Water On Exmoor
Exmoor can be very wet! Situated close to the coast of North Devon and Somerset, the high moor causes the warm, damp air from the Atlantic to rise, cool and drop its moisture. Annual precipitation i.e. rain, snow, sleet, on the Chains (487m, 1600 ft) is over 2000 mm compared with 800 mm to the east of the moor. Generally the months between May and September are much drier than the rest of the year.
Some of this rain soaks into the ground, a small proportion is trapped in reservoirs, about a quarter evaporates into the atmosphere and the rest, known as run-off, flows into the rivers and streams and so back to the sea. There are about (483 km) 300 miles of named rivers on Exmoor.
Over centuries people and animals have adapted to the wet climate of the moor. Cattle and sheep have been bred to withstand the cold and wet of an Exmoor winter. The hardy Exmoor pony, which has lived on the high moorland longer than humans, has developed a special coat. An undercoat of short wool type hair is topped by a longer greasy coat. This repels the rain which simply runs off. Whorls of hair strategically placed help to direct water away from sensitive parts of the body. The two layered coat retains body heat while the snow lies on the pony's back for days.
Some years heavy falls of snow block the lanes for weeks, cutting off people living in isolated farms and villages and making daily work on the land slow and difficult. Sheep have to be rescued from the drifts and occasionally children aren't able to get to school for a month or more! These days well-stocked freezers, radio weather reports and supply helicopters which can provide an emergency link if needed, make it easier to manage.
Rivers
The high ground of Exmoor with its heavy rainfall is the catchment area for Exmoor's 5 eight main rivers and numerous tributaries. Many springs also feed into the river system. The rivers are clear and fast-running. They provide excellent spawning grounds for salmon and trout and the presence of salmon particularly indicates good quality clean water which is valuable for the reservoirs which supply water to much of Devon and Somerset.
Drainage patterns on Exmoor are varied and relate to a complex history of uplifting and changes in sea level. In general, the main ridge of Exmoor, running from Challacombe Common in the west, over Dunkery to the Brendon Hills in the east, divides rivers flowing south to the English Channel from those flowing north to the Bristol Channel. There are exceptions, however, such as the Tone, which flows south, then east to the Parrett, then north and rivers such as the Mole and Bray, flowing from Exmoor's southern ridge, which flow south to the Taw then north to the Atlantic. The Yeo, which in part defines the southern edge of the Exmoor upland, appears to follow an ancient valley westwards towards Barnstaple before meeting the Mole and flowing south. Exmoor has a large number of what are known as 'first order' streams, meeting no tributaries before they plunge to the Bristol Channel.
Main rivers: length from source to mouth:
| River | Length to sea |
| Exe | 54 miles |
| Barle, via Exe | 54 miles |
| Bray, via Taw | 39 miles |
| Mole, via Taw | 39 miles |
| East Lyn\Oare Water\ Weir Water | 10 miles |
| Washford River | 9 miles |
| Avill | 8 miles |
| Horner Water\Chetsford Water | 8 miles |
Exmoor rivers are spate rivers, which react rapidly to rainfall and do not maintain an even flow. The flow of the Barle within the National Park is generally greater than that of the Exe and the Barle could thus be considered to be Exmoor’s main river. The greatest recorded flow, however, was for the combined Lyn rivers at Lynmouth during the flood of August 1952, which equalled four times the average flow of the Thames.
Coast
The coastline within the National Park stretches for (59 km) 37 miles. It is outstanding for both its scenery and its wildlife and was one of the prime reasons for the designation of Exmoor as a National Park. Exmoor has the highest coastline in England and Wales with coastal hills rising to 433m (1421ft) at Culbone Hill. The highest sheer cliff is 244m (800ft) on Great Hangman, which is the highest sea cliff in England and Wales.
A special feature of the coast is that it is remarkably sheltered. This allows for the unusual development of coastal woods. The woods between The Foreland and Porlock represent the longest stretch of coastal woodland in England and Wales. The inaccessibility of much of the woodland leaves it remarkably close to natural vegetation for Britain and it contains diverse plant life, including whitebeam varieties unique to Exmoor. The Exmoor coast must also rank amongst the most unspoilt and best protected stretches of coastline in England and Wales. It is all a Heritage Coast and all of its cliff and foreshore is covered under Section 3 of the Wildlife and Countryside Act. If the National Trust is included as a public landowner, 82% of the coastline is in public ownership. Most of the remainder is protected as Sites of Special Scientific Interest. 82% of the coastline (not just areas in public ownership) is contained within six SSSIs.
At Combe Martin, Lynmouth and Porlock Weir there are small harbours that used to be busy with coastal trade. Now sailing and fishing for pleasure are their mainstay.
