View source for River Mole

{{short description|Tributary of the River Thames in southern England}}
{{About|the river in south east England|the river in Devon|River Mole, Devon}}
{{Use dmy dates|date=October 2017}}
{{Use British English|date=October 2017}}
{{Infobox river
| name               = River Mole
| native_name        = 
| native_name_lang   = 
| name_other         = 
| name_etymology     = 
<!---------------------- IMAGE & MAP -->
| image              = Stepping stones.jpg
| image_size         = 
| image_caption      = The River Mole at the foot of [[Box Hill, Surrey|Box Hill]] in [[Surrey]]
| map                = River Mole Map.png
| map_size           = 260
| map_caption        = Map showing the River Mole (dark blue) <br /> and part of the River Thames (light blue)
| pushpin_map        = 
| pushpin_map_size   = 260
| pushpin_map_caption= 
<!---------------------- LOCATION -->
| subdivision_type1  = Country
| subdivision_name1  = [[England]]
| subdivision_type2  = 
| subdivision_name2  = 
| subdivision_type3  = Counties
| subdivision_name3  = [[West Sussex]], [[Surrey]]
| subdivision_type4  = Districts / Boroughs
| subdivision_name4  = [[Horsham District|Horsham]], [[Crawley]], [[Mole Valley]], [[Reigate and Banstead]], [[Borough of Elmbridge|Elmbridge]]
| subdivision_type5  = Towns
| subdivision_name5  = [[Crawley]], [[Horley]], [[Dorking]], [[Leatherhead]], [[Cobham, Surrey]], [[Esher]], [[Walton-on-Thames]], [[Hersham]]
<!---------------------- PHYSICAL CHARACTERISTICS -->
| length             = {{convert|80|km|mi|abbr=on}}
| width_min          = 
| width_avg          = 
| width_max          = 
| depth_min          = 
| depth_avg          = 
| depth_max          = 
| discharge1_location= [[Esher]]
| discharge1_min     = {{convert|1.00|m3/s|cuft/s|abbr=on}}(9&nbsp;August 1993)
| discharge1_avg     = {{convert|5.43|m3/s|cuft/s|abbr=on}}
| discharge1_max     = {{convert|99.9|m3/s|cuft/s|abbr=on}}(9&nbsp;December 1994)
| discharge2_location= Castle Mill, [[Dorking]]
| discharge2_min     = 
| discharge2_avg     = {{convert|3.74|m3/s|cuft/s|abbr=on}}
| discharge2_max     = 
| discharge3_location= Kinnersley Manor, Sidlow
| discharge3_min     = 
| discharge3_avg     = {{convert|2.21|m3/s|cuft/s|abbr=on}}
| discharge3_max     = 
| discharge4_location= [[Horley]]
| discharge4_min     = 
| discharge4_avg     = {{convert|1.40|m3/s|cuft/s|abbr=on}}
| discharge4_max     = 
| discharge5_location= [[Gatwick Airport]]
| discharge5_min     = 
| discharge5_avg     = {{convert|0.33|m3/s|cuft/s|abbr=on}}
| discharge5_max     = 
<!---------------------- BASIN FEATURES -->
| source1            = Baldhorns Copse
| source1_location   = [[Rusper]], [[Horsham]], [[West Sussex]]
| source1_coordinates= {{coord|51|7|30|N|0|16|26|W|display=inline}}
| source1_elevation  = {{convert|105|m|abbr=on}}
| mouth              = [[River Thames]]
| mouth_location     = [[East Molesey]], [[Borough of Elmbridge|Elmbridge]], [[Surrey]]
| mouth_coordinates  = {{coord|51|24|4|N|0|20|21|W|display=inline,title}}
| mouth_elevation    = {{convert|6|m|abbr=on}}
| progression        = 
| river_system       = 
| basin_size         = {{convert|512|km2|abbr=on}}
| tributaries_left   = 
| tributaries_right  = 
| custom_label       = 
| custom_data        = 
| extra              = 
}}
The '''River Mole''' is a [[tributary]] of the [[River Thames]] in [[southern England]]. It [[source (river)|rises]] in [[West Sussex]] near [[Gatwick Airport]] and flows north-west through [[Surrey]] for {{convert|80|km|mi|abbr=in}} to the [[River Thames|Thames]] at [[Hampton Court Palace]].<ref name=CAMs>{{cite web |url= http://www.environment-agency.gov.uk/commondata/acrobat/mole_condoc_pt1_1284016.pdf |title= The Mole Catchment Abstraction Management Strategy |author= <!--Not stated--> |year= 2006 |publisher= Environment Agency |access-date= 1 May 2020 |archive-date= 2 August 2006 |archive-url= http://webarchive.nationalarchives.gov.uk/20060802172124/http://www.environment-agency.gov.uk/commondata/acrobat/mole_condoc_pt1_1284016.pdf |url-status= dead }}</ref> 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.<ref name=physiography>{{cite journal |vauthors=Bull AJ, Gossling F, Green JF, Haywood HA, Turner EA, Wooldridge SW |year= 1934 |title= The River Mole: its physiography and superficial deposits |journal= Proceedings of the Geologists' Association |volume= 45 |pages= 35–67 |doi=10.1016/s0016-7878(34)80032-6}}</ref> Much of the catchment area lies on [[permeability (earth sciences)|impermeable rock]] (including [[Weald Clay]] and [[London Clay]]), meaning that the river level responds rapidly to heavy rainfall.<ref name=physiography/>

During the second half of the 20th century, [[pollution]] levels in the river were high; however, since 1995 the [[water quality#Environmental water quality|water quality]] has improved dramatically and the Mole now boasts the greatest diversity of fish species of any river in England.<ref name=CAMs/><ref name=EA_fish>{{cite web |url= http://www.environment-agency.gov.uk/static/documents/Leisure/fisheries_eng_765655.pdf |title= Our nations' fisheries: The migratory and freshwater fisheries of England and Wales – a snapshot |author= <!--Not stated--> |year= 2003 |publisher= Environment Agency |access-date= 1 May 2020 |archive-date= 28 March 2014 |archive-url= http://webarchive.nationalarchives.gov.uk/20140328111502/http://www.environment-agency.gov.uk/static/documents/Leisure/fisheries_eng_765655.pdf |url-status= dead }}</ref>  Twelve [[Sites of Special Scientific Interest|Sites of Special Scientific Interest (SSSIs)]] that include wetland habitats are located within the Mole [[drainage basin|catchment area]], and the stretch of river through Leatherhead has been designated a [[Local Nature Reserve]].<ref>{{cite web |url= https://designatedsites.naturalengland.org.uk/SiteLNRDetail.aspx?SiteCode=L1123058&SiteName=&countyCode=41&responsiblePerson=&SeaArea=&IFCAArea= |title= River Mole LNR |year= 2005 |publisher= Natural England |access-date= 1 May 2020 |archive-url= https://web.archive.org/web/20181018003155/https://designatedsites.naturalengland.org.uk/SiteLNRDetail.aspx?SiteCode=L1123058&SiteName=&countyCode=41&responsiblePerson=&SeaArea=&IFCAArea= |archive-date= 18 October 2018 |url-status= live }}</ref><ref>{{cite web|url=http://magic.defra.gov.uk/MagicMap.aspx?startTopic=Designations&activelayer=lnrIndex&query=REF_CODE%3D%271123058%27|title=Map of River Mole|series=Local Nature Reserves|publisher=Natural England|access-date=24 July 2013|archive-url=https://web.archive.org/web/20141019163936/http://magic.defra.gov.uk/MagicMap.aspx?startTopic=Designations&activelayer=lnrIndex&query=REF_CODE%3D'1123058'|archive-date=19 October 2014|url-status=live}}</ref> The Mole Gap forms part of a [[Special Area of Conservation]] and is an SSSI of European importance.<ref name=MAls_2013>{{cite web |url= https://www.gov.uk/government/publications/mole-catchment-abstraction-licensing-strategy |title= Mole Abstraction licensing strategy |author= <!--Not stated--> |year= 2013 |publisher= Environment Agency |access-date= 27 April 2020 |archive-url= https://web.archive.org/web/20190723221117/https://www.gov.uk/government/publications/mole-catchment-abstraction-licensing-strategy |archive-date= 23 July 2019 |url-status= live }}</ref>

The river has captured the imagination of [[#Literature|several authors and poets]],<ref name=Judy_Hayden>{{cite book |last=Edwards |first=Jesse |editor-last=Hayden |editor-first=Judy |title=Travel narratives, the new science, and literary discourse, 1569-1750 |publisher=Ashgate |location=Farnham, Surrey |date= 2012 |pages= 181–182 |chapter= Defoe the geographer: Redefining the wonderful in 'A Tour Thro’ the whole Island of Great Britain' |isbn=978-1-409-42042-2}}</ref> particularly since in very hot summers the river channel can become dry between Dorking and Leatherhead, most recently in 2022.<ref name=ITV_News_2022>{{cite news |last= Harris |first= Simon |date= 11 August 2022 |title= Urgent fish rescue in River Mole near Dorking after heatwave causes dramatic fall in water levels |url= https://www.itv.com/news/london/2022-08-11/urgent-fish-rescue-as-heatwave-causes-dramatic-fall-in-water-levels |work= ITV News |access-date= 13 August 2022 |archive-date= 12 August 2022 |archive-url= https://web.archive.org/web/20220812143840/https://www.itv.com/news/london/2022-08-11/urgent-fish-rescue-as-heatwave-causes-dramatic-fall-in-water-levels |url-status= live }}</ref> 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 {{lang|la|mola}} (a mill) or is a [[back-formation]] from ''Molesey'' (Mul's island).<ref name="AD Mills 1998">AD Mills (1998) ''Oxford Dictionary of English Place Names'' (2nd ed.) OUP {{ISBN|0-19-280074-4}}</ref> [[Domesday Book]] lists twenty [[watermill|mills]] on the river in 1086, of which [[Sidlow|Sidlow Mill]] was the oldest, dating from [[History of Anglo-Saxon England|Saxon times]].<ref name=moleseyhistory>{{cite web |url= http://www.moleseyhistory.co.uk/books/surrey/industrialHistory/index.html |title= A guide to the industrial archaeology of the borough of elmbridge |author= Baker RGM |year= 1989 |work= Molesey History |publisher= Surrey Industrial History Group |access-date= 14 December 2010 |archive-url= https://web.archive.org/web/20110722005313/http://www.moleseyhistory.co.uk/books/surrey/industrialHistory/index.html |archive-date= 22 July 2011 |url-status= live }}</ref><ref name=water_mills_surrey>{{cite book |title= The Watermills of Surrey |last= Sidder |first= D |year= 1990 |publisher= Barracuda|location= Buckingham |isbn= 0-86023-480-0}}</ref>

==Catchment area==
The drainage area of the Mole is {{cvt|477|km2}} and forms 5% of the [[River Thames]]'s catchment area above [[Teddington]].<ref name=MAls_2013/> The catchment area receives {{cvt|761|mm}} of rain each year; the greatest average level of rainfall is {{cvt|800|mm|1}} around [[Crawley]]. The Mole catchment reaches a maximum elevation of {{convert|265|m|ft|abbr=on}} above [[Ordnance Datum]] at [[Leith Hill]] to the southwest of [[Dorking]].<ref name=CEH>{{cite book |title=UK Hydrographic Register |editor1-last=Marsh |editor1-first=T |editor2-last=Hannaford |editor2-first=J |publisher=Centre for Ecology & Hydrology |location=Wallingford, Oxfordshire |year=2008 |series=Hydrological data UK series |isbn=978-0-9557672-2-7 |url=http://nora.nerc.ac.uk/id/eprint/3093/1/HydrometricRegister_Final_WithCovers.pdf |access-date=9 September 2020 |archive-url=https://web.archive.org/web/20131005215639/http://www.ceh.ac.uk/products/publications/documents/hydrometricregister_final_withcovers.pdf |archive-date=5 October 2013 |url-status=live }}</ref> There is only one [[aquifer]] in the drainage basin, at [[Fetcham]], which means that the majority of the water in the river is from surface drainage, particularly from [[Gatwick Airport]] and the urban areas of [[Horley]] and Crawley, and that the flow rate responds rapidly to rainfall.<ref name=CAMs/>

==Course==
[[File:River Mole at Baldhorns Park - geograph.org.uk - 1811633.jpg|thumb|River Mole at Baldhorns Park, approximately {{cvt|1|km|1}} downstream of the source at Rusper]]

===Upper Mole===
The Mole rises in Baldhorns Copse {{convert|700|m|mi|1|abbr=on}} to the south of the village of [[Rusper]] in [[West Sussex]]. It flows initially southwards for {{convert|1|km|mi|1|abbr=on}} to a small lake at Baldhorns Park, before running eastwards through a largely rural area towards Crawley.<ref name=OS_Rusper>{{cite map |publisher=Ordnance Survey |title=Crawley & Horsham |year=2009 |scale=1:25000 |series=Explorer |isbn=978-0-319-24085-4}}</ref> The first tributaries to join the young river drain the northernmost part of [[St Leonard's Forest]], between [[Horsham]] and Crawley, although much of the forest is in the catchment area of the [[River Arun]]. The Mole skirts the northern suburbs of Crawley where it is joined by its first major tributary, Ifield Brook, which drains [[Ifield Water Mill|Ifield Mill Pond]].

