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River Mole

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Template:Short description Template:About Template:Use dmy dates Template:Use British English Template:Infobox river The River Mole is a tributary of the River Thames in southern England. It rises in West Sussex near Gatwick Airport and flows north-west through Surrey for Template:Convert to the Thames at Hampton Court Palace.<ref name=CAMs>Template:Cite web</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>Template:Cite journal</ref> Much of the catchment area lies on impermeable rock (including Weald Clay and London Clay), meaning that the river level responds rapidly to heavy rainfall.<ref name=physiography/>

During the second half of the 20th century, pollution levels in the river were high; however, since 1995 the water quality has improved dramatically and the Mole now boasts the greatest diversity of fish species of any river in England.<ref name=CAMs/><ref name=EA_fish>Template:Cite web</ref> Twelve Sites of Special Scientific Interest (SSSIs) that include wetland habitats are located within the Mole catchment area, and the stretch of river through Leatherhead has been designated a Local Nature Reserve.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> The Mole Gap forms part of a Special Area of Conservation and is an SSSI of European importance.<ref name=MAls_2013>Template:Cite web</ref>

The river has captured the imagination of several authors and poets,<ref name=Judy_Hayden>Template:Cite book</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>Template:Cite news</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 Template:Lang (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 Template:ISBN</ref> Domesday Book lists twenty mills on the river in 1086, of which Sidlow Mill was the oldest, dating from Saxon times.<ref name=moleseyhistory>Template:Cite web</ref><ref name=water_mills_surrey>Template:Cite book</ref>

Catchment area

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The drainage area of the Mole is Template:Cvt and forms 5% of the River Thames's catchment area above Teddington.<ref name=MAls_2013/> The catchment area receives Template:Cvt of rain each year; the greatest average level of rainfall is Template:Cvt around Crawley. The Mole catchment reaches a maximum elevation of Template:Convert above Ordnance Datum at Leith Hill to the southwest of Dorking.<ref name=CEH>Template:Cite book</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

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File:River Mole at Baldhorns Park - geograph.org.uk - 1811633.jpg
River Mole at Baldhorns Park, approximately Template:Cvt downstream of the source at Rusper

Upper Mole

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The Mole rises in Baldhorns Copse Template:Convert to the south of the village of Rusper in West Sussex. It flows initially southwards for Template:Convert to a small lake at Baldhorns Park, before running eastwards through a largely rural area towards Crawley.<ref name=OS_Rusper>Template:Cite map</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 Mill Pond.

The first gauging station on the Mole is south of Gatwick Airport (Template:Cvt above OD).<ref group=note>The gauging station south of Gatwick Airport was installed in 2005, replacing an earlier station located Template:Cvt downstream.</ref> The mean flow is Template:Convert 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>Template:Cite web</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 Template:Cvt stretch immediately north of the runway were reinstated in 1999, in a £1.2 million project to facilitate airport expansion.<ref>Template:Cite web</ref><ref name="autogenerated1">Template:Cite web</ref>

The Mole enters Surrey to the south of Horley, where it meets the Gatwick Stream, a tributary draining Worth Forest to the southeast of Crawley. The second-largest Sewage Treatment Works (STW) in the Mole catchment is located on the Gatwick Stream Template:Convert upstream of the confluence with the Mole: Crawley STW discharges Template:Cvt 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>Template:Cite journal</ref> The mean flow measured at Horley gauging station (Template:Cvt above OD) is Template:Convert.<ref name=CEH/>

The Mole passes Horley to the west, flowing north towards Sidlow and entering a largely rural area. Template:Convert south of Sidlow the mean flow is measured as Template:Convert at Kinnersley Manor gauging station (Template:Cvt above OD).<ref name=CEH/> The Earlswood Brook, a tributary draining the urban area of Reigate and Redhill, joins the Mole at Sidlow. The largest STW in the Mole catchment (Reigate STW) discharges up to Template:Cvt 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 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 kW low-head 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>Template:Cite web</ref> The river leaves the Weald Clay at Brockham, passing Betchworth Castle <ref>Template:National Heritage List for England</ref> and flowing briefly across greensand and Gault Clay to Pixham, Template:Convert northeast of Dorking. A mean flow of Template:Convert is measured at a fourth gauging station, located at Castle Mill (Template:Cvt 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, Westcott and Dorking.</ref>

