biological and geological Site of Special Scientific Interest
A Site of Special Scientific Interest (SSSI) in Great Britain or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland is a conservation designation denoting a protected area in the United Kingdom and Isle o ...
The site, which includes an active tufa-forming stream, is in the Forest of Dean plateau and Wye ValleyArea of Outstanding Natural Beauty. The stream system has a series of tufa dams, plunge pools and connecting stream sections. This results from a combination of physical and chemical processes.
The Slade Brook rises on the Carboniferous Limestone of the Forest of Dean. It flows for two kilometres before joining the
River Wye
The River Wye (; cy, Afon Gwy ) is the Longest rivers of the United Kingdom, fourth-longest river in the UK, stretching some from its source on Plynlimon in mid Wales to the Severn estuary. For much of its length the river forms part of Wal ...
, which is also notified as an SSSI. Approximately a kilometre section of the stream includes the main focus of tufa deposition.
Rainwater (which percolates into sinkholes in the limestone), is enriched with dissolved calcium carbonate. When emerging from springs along the brook, the removal of carbon dioxide causes precipitation of calcium carbonate. The main deposits of the calcium carbonate are at a series of dam-like structures, which are constructed of tufa.
The process is assisted by vegetation (which includes tree litter such as twigs and branches), algae and mosses. The flow of the stream is slowed and photosynthesis encourages the removal of the carbon dioxide. The vegetation and debris then become the area for tufa accumulation.
The site is significant as tufa dams actively forming are relatively rare and this site has approximately sixty. They enable research into the origins of fossil tufa dams as well as modern formations