The first [[stream gauge|gauging station]] on the Mole is south of Gatwick Airport ({{cvt|57|m|disp=sqbr}} above [[Ordnance Datum|OD]]).<ref group=note>The gauging station south of Gatwick Airport was installed in 2005, replacing an earlier station located {{cvt|200|m|yd}} downstream.</ref> The mean flow is {{convert|0.33|m3/s|cuft/s|abbr=on}} and the river ran dry at this point for the first time in the summer of 1995.<ref name=CEH/> The Mole runs under the airport runway in a culvert completed in 1985.<ref>{{cite web |url= https://www.environmental-expert.com/news/forty-years-on-from-the-floods-of-1968-37047 |title= Forty years on from the floods of 1968 |date= 11 September 2008 |publisher= Environmental Expert |access-date= 11 February 2023 |archive-date= 11 February 2023 |archive-url= https://web.archive.org/web/20230211210036/https://www.environmental-expert.com/news/forty-years-on-from-the-floods-of-1968-37047 |url-status= live }}</ref> The course of the Mole within the airport perimeter has been altered several times since commercial flights began in 1945; however the meanders visible on the 1839 [[tithe map]] in the {{cvt|1.5|km}} stretch immediately north of the runway were reinstated in 1999, in a £1.2 million project to facilitate airport expansion.<ref>{{cite web |url= http://www.baa.com/assets//B2CPortal/Static%20Files/glsstnbltyrprt2002.pdf |title= Sustainability Report 2001/02 |author= Earl G |year= 2001 |publisher= BAA London Gatwick |access-date= 9 February 2010 |archive-url= https://web.archive.org/web/20110522191841/http://www.baa.com/assets//B2CPortal/Static%20Files/glsstnbltyrprt2002.pdf |archive-date= 22 May 2011 |url-status= live }}</ref><ref name="autogenerated1">{{cite web |url= http://www.tpsconsult.co.uk/tps/assets/pdf/profiles/gatwick_river_mole.pdf |title= River Mole Diversion, Gatwick |year= 2001 |publisher= TPS |access-date= 9 February 2010 |archive-url= https://web.archive.org/web/20080627171133/http://www.tpsconsult.co.uk/tps/assets/pdf/profiles/gatwick_river_mole.pdf |archive-date= 27 June 2008 |url-status= live }}</ref>

The Mole enters [[Surrey]] to the south of Horley, where it meets the [[Gatwick Stream]], a tributary draining [[Worth, West Sussex|Worth Forest]] to the southeast of Crawley. The second-largest Sewage Treatment Works (STW) in the Mole catchment is located on the Gatwick Stream {{convert|3|km|mi|abbr=on}} upstream of the confluence with the Mole: Crawley STW discharges {{cvt|15000|m3}} of water per day, and in prolonged dry periods it accounts for up to 75% of the flow of the Mole downstream of the confluence.<ref name=Hazelton>{{cite journal |author= Hazelton C|year= 1998 |title=Variations between continuous and spot-sampling techniques in monitoring a change in river-water quality |journal= Water and Environment Journal |volume=12 |issue=2 |pages=124–129 |doi=10.1111/j.1747-6593.1998.tb00161.x|s2cid= 108508464 }}</ref> The mean flow measured at Horley gauging station ({{cvt|52|m|disp=sqbr}} above OD) is {{convert|1.40|m3/s|cuft/s|abbr=on}}.<ref name=CEH/>

The Mole passes Horley to the west, flowing north towards [[Sidlow]] and entering a largely rural area. {{convert|0.7|km|mi|1|abbr=on}} south of Sidlow the mean flow is measured as {{convert|2.21|m3/s|cuft/s|abbr=on}} at Kinnersley Manor gauging station ({{cvt|48|m|disp=sqbr}} above OD).<ref name=CEH/> The Earlswood Brook, a tributary draining the urban area of [[Reigate]] and [[Redhill, Surrey|Redhill]], joins the Mole at Sidlow. The largest STW in the Mole catchment (Reigate STW) discharges up to {{cvt|118,500|m3}} per day into the Earlswood Brook.<ref group=note>A principal tributary of the Earlswood Brook is the Redhill Brook, which includes The Moors wetland nature reserve within its catchment area.</ref>

From Sidlow, the Mole turns northwest towards [[Brockham]]. A number of minor tributaries join the river from the west and are typically [[Strahler number|second order streams]] draining the woodland and arable land between Horsham and Dorking. The 18th-century weir at [[Betchworth]] was modified in 2004 to facilitate the installation of two 27.5&nbsp;kW [[low head hydro power|low-head]] [[water turbine|hydro turbines]]. About 90% of the energy generated is fed into the regional [[electricity grid]], while the remainder is used to supply the Betchworth Park Estate, where the weir is situated.<ref>{{cite web |url= http://www.tvenergy.org/pdfs/betchworth-estate.pdf |title= Small hydroelectric power: Betchworth Park |publisher= TV Energy |access-date= 8 February 2010 |archive-url= https://web.archive.org/web/20091229075037/http://www.tvenergy.org/pdfs/betchworth-estate.pdf |archive-date= 29 December 2009 |url-status= live }}</ref> The river leaves the [[Weald Clay]] at Brockham, passing Betchworth Castle <ref>{{National Heritage List for England|num=1017996|desc=Betchworth Castle|access-date=16 June 2013}}</ref> and flowing briefly across [[greensand]] and [[Gault Clay]] to [[Pixham]], {{convert|1|km|mi|1|abbr=on}} northeast of [[Dorking]]. A mean flow of {{convert|3.74|m3/s|cuft/s|abbr=on}} is measured at a fourth gauging station, located at Castle Mill ({{cvt|39|m|disp=sqbr}} above OD).<ref name=CEH/> At Pixham the Mole meets the [[Pipp Brook]], a tributary draining the northeastern slopes of Leith Hill.<ref group=note>The Pipp Brook drains the northernmost heavily wooded slopes of Leith Hill (which include Squire's Great Wood and Abinger Forest), as well as areas of [[Wotton, Surrey|Wotton]], [[Westcott, Surrey|Westcott]] and Dorking.</ref>

===Mole Gap===
Between Dorking and [[Leatherhead]] the Mole cuts a steep-sided valley (the Mole Gap) though the [[North Downs]], carving a {{convert|170|m|ft|adj=mid|-high}} river cliff on the western flank of [[Box Hill, Surrey|Box Hill]] and a smaller {{convert|50|m|adj=on}} cliff at Ham Bank in [[Norbury Park]]. The sudden change from [[permeability (earth sciences)|impermeable]] [[Weald Clay]] to [[permeability (earth sciences)|permeable]] [[chalk]] and the increased gradient<ref group=note>The Mole descends {{cvt|15|m|disp=sqbr}} in the {{cvt|10|km|0|disp=sqbr}} stretch between Brockham and Leatherhead, compared to {{cvt|3|m|disp=sqbr}} in {{cvt|12|mi|disp=sqbr|order=flip}} between Horley and Brockham.</ref> of the river, allow the water table to drop below the bed of the river. Water is therefore able to flow out of the river through [[swallow hole]]s in the bed and banks, decreasing the volume of water carried in the main channel.

The course of the river through Norbury Park was partially straightened when the [[Sutton & Mole Valley Lines|Epsom to Horsham railway]] was built in 1837, with the removal of a small meander north of [[Westhumble]].<ref>Shepperd R (1982) The Manor of Wistomble in the Parish of Mickleham ''Westhumble Association''</ref> The meander was reinstated in 1997, in an attempt to enhance this area of the Park, although it has since become blocked by [[silt deposit|silt]]. The entirety of the Mole Gap lies within the [[Surrey Hills AONB|Surrey Hills Area of Outstanding Natural Beauty]].<ref>{{cite web |url= http://www.surreyhills.org/ |title= Surrey Hills Area of Outstanding Natural Beauty |year= 2010 |publisher= Surrey Hills Partnership |access-date= 9 February 2010 |archive-url= https://web.archive.org/web/20100126045834/http://www.surreyhills.org/ |archive-date= 26 January 2010 |url-status= live }}</ref>

===Lower Mole===
[[File:Painshill-Waterwheel.jpg|thumb|upright|Painshill Park Waterwheel (on its [[Leat|millstream]] channel)]]
At Leatherhead, the Mole leaves the chalk and turns northwestwards to flow across impermeable [[London Clay]], winding towards Cobham.  The water table rises at this point and much of the water which drained out of the channel through the chalk returns through springs in the riverbed.<ref name=Wooldridge_Hutchings>{{cite book |title= London's Countryside : Geographical Field Work for Students and Teachers of Geography |url= https://archive.org/details/londonscountrysi0000wool |url-access= registration |last1= Wooldridge |first1= SW |last2= Hutchings |first2= GE |year= 1957 |publisher= Methuen |location= London |pages=[https://archive.org/details/londonscountrysi0000wool/page/89 89–90]}}</ref> The aquifer at [[Fetcham]] is the only one in the entire catchment area.<ref name=CAMs/>  The next major tributary, [[The Rye (brook)|The Rye]], (which drains [[Ashtead]]) joins to the north of Leatherhead, before the river is crossed by the [[M25 motorway]].  At Cobham the river swings round in a pronounced axehead [[meander]] skirting [[Painshill Park|Painshill Landscape Garden]], where a {{convert|35|ft|m|order=flip|adj=on}} diameter [[waterwheel]] raises water {{convert|5|m|ft}} from the river to feed the ornamental lake in the park.<ref>{{National Heritage List for England|num=1030126|desc=The Water Wheel|grade=II|access-date=16 June 2013}}</ref><ref>{{cite web |url=http://www.painshill.co.uk/The-Park/The-Hamilton-Landscapes.aspx |title=The Bramah Waterwheel |publisher=Painshill Park |access-date=23 February 2010 |archive-url=https://web.archive.org/web/20100607121017/http://www.painshill.co.uk/The-Park/The-Hamilton-Landscapes.aspx |archive-date=7 June 2010 |url-status=live }}</ref><ref group=note>The undershot wheel at Painshill Park was restored in 1987 and is located at the end of an artificial [[leat]], rather than on the main river channel.</ref>

From Painshill Park the river flows northeastwards to the Thames, passing to the west of [[Esher Commons]] and then forming the boundary between [[Hersham, Surrey|Hersham]] and [[Esher]], where the mean flow of the river is {{convert|5.43|m3/s|cuft/s|abbr=on}}.  In response to [[Great Flood of 1968|heavy flooding of East Molesey and Thames Ditton in September 1968]], the river was modified downstream of Albany Bridge to the Thames and new flood defences were constructed.<ref name=Riddell>{{cite conference |title= Channel Protection, Operation and Maintenance in Flood Alleviation Schemes |year= 1984 |conference= Channels and Channel Control Structures |author= Riddell KJ |editor= Smith KVH |book-title= Proceedings of the 1st International Conference|publisher= Springer-Verlag |location= Heidelberg, Germany |volume= 4|pages= 53–71 |isbn=0-905451-21-X}}</ref> Finally the Mole splits into two branches at the [[Island Barn Reservoir]] near [[Molesey]]: the northern (and smaller) branch continues as the River Mole and the southern branch is known as the [[River Ember]].<ref name=FASLRM>WE Foster WB Harris (1988) Flood Alleviation Scheme for the Lower River Mole ''Proceedings of the Institution of Civil Engineers'' 84 235-263</ref> The two rivers flow either side of the reservoir, before running side by side in a northeasterly direction, merging {{cvt|400|m|yd}} before the [[confluence]] with the River Thames, on the reach above [[Teddington Lock]].<ref name=FASLRM/> (For the purposes of the remainder of this article, the River Mole and the River Ember are treated as a single entity.)

Prior to the [[Last Glacial Period|last ice age]], the River Thames followed a more northerly route to the [[North Sea]], from [[Reading, Berkshire|Reading]] via [[Marlow, Buckinghamshire|Marlow]], [[Chorleywood]], [[St Albans]], [[Hertford]] and along the present [[Suffolk]]–[[Essex]] border.<ref>Wooldridge SW (1938) The glaciation of the London Basin and the evolution of the lower Thames drainage system ''Quarterly Journal of the Geology Society'' 94 627-668</ref> During this period, the Mole is thought to have merged with the [[River Wey]] near [[Byfleet]] and then flowed in a north-easterly direction via [[Richmond, London|Richmond]] to meet the proto-Thames near [[Ware, Hertfordshire|Ware]] in [[Hertfordshire]]. Today the Mole and Wey are less than {{convert|2|km|mi|abbr=on}} apart at their closest point near Painshill Park. During the [[Middle Pleistocene]] period,<ref group=note>The Middle Pleistocene period was {{circa|781,000–126,000}} [[before present|years ago]]</ref> a large ice sheet built up across much of the East of England, reaching as far south as [[St Albans]] and [[Chelmsford]], blocking the path of the proto-Thames. [[Meltwater|Glacial meltwater]] from the Anglian ice sheet caused the Thames to divert southwards and flood the valley of the Mole–Wey river, thus adopting its present route through [[London]].<ref>Bridgland and Gibbard (1997) Quaternary River Diversions in the London Basin and the Eastern English Channel {{lang|fr|Géographie physique et Quaternaire|italic=yes}} 51 (3) 337–346</ref>

==Ecology==

===Water quality===
Standard water quality of Mole and its tributaries has improved markedly since the 1990s.  In 1990 the [[Environment Agency]] assessed 23% of the watercourses as Grade B (good) or better.  In 2002 this figure was 60%.<ref name=CAMs/>  Investment in the Sewage Treatment Works in the catchment area has improved the quality of the discharges into the river,<ref name=CAMs/> and modifications to the runway and apron drainage systems at [[Gatwick Airport]] mean that surface water is diverted to aerated pollution control lagoons and [[balancing lake|balancing pond]]s for treatments, including acid/alkali neutralisation, before release into the river.<ref>{{cite web |url= http://www.gatwickairport.com/PageFiles/202/corpresponse/BAA%20Gatwick%20Corporate%20Responsibility%20Report%2005-06.pdf |title= Gatwick Airport Corporate Responsibility Report |author= Griffifths P |year= 2006 |publisher= London Gatwick Airport |access-date= 5 January 2011 |archive-url= https://web.archive.org/web/20100923033214/http://www.gatwickairport.com/PageFiles/202/corpresponse/BAA%20Gatwick%20Corporate%20Responsibility%20Report%2005-06.pdf |archive-date= 23 September 2010 |url-status= live }}</ref>

