Lower Mole Flood Alleviation Scheme, we have been referencing a figure of approximately 3,000 homes and businesses protected from flooding. This estimate was established a decade ago, based on the number of properties that would be at risk in a 'do nothing' scenario over the following 100 years. However, the area at risk of flooding in the 1980s before the Scheme was constructed, differs from the area that would be affected today if the gates were not operational and remained closed.

Our current flood risk modelling indicates that if the gates at Viaduct Sluice were not to open today, floodwaters would primarily exit the river on its eastern side, near the railway line, and flow northwards, flooding properties between Esher and Thames Ditton. This would impact approximately 1,300 properties. We have calculated that Options Red, Blue, Pink, and Orange would protect these 1,300 properties for the next 100 years