Much of the area is on impermeable clays, and is mostly flat. Because of the characteristics of the area, flooding can last for 3 days after any storms are gone.
Types of flooding
- Drainage capacity can be overwhelmed by the water, leading to surface water flooding.
- Blocked gullies and surcharging of outfall pipes can cause flooding by major roads.
- Groundwater flooding can occur when groundwater rises above the ground surface, which is heavily effected by the local geology. In surrey this is most common in chalk-based areas, such as the north downs.
River Mole floods, December 2013- January 2014
Although naturally being a small river,the Mole has the potential to cause major disruptions due to having several major transport routes, namely Gatwick airport, East Surrey Hospital, the M25 and M23, and the London-Brighton railway housed (at least partially) within it. Below are the specific impacts of the 12/13-01/14 floods:
- Gatwick airport power failure; delays with baggage handling on 24/12/13; 100 flights delayed or cancelled; thousands left stranded or abandoned as rails disrupted too.
- Power cuts; 100 homes in Merstham (Near Reigate) and Sidlow left without power for 3 days.
- Leatherhead crematorium; closed due to flooding.
- Burford Bridge Hotel, Dorking and Ye Olde Six Bells, Horley; among various businesses submerged and closed during the flooding.
- Plane Damage: Damage to planes in Redhill Aerodrome (South-East of Reigate)- 71mile per hour winds measured on Kinley in the North Downs.
- Road closures and rail closures; two closures of the M24 at Mickleham, A217, A23 around Horley and Leatherhead. Creates “islands” making the job of the emergency services very difficult.
- Flanchford bridge, Reigate, damaged by the waters, and some bridges in the area are still yet to be repaired.
- Flooding of hundreds of residential properties; 40 in just Fetcham underwater for 15/12/13.
- Morrisons in Reigate, and other businesses elsewhere, flooded.
- Damage to telephone land-lines in Brockham village.
- Cars swept away, or people stranded in stalled cars.
- People stranded in buildings, including 27 at the Burford Bridge Hotel.
Governmental/Local Council level:
- A long term drainage strategy is being developed, including sustainable drainage systems
- The Environment Agency is implementing flood management strategies along the Lower Thames.
- Insurance policies by the government (and energy companies) to recompensate families with losses from the floods.Similarly, management schemes are being funded, such as property level management schemes.
- New technologies being created and implemented to better understand the flood risks.
- Engineered components: Three flood diversion channels and improvements to weirs (naturally-designed barriers over the top of a river to slow or redirect some of the water flow).
- Floodplain management component: working more closely with local authorities to ensure future developments account for flood risks, routes for flood flow and potentially diversion channels.
- Community-based flood protection measures: Flood warning services and property-level protection.
The Gatwick flooding scheme and other factors will be mentioned elsewhere as this post is already long.
(Part II here: https://deigmologyblog.wordpress.com/2016/05/10/river-mole-part-ii/)
(Image sources: https://rgsweather.com/2014/01/04/flooding-on-the-river-mole-surrey-causes-and-management/ https://en.wikipedia.org/wiki/River_Mole I would highly recommend the http://www.rgsweather.com site – and not just because it’s run by one of my geography teachers- it is genuinely a very good site!)