The River Blackwater is a tributary of the Loddon in England and sub-tributary of the Thames. It rises at two springs in Rowhill Nature Reserve between Aldershot, Hampshire and Farnham, Surrey. It curves a course north then west to join the Loddon in Swallowfield civil parish, central Berkshire. Part of the river splits Hampshire from Surrey; a smaller part does so as to Hampshire and Berkshire.
The source is locally rare heath within the Thames Basin Heaths Special Protection Area, due to the Farnborough/Aldershot Built-up Area.
After the Blackwater is joined by the Whitewater near Eversley. The river gives its name to the town of Blackwater, extending back from the bank facing Camberley, and the wider urban area including Aldershot, Farnborough, and Camberley is sometimes collectively referred to as the Blackwater Valley.
Naming
This article reverses the term found by Ordnance Survey mapmakers, old and continued there, Blackwater River.
A stretch west of Finchampstead is called Long Water in 1897 and on recent maps. The adjacent final section from the Whitewater to the Loddon is known by alternative names. In Ordnance Survey maps: the 1:50,000 calls it as in general; the 1:25,000 calls it (the) Broadwater; the 1:2500 calls it as in general at each end and Broadwater in the middle, reflecting local broadening. This last option was the convention in the 1899 (forerunner) map at that scale.
Blackwater Valley
The river runs along the centre of the Blackwater Valley, which is maintained as a largely tree-planted open space, with some bog, marsh and water-meadows. It runs for approximately from the source at Rowhill Nature Reserve near Aldershot in the south, northwards to Swallowfield where the river is joined by the "Whitewater" and then joins the River Loddon. The Loddon flows into the Thames on the southern borders of Wargrave.
For many miles banks of the lower half are semi-rural or rural. The upper half of the river for more than a mile each side is highly urbanised – the river passes Aldershot, Ash, Ash Vale, Frimley, Farnborough, Camberley, Blackwater, Sandhurst and Yateley; the continuous urbanisation extends to Fleet in the west and to Farnham in the south, with a combined population of over 300,000 people at the 2011 Census. Beneath the catchment are chalk, Bagshot Formation sand and greensand aquifers, covered by varying depths of London clay-based soil, mostly very weakly permeable. Some of the water flows from springs from the aquifers, but by far the largest component of the flow is the discharge from five major sewage treatment works on the upper reaches and two smaller ones on the lower reaches. The springs are quite acidic for natural, non-hydrothermal springs. After flowing over the London clay deposits, the underlying geology is more permeable near the mouth, the "Bagshot and Bracklesham" Sands. In 1992, the five works could discharge up to 74.4 Ml per day, and in summer months accounted for around 85% of flow above the confluence with the Whitewater.
The valley has large pockets of deep gravels, quarried since the 1950s. This explains the many lakes in the valley, as old workings (pits) fill with water. Many have been landscaped as park lakes and used for fishing and sailing. A number of them are designated Sites of Special Scientific Interest (SSSI), having rich and diverse ecology. The Blackwater Valley SSSI covers , comprising unimproved alluvial meadows, swamp, and wet woodland. Part of it is managed by the Berkshire, Buckinghamshire and Oxfordshire Naturalists Trust. The rest is managed by Bracknell Forest Council, Shepherd Meadows.
A cycle route runs alongside the river for most of its length.
Route
The Blackwater rises as a series of springs on Rowhill Copse, a nature reserve to the south-west of Aldershot. The site contains a range of habitats, its estate once produced timber and bricks. From its source up until the three-county tripoint east of Blackwater station, the river almost exactly marks the longstanding boundary between the counties of Surrey and Hampshire.
left|thumb|The Source of the River Blackwater at [[Rowhill Nature Reserve]]
On the left bank is Aldershot sewage treatment works that in dry weather supplies more than half of the local flow and produced animal feed until the 1950s, when the building was sold. The watermill and mill house are grade II listed, with parts of the buildings dating from the 15th century. They were subsequently used as a restaurant, with the restored mill wheel, gears and machinery visible from the seating area, encased behind glass screens. The river follows the northern edge of Bramshill Plantation, of woodland managed by the Forestry Commission. It is a Special Protection Area in view of the number of bird species to be found there, and also has large populations of damselflies, dragonflies and silver studded blue butterflies. Notable flora includes marsh clubmoss and pillwort. The large country house was built in the late 17th century, was altered in 1820, and restored in the 1970s. The house and adjoining stable block are grade II* listed. The main drive to the house crosses the river on a five-arched brick bridge, dating from the late 18th century. The river continues through the park until it reaches the River Loddon.
Ash Aqueduct
The Basingstoke Canal runs from the Greywell Tunnel at Greywell in the west to the River Wey in the east, and crosses the Blackwater Valley on an embankment in the village of Ash. Thk Blackwater used to flow through a brick culvert under the embankment,
The water quality of the Blackwater system was as follows in 2019.
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Reasons for the quality being less than good include discharge from sewage treatment works; drainage from roads and transport infrastructure; contaminated land adjacent to the river; physical barriers such as weirs and impounding of the water which prevent the free migration of fish and other species; and the presence of the North American signal crayfish, an invasive species.
See also
- List of rivers in England
Bibliography
References
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External links
- Blackwater Valley runners - Running club that runs the BlackWater Valley path