In 1972 a sub-debate on the future cleanliness of the Mole was had by the [[House of Lords]], involving a member of the [[South-East Strategic Committee]] of the [[Thames Conservancy]] (succeeded by the [[Environment Agency]]) and four others.  In this it was said, "...I can see no future for [The Mole]. The Mole Valley has been polluted. The Mole where I used to tickle [[trout]] in my youth is a drain, and it will remain a drain." Rebuttals included that the Mole is a "charming Surrey steam" and "If [[Earl of Lytton|Lord Lytton]] went to fish in the River Mole – and there are still angling clubs there – he would find that he would still be able to catch a [[trout]]".<ref>{{ukhansard | house=HL | date= 11 September 1972 | vol=335 | cc=138-165}}</ref>

Highly polluting discharges have become less common but have taken place since 2000. In 2003, Gatwick Airport Ltd pleaded guilty to charges of allowing chemical pollution to enter the River Mole after a detergent, used to clean rubber and oil from the runway, was washed into Crawters Brook by airport workers.<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/england/southern_counties/3237285.stm |title=Airport Guilty of Killing Fish |date=November 2003 |work=[[BBC News Online]] |access-date=10 February 2010 |archive-url=https://web.archive.org/web/20031211213351/http://news.bbc.co.uk/1/hi/england/southern_counties/3237285.stm |archive-date=11 December 2003 |url-status=live }}</ref> The [[Environment Agency]] estimated that up to 5200 fish of 14 different species were killed as the pollution drained downstream.  The airport was fined £30,000 by [[Lewes]] [[Crown Court]].<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/england/southern_counties/3456215.stm |title=Airport Fined for Killing Fish |date=February 2004 |work=[[BBC News Online]] |access-date=9 February 2010 |archive-date=2 January 2021 |archive-url=https://web.archive.org/web/20210102110412/http://news.bbc.co.uk/2/hi/uk_news/england/southern_counties/3456215.stm |url-status=live }}</ref>  In May 2003, sewage leaking from a pump operated by Thames Water leaked into the Stanford Brook, killing coarse fish in the Gatwick stream.<ref>{{cite web |url=https://www.telegraph.co.uk/news/uknews/1437261/Water-firms-abusing-sewage-law-loophole.html |title=Water firms 'abusing' sewage law loophole |first1=Rajeev |last1=Syal |first2=Graham |last2=Mole |date=27 July 2003 |work=[[The Daily Telegraph]] |access-date=5 January 2011 |archive-url=https://web.archive.org/web/20120416210020/http://www.telegraph.co.uk/news/uknews/1437261/Water-firms-abusing-sewage-law-loophole.html |archive-date=16 April 2012 |url-status=live }}</ref>

Water quality of the River Mole in 2019:
{| class="wikitable"
|-
! Section !! Ecological<br/>Status !! Chemical<br/>Status !! Overall<br/>Status !! Length !! Catchment !! Channel
|-
| {{waterqual_title |desc=Mole (Horley to Hersham) |asset= GB106039017621}}
| {{waterqual_mod}}
| {{waterqual_fail}}
| {{waterqual_mod}}
| {{convert| 60.133 |km|mi|abbr=on}}
| {{convert| 151.017 |km2|sqmi|abbr=on}}
| 
|-
| {{waterqual_title |desc=Mole (Hersham to R. Thames conf at East Molesey) |asset= GB106039017622}}
| {{waterqual_mod}}
| {{waterqual_fail}}
| {{waterqual_mod}}
| {{convert| 9.507 |km|mi|abbr=on}}
| {{convert| 21.803 |km2|sqmi|abbr=on}}
|  Heavily modified
|}

===Biodiversity===
The [[marsh frog]] (''Pelophylax ridibundus'', a non-native species introduced from Europe in the 1930s) is now commonly found in the upper Mole and its tributaries around [[Newdigate]] and Gatwick.<ref name=little_book_Surrey>{{cite book |last= Matthews |first= Rupert |year= 2010 |title= The little book of Surrey |location= Stroud |publisher= History Press |pages= 118–119 |isbn=9780752456331}}</ref> There is no evidence that the presence of the frogs has had a deleterious effect on [[indigenous (ecology)|indigenous]] amphibians.<ref>{{cite web |url= http://surrey-arg.org.uk/cgi-bin/SARG2ReptileSpeciesData.asp?Species=Marsh_Frog |title= Marsh Frog |author= Wycherley J |date= January 2008 |work= Database of amphibian species |publisher= Surrey Amphibian and Reptile Group |access-date= 7 February 2010 |archive-url= https://web.archive.org/web/20111004062024/http://www.surrey-arg.org.uk/cgi-bin/SARG2ReptileSpeciesData.asp?Species=Marsh_Frog |archive-date= 4 October 2011 |url-status= live }}</ref> A second non-native species, the [[edible frog]] (''Pelophylax'' [[klepton|kl.]] ''esculentus'') was introduced to a site at [[Newdigate]] in the early 1900s. It has in 2008 been recorded in tributaries of the River Mole at [[Capel, Surrey|Capel]] and [[Brockham]].<ref name=little_book_Surrey/>

[[File:River Mole from Common Meadow, Leatherhead.jpg|thumb|River Mole from Common Meadow, Leatherhead]]
The River Mole has the most diverse fish population of any river in England.<ref name=EA_fish/> The '''Gatwick Stream''' is dominated by coarse fish such as [[brown trout]], [[brook lamprey]], and [[European eel|eel]]. In 2003, the upper River Mole near Meath Green Lane, Horley, was enhanced to create a gravel [[Spawn (biology)|spawning]] area to encourage [[European chub|chub]] and [[Common dace|dace]] in addition to [[Common roach|roach]].<ref name=CAMs/> In 1974 [[zander]], a non-indigenous coarse fish native to Europe, were introduced legally to Old Bury Hill Lake which supplies the Pipp Brook. Zander have been caught in the Lower Mole below Dorking since the 1980s.<ref>{{cite journal |author=GH Copp |year=2003 |title=Introduction and establishment of the pikeperch ''Stizostedion lucioperca''(L.) in Stanborough Lake (Hertfordshire) and its dispersal in the Thames catchment |journal=The London Naturalist |volume= 82 |pages=139–153 }}</ref>

In the Mole Gap between Dorking and Leatherhead the river supports populations of chub, dace, [[barbel (fish species)|barbel]], and brown trout. Both barbel and brown trout are extremely sensitive to water quality and pollution. Below Leatherhead the river has historically supported larger predatory fish including chub, [[European perch|perch]], [[Northern pike|pike]], and eels, however in recent years chub and eel numbers have begun to decline. North of Esher the old river channel is dominated by [[Hydrocotyle umbellata|floating pennywort]], a highly invasive weed, which cuts off all light to the river bed, reducing oxygen levels and resulting in a poor habitat for fish. The Ember flood relief channel has a diverse fish population, including chub, dace, roach, [[Common bleak|bleak]], large pike and barbel.<ref name=CAMs/> At the [[confluence]] of the Mole and the River Thames at Hampton Court Palace it is possible to catch a wide variety of [[coarse fish]] species.<ref name=CAMs/>

The geographical distribution of many species of [[invertebrate]] in the river reflects the geology of the catchment area. Viviparid [[snails]] and water scorpions (of the genus ''Nepidae'') are commonly found where the river runs over the [[London Clay]]. Crayfish are common in areas associated with high [[alkaline|alkalinity]], particularly around Brockham, and the tributaries which run over the [[Weald Clay]] provide an excellent habitat for [[stoneflies]], [[Trichoptera|caddisflies]], fast swimming [[mayflies]] and [[beetles|riffle beetles]].<ref>Ruse LP (1996) Multivariate techniques relating macroinvertebrate and environmental data from a river catchment ''Water Research'' 30 (12) 3017–3024</ref>
The [[beautiful demoiselle]] (''Calopteryx virgo'') disappeared from the River Mole during the 1960s owing to deteriorating water quality, but has since recolonised.<ref name=sbdp>{{cite web |url= http://www.surreybiodiversitypartnership.org/xwiki/bin/view/Wetland/ActionPlan |title= Wetland Action Plan |author= Cousins D |date= March 2007 |work= Priority Habitats |publisher= Surrey Biodiversity Partnership |access-date= 8 February 2010 |archive-url= https://web.archive.org/web/20080905131921/http://www.surreybiodiversitypartnership.org/xwiki/bin/view/Wetland/ActionPlan |archive-date= 5 September 2008 |url-status= live }}</ref> The [[white-legged damselfly]] (''Platycnemis pennipes'') is also found along the river, and the [[downy emerald]] (''Cordulia aenea'') is found between [[Box Hill, Surrey|Box Hill]] and Leatherhead.<ref name=sbdp/><ref>P. Follett (1996) Mole Valley Natural History Audit: Survey of ''Odonata'' - Dragonflies and Damselflies</ref>  The Mole is one of only three locations in England where the river shingle beetle (''Meotica anglica'') is found.<ref>{{cite web |url= http://jncc.defra.gov.uk/PDF/UKBAP_Tranche2-ActionPlans-Vol6-1999.pdf |title= Grouped Plan for River Shingle Beetles |author= Williams M |date= October 1999 |work= UK Biodiversity Group Tranche 2 Action Plans |publisher= UK Biodiversity Action Plan |access-date= 7 February 2010 |archive-url= https://web.archive.org/web/20110704193928/http://jncc.defra.gov.uk/PDF/UKBAP_Tranche2-ActionPlans-Vol6-1999.pdf |archive-date= 4 July 2011 |url-status= live }}</ref>

A nationally scarce species which is locally common on the River Mole is the [[Cuscuta europaea|greater dodder]] (''Cuscuta europaea''), a [[parasitic plant]].<ref name=little_book_Surrey/>

===Conservation===
The Mole [[drainage basin|catchment area]] includes twelve [[Sites of Special Scientific Interest|Sites of Special Scientific Interest (SSSIs)]] that include wetland habitats,<ref name=MAls_2013/> The Mole Gap forms part of a [[Special Area of Conservation]] and is an SSSI of European importance.<ref name=MAls_2013/>

The stretch of river between Thorncroft Manor ({{cvt|1|km|1|disp=sqbr}} south of [[Leatherhead]]) and River Lane in [[Fetcham]] has been designated a Local Nature Reserve.<ref name=MVDC2>{{cite web |url= http://www.molevalley.gov.uk/index.cfm?Articleid=1934 |title= Local Nature Reserve |author= Shaw R |date= June 2005 |publisher= Mole Valley District Council |access-date= 10 February 2010 |archive-url= https://web.archive.org/web/20110614053810/http://www.molevalley.gov.uk/index.cfm?Articleid=1934 |archive-date= 14 June 2011 |url-status= live }}</ref>  Although much of the surrounding land has been taken by residential and commercial development, this section of the Mole supports 20 different [[mammal]] species,  20 [[butterfly]] species and 15 species of [[dragonfly]].  The geology of the local area is complex, since the river leaves the chalk of the Mole Gap at this point and flows over gravel and clay, creating a patchwork of different habitats including [[scrubland|scrub]], [[woodland]], [[hedge (barrier)|hedge]]s, banks, and [[meadow]]s as well as the water itself.  The river also provides a corridor for wildlife through the centre of Leatherhead.<ref name=MVDC2/>

The West End Common forms part of the [[Esher Commons]], owned and managed by [[Elmbridge Borough Council]]. The River Mole forms the western boundary of the common, flowing past a steep sandy area known locally as ''The Ledges''.  Plant species typical of ancient woodland are found in this area, including [[Common bluebell|bluebells]] (''Hyacinthoides non-scriptus''), [[marsh marigold]]s (''Caltha palustris'') and [[Saxifrage|golden saxifrages]] (''Chrysosplenium'' sp.). [[Cardamine|large bittercress]] (''Cardamine amara'') and the non-native [[Himalayan balsam]] (''Impatiens glandulifera'').<ref>[http://www.elmbridge.gov.uk/Elmbridge%20Borough%20Council/Leisure/Esher%20Commons%20Map%20Final%20February%202007.pdf Esher Commons Map and Information Sheet] {{Webarchive|url=https://web.archive.org/web/20140714182819/http://www.elmbridge.gov.uk/Elmbridge%20Borough%20Council/Leisure/Esher%20Commons%20Map%20Final%20February%202007.pdf |date=14 July 2014 }} Elmbridge Borough Council. Retrieved 2014-06-15</ref>

Molesey Heath Local Nature Reserve lies on the west bank of the Mole, west of the Island Barn Reservoir.  The Heath is an area of rough scrubland and, despite its name, is a reclaimed landfill site hence its large but artificial mound and small plateau.  The site is a rich habitat for birds including the [[common redshank|redshank]] and [[little ringed plover]].<ref>{{cite web |url= https://designatedsites.naturalengland.org.uk/SiteLNRDetail.aspx?SiteCode=L1009381&SiteName=&countyCode=41&responsiblePerson=&SeaArea=&IFCAArea= |title= Molesey Heath |year= 1999 |publisher= Natural England |access-date= 1 May 2020 |archive-url= https://web.archive.org/web/20181018003058/https://designatedsites.naturalengland.org.uk/SiteLNRDetail.aspx?SiteCode=L1009381&SiteName=&countyCode=41&responsiblePerson=&SeaArea=&IFCAArea= |archive-date= 18 October 2018 |url-status= live }}</ref>

==Geology==

===Upper Mole <span style="display:none">(geology)</span>===

The Mole rises south of Rusper in West Sussex, where an outcrop of the [[Wealden Group|Hastings Beds sandstone]] dips below the impermeable [[Weald Clay]].<ref name=MAls_2013/> From the source to [[Dorking]], the river drains an area of {{convert|340|km2|sqmi|abbr=on}}, of which approximately 60% is on Wealden or Atherfield Clay, 20% is on Tunbridge Wells Sand and 20% is on [[greensand]].<ref name=physiography/> [[Brickearth]] deposits are common in the valley around Betchworth and east of Dorking.<ref>{{cite web |url= http://www.surreymuseums.org.uk/collections/geology/geosur.html |title= The geology of the county of Surrey |date= November 2006 |work= Geological Collections in Surrey Museums |publisher= Surrey Museums Consultative Committee |access-date= 6 February 2012 |url-status= dead |archive-url= https://web.archive.org/web/20120229212044/http://www.surreymuseums.org.uk/collections/geology/geosur.html |archive-date= 29 February 2012 |df= dmy-all }}</ref>

