South East England Biodiversity Forum

Chalk rivers

What are they?

Chalk rivers are watercourses dominated by groundwater discharge from chalk geology and are an irreplaceable feature of the landscape of the South East. Characterised by clear water and generally stable flows, these groundwater-fed streams support an abundance of wildlife including species such as water crowfoot (Ranunculus spp.), brown trout (Salmo trutta), bullhead (Cottus gobio), white clawed crayfish (Austropotamobius pallipes), water vole (Arvicola terrestris) and otter (Lutra lutra).

For more information please see the old BAP definition or the UK BAP website. Please note that the new habitat definition is for rivers. 

The situation in the South East

Chalk rivers stretch across the South East, following the underlying chalk geology. They include the famous rivers Itchen, Test, Kennet, Hampshire Avon and Lambourn, which are nationally recognised as Sites of Special Scientific Interest (SSSI). The Itchen, Hampshire Avon and Lambourn are internationally recognised as Special Areas of Conservation under European legislation.

The South East contains 1500km of chalk rivers. The region’s designated SSSI chalk rivers – the Itchen, Test, Hampshire Avon and Kennet – remain in unfavourable condition. Considerable investment has been made to reduce the impact of sewage effluent through the removal of phosphate. Catchment sensitive farming initiatives have been established to tackle agricultural derived diffuse pollution. Under the Habitats Directive Review of Consents, the licensed amount of abstraction on the Itchen has been reduced.

River habitat has been improved by landowners, fisheries interests and the Environment Agency’s habitat improvement programme. However, more needs to be done, most notably on the region’s non-designated chalk rivers, which are under the greatest pressure. These include the Dour, Stour Darent and Cray in Kent; the Lavant, Ems and Meon in Sussex and Hampshire; and the Chilterns chalk streams. 


Current threats

The main threats to the chalk rivers in the region are as follows:

  • Abstraction: Excessive abstraction (mainly for public water supply) has contributed to low flows on a number of chalk rivers. This has led not only to drying out of upper and middle sections and riparian zones, but also to accumulation of silt and changes in the aquatic vegetation structure. Artificial measures to counter these effects, such as sealing of the bed with concrete and narrowing of the channel, can themselves have negative ecological consequences.
  • Physical modification: Like most lowland rivers, many chalk rivers have had their beds dredged and lowered and have been confined to specific channels for flood defence, drainage, navigation and other purposes. Urban and infrastructure development in the South East is putting increased pressure on this fragile resource.
  • Pollution: In common with most lowland rivers, chalk rivers are significantly affected by sewage discharges and, in times of low flow, de-oxygenation may occur. High levels of nitrates (leaching from ploughed land into groundwater) and phosphate (from sewage effluent) are found in many chalk rivers. Because of this enrichment, excessive growths of blanket-weed have been observed on what were previously clear waters. Changes in plant communities have occurred, including loss of water crowfoot beds from some river stretches. Effluent from fish farms, watercress beds and light industry can have similar effects. In spite of many of the region’s chalk rivers meeting their chemical, biological and nutrient water quality objectives, algae and poor aquatic plant growth is a common cause of concern.
  • Fisheries management: Management is intensive along many chalk rivers, with regular 'weed' cuts in the channel; fencing off and mowing of strips along the bank; infilling and stabilisation of banks; removal of unwanted fish species (eg. pike, grayling); and stocking with farm-reared trout. Some fisheries management practices are evidently beneficial to conservation, such as cleaning gravels; others are neutral, providing they do not impact on characteristic plant and animal communities or are carried out in previously unmanaged areas.

Please follow this link for a copy of the 2008 report on chalk rivers in the South East. 

 

Vision for chalk rivers

The South East Biodiversity Forum's vision for this habitat is that:

  • The characteristic habitats, plants and animals of chalk rivers, including winterbourne streams, should be maintained and enhanced
  • Water quality, flows and habitat diversity should be restored
  • Cost-effective means of restoring damaged river reaches should be identified

How we can deliver this vision