Mole Gap

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Between Dorking and Leatherhead the Mole cuts a steep-sided valley (the Mole Gap) though the North Downs, carving a Template:Convert river cliff on the western flank of Box Hill and a smaller Template:Convert cliff at Ham Bank in Norbury Park. The sudden change from impermeable Weald Clay to permeable chalk and the increased gradient<ref group=note>The Mole descends Template:Cvt in the Template:Cvt stretch between Brockham and Leatherhead, compared to Template:Cvt in Template:Cvt 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 holes 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 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. The entirety of the Mole Gap lies within the Surrey Hills Area of Outstanding Natural Beauty.<ref>Template:Cite web</ref>

Lower Mole

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File:Painshill-Waterwheel.jpg
Painshill Park Waterwheel (on its 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>Template:Cite book</ref> The aquifer at Fetcham is the only one in the entire catchment area.<ref name=CAMs/> The next major tributary, 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 Landscape Garden, where a Template:Convert diameter waterwheel raises water Template:Convert from the river to feed the ornamental lake in the park.<ref>Template:National Heritage List for England</ref><ref>Template:Cite web</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 and Esher, where the mean flow of the river is Template:Convert. In response to 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>Template:Cite conference</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 Template:Cvt 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 ice age, the River Thames followed a more northerly route to the North Sea, from Reading via 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 to meet the proto-Thames near Ware in Hertfordshire. Today the Mole and Wey are less than Template:Convert apart at their closest point near Painshill Park. During the Middle Pleistocene period,<ref group=note>The Middle Pleistocene period was Template:Circa 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. 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 Template:Lang 51 (3) 337–346</ref>

Ecology

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Water quality

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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 ponds for treatments, including acid/alkali neutralisation, before release into the river.<ref>Template:Cite web</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 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>Template:Ukhansard</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>Template:Cite news</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>Template:Cite news</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>Template:Cite web</ref>

Water quality of the River Mole in 2019:

Section Ecological
Status		 Chemical
Status		 Overall
Status		 Length Catchment Channel
Template:Waterqual title Template:Waterqual mod Template:Waterqual fail Template:Waterqual mod Template:Convert Template:Convert
Template:Waterqual title Template:Waterqual mod Template:Waterqual fail Template:Waterqual mod Template:Convert Template:Convert Heavily modified

Biodiversity

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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>Template:Cite book</ref> There is no evidence that the presence of the frogs has had a deleterious effect on indigenous amphibians.<ref>Template:Cite web</ref> A second non-native species, the edible frog (Pelophylax 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 and Brockham.<ref name=little_book_Surrey/>

File:River Mole from Common Meadow, Leatherhead.jpg
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 eel. In 2003, the upper River Mole near Meath Green Lane, Horley, was enhanced to create a gravel spawning area to encourage chub and dace in addition to 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>Template:Cite journal</ref>

In the Mole Gap between Dorking and Leatherhead the river supports populations of chub, dace, 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, perch, 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 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, 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 alkalinity, particularly around Brockham, and the tributaries which run over the Weald Clay provide an excellent habitat for stoneflies, caddisflies, fast swimming mayflies and 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>Template:Cite web</ref> The white-legged damselfly (Platycnemis pennipes) is also found along the river, and the downy emerald (Cordulia aenea) is found between 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>Template:Cite web</ref>

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

Conservation

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The Mole catchment area includes twelve 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 (Template:Cvt south of Leatherhead) and River Lane in Fetcham has been designated a Local Nature Reserve.<ref name=MVDC2>Template:Cite web</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 scrub, woodland, hedges, banks, and meadows 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 bluebells (Hyacinthoides non-scriptus), marsh marigolds (Caltha palustris) and golden saxifrages (Chrysosplenium sp.). large bittercress (Cardamine amara) and the non-native Himalayan balsam (Impatiens glandulifera).<ref>Esher Commons Map and Information Sheet Template:Webarchive 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 redshank and little ringed plover.<ref>Template:Cite web</ref>