The upper Mole catchment is dominated by a single broad terrace, which runs continuously from [[Tilgate|Tilgate Forest]] to the entry to the Mole Gap. Above Meath Green (near [[Horley]]), the terrace corresponds to the [[flood plain]] of the river, however from this point downstream to Brockham, the river cuts a narrow trench no more than {{cvt|150|m|yd}} wide. A similar trench is runs up several of the Mole's tributaries, notably along Deanoak Brook which follows a local [[strike and dip|strike]]. The presence of the trench protects the land from flooding, rendering it suitable for [[agriculture]].<ref name=physiography/>

===Mole Gap <span style="display:none">(geology)</span>===
[[File:Dry River Mole, 20 July 2022.jpg|thumb|The dry channel of the River Mole in [[Norbury Park]] in July 2022. The main flow has ceased leaving isolated shallow pools.]]
Between Dorking and Leatherhead the Mole cuts a steep-sided valley through the North Downs, creating a {{convert|170|m|ft|adj=mid|-high}} river cliff on the western flank of Box Hill. The bedrock is permeable chalk and the [[water table]] lies permanently below the level of the riverbed, allowing water to drain out of the river through swallow holes in the bed and banks.<ref name=Edmunds>{{cite journal |author= Edmunds FH |year= 1943 |title= Swallow holes and openings in the chalk of the Mole Valley |journal= The London Naturalist |pages= 2–7 }}</ref> The amount of water lost from the river is significant and in very hot summers the channel can become dry between Mickleham and Thorncroft Manor; this was recorded most recently in 1949,<ref>{{cite web |url= http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=65886&index=2&total=4&collection=Swallow%20hole&categoryId=1330&categoryTypeId=1&filterId=0&sortAttributeId=1050&sortDescending=true&movedBr=null |title= Photograph of swallow-hole in bed of River Mole |author= Rhodes J |year= 1949 |work= Geoscenic Digital Assets |publisher= British Geological Survey |access-date= 16 February 2012 |archive-url= https://web.archive.org/web/20160304230326/http://geoscenic.bgs.ac.uk/asset-bank/action/viewAsset?id=65886&index=2&total=4&collection=Swallow%20hole&categoryId=1330&categoryTypeId=1&filterId=0&sortAttributeId=1050&sortDescending=true&movedBr=null |archive-date= 4 March 2016 |url-status= live }}</ref><ref name=Chouler>{{cite book |last1= Chouler |first1= WH |title= Horley: Pageant of a Wealden Parish |year= 1975 |publisher= WH Chouler |location= Horley |isbn= 0-9502949-1-8 }}</ref> 1976<ref name=Currie>{{cite book |last1= Davison |first1= M |last2= Currie |first2= I |title= Surrey Weather Book |edition= 4th |year= 1996 |publisher= Frosted Earth |location= Coulsdon |isbn= 978-0-9516710-6-1}}</ref> and 2022.<ref name=ITV_News_2022/><ref>{{cite news |last= Seymour |first= Jenny |date= 19 August 2022 |title= Environment Agency rescue fish from River Mole in Surrey as water levels drop |work= Surrey Live |url= https://www.getsurrey.co.uk/news/surrey-news/fish-river-mole-rescued-drought-24797230 |access-date= 5 September 2022 |archive-date= 4 September 2022 |archive-url= https://web.archive.org/web/20220904162156/https://www.getsurrey.co.uk/news/surrey-news/fish-river-mole-rescued-drought-24797230 |url-status= live }}</ref><ref>{{cite news |last= Bradshaw |first= David |date= 19 August 2022 |title= In pictures: Environment Agency workers rescue fish from dried-out River Mole |work= Surrey Live |url= https://www.getsurrey.co.uk/news/surrey-news/gallery/pictures-fish-rescued-river-mole-24797394 |access-date= 5 September 2022 |archive-date= 5 September 2022 |archive-url= https://web.archive.org/web/20220905170650/https://www.getsurrey.co.uk/news/surrey-news/gallery/pictures-fish-rescued-river-mole-24797394 |url-status= live }}</ref> At [[Leatherhead]], the river leaves the chalk and flows across impermeable [[London Clay]]. At this point, the water table rises enough for the water to flow back into the main river channel.<ref name=Edmunds/>

In a survey in 1958, the geologist C.&nbsp;C. Fagg identified 25 active swallow holes between Dorking and [[Mickleham, Surrey|Mickleham]]; the majority were only a few centimetres in diameter and were located in the vertical banks of the river below the water line.<ref name=Fagg>{{cite journal |author= Fagg CC |year= 1957 |title= Swallow holes in the Mole Gap |journal= The South-eastern Naturalist and Antiquary |volume= 62 |pages= 1–13 }}</ref> Most holes were difficult to observe in times of normal or heavy flow and were susceptible to silting up as new holes were continually being formed.<ref name=Fagg/> A few much larger swallow holes were also observed separated from the main river by a channel{{clarify|date=November 2012}} of about a metre.<ref name=Fagg/><ref name=Sheppard>Shepperd R (1982) ''The Manor of Wistomble in the Parish of Mickleham: A local history'' chapter 9 page 85</ref> About six of these larger swallow holes were found to the west of the [[Burford Bridge Hotel]], along the course of the [[A24 road (Great Britain)|A24 Mickleham Bypass]] during its construction in 1936. Initially the surveyors tried to fill the holes with rubble to prevent the foundations of the new road subsiding. However this proved to be impractical and they were instead covered by concrete domes, up to 18 m in diameter, each fully supported by the surrounding chalk and provided with a manhole and access shaft to allow periodic inspection.<ref name=Sheppard/><ref name=Dumbleton>{{cite journal |vauthors=West G, Dumbleton MJ |year= 1972 |title= Some observations on swallow holes and mines in the Chalk |journal= Quarterly Journal of Engineering Geology |volume= 5 |issue=1–2 |pages= 171–177 |publisher= Geological Society of London |doi=10.1144/gsl.qjeg.1972.005.01.16|s2cid= 129120488 }}</ref> In the late 1960s the domes were reopened and inspected and the alluvium in the largest swallow hole was observed to have subsided by {{convert|1.5|m|0}} under the centre of one of the domes.<ref name=Dumbleton/> When the Dorking to Leatherhead railway was constructed in 1859, a fossilised swallow hole was discovered in the cutting at the south end of [[Box Hill & Westhumble railway station]], suggesting that even in its early history, the river had swallow holes.<ref name=Fagg/>

The author [[Daniel Defoe]], who attended school in [[Dorking]] and probably grew up in the village of [[Westhumble]],<ref>{{cite journal |author= Andrews JH |year= 1960 |title= Defoe and the Sources of His 'Tour' |journal= The Geographical Journal |volume= 126 |issue= 3 |pages= 268–277 |publisher= The Royal Geographical Society |doi=10.2307/1793630|jstor= 1793630 }}</ref><ref name=SAC_Defoe>{{cite journal |author= Bastian F |year= 1957 |title= Daniel Defoe and the Dorking District |journal= Surrey Archaeological Collections |volume= 55 |pages= 41–64 |url= https://archaeologydataservice.ac.uk/catalogue/adsdata/arch-379-1/dissemination/pdf/vol_55/surreyac055_041-064_bastian.pdf |access-date= 27 September 2020 |doi= 10.5284/1068897 |archive-date= 2 January 2021 |archive-url= https://web.archive.org/web/20210102102002/https://archaeologydataservice.ac.uk/archiveDS/archiveDownload?t=arch-379-1%2Fdissemination%2Fpdf%2Fvol_55%2Fsurreyac055_041-064_bastian.pdf |url-status= live }}</ref> described the swallow holes in the River Mole in his book ''[[A tour thro' the Whole Island of Great Britain]]'' (first published in 1724):
{{blockquote|...the current of the river being much obstructed by the interposition of those hills, called Box Hill ... it forces the waters as it were to find their way through as well as they can; and in order to do this, beginning, I say, where the river comes close to the foot of the precipice of Box-Hill, called the Stomacher, the waters sink insensibly away, and in some places are to be seen (and I have seen them) little channels which go out on the sides of the river, where the water in a stream not so big as would fill a pipe of a quarter of an inch diameter, trills away out of the river, and sinks insensibly into the ground. In this manner it goes away, lessening the stream for above a mile, near two, and these they call the Swallows.|<small>Daniel Defoe (1724)</small><ref>{{cite book |last= Defoe |first= Daniel |author-link=Daniel Defoe |year= 1724 |title= A tour thro' the whole island of Great Britain: divided into circuits or journies, giving a particular and diverting account of whatever is curious and worth observation ... |location= London |publisher= G. Strahan |page= 95 }}</ref>}}

Not all of the water removed from the river by the swallow holes is returned to the channel at [[Leatherhead]]. The chalk aquifer also feeds the springs at the southern end of [[Fetcham]] Mill Pond, which have never been known to run dry.<ref name=Edmunds/> A survey in March 1883 estimated that the Fetcham springs were producing about {{convert|3.6|e6impgal|m3}} every day.<ref>JW Grover (1887) Chalk springs in the London basin, illustrated by the Newbury, Wokingham, Leatherhead and Rickmansworth Water Works ''Proceedings of the Institution of Civil Engineers'' 90</ref> A second survey in 1948 estimated that the same springs were yielding about {{convert|5|e6impgal|m3}} a day.<ref>{{cite journal |author= Edmunds FH |year= 1948 |title= Correspondence on the movement of water in the middle and lower chalk of the River Dour catchment |journal= Journal of the Institution of Civil Engineers |volume= 29 |page= 73 |publisher= Institution of Civil Engineers }}</ref> The [[water table]] in the chalk of the [[River Wey|Wey Gap]] is significantly higher than might be expected from natural [[groundwater recharge|rainwater percolation]] alone. It has been suggested that a proportion of the excess water originates from the Mole Gap.<ref name=Dines>{{cite book |title= The geology of the country around Reigate and Dorking |last1= Dines |first1= HG |last2= Edmunds |first2= FH |year= 1933 |series= Memoirs of the Geological Survey, England and Wales |publisher= HM Stationery Office |location= London }}</ref>

===Lower Mole <span style="display:none">(geology)</span>===
At Leatherhead the river leaves the chalk bedrock, moving onto [[London Clay]].<ref>{{cite journal |author=Green JFN |year= 1936 |title= Field Meeting in the Region of the River Mole |journal= Proceedings of the Geologists' Association |volume= 47 |pages= 11–14 |doi= 10.1016/s0016-7878(36)80018-2}}</ref> The river meanders across an [[alluvial plain]] between {{cvt|400|and(-)|800|m|yd}} wide towards Cobham, where it begins to descend to a lower flood plain, which broadens as the river turns in an axehead meander. At the east end of Painshill Park, the flood plain narrows into a trench about {{cvt|60|m|yd}} wide, in which the river runs northwards for {{convert|6.5|km|mi|abbr=on}} towards Hersham, where the river enters the flood plain of the River Thames.<ref name=physiography/>

Between Cobham and Esher, the Mole's historic courses have deposited gravel on top of the London Clay.<ref>{{cite journal |author=Monckton HW |year=1904 |title=Excursions to the Farnham Gravel Pits on April 23rd and to the Brickfields and Gravel Pits at Dawley, between Hayes and West Drayton on April 30th 1904 |journal=Proceedings of the Geologists' Association |volume=18 |issue=8 |pages=409–414 |doi=10.1016/s0016-7878(04)80055-5 |url=https://zenodo.org/record/1428520 |access-date=5 July 2019 |archive-date=2 January 2021 |archive-url=https://web.archive.org/web/20210102110414/https://zenodo.org/record/1428520 |url-status=live }}</ref> The depth of the deposits generally varies from {{convert|2.5|to(-)|7|m|ft|0|abbr=on}};<ref name=ChertseyGeology>{{cite book |author=Dewey H |title=The Geology of the county around Windsor and Chertsey |series= Memoirs of the Geological Survey |year=1915 |publisher= British Geological Survey |location=London |pages=71–72}}</ref> the lower layers are generally highly compacted and cemented together with brick-red iron oxide, whereas the upper layers are loosely packed with angular flints and sand.<ref>{{cite journal |author= Hudleston WH |year= 1886 |title= On a recent Section through Walton Common exposing the London Clay, Bagshot Beds, and Plateau-gravel |journal= Quarterly Journal of the Geological Society |volume= 42 |issue= 1–4 |pages= 147–172 |doi= 10.1144/gsl.jgs.1886.042.01-04.18 |s2cid= 129839441 |url= https://zenodo.org/record/1448529 |access-date= 5 July 2019 |archive-date= 2 January 2021 |archive-url= https://web.archive.org/web/20210102110415/https://zenodo.org/record/1448529 |url-status= live }}</ref> Remains of a further gravel terrace, containing cherts and flints to a depth of {{convert|4|m|ft|0|abbr=on}}, line the east side of [[St George's Hill]].<ref name=ChertseyGeology/>

