Chalk streams are rivers that rise from springs in landscapes with chalk bedrock. Since chalk is permeable, water percolates easily through the ground to the water table and chalk streams therefore receive little surface runoff. As a result, the water in the streams contains little organic matter and sediment and is generally very clear. [c]
The beds of the rivers are generally composed of clean, compacted gravel and flints, which are good spawning areas for Salmonidae fish species. [3] Since they are fed primarily by aquifers, the flow rate, mineral content and temperature range of chalk streams exhibit less seasonal variation than other rivers. [3] [4] They are mildly alkaline [5] and contain high levels of nitrate, phosphate, potassium and silicate. [3] In addition to algae and diatoms, the streams provide a suitable habitat for macrophytes (including water crowfoot) [6] and oxygen levels are generally supportive of coarse fish populations. [3]
Of the 210 rivers classified as chalk streams globally, 160 are in England. [5]
A list of chalk streams in England gives a total of 224. [g]
Chalk is a highly porous and permeable rock, and rain falling onto chalk topography percolates directly into the ground, where the chalk layer acts as an aquifer. The groundwater flows through the chalk bedrock, re-emerging lower down the slope in springs. The chalk acts as a temporary reservoir by regulating the amount of water supplied to the springs. This is why many chalk streams in the UK have stable flow regimes that vary only slightly over time. The temperature of the emerging surface water is fairly stable and rarely deviates from 10 °C (50 °F). On cold winter mornings, water vapour from the relatively warm stream condenses in the cold air above to form fog.
Chalk is slightly soluble in rainwater because rain is naturally slightly acidic. [7] The products of chalk weathering are dissolved in rainwater and are transported in stream flow. Chalk streams transport little suspended material (unlike most rivers), but are considered "mineral-rich" due to the dissolved calcium and carbonate ions. The surface water of chalk streams is commonly described as "gin clear". The channel bed consists of angular flint gravel derived from the natural flint deposits found embedded within the chalk geology that contains relatively low amounts of clay and silt deposits.
The unique characteristics of chalk stream ecology are due to stable temperature and flow regimes combined with highly transparent water and lack of sand grade sediment particles.
The chalk streams have been intensively managed for many generations. In the 20th and 21st centuries, much of that management has been aimed at producing the best conditions for fly fishing, and most specifically, dry fly fishing. The chalk streams hold a good number of wild salmonid fish species such as the brown trout (Salmo trutta), and grayling (Thymallus thymallus). In addition to these there are also considerable numbers of stocked brown trout and stocked rainbow trout (Oncorhynchus mykiss). The rich invertebrate life and characteristic transparent shallow water make chalk rivers and streams particularly suited to fly fishing.
Many of the chalk stream springs are also used as sites for watercress production, due to the constant temperature and clean, alkaline, mineral-rich spring water. [h] The Mid Hants Watercress Railway in Hampshire is so named on account of its use for transporting watercress to London from local chalk streams. A number of the chalk aquifers and associated groundwater sources related to chalk streams and rivers are used for water abstraction by local and national water utility companies.
The over-abstracting of chalk streams by private water companies in the UK has caused the chalk streams to dry up. This has caused ecological damage and stagnant sewage that flows through the rivers and increasing phosphate levels. [9]
Although chalk streams are generally watercourses originating from chalk hills, including winterbournes, streams, and rivers, the term chalk stream is used even for larger rivers, which would normally be considered too large for the term stream. The Somme in northern France is a chalk stream on a larger scale.
Winterbournes [i] are known by different names depending on region:
Region | Count [n] | Discharge | Count |
---|---|---|---|
Eastern Wolds (Yorkshire) | 35 | North Sea | 1 |
Humber | 34 | ||
Eastern Wolds (Lincolnshire) | 19 | Humber | 8 |
North Sea | 9 | ||
The Wash | 2 | ||
East Anglia | 58 | North Sea | 4 |
The Wash | 4 | ||
The Broads | 11 | ||
River Great Ouse | 39 | ||
Thames | 47 | River Thames and Thames Estuary | 41 |
English Channel | 6 | ||
Wessex | 64 | The Solent | 17 |
Christchurch Harbour | 29 | ||
Poole Harbour | 14 | ||
English Channel | 4 | ||
Isle of Wight | 1 | English Channel | 1 |
Total | 224 | 224 |
Chalk streams of the Southern England Chalk Formation in Berkshire, Hampshire, Wiltshire, Dorset and the Isle of Wight:
Chalk streams of the Southern England Chalk Formation in the Chiltern Hills, Hertfordshire and Surrey (tributaries of the River Thames, River Lea and River Colne):
Chalk streams of the Yorkshire Wolds:
Chalk streams of Lincolnshire: [10] There are several chalk streams in the Lincolnshire Wolds including
Chalk streams of Kent:
Chalk streams of Norfolk: [11]
Chalk streams of Suffolk:
The Little Stour is one of the tributaries of the River Stour in the English county of Kent. The upper reaches of the river is known as the Nailbourne, whilst the lower reaches were once known as the Seaton Navigation.