Geology

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Upper Mole (geology)

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The Mole rises south of Rusper in West Sussex, where an outcrop of the Hastings Beds sandstone dips below the impermeable Weald Clay.<ref name=MAls_2013/> From the source to Dorking, the river drains an area of Template:Convert, 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>Template:Cite web</ref>

The upper Mole catchment is dominated by a single broad terrace, which runs continuously from 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 Template:Cvt wide. A similar trench is runs up several of the Mole's tributaries, notably along Deanoak Brook which follows a local strike. The presence of the trench protects the land from flooding, rendering it suitable for agriculture.<ref name=physiography/>

Mole Gap (geology)

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File:Dry River Mole, 20 July 2022.jpg
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 Template:Convert 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>Template:Cite journal</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>Template:Cite web</ref><ref name=Chouler>Template:Cite book</ref> 1976<ref name=Currie>Template:Cite book</ref> and 2022.<ref name=ITV_News_2022/><ref>Template:Cite news</ref><ref>Template:Cite news</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. C. Fagg identified 25 active swallow holes between Dorking and 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>Template:Cite journal</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 channelTemplate:Clarify 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 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>Template:Cite journal</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 Template:Convert 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>Template:Cite journal</ref><ref name=SAC_Defoe>Template:Cite journal</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): Template:Blockquote

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 Template:Convert 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 Template:Convert a day.<ref>Template:Cite journal</ref> The water table in the chalk of the Wey Gap is significantly higher than might be expected from natural rainwater percolation alone. It has been suggested that a proportion of the excess water originates from the Mole Gap.<ref name=Dines>Template:Cite book</ref>

Lower Mole (geology)

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At Leatherhead the river leaves the chalk bedrock, moving onto London Clay.<ref>Template:Cite journal</ref> The river meanders across an alluvial plain between Template:Cvt 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 Template:Cvt wide, in which the river runs northwards for Template:Convert 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>Template:Cite journal</ref> The depth of the deposits generally varies from Template:Convert;<ref name=ChertseyGeology>Template:Cite book</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>Template:Cite journal</ref> Remains of a further gravel terrace, containing cherts and flints to a depth of Template:Convert, line the east side of St George's Hill.<ref name=ChertseyGeology/>

History

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Etymology

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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>Template:Cite journal</ref><ref name=Ekland>Template:Cite book</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>Template:Cite journal</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>Template:Cite book</ref><ref>Template:Cite web</ref><ref group=note>The prefix of the former 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 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>Template:Cite web</ref>

Archaeology

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In common with much of the rest of the Weald, the earliest evidence of human settlement along the Upper Mole is from the Mesolithic Period (20,000–7000 BC). Mesolithic sites at Wonham, Flanchford and Sidlow. Finds at Wonham include arrowheads and a plano-convex knife.<ref>Template:Cite journal</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>Template:Cite journal</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>Template:Cite web</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>Template:Cite journal</ref> A flint mine of the same period has been discovered at East Horsley along with Neolithic flakes of flint at Fetcham and Headley Heath.<ref>Template:Cite journal</ref>

Significant Bronze Age finds include a bronze sword found close to the river north of Amberley Farm near Charlwood<ref>Template:Cite journal</ref> and a small hoard of weaponry consisting of two palstave axes and a scabbard chape was discovered in 2003 in Norbury Park close to Ham Bank.<ref>Template:Cite journal</ref>

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File:MoleThames.JPG
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 Template:Convert in length used to carry produce to market<ref>Template:Cite book</ref> and it has been suggested that stone cut from quarries in Reigate was transported to London via the river.<ref>Template:Cite journal</ref>

During the 17th century, two bills came before parliament to make sections of the river navigable. The first, in 1663, was passed by the 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>Template:Cite book</ref><ref>Template:Cite web</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>Template:Cite book</ref> In 1810 the engineer 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>Template:Cite book</ref>

Today the Mole is navigable for the Template:Cvt from the confluence with the River Thames to Molember Weir at East Molesey where there is a private mooring facility.<ref>Template:Cite web</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

