River Mole

This article is about the river in south east England. For the river in Devon, see River Mole, Devon.

River Mole
The River Mole at the foot of Box Hill in Surrey
Map showing the River Mole (dark blue)
and part of the River Thames (light blue)
Location
CountryEngland
CountiesWest Sussex, Surrey
Districts / BoroughsHorsham, Crawley, Mole Valley, Reigate and Banstead, Elmbridge
TownsCrawley, Horley, Dorking, Leatherhead, Cobham, Surrey, Esher, Walton-on-Thames, Hersham
Physical characteristics
SourceBaldhorns Copse
 • locationRusper, Horsham, West Sussex
 • coordinates51°7′30″N 0°16′26″W / 51.12500°N 0.27389°W / 51.12500; -0.27389
 • elevation105 m (344 ft)
MouthRiver Thames
 • location
East Molesey, Elmbridge, Surrey
 • coordinates
51°24′4″N 0°20′21″W / 51.40111°N 0.33917°W / 51.40111; -0.33917
 • elevation
6 m (20 ft)
Length80 km (50 mi)
Basin size512 km2 (198 sq mi)
Discharge 
 • locationEsher
 • average5.43 m3/s (192 cu ft/s)
 • minimum1.00 m3/s (35 cu ft/s)(9 August 1993)
 • maximum99.9 m3/s (3,530 cu ft/s)(9 December 1994)
Discharge 
 • locationCastle Mill, Dorking
 • average3.74 m3/s (132 cu ft/s)
Discharge 
 • locationKinnersley Manor, Sidlow
 • average2.21 m3/s (78 cu ft/s)
Discharge 
 • locationHorley
 • average1.40 m3/s (49 cu ft/s)
Discharge 
 • locationGatwick Airport
 • average0.33 m3/s (12 cu ft/s)

The River Mole is a tributary of the River Thames in southern England. It rises in West Sussex near Gatwick Airport and flows north-west through Surrey for 80 km (50 miles) to the Thames at Hampton Court Palace.[1] The river gives its name to the Surrey district of Mole Valley.

The Mole crosses the North Downs between Dorking and Leatherhead, where it cuts a steep-sided valley, known as the Mole Gap, through the chalk.[2] Much of the catchment area lies on impermeable rock (including Weald Clay and London Clay), meaning that the river level responds rapidly to heavy rainfall.[2]

During the second half of the 20th century, pollution levels in the river were high; however, since 1995 the water quality has improved dramatically and the Mole now boasts the greatest diversity of fish species of any river in England.[1][3] Twelve Sites of Special Scientific Interest (SSSIs) that include wetland habitats are located within the Mole catchment area, and the stretch of river through Leatherhead has been designated a Local Nature Reserve.[4][5] The Mole Gap forms part of a Special Area of Conservation and is an SSSI of European importance.[6]

The river has captured the imagination of several authors and poets,[7] particularly since in very hot summers the river channel can become dry between Dorking and Leatherhead, most recently in 2022.[8] In John Speed's 1611 map of Surrey, this stretch of the river is denoted by a series of hills accompanied by the legend "The river runneth under". However the river's name is unlikely to have derived from this behaviour: The Oxford Dictionary of English Place Names suggests that Mole either comes from the Latin mola (a mill) or is a back-formation from Molesey (Mul's island).[9] Domesday Book lists twenty mills on the river in 1086, of which Sidlow Mill was the oldest, dating from Saxon times.[10][11]

  1. ^ a b "The Mole Catchment Abstraction Management Strategy" (PDF). Environment Agency. 2006. Archived from the original (PDF) on 2 August 2006. Retrieved 1 May 2020.
  2. ^ a b Bull AJ, Gossling F, Green JF, Haywood HA, Turner EA, Wooldridge SW (1934). "The River Mole: its physiography and superficial deposits". Proceedings of the Geologists' Association. 45: 35–67. doi:10.1016/s0016-7878(34)80032-6.
  3. ^ "Our nations' fisheries: The migratory and freshwater fisheries of England and Wales – a snapshot" (PDF). Environment Agency. 2003. Archived from the original (PDF) on 28 March 2014. Retrieved 1 May 2020.
  4. ^ "River Mole LNR". Natural England. 2005. Archived from the original on 18 October 2018. Retrieved 1 May 2020.
  5. ^ "Map of River Mole". Local Nature Reserves. Natural England. Archived from the original on 19 October 2014. Retrieved 24 July 2013.
  6. ^ "Mole Abstraction licensing strategy". Environment Agency. 2013. Archived from the original on 23 July 2019. Retrieved 27 April 2020.
  7. ^ Edwards, Jesse (2012). "Defoe the geographer: Redefining the wonderful in 'A Tour Thro' the whole Island of Great Britain'". In Hayden, Judy (ed.). Travel narratives, the new science, and literary discourse, 1569-1750. Farnham, Surrey: Ashgate. pp. 181–182. ISBN 978-1-409-42042-2.
  8. ^ Harris, Simon (11 August 2022). "Urgent fish rescue in River Mole near Dorking after heatwave causes dramatic fall in water levels". ITV News. Archived from the original on 12 August 2022. Retrieved 13 August 2022.
  9. ^ AD Mills (1998) Oxford Dictionary of English Place Names (2nd ed.) OUP ISBN 0-19-280074-4
  10. ^ Baker RGM (1989). "A guide to the industrial archaeology of the borough of elmbridge". Molesey History. Surrey Industrial History Group. Archived from the original on 22 July 2011. Retrieved 14 December 2010.
  11. ^ Sidder, D (1990). The Watermills of Surrey. Buckingham: Barracuda. ISBN 0-86023-480-0.