==History==

===Etymology===
The river is first recorded in the ''Red Book of Thorney'' in AD 983 as ''Emen'' and in the AD 1005 ''Cartulary of the Abbey of Eynsham'' as both ''Emen'' and ''Æmen''.<ref>{{cite journal |author= Bonner A |title= Surrey River Names: Mole |journal= Surrey Archaeological Collections |publisher= Surrey Archaeological Society |volume= 38 |pages= 107–108}}</ref><ref name=Ekland>{{cite book |title= English River Names |author= Ekland E |year= 1928 |publisher= Clarendon Press |location= Oxford |pages= 146–147}}</ref> Variations in the name are recorded throughout the Middle Ages and the river appears as ''Amele'' in the [[Domesday Book]] of 1086, and subsequently as ''Emele'' in 12th- and 13th-century Court Rolls.<ref name=Bonner>{{cite journal |author= Bonner A |year= 1925 |volume= 37 |pages= 117–143 |title= Surrey Place Names: River Names |journal= Surrey Archaeological Collections |url= https://archaeologydataservice.ac.uk/catalogue/adsdata/arch-379-1/dissemination/pdf/vol_36/surreyac036_085-101_bonner.pdf |access-date= 27 September 2020 |doi= 10.5284/1068742 |archive-date= 2 January 2021 |archive-url= https://web.archive.org/web/20210102110414/https://archaeologydataservice.ac.uk/archiveDS/archiveDownload?t=arch-379-1%2Fdissemination%2Fpdf%2Fvol_36%2Fsurreyac036_085-101_bonner.pdf |url-status= live }}</ref> This name is probably derived from the [[Old English]] word ''æmen'' meaning ''misty'' or ''causing mists'',<ref name=Ekland/>  and the name of the River Ember probably has its origins in this name.<ref name=Bonner/><ref>{{cite book|author=Room, Adrian|title=Dictionary Of Place Names In The British Isles|url=https://archive.org/details/dictionaryofplac0000room|url-access=registration|publisher=Bloomsbury|year=1988|page=[https://archive.org/details/dictionaryofplac0000room/page/128 128]|isbn=9780747501701 }}</ref><ref>{{cite web |url=http://www.british-history.ac.uk/report.aspx?compid=50887 |title=A Topological Dictionary of England |access-date=10 April 2013 |archive-url=https://web.archive.org/web/20121102092003/http://www.british-history.ac.uk/report.aspx?compid=50887 |archive-date=2 November 2012 |url-status=live }}</ref><ref group=note>The prefix of the former [[Hundred of Elmbridge|hundred]] and present [[borough of Elmbridge]], which is referred to as Emley Bridge in some 19th-century records, probably also has its origins in the [[Old English]] word ''æmen''.</ref>

The name ''Mole'' does not appear until the 16th century, first occurring as ''Moule'' in [[William Harrison (clergyman)|Harrison's]] ''Description of Britain'' of 1577. The antiquarian [[William Camden]] uses the Latinized form ''Molis'' in the 1586 edition of ''Britannia'' and [[Michael Drayton]] is the first to use ''Mole'' in his poem ''Poly-Olbion'' published in 1613.<ref name=Bonner/> 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).<ref name="AD Mills 1998"/> In [[John Rocque]]'s 1768 map of Surrey, the name ''Moulsey River'' is used.<ref>{{cite web |url= http://www.moleseyhistory.co.uk/maps/pages/map_0002.htm |title= Detail from Rocque's Map of Surrey, c1768. |author= Baker R |work= Maps |publisher= Molesey History |access-date= 5 December 2010 |archive-url= https://web.archive.org/web/20110722005955/http://www.moleseyhistory.co.uk/maps/pages/map_0002.htm |archive-date= 22 July 2011 |url-status= live }}</ref>

===Archaeology===
In common with much of the rest of the Weald, the earliest evidence of human settlement along the Upper Mole is from the [[Mesolithic|Mesolithic Period]] (20,000–7000&nbsp;BC).  Mesolithic sites at Wonham, Flanchford and Sidlow. Finds at Wonham include arrowheads and a plano-convex knife.<ref>{{cite journal |author= Ellaby EL |year= 1977 |title= A Mesolithic Site at Wonham |journal= Surrey Archaeological Collections |publisher= Surrey Archaeological Society |volume= 71 |pages= 7–12 |url= https://archaeologydataservice.ac.uk/catalogue/adsdata/arch-379-1/dissemination/pdf/vol_71/surreyac071_007-012_ellaby.pdf |access-date= 27 September 2020 |doi= 10.5284/1069028 |archive-date= 2 January 2021 |archive-url= https://web.archive.org/web/20210102110414/https://archaeologydataservice.ac.uk/archiveDS/archiveDownload?t=arch-379-1%2Fdissemination%2Fpdf%2Fvol_71%2Fsurreyac071_007-012_ellaby.pdf |url-status= live }}</ref>  The Lower Mole appears to have been settled during the same period and a flint axe dating from Mesolithic period found on spit of land close to River Mole in Cobham in 1965.<ref>{{cite journal |author= Holling F |year= 1966 |title= Mesolithic Flint Axe from Cobham |journal= Surrey Archaeological Collections |publisher= Surrey Archaeological Society |volume= 63 |page= 167}}</ref>  Remains of a flat-bottomed dug-out canoe were found at the confluence of the Mole and Thames in 1877 by a local boatman.  The canoe is preserved at the [[Pitt Rivers Museum]] in [[Oxford]].<ref>{{cite web |url= http://england.prm.ox.ac.uk/englishness-Hampton-Court-canoe.html |title= The Hampton Court Canoe |author= Petch A |year= 2010 |work= ENGLAND: THE OTHER WITHIN: Analysing the English Collections at the Pitt Rivers Museum |publisher= Pitt Rivers Museum, Oxford University |access-date= 12 December 2010 |archive-url= https://web.archive.org/web/20110815173948/http://england.prm.ox.ac.uk/englishness-Hampton-Court-canoe.html |archive-date= 15 August 2011 |url-status= live }}</ref>

The Mole Gap and North Downs do not appear to have been settled until the late Stone Age: A large axe, typical of a "rough-out" axe produced during the [[Neolithic]] period, which was discovered in 1952 during building work in Westhumble,<ref>{{cite journal |author= Rankine WF |year= 1952 |title= Neolithic Axe from Westhumble |journal= Surrey Archaeological Collections |publisher= Surrey Archaeological Society |volume= 52 |page= 80 }}</ref> A flint mine of the same period has been discovered at [[East Horsley]] along with Neolithic flakes of flint at [[Fetcham]] and [[Headley, Surrey|Headley Heath]].<ref>{{cite journal |author= Wood ES |year= 1952 |title= Neolithic Sites in West Surrey |journal= Surrey Archaeological Collections |volume= 52 |pages= 11–28 |url= https://archaeologydataservice.ac.uk/catalogue/adsdata/arch-379-1/dissemination/pdf/vol_52/surreyac052_011-028_wood.pdf |access-date= 27 September 2020 |doi= 10.5284/1068871 |archive-date= 2 January 2021 |archive-url= https://web.archive.org/web/20210102110414/https://archaeologydataservice.ac.uk/archiveDS/archiveDownload?t=arch-379-1%2Fdissemination%2Fpdf%2Fvol_52%2Fsurreyac052_011-028_wood.pdf |url-status= live }}</ref>

Significant [[Bronze Age]] finds include a bronze sword found close to the river north of Amberley Farm near Charlwood<ref>{{cite journal |author= Lowther AWG |year= 1958 |title= A Late Bronze Age Sword from Charlwood |journal= Surrey Archaeological Collections |publisher= Surrey Archaeological Society |volume= 55 |pages= 122–123}}</ref> and a small hoard of weaponry consisting of two [[palstave|palstave axes]] and a scabbard chape was discovered in 2003 in Norbury Park close to Ham Bank.<ref>{{cite journal |author= Williams D |year= 2008 |title= A late Bronze Age hoard from Norbury Park, Mickleham |journal= Surrey Archaeological Collections |volume= 94 |pages= 293–301 |url= https://archaeologydataservice.ac.uk/catalogue/adsdata/arch-379-1/dissemination/pdf/vol_94/surreyac094_293-301_williams.pdf |access-date= 27 September 2020 |archive-date= 2 January 2021 |archive-url= https://web.archive.org/web/20210102110418/https://archaeologydataservice.ac.uk/archiveDS/archiveDownload?t=arch-379-1%2Fdissemination%2Fpdf%2Fvol_94%2Fsurreyac094_293-301_williams.pdf |url-status= live }}</ref>

===Navigation===
[[File:MoleThames.JPG|right|thumb|Confluence of the Mole with the Thames opposite Hampton Court]]
It is not clear to what extent the Mole was used for navigation in the past: In the late 13th century, Thorncroft Manor (south of Leatherhead) purchased a ''shout'', a type of boat up to {{convert|16|m|ft}} in length used to carry produce to market<ref>{{cite book |author= Campbell MWB |title= A Medieval capital and its grain supply: agrarian production and distribution in the London region c.1300 |volume= Historical Geography Research Series |year= 1993 |publisher= Institute of British Geographers |isbn=1-870074-12-2}}</ref> and it has been suggested that stone cut from quarries in Reigate was transported to London via the river.<ref>{{cite journal |author= de Domingo |year= 1994 |title= The Provenance of some Building Stones in St Mary Spital by Geological Methods |journal= London Archaeologist |volume= 7 |issue= 9 |pages= 240–243 |publisher= London Archaeologist Association}}</ref>

During the 17th century, two bills came before parliament to make sections of the river [[Canalized|navigable]].  The first, in 1663, was passed by the [[British House of Commons|House of Commons]] but was defeated in the [[House of Lords]]. During the following year (1664), an act was passed by both [[Houses of Parliament]] to make the River Mole navigable from Reigate to the River Thames, but was never executed.<ref name=Vine>{{cite book |title=London's lost route to the sea : an historical account of the inland navigations which linked the Thames to the English Channel |last= Vine |first= PAL |year= 1996 |publisher= Middleton |location= Midhurst |isbn= 1-873793-78-2 |edition= 5th}}</ref><ref>{{cite web |url= http://www.iisg.nl/hpw/papers/law-bogart.pdf |title= Political Institutions and the Emergence of Regulatory Commitment in England: Evidence from Road and River Improvement Authorities, 1600-1750 |author= Bogart D |date= August 2007 |publisher= International Institute of Social History |access-date= 7 February 2010 |archive-url= https://web.archive.org/web/20110608072734/http://www.iisg.nl/hpw/papers/law-bogart.pdf |archive-date= 8 June 2011 |url-status= live }}</ref> The only [[Surrey]] river to have been made fully navigable is the combined lower section of the [[River Wey]].<ref name=Vine/>

In 1798 William Marshall advocated the canalisation of a short stretch of the River Mole between [[Betchworth]] and [[Dorking]] to facilitate the movement of chalk from quarry to market.<ref>{{cite book |title= The rural economy of the southern counties |url= https://archive.org/details/b28774942_0001 |last= Marshall |first= WH |year= 1798 |publisher= Nicol |location= London}}</ref> In 1810 the engineer [[John Rennie the Elder|John Rennie]] proposed a canal linking the [[River Medway]] to [[Portsmouth]] which was to have a branch to London following the Mole for much of its length.<ref name=Vine/>  Between 1825 and 1828 the architect and civil engineer [[Nicholas Wilcox Cundy]] proposed a Grand Imperial Ship Canal from [[Deptford]] to [[Chichester]] passing through the Mole Gap, however he was unable to attract sufficient financial interest in his scheme.<ref>{{cite book |title= Reports on the Grand Ship Canal from London to Arundel Bay and Portsmouth |last= Cundy |first= NW |year= 1827 |publisher= Clowes |location= London}}</ref>

Today the Mole is navigable for the {{cvt|400|m|yd}} from the confluence with the [[River Thames]] to Molember Weir at [[East Molesey]] where there is a private mooring facility.<ref>{{cite web |url= http://www.londoncanals.co.uk/smlnavs/molember.html |title= The River Molember |year= 2010 |work= London Canals |access-date= 5 December 2010 |archive-url= https://web.archive.org/web/20100730033117/http://www.londoncanals.co.uk/smlnavs/molember.html |archive-date= 30 July 2010 |url-status= live }}</ref>  The river may be paddled all year by [[canoe]] between [[Brockham]] and [[Fetcham]] with an appropriate licence from the [[British Canoe Union]].

===Second World War defences===
During the [[Second World War]] several sites along the course of the Mole were fortified for the defence of London against invasion from the south. [[GHQ Line|GHQ Line B]] ran along the North Downs from Farnham and Guildford, crossing the Mole Gap to the north of Dorking and following the river to Horley.<ref name=DA12>{{cite web |url= http://ads.ahds.ac.uk/catalogue//adsdata/arch-455-1/dissemination/pdf/Text_Reports/DA12_TEXT_-_DORKING_GAP.pdf |title= Defence Area 12: Dorking Gap |author= Foot W |year= 2009 |work= Defence Areas: a national study of Second World War anti-invasion landscapes in England |publisher= English Heritage |access-date= 11 December 2010 |archive-url= https://web.archive.org/web/20110811042351/http://ads.ahds.ac.uk/catalogue//adsdata/arch-455-1/dissemination/pdf/Text_Reports/DA12_TEXT_-_DORKING_GAP.pdf |archive-date= 11 August 2011 |url-status= live }}</ref> Between Betchworth and Box Hill, the north bank of the River Mole was stabilised and made steeper to prevent wheeled vehicles from crossing. At Boxhill Farm, where access to the river from the north bank was required for the herd of dairy cows, a row of twelve concrete cylinders were cast as an anti-tank measure. Gun mounts were also installed to protect both Boxhill and Deepdene bridges and several [[Bunker#Pillbox|pillboxes]] were installed.<ref name=DA12/><ref name="Marchington T 2000 96–100">{{cite journal |author= Marchington T |year= 2000 |title= Wartime Defences: A Second Look |journal= Proceedings of the Leatherhead and District Local History Society |volume= 6 |issue= 4 |pages= 96–100 |publisher= Leatherhead and District Local History Society}}</ref><ref name=Telegraph_walk>{{cite journal |date=2 March 2011 |title=Box Hill, Surrey: walk of the week |journal=Daily Telegraph |url=https://www.telegraph.co.uk/travel/activityandadventure/walkingholidays/8356605/Box-Hill-Surrey-walk-of-the-week.html |access-date=29 March 2011 |archive-url=https://web.archive.org/web/20110309211404/http://www.telegraph.co.uk/travel/activityandadventure/walkingholidays/8356605/Box-Hill-Surrey-walk-of-the-week.html |archive-date=9 March 2011 |url-status=live }}</ref> An anti-tank ditch was dug from the Stepping Stones eastwards across the fields belonging to Bradley Farm (now [[Denbies Wine Estate|Denbies vineyard]]).<ref name=DA12/>

The river crossing at Sidlow Bridge was heavily defended and a line of pill boxes was constructed on the north bank of the river. Concrete anti-tank [[dragon's teeth (fortification)|dragon's teeth]] were built on both sides of the river, a short distance upstream of the bridge, as an obstacle to [[armoured fighting vehicle|armoured vehicles]].<ref name=DA38>{{cite web |url= http://ads.ahds.ac.uk/catalogue//adsdata/arch-455-1/dissemination/pdf/Text_Reports/DA38_TEXT_-_SIDLOW_BRIDGE.pdf |title= Defence Area 38: Sidlow Bridge |author= Foot W |year= 2009 |work= Defence Areas: a national study of Second World War anti-invasion landscapes in England |publisher= English Heritage |access-date= 11 December 2010 |archive-url= https://web.archive.org/web/20110811042500/http://ads.ahds.ac.uk/catalogue//adsdata/arch-455-1/dissemination/pdf/Text_Reports/DA38_TEXT_-_SIDLOW_BRIDGE.pdf |archive-date= 11 August 2011 |url-status= live }}</ref>

==Crossings of the Mole==

=== Mole Gap ===

The [[North Downs Way]] crosses the river at [[Box Hill, Surrey|Box Hill]] via seventeen hexagonal [[step-stone bridge|stepping stone]]s, which are frequently submerged after heavy rainfall.  The current stones were dedicated in September 1946 by the then Prime Minister [[Clement Attlee]], replacing those destroyed during the Second World War as an anti-invasion measure.<ref name=Telegraph_walk/><ref>{{cite magazine |year= 1946 |title= Picture of the Week |magazine= Life |volume= 21 |issue= 13 |page= 36 |publisher= Time Inc. }}</ref> The location is popular with anglers and families, but swimming is strongly discouraged as the water is polluted in places. The stones give their name to the pub in the nearby village of [[Westhumble]].

