The main source of flooding in Elmbridge is from rivers associated with a number of different watercourses including the Thames, Wey, Mole, Dead River, Rythe and Wey. The risk of flooding from rivers is set out in terms of Flood Zones based on the predicted frequency and extent of flooding expected:

• Flood Zone 1 - Low risk (less than 1 in 1000 year chance of flooding)
• Flood Zone 2 - Medium risk (Between 1 in 100 year and 1 in 1000 year chance of flooding)
• Flood Zone 3a - High risk (1 in 100 year or greater chance of flooding)
• Flood Zone 3b - Undeveloped land within the 1 in 20 year chance of flooding outline where water has to flow or be stored in times of flood, or land purposely designed to be flooded in an extreme flood event.

The Borough is also affected by more localised flooding from surface water, groundwater, existing drainage systems as well as artificial sources e.g. reservoirs.