Downland, chalkland, chalk downs or just downs are areas of open chalk hills, such as the North Downs. This term is used to describe the characteristic landscape in southern England where chalk is exposed at the surface. The name "downs" is derived from the Celtic word "dun", meaning "fort" or "fastness", though the original meaning would have been "hill", as early forts were commonly hillforts - compare Germanic "burg" (fort) and "berg" (mountain).
Watercress or yellowcress is a species of aquatic flowering plant in the cabbage family, Brassicaceae.
The River Itchen in Hampshire, England, rises to the south of New Alresford and flows 26 miles (42 km) to meet Southampton Water below the Itchen Bridge. The Itchen Navigation was constructed in the late 17th and early 18th centuries to enable barges to reach Winchester from Southampton Docks, but ceased to operate in the mid-19th century and is largely abandoned today.
The River Lambourn is a chalk stream in the English county of Berkshire. It rises in the Berkshire Downs near its namesake village of Lambourn and is a tributary of the River Kennet, which is itself a tributary of the River Thames.
A winterbourne is a stream or river that is dry through the summer months, a special case of an intermittent stream. Winterbourne is a British term derived from the Old English winterburna. A winterbourne is sometimes simply called a bourne, from the Anglo-Saxon word for a stream flowing from a spring, although this term can also be used for all-year water courses. Winterbournes generally form in areas where there is chalk downland bordering clay valleys or vales. When it rains, the porous chalk holds water in its aquifer, releasing the water at a steady rate. During dry seasons the water table may fall below the level of the stream's bed, causing it to dry out.
The River Allen is a river in Dorset in South West England. It flows for 14 miles (23 km) to its confluence with the River Stour at Wimborne Minster. It has two main tributaries, the Gussage Stream and the Crichel Stream.
The River Chess is a chalk stream that rises near Chesham in the Chiltern Hills, and flows for 11 miles (18 km) through Buckinghamshire and Hertfordshire to its confluence with the River Colne in Rickmansworth. The Chess, along with the Colne and Gade, gives rise to the name of the district of Three Rivers.
The Bourne Rivulet is a river in the English county of Hampshire. It is a tributary of the River Test.
The River Alre is a tributary of the River Itchen in Hampshire in the south of England. It rises in Bishop's Sutton and flows west for 6 km (3.7 mi) to meet the Itchen below New Alresford.
Barrow Haven is a hamlet and small port in North Lincolnshire, England. It was the site of a former ferry crossing that spanned from the Humber Estuary to Hull, serving as a place for ships and boats crossing the Humber to moor away from the tidal flow. A port continues to exist nearby and the area's rail access is based at the Barrow Haven railway station, a stop on the Barton Line.
A losing stream, disappearing stream, influent stream or sinking river is a stream or river that loses water as it flows downstream. The water infiltrates into the ground recharging the local groundwater, because the water table is below the bottom of the stream channel. This is the opposite of a more common gaining stream which increases in water volume farther downstream as it gains water from the local aquifer.
West Beck is the common name given to the upper section of the old River Hull, as it rises in the foothills of the Yorkshire Wolds. After reaching Frodingham Beck at Emmotland, it becomes called the River Hull. It is noteworthy for being the most northerly chalk stream in England. It provides fly fishing for wild brown trout and grayling.
The River Beane is a short river in the county of Hertfordshire, England. A tributary of the River Lea, it rises to the south-west of Sandon in the hills northeast of Stevenage and joins the Lea at Hartham Common in Hertford.
The River Whitewater rises at springs near Bidden Grange Farm between Upton Grey and Greywell in Hampshire, England. It flows northeast and is a tributary of the River Blackwater near Swallowfield. Its headwaters flow over chalk and there is little pollution making the River Whitewater rich in wildlife. It was noted on Jansson's map of Hampshire of 1646.
A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long, large streams are usually called rivers, while smaller, less voluminous and more intermittent streams are known as streamlets, brooks or creeks.
The Gypsey Race is a winterbourne stream that rises to the east of Wharram-le-Street and flows through the villages of Duggleby, Kirby Grindalythe, West Lutton, East Lutton, Helperthorpe, Weaverthorpe, Butterwick, Foxholes, Wold Newton, Burton Fleming, Rudston and Boynton. The stream flows into the North Sea in Bridlington harbour. It is the most northerly of the Yorkshire chalk streams.
A gypsey is a name given to intermittent springs and streams in the Yorkshire Wolds, England. Gypseys are streams formed from springs from the waterladen chalk that constitutes the Yorkshire Wolds. The springs flow in late winter or early spring, with the water emanating through unbroken turf.
The River Rase is a 16 mile (25 km) long tributary of the River Ancholme that flows through Lincolnshire, in the east of England.
The River Lyde or Lyde River is a small river in the English county of Hampshire. It rises near Mapledurwell, where the water is used in watercress beds before entering the main channel. It flows in a generally northerly direction, and used to supply power to watermills along its route. Near Sherfield on Loddon it joins the River Loddon, which is a tributary of the River Thames.