When the Burford Bridge was rebuilt in 1937, excavations revealed a "flint-surfaced approach to [a] ford at low level having all the signs of Roman workmanship" suggesting that [[Stane Street (Chichester)|Stane Street]] (which ran from [[London]] to [[Chichester]] via [[Dorking]]) crossed the river at this point.<ref>{{Cite newspaper The Times |author=<!--Staff writer(s); no by-line.--> |title= The Mole Crossing at Burford  |location= London |date= 25 March 1937 |issue= 47642 |page= 17}}</ref> In Defoe's time, there was a footbridge at this point, but carts and waggons had to cross the river by a ford.

=== Leatherhead ===
[[File:Leatherhead Bridge - geograph.org.uk - 244353.jpg|right|thumb|Leatherhead Town Bridge across the River Mole]]
There are three [[listed building|listed]] bridges in Leatherhead of which the 14 arch Leatherhead Town Bridge is the oldest.<ref name = visit_leatherhead>{{cite web |url= http://www.visitleatherhead.com/historyAndHeritage_theRiverMole.php |title= History and Heritage: The River Mole |work= Discover Leatherhead: Gateway to the Surrey Hills |publisher= Visit Leatherhead |access-date= 7 February 2010 |archive-url= https://web.archive.org/web/20101014145922/http://www.visitleatherhead.com/historyAndHeritage_theRiverMole.php |archive-date= 14 October 2010 |url-status= live }}</ref> The first bridge on this site was probably constructed during the late Middle Ages and was rebuilt and enlarged by the [[county surveyor]], [[George Gwilt]] in 1782–83.  The bridge is a long structure of 14 segmental arches resting on low piers, finished in red brick in [[Flemish bond]], with some [[Portland stone]] dressing.<ref>{{National Heritage List for England|num=1028646|desc=Leatherhead Bridge, Bridge Street|access-date=1 May 2020}}</ref>

A few metres downstream of Leatherhead Bridge stands the Grade&nbsp;II listed railway viaduct which carries the [[Sutton & Mole Valley Lines|Leatherhead to Dorking line]] over the river.<ref>{{National Heritage List for England|num=1028596|desc=Railway viaduct approximately 15 metres west of road bridge over River Mole|access-date=1 May 2020}}</ref>  The bridge was constructed in 1867 and, at the insistence of [[Thomas Grissell]] the landowner, was given lavish architectural treatment.<ref name=Jackson>{{cite book |title= Dorking's Railways |last= Jackson |first= AA |year= 1988 |publisher= Dorking Local History Group|location= Dorking |isbn= 1-870912-01-2}}</ref>

The single-span Shell Bridge stands in the grounds of Thorncroft Manor, to the south of the Town Centre.<ref name = visit_leatherhead/> The bridge was constructed as an ornamental feature in parkland laid out by [[Capability Brown]] in the late 18th century.  The bridge is largely composed of flint and has a large inverted scallop shell in the place of the [[keystone (architecture)|keystone]] and similar shells in the [[spandrel arch|spandrels]] at each side.<ref>{{National Heritage List for England|num=1293520|desc=Ornamental bridge approximately 70 metres north of Thorncroft Bridge|access-date=1 May 2020}}</ref>  The bridge was renovated and strengthened in 1999 by a group of Canadian engineers working on the Terra Nove project. The restoration project was dedicated to the memory of the Canadian servicemen who were billeted in the manor during the Second World War.<ref>{{cite web |url= http://www.vac-acc.gc.ca/REMEMBERS/sub.cfm?source=memorials/ukmem/leatherhead |title= The Shell Bridge and Thorncroft Manor |work= UK Memorials: Commemorating Canada's Fallen |date= December 2005 |publisher= Veterans' Affairs Canada |access-date= 7 February 2010 }}{{Dead link|date=July 2021 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

=== Cobham ===
A wooden bridge is thought to have existed on the site of Cobham Bridge since the 12th century, the upkeep of which was the responsibility of the adjacent landowners.  The present bridge was constructed by [[George Gwilt]] in 1792, after responsibility for maintenance had been transferred to the county council by Act of Parliament.<ref name=moleseyhistory/>  The bridge has nine low arches and is primarily built of red brick with stone coping.  The parapets were rebuilt in 1914 and the structure was given a Grade&nbsp;II listing in 1953.<ref>{{National Heritage List for England|num=1377488|desc=Cobham Bridge|access-date=1 May 2020}}</ref>