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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 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>Template:Cite web</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 pillboxes were installed.<ref name=DA12/><ref name="Marchington T 2000 96–100">Template:Cite journal</ref><ref name=Telegraph_walk>Template:Cite journal</ref> An anti-tank ditch was dug from the Stepping Stones eastwards across the fields belonging to Bradley Farm (now 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 were built on both sides of the river, a short distance upstream of the bridge, as an obstacle to armoured vehicles.<ref name=DA38>Template:Cite web</ref>

Crossings of the Mole

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Mole Gap

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The North Downs Way crosses the river at Box Hill via seventeen hexagonal stepping stones, 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>Template:Cite magazine</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 (which ran from London to Chichester via Dorking) crossed the river at this point.<ref>Template:Cite newspaper The Times</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

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File:Leatherhead Bridge - geograph.org.uk - 244353.jpg
Leatherhead Town Bridge across the River Mole

There are three listed bridges in Leatherhead of which the 14 arch Leatherhead Town Bridge is the oldest.<ref name = visit_leatherhead>Template:Cite web</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>Template:National Heritage List for England</ref>

A few metres downstream of Leatherhead Bridge stands the Grade II listed railway viaduct which carries the Leatherhead to Dorking line over the river.<ref>Template:National Heritage List for England</ref> The bridge was constructed in 1867 and, at the insistence of Thomas Grissell the landowner, was given lavish architectural treatment.<ref name=Jackson>Template:Cite book</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 and similar shells in the spandrels at each side.<ref>Template:National Heritage List for England</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>Template:Cite webTemplate:Dead link</ref>

Cobham

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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 II listing in 1953.<ref>Template:National Heritage List for England</ref>

Watermills

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

Upper Mole

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File:The Mill at Dorking, Henry Hewitt (1869).jpg
The Mill at Dorking, by 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 Saxon times. The final mill on the site was demolished in 1790, however remains of the 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>Template:NHLE</ref> It was a corn mill, built in the early 19th century, and has been converted into a bed and breakfast hotel.<ref>Template:Cite web</ref>

Lower Mole

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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/>

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
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 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 pm to 5 pm on the second Sunday of each month (between April and October).<ref>Template:Cite web</ref>

Esher Mill also known as Royal Mill was at the end of Mill Road in Lower Green, where there is now an industrial estate. It was used to process corn, brass wire, iron, paper, linoleum, and books.<ref>Template:Cite book</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>Template:Cite web</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>Template:Cite web</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

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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 and 1968.<ref>Template:Cite web</ref>

Literature

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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 drought).<ref name="Wooldridge_Hutchings"/><ref name="Currie"/>

File:The Faerie Queene frontispiece.jpg
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:

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>
File:Michael-Drayton-Poly-Olbion.jpg
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:

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>

He writes in the appendix to Song XVII

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.

John Milton (Template:Circa–1647) described the river as

sullen Mole that runneth underneath

In a similar vein, Alexander Pope (1688–1744) wrote in his poem Windsor Forest (first published 1713)

And sullen Mole that hides his diving flood

Robert Bloomfield (1766–1823) writes the following lines about the Mole Valley in his 1806 poem Wild Flowers.

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>

Extract from The River Mole or Emlyn Stream by Mary Drinkwater Bethune, which was published in 1839.<ref group="note">Mary Drinkwater Bethune was the daughter of the English army officer and military historian Colonel John Drinkwater Bethune, who lived at Thorncroft Manor, Leatherhead, from 1836 to 1844.<ref>Template:Cite book</ref> Mary Drinkwater Bethune married Norman Uniacke at St George's, Hanover Square in September 1844.<ref>Template:Cite newspaper The Times</ref></ref>

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.

Tributaries

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The major tributaries of the River Mole are the Ifield Brook, Gatwick Stream, Earlswood Brook, Pipp Brook and The Rye, which drains Ashtead. A full list of the tributaries is given in the table below.

Distributary

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See also

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Template:Commons category

Notes

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References

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Template:Surrey Hills AONB Template:Surrey Template:West Sussex Template:Hydrology of Surrey

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