Pressures on the coast
Some pressures are man-made. The coast is very popular with visitors and the few places where access by road is possible, such as Lee Bay and Lynmouth, tend to become congested in summer. Haphazard car-parking clogs the roads and erodes wayside areas. Attempts to cater for tourists can lead to unsightly developments.
Other pressures are natural and are part of the ongoing formation of the landscape by the erosive action of wind, weather and, especially, sea. For example, between Foreland Point and Porlock Bay landslips are commonplace. As a result the coastal footpath has had to be diverted and limits have been placed on access to the area by vehicles.
Water at work
Water has been an important source of power on Exmoor for centuries. Used first for grinding corn, the water wheel was gradually adapted to a variety of tasks and only in this century has it been ousted by modern power supplies. In the medieval villages there were mills for fulling woollen cloth. With the introduction of machinery, farmers installed wheels to work threshing machines, feed crushers and root pulpers. On estates there were saw-mills. Water wheels drove the pumps, whims and crushers in the Exmoor mines and pulled loads and worked pumps in the limestone quarries.
In 1890 a hydro generating plant was installed at Lynmouth to supply electricity to the town. Dulverton and Porlock followed with similar schemes. The Lynmouth plant continued in use until 1952 when the station was destroyed in the great flood, but a new plant elsewhere in Lynmouth supplies electricity to the National Grid. Some private houses had their own hydro-driven generators but perhaps the most unusual use was a wheel at Woolhanger which provided the power to drive the bellows of a pipe-organ!
Some aspects of erosion
A more common problem than flooding is erosion caused by excessive rainfall.
Following heavy rain, torrents of water pour down the hillsides turning footpaths and tracks into temporary streams. Topsoil is washed away leaving a dangerous surface of loose stones. After swaling or burning the moorland vegetation, the peat is washed away more easily until it builds up again.
In the rivers heavy loads of silt, pebbles and debris are carried downstream by the rushing waters, which pound the river banks in times of flood. Where fields or moorland have been drained, rain runs off more easily into the rivers contributing to a faster flow. On vulnerable curves the bank can be cut away underneath so that trees and paths slip into the stream. One way of preventing this is to shore up the bank with gabions (steel cages filled with pebbles), but this can be unsightly.
On the coast many landslips are caused after high winds bring down trees. As a result the soil is loosened and heavy rainfall washes away both soil and trees. In the National Park repairs to footpaths and preventative measures are carried out chiefly by the Park Authority's estate staff. More information about erosion on Exmoor can be found in Questex also published by ENPA.
Pollution
Although there has been an increase in the number of reported cases of water pollution nationally, few have occurred on Exmoor where the monitored quality of water is usually very good. Possible concerns are of nitrates which enter the water in run-off from fertilised land and of pollution from household waste and slurry from farms.
It has been the practice in many parts of the South West to discharge crude sewage into the sea. There are still problems of pollution on beaches but both South West Water and Wessex Water have begun schemes to replace the old out-dated sewage outfalls with modern coastal treatment works.
The water of the Bristol Channel is sometimes polluted by heavy metal discharges from the industrial works at Bristol and Avonmouth and South Wales.
Porlock shingle ridge
A particular problem in recent years has been the weakening of the shingle ridge that protects Porlock Marsh, much of which is an SSSI. The ridge was probably first formed more than 8000 years ago and has been sustained, on and off, by stones from cliff falls at Culbone. The natural supply of stone from Culbone cliffs no longer reaches the beach while the shingle already there is constantly being transported by the sea to build up the eastern end of the beach while the western end becomes thinner. A combination of high water levels and storm waves has led to the ridge being breached on several occasions, most recently in October 1996.
For many years attempts have been made to strengthen the ridge by the use of timber groynes and by replenishing the shingle but this has proved unsuccessful. In fact it has been suggested that the failure of the ridge was due partly to management measures over years which altered and steepened the profile of the ridge making it less stable. The October storm in fact made the ridge lower and wider and thus more stable.
Now, after consultation with the National Trust who own the eastern end of the ridge, the NPA, English Nature and environmental consultants, it has been decided to follow a policy of 'managed retreat'. Nature will be allowed to take its course and this is likely to result in a return to the situation of 200 years ago shown on maps of that period, with a breached ridge and a lagoon instead of a marsh.
Environment Agency
The EA are the 'guardians of the water environment'. They have statutory responsibilities for water resources, controlling pollution, flood defences, fisheries, water-related recreation and conservation. They therefore work closely with the National Park Authority to protect the water-based environment for the benefit of local communities and visitors.