{| class="wikitable sortable collapsible collapsed"
! colspan="5" style="text-align:center;"|List of crossings of the River Mole <small>(from mouth to source)</small>
|-
! width=180pt| Name
! scope="col" | Grid Reference
! scope="col" |  Type
! scope="col" class="unsortable" | Road/Railway
! scope="col" class="unsortable" | Notes
|- style="background:#F8F8FF"
|Confluence with River Thames||{{hs|676}}{{gbmappingsmall|TQ156683}}|| || ||East Molesey, Surrey
|-
|Hampton Court Railway Station||{{hs|676}}{{gbmappingsmall|TQ155683}}||Railway|| Hampton Court Branch Line ||<ref>{{cite web |url= https://www.geograph.org.uk/photo/1169879 |title= Railway bridge and platform over the River Ember |year= 2008 |work= TQ1568 |publisher= Geograph Britain and Ireland |access-date= 20 April 2013 |archive-url= https://web.archive.org/web/20170626212334/http://www.geograph.org.uk/photo/1169879 |archive-date= 26 June 2017 |url-status= live }}</ref><ref>{{cite web |url= https://www.geograph.org.uk/photo/927778 |title= River Ember: Hampton Court railway station bridge |last1= Cox |first1= N |year= 2008 |work= TQ1467 |publisher= Geograph Britain and Ireland |access-date= 20 April 2013 |archive-url= https://web.archive.org/web/20170626213016/http://www.geograph.org.uk/photo/927778 |archive-date= 26 June 2017 |url-status= live }}</ref>
|-
|Hampton Court Way Bridge||{{hs|676}}{{gbmappingsmall|TQ154683}}||Road|| A309 ||
|-
|Tanner's Bridge||{{hs|676}}{{gbmappingsmall|TQ145676}}||Footbridge||||<ref>{{cite web |url= https://www.geograph.org.uk/photo/928778 |title= River Mole: Tanner's Bridge |last1= Cox |first1= N |year= 2008 |work= TQ1467 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112456/http://www.geograph.org.uk/photo/928778 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Hersham Viaduct|| {{hs|656}}{{gbmappingsmall|TQ130656}} ||Railway|| || <ref>{{cite web |url= https://www.geograph.org.uk/photo/2152756 |title= Heading for Esher |last1= Baker |first1= G |year= 2010 |work= TQ1265 |publisher= Geograph Britain and Ireland |access-date= 2 July 2011 |archive-url= https://web.archive.org/web/20121019112627/http://www.geograph.org.uk/photo/2152756 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Albany Bridge||{{hs|645}}{{gbmappingsmall|TQ130645}}||Road||A244||Named after the Duchess of Albany (resident of Claremont).  Original wooden Victorian bridge replaced by a stone parapet bridge in 1907 and the present concrete bridge dates from 1965.<ref name=Elmbridge_History>{{cite web |url=http://www.moleseyhistory.co.uk/books/surrey/industrialHistory/index.html#E4 |title=A Guide to the Industrial Archaeology of Elmbridge |vauthors=Baker RG, Oliver R |year=1989 |publisher=Surrey Industrial History Group |access-date=5 December 2010 |archive-url=https://web.archive.org/web/20110722005313/http://www.moleseyhistory.co.uk/books/surrey/industrialHistory/index.html#E4 |archive-date=22 July 2011 |url-status=live }}</ref>
|-
|Burhill Bridge|| {{hs|623}}{{gbmappingsmall|TQ103623}}||Road|| || A multi-span composite deck supported on steelwork tresses with a total span of {{cvt|48|m}} and a main span of {{cvt|22|m}} over the river itself.  Constructed between January and March 2008, replacing an earlier bridge on the same site.<ref>{{cite web |url= http://www.atornconstruction.co.uk/projects/bridge-river-mole-bridge.html |title= Bridge over the River Mole |year= 2008 |work= Building and Civil Engineering Projects |publisher= A Torn Construction Ltd |access-date= 3 September 2011 |archive-url= https://web.archive.org/web/20120331172334/http://www.atornconstruction.co.uk/projects/bridge-river-mole-bridge.html |archive-date= 31 March 2012 |url-status= live }}</ref>
|-
|A3 River Mole Bridge || {{hs|609}}{{gbmappingsmall|TQ099609}} ||Road||A3|| Opened as part of the A3 Esher Bypass in December 1976.<ref>{{cite journal |author= Clarke CW |year= 1977 |title= A3 Esher Bypass Open |journal= Highways & Road Construction International |volume= 44 |issue= 1805 |page= 26 |publisher= Embankment Press }}</ref>
|-
|Cobham Bridge || {{hs|605}}{{gbmappingsmall|TQ099605}}||Road||A245||
|-
|Painshill Park Bridge||{{hs|602}}{{gbmappingsmall|TQ102602}}||Footbridge||||A part suspended steel and timber deck bridge, spanning {{convert|42|m|ft}}.  The bridge was designed by the architect Howard Humphreys and the westernmost section is a drawbridge which may be raised to prevent access to Painshill Park.<ref>{{cite web |url= http://www.littlehamptonwelding.co.uk/bridges2.htm |title= Painshill Park Footbridge |work= Bridges 2 |publisher= Littlehampton Welding |access-date= 29 June 2011 |archive-url= https://web.archive.org/web/20110108175133/http://www.littlehamptonwelding.co.uk/bridges2.htm |archive-date= 8 January 2011 |url-status= live }}</ref>
|-
|Downside Bridge||{{hs|595}}{{gbmappingsmall|TQ107595}}||Road||||The medieval bridge was rebuilt by Gwilt in 1786, but was washed away during the September 1968 floods.  The present bridge opened in 1971.<ref name= Elmbridge_History/>
|-
|Ash Bridge||{{hs|590}}{{gbmappingsmall|TQ120590}}|| Bridleway || style=white-space:nowrap|River Lane,<br />Stoke D'Abernon || Built in 1990 to replace an existing ford.<ref>{{cite web |url= https://www.geograph.org.uk/photo/777758 |title= Ash Bridge |author= Craddock H |year= 2008 |work= TQ1259 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112354/http://www.geograph.org.uk/photo/777758 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Cobham Viaduct || || Railway || New Guildford Line || The original viaduct was washed away by floods on 15 September 1968.<ref>{{cite book |title= Branch Lines around Effingham Junction |last1= Mitchell |first1= V |last2= Smith |first2= K |year= 1990 |publisher= Middleton Press |location= Midhurst |isbn= 0906520746 |page= 40 }}</ref>
|-
|Lane Viaduct || {{hs|580}}{{gbmappingsmall|TQ131581}} ||Road || M25 || A seven-span {{convert|170|m|yd|abbr=on|adj=mid|-long}} reinforced concrete viaduct, cast ''in situ'' in 1983–4.<ref>{{cite book |last1= Baldwin |first1= Peter |last2= Baldwin |first2= Robert |last3= Evans |first3=Dewi Ieuan |year= 2007 |title= The motorway achievement: Building the network in southern and eastern England |location= Chichester |publisher= Phillimore |isbn= 978-1-86-077446-1 |pages= 238–239}}</ref>
|-
|Stoke D'Abernon Bridge || {{hs|580}}{{gbmappingsmall|TQ132580}} ||Road || A245 ||
|-
|Railway Bridge || {{hs|565}}{{gbmappingsmall|TQ160565}} || Railway || Bookham Branch Line ||
|-
|Railway Bridge || {{hs|564}}{{gbmappingsmall|TQ162564}}  || || ||
|-
|Waterway Road Bridge || {{hs|562}}{{gbmappingsmall|TQ162563}} || Road ||B2122 ||
|-
|Town Bridge||{{hs|561}}{{gbmappingsmall|TQ163563}} || || ||
|-
|Thorncroft Bridge||{{hs|558}}{{gbmappingsmall|TQ166558}} || || ||
|-
|Young Street Bridge||{{hs|552}}{{gbmappingsmall|TQ164552}}|| Road|| A246 || Concrete girder bridge.<ref>{{cite web |url= https://www.geograph.org.uk/photo/687745 |title= Bridge at Young Street |author= Smith C |year= 2008 |work= TQ1655 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112402/http://www.geograph.org.uk/photo/687745 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Pressforward Bridge||{{hs|544}}{{gbmappingsmall|TQ168544}}|| Road || || Built {{circa|1790}}, strengthened and refurbished by [[Surrey County Council]] in 1990.<ref>{{cite web |url= https://www.flickr.com/photos/paulmdt/361590545/ |title= Pressforward Bridge |year= 2006 |work= Paul (England)'s Photostream |publisher= Flickr |access-date= 29 June 2011 |archive-url= https://web.archive.org/web/20161024185450/https://www.flickr.com/photos/paulmdt/361590545/ |archive-date= 24 October 2016 |url-status= live }}</ref>
|-
|Weir Bridge||{{hs|537}}{{gbmappingsmall|TQ170537}}||Road||||Grade II listed. Early to mid-19th-century brick bridge with two semi-circular arches and one elliptical arch.<ref>{{National Heritage List for England|num=1229319|desc=Bridge over River Mole|access-date=1 May 2020}}</ref>
|-
|Railway Bridge||{{hs|538}}{{gbmappingsmall|TQ165538}}||Railway||Epsom to Horsham line||
|-
|Swanworth Bridge||{{hs|534}}{{gbmappingsmall|TQ163534}}|||||| <ref>{{cite journal |last1= Docherty |first1= J |year= 1969 |title= The Geomorphology of some Late Glacial Deposits in the Western Part of the North Downs|journal= Area |volume= 1 |issue= 2 |pages= 24–48 }}</ref>
|-
|Cowslip Bridge || {{hs|529}}{{gbmappingsmall|TQ163529}} || Road||
|-
|Railway Bridge||{{hs|523}}{{gbmappingsmall|TQ166523}}||Railway||Epsom to Horsham line||Three arch bridge
|-
|Burford Bridge||{{hs|519}}{{gbmappingsmall|TQ171519}}||Road||A24||
|-
|Stepping Stones Footbridge||{{hs|513}}{{gbmappingsmall|TQ173513}}||Footbridge||North Downs Way||Erected in 1992 to replace the original bridge presented by the [[Ramblers|Ramblers' Association]] in memory of their members who died in the Second World War<ref>{{cite web |url= https://www.geograph.org.uk/photo/1529502 |title= Stepping Stones Footbridge over the River Mole, at the foot of Box Hill, near Dorking Surrey |author= Rogerson R |year= 2009 |work= TQ1751 |publisher= Geograph Britain and Ireland |access-date= 2 September 2011 |archive-url= https://web.archive.org/web/20121019235333/http://www.geograph.org.uk/photo/1529502 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Stepping Stones||{{hs|512}}{{gbmappingsmall|TQ172512}}||Ford||North Downs Way||
|-
|style=white-space:nowrap|Deepdene Viaduct||{{hs|504}}{{gbmappingsmall|TQ176504}}||style=white-space:nowrap|Railway||Guildford to Redhill Line||A five-arch brick viaduct constructed by the [[Reading, Guildford and Reigate Railway]] Company in 1847–48.<ref>{{cite book |editor1-first= E |editor1-last= Course |title= Minutes of the Reading, Guildford and Reigate Railway Company |series= Surrey Record Society |volume= XXXIII |year= 1987 |publisher= Surrey Record Society |location= Guildford |isbn= 090297808X |page= xlix}}</ref>
|-
|Castle Mill Footbridge||{{hs|502}}{{gbmappingsmall|TQ179502}}||Footbridge|| ||<ref>{{cite web |url= https://www.geograph.org.uk/photo/258417 |title= Footbridge over the River Mole |last1= Davies |first1= M |year= 2006 |work= TQ1750 |publisher= Geograph Britain and Ireland |access-date= 2 July 2011 |archive-url= https://web.archive.org/web/20121019112618/http://www.geograph.org.uk/photo/258417 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Boxhill Bridge||{{hs|503}}{{gbmappingsmall|TQ184503}}||Footbridge||||The original road bridge on this site was destroyed during flooding in 1968.<ref name="Marchington T 2000 96–100"/>
|-
|Deepdene Bridge||{{hs|504}}{{gbmappingsmall|TQ187504}}||Road||A25|| Opened in 1927 by Henry Cubitt, 2nd Baron Ashcombe.<ref>{{cite web |url= https://www.geograph.org.uk/photo/2227491 |title= Plaque, Deepdene Bridge |last1= Capper |first1= I |year= 2010 |work= TQ1850 |publisher= Geograph Britain and Ireland |access-date= 2 July 2011 |archive-url= https://web.archive.org/web/20121019112608/http://www.geograph.org.uk/photo/2227491 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Borough Bridge (Brockham)||{{hs|497}}{{gbmappingsmall|TQ196497}}||Road||||A single track bridge built in 1737 by Richard and Thomas Skilton.  The bridge was rebuilt in 1991.<ref>{{National Heritage List for England|num=1278439|desc=The Borough Bridge|access-date=1 May 2020}}</ref>
|-
|Betchworth Bridge||{{hs|495}}{{gbmappingsmall|TQ212495}}||Road||||Single track bridge built in 1842 and refurbished in 1993.<ref>{{cite web |url= https://www.geograph.org.uk/photo/1631092 |title= Betchworth Bridge |last1= Capper |first1= I |year= 2009 |work= TQ2149 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112435/http://www.geograph.org.uk/photo/1631092 |archive-date= 19 October 2012 |url-status= live }}</ref><ref>{{cite web |url= https://www.geograph.org.uk/photo/230483 |title= Betchworth Bridge |last1= Cox |first1= N |year= 2006 |work= TQ2149 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112427/http://www.geograph.org.uk/photo/230483 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Rice Bridge||{{hs|487}}{{gbmappingsmall|TQ223487}}||Footbridge|| ||<ref>{{cite web |url= https://www.geograph.org.uk/photo/853657 |title= Rice Bridge |last1= Capper |first1= I |year= 2008 |work= TQ2248 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112415/http://www.geograph.org.uk/photo/853657 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Flanchford Bridge||{{hs|480}}{{gbmappingsmall|TQ234480}}||Road|||| <ref>{{cite web |url= https://www.geograph.org.uk/photo/244974 |title= Leigh: Flanchford Bridge |last1= Cox |first1= N |year= 2006 |work= TQ2347 |publisher= Geograph Britain and Ireland |access-date= 2 July 2011 |archive-url= https://web.archive.org/web/20121019112553/http://www.geograph.org.uk/photo/244974 |archive-date= 19 October 2012 |url-status= live }}</ref> Flanchford Bridge was severely damaged by flooding in December 2013,<ref>{{cite news |last= Seymour |first= Jenny |date= 24 July 2015 |title= Flanchford Bridge rebuilding project delayed again |url= http://www.dorkingandleatherheadadvertiser.co.uk/Flanchford-Bridge-rebuilding-project-delayed/story-27463055-detail/story.html |newspaper= Surrey Mirror |access-date= 9 September 2015 |archive-url= https://web.archive.org/web/20150806161100/http://www.dorkingandleatherheadadvertiser.co.uk/Flanchford-Bridge-rebuilding-project-delayed/story-27463055-detail/story.html |archive-date= 6 August 2015 |url-status= live }}</ref> but was rebuilt.
|-
|Sidlow Bridge||style=white-space:nowrap|{{hs|470}}{{gbmappingsmall|TQ258470}}||Road||A217|| <ref>{{cite web |url= https://www.geograph.org.uk/photo/1539820 |title= Bridge over the River Mole, Sidlow Bridge, Surrey |last1= Rogerson |first1= R |year= 2009 |work= TQ2547 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112409/http://www.geograph.org.uk/photo/1539820 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Lee Street Bridge||{{hs|433}}{{gbmappingsmall|TQ269433}}||Road||||<ref>{{cite web |url= https://www.geograph.org.uk/photo/1599323 |title= River Mole, west of Horley from the Lee Street Bridge |last1= Rogerson |first1= R |year= 2009 |work= TQ2643 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112444/http://www.geograph.org.uk/photo/1599323 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Long Bridge||style=white-space:nowrap|{{hs|426}}{{gbmappingsmall|TQ275425}}||Road||A23||<ref>{{cite book |title= The street Where you live: The story of Horley Road Names |last= Hall |first= D |year= 2000 |publisher= Horley Local History Society |location= Horley, Surrey |isbn= 0951929194}}</ref>
|-
|London Road Bridge||style=white-space:nowrap|{{hs|424}}{{gbmappingsmall|TQ275424}}||Road||A23|| Built in 1957 as part of the scheme to divert the A23 around the eastern periphery of Gatwick Airport.  The bridge has a {{convert|15|m|ft|abbr=on}} span with mass concrete abutments and a pre-stressed concrete deck.<ref name=Allen_Gatwick>{{cite journal |author= Allen R |year= 1958 |title= Gatwick: London's Airport |journal=Aeronautics |volume=38 |issue=2 |pages=30–42 }}</ref>
|-
|Gatwick Airport||{{hs|402}}{{gbmappingsmall|TQ261402}}||style=white-space:nowrap|Runway and<br />taxiways|||| The river passes under the airport in a {{convert|425|m|yd|abbr=on}} long concrete culvert with {{convert|50|cm|abbr=on}} thick walls and roof.  The culvert was constructed in 1957.<ref name=Allen_Gatwick/>
|-
|Stafford Bridge||{{hs|384}}{{gbmappingsmall|TQ252384}}||Road||||
|-
|Granthams Bridge||{{hs|372}}{{gbmappingsmall|TQ232372}}||Road||||<ref>{{cite web |url= https://www.geograph.org.uk/photo/27856 |title= River Mole at Granthams Bridge |last1= Chapman |first1= P |year= 2005 |work= TQ2337 |publisher= Geograph Britain and Ireland |access-date= 2 July 2011 |archive-url= https://web.archive.org/web/20121019112600/http://www.geograph.org.uk/photo/27856 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|style=white-space:nowrap|Lambs Green Bridge||{{hs|371}}{{gbmappingsmall|TQ219371}}||Road||||<ref>{{cite web |url= https://www.geograph.org.uk/photo/4882879 |title= TQ2137: The River Mole gushes out from under Lambs Green Bridge |author= Shazz |date= 28 March 2016 |publisher= Geograph Britain and Ireland |access-date= 25 August 2021 |archive-date= 25 August 2021 |archive-url= https://web.archive.org/web/20210825201215/https://www.geograph.org.uk/photo/4882879 |url-status= live }}</ref>
|-
|Rusper Court Bridge||{{hs|362}}{{gbmappingsmall|TQ208362}}||Bridleway||||<ref>{{cite web |url= https://www.geograph.org.uk/photo/1811602 |title= Footbridge over the River Mole |last1= Smith |first1= C |year= 2010 |work= TQ2036 |publisher= Geograph Britain and Ireland |access-date= 28 June 2011 |archive-url= https://web.archive.org/web/20121019112450/http://www.geograph.org.uk/photo/1811602 |archive-date= 19 October 2012 |url-status= live }}</ref>
|-
|Baldhorns Park Bridge||{{hs|361}}{{gbmappingsmall|TQ203361}}||Bridleway|| ||
|- style="background:#F8F8FF"
|Source of River Mole||{{hs|361}}{{gbmappingsmall|TQ203368}}|| || ||Baldhorns Copse, Rusper, West Sussex
|}

==Watermills==
[[Domesday Book]] listed twenty mills on the River Mole in 1086.<ref name=moleseyhistory/><ref name=water_mills_surrey/>

=== Upper Mole ===
[[File:The Mill at Dorking, Henry Hewitt (1869).jpg|thumb|''The Mill at Dorking'', by [[Henry Hewitt (painter)|Henry Hewitt]], a view of Castle Mill in 1869]]
Horley Mill was first mentioned in a deed of the early 13th century.  The most recent mill was demolished in 1959, although the mill house still stands.<ref name=water_mills_surrey/>

The first mill at [[Sidlow]] was built during [[History of Anglo-Saxon England|Saxon times]]. The final mill on the site was demolished in 1790, however remains of the [[leat|mill leat]] are still visible.<ref name=water_mills_surrey/>

Mention is made of a mill at [[Brockham]] in 1634 and remains of the mill race are still visible.<ref name=water_mills_surrey/>

Castle Mill at Pixham is a Grade II [[listed building]].<ref>{{NHLE|grade=II|desc=Old Castle Mill|num= 1279088 |date=11 June 1973}}</ref> It was a corn mill, built in the early 19th century, and has been converted into a [[bed and breakfast]] hotel.<ref>{{cite web |title=Castle Mill |url=https://www.facebook.com/castlemill17/ |website=Facebook |access-date=10 January 2022 |archive-date=11 January 2022 |archive-url=https://web.archive.org/web/20220111091848/https://www.facebook.com/castlemill17/ |url-status=live }}</ref>

=== Lower Mole ===

Slyfield Mill near [[Stoke d'Abernon]] is first mentioned in [[Domesday Book]].  It was used for [[fulling]] woollen cloth and milling corn.<ref name=water_mills_surrey/>

[[File:CobhamMill.JPG|right|thumb|alt=Brick building with tiled roof and two square windows, below which is a water wheel. Between the windows there is a wooden plaque, which reads "Cobham Mill Restored 1993 by Cobham Mill Preservation Trust and the National Rivers Authority".|Cobham Mill]]
[[File:RivMole01.JPG|right|thumb|The River Mole where it runs separately from the River Ember - at the site of East Molesey Upper Mill near The Wilderness]]
Five of the mills mentioned in [[Domesday Book]] were in the borough of Elmbridge.<ref name=moleseyhistory/>

Downside Mill, [[Cobham, Surrey|Cobham]] was the mill of the manor of Downe.  Until the [[Dissolution of the Monasteries]] it was owned by [[Chertsey Abbey]].<ref name=water_mills_surrey/> It has been used for many purposes including the processing of corn, paper, iron, tinplate and flock and the generation of electricity. The present building dates from the 18th century but it is inaccessible to the public.

