Geology Site Account

Site name: Cobbins Brook, between Epping Upland and Waltham Abbey.

Grid reference: TL 430 030

Brief description of site:

This stretch of Cobbins Brook is valuable because it is largely natural, exhibiting many features of erosion and deposition including meanders, low cliffs and gravel bars.

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Summary of the geological interest

This site consists of approximately seven kilometres of Cobbins Brook between Epping Upland and Waltham Abbey. The site includes the brook channel and banks and the land for a distance of 3 metres each side of the brook. The same stretch of Cobbins Brook is notified as a Local Wildlife Site.

This stretch of Cobbins Brook has a largely natural appearance, with the kind of characteristic river features that have been lost from many watercourses in lowland England due to human interference, such as channel straightening and bank re-profiling. The brook exhibits many natural features of erosion and deposition including meanders, low cliffs and gravel bars. Some tributaries of the brook are lime-rich due to water flowing out of the junction between the chalky boulder clay and the underlying impervious London Clay, sometimes forming deposits of tufa.

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Scientific interest and site importance

Cobbins Brook exhibits many natural features of erosion and deposition including meanders, low cliffs and gravel bars. Features such as this are now rare on rivers in lowland England.

Meanders are loop-like bends in a river, characterised by an actively-eroding cliff on the outside of the curve and a gentle slope of deposited material on the inside. Usually meanders occur on the part of the river with the least gradient. The precise reasons why a river adopts a meandering course are uncertain but the sinuous curves may be the result of the balance between energy and friction when a low energy river moves fine sediments down a shallow gradient.

A bar is an elevated region of sediment that has been deposited by the flow of the river. Types of bars include mid-channel bars and point bars, which are crescent-shaped and located on the inside of a meander.

A small tributary of Cobbins Brook near Epping Upland has formed a deposit of calcareous tufa, which has encrusted leaves and twigs with calcium carbonate (Cole 1898). The origin of the tufa is the chalky boulder clay, or till, which lies directly on the impervious London Clay in this area.