Physical & Natural Environment



The rocks which form the shoreline of the Severn Estuary range in age from about 400 million to about 200 million years old. The rocks along the Severn Estuary coast record changes of environment and climate through time, from the river-deposited sandstones of the Exmoor coast in the Devonian Period, the tropical seas of the Carboniferous, the desert plains and hills of the Triassic, and the spread of the Jurassic sea over the region. MORE

Freshwater Inputs

The Severn Estuary catchment area, that is, the land area draining into the Estuary, covers an area of 21,590 square kilometres. There are over 600 natural watercourses; with the main rivers draining in to the Estuary being the Ely and Taff (impounded by the Cardiff Bay Barrage), the Rhymney, Ebbw, Usk, Wye, the Severn (the longest river in Great Britain at 354km), the Avon and the Parrett. MORE


Estuaries are complex systems that are comprised of subtidal, intertidal and terrestrial habitats, all interconnected and interdependent. The Severn Estuary hosts some of the most important and protected habitats in the UK, with its vast tidal range playing a major role in creating the unusual physical conditions of the Estuary. The tidal characteristics not only influence the type and distribution of habitats but also affect the biological productivity of the Estuary. Whilst the Estuary is biologically poor compared with other UK estuaries, its unique set of physical characteristics still create a highly dynamic environment and support a wide range of communities. MORE


With its world renowned tidal range the Severn Estuary provides an extremely dynamic estuarine environment for many species. This high energy Estuary carries an immense volume of sediment (estimated at 30 million tonnes on the largest Spring tides). The deposition of this sediment creates and maintains the mudflats and saltmarshes around the Estuary which are important feeding grounds for large numbers of wintering wildfowl and waders migrating on the north Atlantic flyway. The Estuary acts as a resting and re-fuelling station for the birds with many staying here for the entire winter as the mild climate keeps the Estuary free from ice. During peak times, the Severn Estuary can be one of only 6 British estuaries to accommodate more than 100,000 waders. MORE


The Severn Estuary and the waters further west to Bridgwater Bay have a very rich fish community with a combined total of 111 species. Though some of these are probably accidental marine visitors and only rarely observed such as the basking shark and sunfish, with others inadvertently swept downstream from rivers, it is considered that the fish assemblage in the Severn Estuary is one of the most diverse in the UK. It is also one of the more important nursery areas in Britain. MORE

Non-Native Species

The Severn Estuary and the land and sea areas bordering it, like many other regions world-wide, are experiencing the arrival of new ‘non-native’ species of both animals and plants. Humans have introduced new (or alien) species to environments both inadvertently and deliberately for centuries, many of which have been benign or even contributed positively to Britain’s natural heritage. However, whilst deliberate introductions are generally well managed, the increased global movement of people and goods through trade and tourism, coupled with the effects of climate change, has resulted in increasing numbers of ‘uninvited’ non-native species now reaching our shores. MORE

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