Cobham Mill, downstream of Leatherhead, consisted of two mills used for grinding corn. In 1953 the larger mill was demolished by Surrey County Council to allieviate traffic congestion on Mill Road. The remaining red brick mill dates from the 1822 and was in use until 1928. It was restored to full working order by the Cobham Mill Preservation Trust, and is now open to the public from 2&nbsp;pm to 5&nbsp;pm on the second Sunday of each month (between April and October).<ref>{{cite web |url=https://cobhammill.org.uk/ |title=Welcome to Cobham Mill |author=<!--Staff writer(s); no by-line.--> |year=2012 |work=Cobham Mill |publisher=Cobham Mill Preservation Trust |access-date=19 April 2013 |archive-url=https://web.archive.org/web/20130417125014/http://cobhammill.org.uk/ |archive-date=17 April 2013 |url-status=live }}</ref>

Esher Mill also known as Royal Mill was at the end of Mill Road in [[Lower Green, Esher|Lower Green]], where there is now an industrial estate. It was used to process corn, brass wire, iron, paper, linoleum, and books.<ref>{{Cite book|last=Tarplee, Peter.|title=A guide to the industrial history of the borough of Elmbridge|date=1998|publisher=Surrey Industrial History Group|others=Surrey Industrial History Group.|isbn=0-9523918-6-4|location=Guildford|oclc=1000982567}}</ref> For many years there may have been two mills on the site for corn grinding and industrial use. There were a series of fires over a century and after the last in 1978 the buildings were demolished.<ref>{{Cite web|url=https://lowergreenesher.co.uk/2019/11/15/the-great-fire-at-burns-and-co/|title=The Great Fire At Burns And Co, Lower Green Esher|date=2019-11-15|website=Lower Green Esher|language=en|access-date=2020-03-28|archive-url=https://web.archive.org/web/20200327145204/https://lowergreenesher.co.uk/2019/11/15/the-great-fire-at-burns-and-co/|archive-date=27 March 2020|url-status=live}}</ref>

East Molesey Upper Mill was associated with the manor of Molesey Matham. It was used to produce gunpowder from the time of the Commonwealth until about 1780. The island where it stood now forms part of the ornamental gardens of a housing development called "The Wilderness".<ref name=molesey_mills>{{cite web |url=http://www.moleseyhistorysociety.org/Molesey%20Mills.pdf |title=Molesey Mills: A history of the mills and milling |author=Brian Smith |year=2009 |publisher=Molesey History Society |access-date=19 April 2013 |archive-url=https://web.archive.org/web/20160303204618/http://www.moleseyhistorysociety.org/Molesey%20Mills.pdf |archive-date=3 March 2016 |url-status=live }}</ref>

East Molesey Lower Mill, also known as Sterte Mill, was associated with the manor of Molesey Prior. During the Commonwealth it was used for gunpowder manufacture, but after the restoration of the monarchy in 1660 it reverted to corn milling. An old timber structure was replaced by a brick building in the 1820s which can be seen from the bridge over the Ember in Hampton Court Way.<ref name=molesey_mills/>

In addition there was Ember Mill, which stood on the banks of the old course of the River Ember near Hampton Court Way.<ref name=molesey_mills/>

==River Ember Flood Relief Channel and confluence with the Thames==
[[File:MoleEmber.JPG|right|thumb|alt=Photograph taken from centre of river underneath a wide-arched bridge. View upstream towards a weir in the far distance.|Confluence of the Mole and Ember with the Hampton Court Way crossing in the foreground]]
The River Mole originally flowed into the River Thames at the point where the present Hampton Court bridge now crosses the Thames (approximately 500 m upstream of the present [[confluence]], on the reach above [[Teddington Lock]]).

However, during the early 1930s, when Hampton Court Way and the bridge were built, the River Mole was redirected to flow into the [[River Ember]] and both rivers now enter the Thames in a single widened and straightened channel once occupied only by the [[River Ember]]. There have been further alterations to the courses of these two rivers in a major flood prevention scheme since serious flooding in the area in [[1947 Thames flood|1947]] and [[Great Flood of 1968|1968]].<ref>{{cite web |url= http://www.surreyproperty.com/east-molesey-history.html |title= East Molesey History |author= Broad P |year= 2008 |work= Surrey Towns |publisher= SurreyProperty.com |access-date= 9 February 2010 |archive-url= https://web.archive.org/web/20110720091828/http://www.surreyproperty.com/east-molesey-history.html |archive-date= 20 July 2011 |url-status= live }}</ref>

==Literature==
The river has captured the imagination of several authors and poets,<ref name=Judy_Hayden/> particularly since in very hot summers the river channel can become dry between Dorking and Leatherhead (most recently during the [[1976 United Kingdom heat wave|1976 drought]]).<ref name="Wooldridge_Hutchings"/><ref name="Currie"/>

[[File:The_Faerie_Queene_frontispiece.jpg|thumb|upright|Title-page of ''The Faerie Queene'' by Edmund Spenser, published in 1590.]]
In ''[[The Faerie Queene]]'' (first published in 1590) [[Edmund Spenser]] wrote of the river:
<blockquote>
:And Mole, that like a nousling mole doth make
:His way still under ground till Thamis he overtake.<ref>The Fairie Queen, book 4, canto 11, verse 32</ref>
</blockquote>

[[File:Michael-Drayton-Poly-Olbion.jpg|thumb|upright|Title-page of ''Poly-Olbion'' by Michael Drayton, published in 1612.]]
In ''[[Poly-Olbion]]'' (first published in 1612) the poet [[Michael Drayton]] described the journey taken by the River Thames to the sea:
<blockquote>
:As still his goodly traine yet every houre increast,
:And from the ''Surrian'' shores cleer ''Wey'' came down to meet
:His Greatnes, whom the ''Tames'' so gratiously doth greet
:That with the Fearne-crown'd Flood he Minion-like doth play:
:Yet is not this the Brook, entiseth him to stay.
:But as they thus, in pompe, came sporting on the shole,
:Gainst ''Hampton-Court'' he meets the soft and gentle ''Mole''.
:Whose eyes so pierc't his breast, that seeming to foreslowe
:The way which he so long intended was to go,
:With trifling up and down, he wandreth here and there;
:And that he in her sight, transparent might appeare,
:Applyes himselfe to Fords, and setteth his delight,
:On that which might make him gratious in her sight.<ref>Poly-Olbion, Song XVII lines 20-32</ref>

:But ''Tames'' would hardly on: oft turning back to show,
:For his much loved ''Mole'' how loth he was to go.
:The mother of the ''Mole'', old ''Holmsdale'', likewise beares
:Th'affection of her childe, as ill as they do theirs:
:But ''Mole'' respects her words, as vaine and idle dreames,
:Compar'd with that high joy, to be belov'd of ''Tames:''
:And head-long holds her course, his company to win.
:''Mole'' digs her selfe a path, by working day and night
:(According to her name, to shew her nature right)
:And underneath the Earth, for three miles space doth creep:
:Till gotten out of sight, quite from her mothers keep,
:Her foreintended course the wanton Nymph doth run;
:As longing to imbrace old ''Tame'' and ''Isis'' son...<ref>Poly-Olbion, Song XVII lines 47-50, 53-57, 59-64</ref>
</blockquote>
He writes in the appendix to Song XVII
<blockquote>
This ''Mole'' runnes into the earth, about a mile from ''Darking'' in ''Surrey'', and after some two miles sees the light againe, which to be certaine hath been affirmed by Inhabitants thereabout reporting triall made of it.
</blockquote>

[[John Milton (composer)|John Milton]] ({{circa|1562}}–1647) described the river as
<blockquote>
:sullen Mole that runneth underneath
</blockquote>

In a similar vein, [[Alexander Pope]] (1688–1744) wrote in his poem ''Windsor Forest'' (first published 1713)
<blockquote>
:And sullen Mole that hides his diving flood
</blockquote>

[[Robert Bloomfield]] (1766–1823) writes the following lines about the Mole Valley in his 1806 poem ''Wild Flowers''.
<blockquote>
:Sweet Health, I seek thee! Hither bring
:Thy balm that softens human ills;
:Come on the long drawn clouds that fling
:Their shadows o'er the Surry-Hills.
:Yon green-topt hills, and far away
:Where late as now I freedom stole,
:And spent one dear delicious day
:On thy wild banks romantic Mole.

:Ay there's the scene! Beyond the sweep
:Of London's congregated cloud,
:The dark-brow'd wood, the headlong steep,
:And valley paths without a crowd!
:Here Thames I watch thy flowing tides,
:Thy thousand sails am proud to see;
:But where the Mole all silent glides
:Dwells Peace - and Peace is wealth to me.<ref>R Bloomfield (1806) ''Wild Flowers; or Pastoral and Local Poetry''</ref>
</blockquote>

Extract from ''The River Mole or Emlyn Stream'' by Mary Drinkwater Bethune, which was published in 1839.{{#tag:ref|Mary Drinkwater Bethune was the daughter of the English army officer and military historian [[John Drinkwater Bethune|Colonel John Drinkwater Bethune]], who lived at Thorncroft Manor, Leatherhead, from 1836 to 1844.<ref>{{cite book |title= A topographical history of Surrey |last1= Brayley |first1= E. W. |author-link1=Edward Wedlake Brayley |last2= Britton |first2=J. |author-link2=John Britton (antiquary) |year= 1841 | publisher= Dorking |location= Surrey}}</ref>  Mary Drinkwater Bethune married Norman Uniacke at [[St George's, Hanover Square]] in September 1844.<ref>{{Cite newspaper The Times |title= Marriages |date= 11 September 1844 |page= 7 |issue= 18712 }}</ref>|group=note}}
<blockquote>
:Who may count back that forgotten time
:When first the waters forced an outlet here:
:When the foundations of these stedfast hills
:Were shaken, and the long imprisoned stream
:Flowed through the yawning chasm? That awful day
:Yet leaves its trace. The waters find their way,
:Now laughing in the sun - now swallowed up
:In caverns pervious to their course alone,
:They leave their channel dry, and hide awhile
:Their silent flow; like bitter tears, unshed
:From the dim eye, before a careless world
:Unheeding of our grief; but swelling still
:In the full heart, which leaves unsoothed, unseen,
:And broods o'er ruined hopes, and days gone by.
</blockquote>

==Tributaries==
The major tributaries of the River Mole are the Ifield Brook, [[Gatwick Stream]], Earlswood Brook, [[Pipp Brook]] and [[The Rye (brook)|The Rye]], which drains [[Ashtead]].  A full list of the tributaries is given in the table below.

{| class="wikitable collapsible collapsed" cellpadding="100"
|-
! colspan="2" style="text-align:center;"|Table of tributaries of the River Mole
|-
! style="width:170px;"| Left
! style="width:170px;"| Right
|- style="background:#F8F8FF"
| colspan="2" style="text-align:center;"| Confluence with [[River Thames]] at [[East Molesey]]
|-
|
| style="text-align:center;"| [[River Ember]] ''as tributary''
|-
| style="text-align:center;"| Dead River
|
|-
|
| style="text-align:center;"| [[River Ember]] ''distributary''
|- style="background:#F8F8FF"
| style="text-align:center;" colspan="2"| [[Cobham, Surrey|Cobham]]
|-
| style="text-align:center;"| Bookham Brook
|
|-
|
| style="text-align:center;"| Pachesham Brook
|-
|
| style="text-align:center;"| [[The Rye (brook)|The Rye]]
|-
| style="text-align:center;"| Fetcham Mill Stream
|
|- style="background:#F8F8FF"
| style="text-align:center;" colspan="2"| Mole Gap
|-
| style="text-align:center;"| [[Pipp Brook]]
|
|-
| style="text-align:center;"| Tanner's Brook
|
|-
|
| style="text-align:center;"| Shag Brook
|-
| style="text-align:center;"| Gad Brook
|
|-
|
| style="text-align:center;"| Wallace Brook
|-
| style="text-align:center;"| Leigh Brook
|
|-
|
| style="text-align:center;"| Baldhorns Brook
|-
| style="text-align:center;"| Deanoak Brook
|
|- style="background:#F8F8FF"
| style="text-align:center;" colspan="2"| [[Sidlow]]
|-
|
| style="text-align:center;"| Earlswood Brook
|-
|
| style="text-align:center;"| Salfords Stream
|-
|
| style="text-align:center;"| Burstow Stream
|-
| style="text-align:center;"| Spencer's Gill
|
|-
| style="text-align:center;"| Hookwood Common Stream
|
|-
|
| style="text-align:center;"| [[Gatwick Stream]]
|-
| style="text-align:center;"| Mans Brook
|
|- style="background:#F8F8FF"
| style="text-align:center;" colspan="2"| Runway of [[Gatwick Airport]]
|-
|
| style="text-align:center;"| Crawter's Brook
|-
|
| style="text-align:center;"| Ifield Brook
|-
|
| style="text-align:center;"| Reubens Gill
|- style="background:#F8F8FF"
| colspan="2" style="text-align:center;"| Source at [[Rusper]], West Sussex
|}

==Distributary==

*[[River Ember]]

==See also==
{{commons category|River Mole}}
* [[List of rivers in England]]
* [[Tributaries of the River Thames]]

==Notes==
{{Reflist|group=note}}

==References==
{{reflist|30em}}

==External links==
*[http://www.environment-agency.gov.uk/homeandleisure/floods/riverlevels/120787.aspx Environment Agency: River Mole information]
*[https://web.archive.org/web/20030429051242/http://216.31.193.173/gwcl/Thames/Chalk-Leatherhead/GW_QRepChalkLeatherhead.html Groundwater quality]

{{river item box|type=confluence
|River=[[River Thames]]
|upstream=[[Longford River]], Water Gallery (north)
|downstream=[[The Rythe]] (south)
|thisis=River Mole and [[River Ember]]}}

{{Surrey Hills AONB}}
{{Surrey}}
{{West Sussex}}
{{Hydrology of Surrey}}

{{authority control}}

{{DEFAULTSORT:Mole}}
[[Category:Rivers of Surrey]]
[[Category:Rivers of West Sussex]]
[[Category:Mole Valley]]
[[Category:Local Nature Reserves in Surrey]]
[[Category:Thames drainage basin|1Mole]]
[[Category:Mole catchment| ]]