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Chalk rivers guide
Chalk rivers of England is an identification guide to the insects, molluscs, mammals, fish and plants of this special habitat.
The guide illustrates 40 species which are characteristic of chalk rivers. Accompanying text gives background information on chalk rivers, how they are formed, their features and the threats they face.
If you’re used to seeing muddy streams and rivers, your first sight of a chalk stream will be an unforgettable experience. With crystal clear water flowing gently over a clean gravel bed, a chalk river is a beautiful and diverse ecosystem. They are globally rare: with fewer than 200 chalk rivers in the world. Most of these are in southern England, with the remainder in northern France.
Chalk is porous, making it extremely permeable to water. Rain soaks into the chalk, which acts as a groundwater reservoir, supplying the springs that flow into the chalk river. The unique conditions within a chalk river system result from the properties of this groundwater. Because it has been filtered through chalk, it is pure, clear, mineral-rich and alkaline. A classic chalk river is influenced relatively little by overland low and runoff. Instead 80% or more of the flow comes from groundwater, water temperature fairly constant. Many chalk river systems have ‘winterbourne’ sections in their upper reaches. These winterbournes usually only flow in late winter, when groundwater levels are highest.
This guide was produced in partnership with the Herts and Middlesex Wildlife Trust.
