When you think of Britain, it’s easy to conjure up images of rolling fields dotted with sheep and wildflowers, charming villages, ornate gardens and friendly pubs.
It may not be so easy to picture a powerful wall of tidewater traveling up the Severn River for more than 20 miles that can swell the depth of the river by 50 feet, attracting surfers from all over the country to try to ride the wave.
Let’s ply the waters of the intriguing Severn to discover the ecological importance of the unique habitats that this tidal surge supports.
Geography of the Severn
At 220 miles, the River Severn is the longest river in Great Britain. It has the most voluminous flow of water by far in all of England and Wales, with an average flow rate of 3,800 cubic feet per second. It rises in a peat bog in the Cambrian Mountains in mid-Wales at an altitude of 2,001 feet, then flows through Shropshire, Worcestershire and Gloucestershire, traveling down to the Severn Estuary where it empties into the Bristol Channel.
The Severn’s major tributaries are the Vyrnwy, the Tern, the Teme, the Warwickshire Avon, and the Worcestershire Stour.
Although it doesn’t mark the exact political border between England and Wales, the Severn River is key to the separation of the history and economy of the peoples of both countries. In fact, the Severn is called Hafren in Welsh, which means “boundary.”
Riding the Waves
The immense tidal range (the difference between high and low tides) flowing into the Severn Estuary and up the river gives rise to the famous Severn bore. A bore is a steep-fronted wave caused by the tide rushing up a narrowing estuary. The tide in the Bristol Channel and the Severn Estuary is one of the highest tides in the world, sometimes reaching up to 50 feet. It is second only to the Bay of Fundy in Canada.
As rising tides in a wide bay or inlet are funneled into a narrower stream or river, they start to create massive waves that flow upriver, against the current. The river continues to flow into the bay and some of the bay’s water also begins to push backwards on this current, flowing upstream.
The Severn bore is a popular natural feature for surfers and canoeists who attempt to ride the waves.
This creates waves that can travel miles upriver. In the case of the Severn, the tidal wave travels upstream for roughly 22 miles until it reaches Gloucester. The tidal bore is strongest twice a day for about 30 days around the spring and autumn equinoxes. While the Severn bore may be observed anywhere in the lower part of the River Severn, it is most impactful and visible at the point where the river narrows south of Gloucester.
The power of the wave is genuinely magnificent to see, especially when there are many surfers, kayakers and paddle boarders surfing it (or trying to). In fact, the River Severn is the birthplace of river surfing, a sport that wouldn’t exist without tidal bores!
A Unique Ecosystem
These huge tides affect everything in the estuary ecosystem. Up to 10 million tons of silt are churned up and carried along in suspension by tidal currents running at almost 30 feet per second, making it one of the most dynamic estuarine systems in the world.
The Severn Estuary supports 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 that are recognized as internationally important for birds and for wildlife habitats.
Because of this, the Severn has received a number of international conservation designations. In 1995, it was classified as a European Union Special Protection Area. It is also a Ramsar site, a Special Area of Conservation and contains seven Sites of Special Scientific Interest protected by UK law. Its tributaries—the rivers Wye and Usk—are also protected under separate SAC designations because of their important habitats for fish. The estuary is a critical part of the Europe-wide network of protected sites known as Natura 2000.
Species of the Severn
The Severn Estuary is the biggest area of salt marsh habitat in the south and southwest area of the UK, representing 4% of the total area of salt marsh in the UK.
Salt Marsh Plants
Salt marshes are made from halophytes (plants that adapted to live in saltwater), which thrive in the salty estuarine environment. Plants such as glasswort, common reed and sea barley populate these marshlands as well as nationally important rare species such as the bulbous foxtail.
The Avian Serengeti
Numerous bird Species of European Conservation Concern, like redshank, Bewick’s swan, shelduck and dunlin also make their homes in the estuary’s salt marshes. The total over-wintering wader and wildfowl population of the Severn Estuary is regularly more than 60,000 individuals, inspiring the nickname “the Avian Serengeti.” These birds take advantage of the salt marsh plants that shelter them from the tide and protect their young.
The Severn Estuary is also a key refueling stop for migrating birds on long-haul international flights between their breeding and wintering grounds as it sits right on the North Atlantic Flyway, a bird migration route from Siberia across Europe and then down to Africa. The estuary functions as a significant service station where birds can take a break and refuel.
During particularly cold winters, the estuary is of even greater national and international importance, as wildfowl and waders such as the European white-fronted goose, dunlin, wigeon and teal from many other regions are attracted to the relatively mild climate and abundant food resources. In especially cold winters, bird numbers in the estuary have hit more than 100,000.
Fish, Fur, Frogs and More
Because of its massive scale, it’s often tricky to get a full impression of the Severn Estuary. In some parts it can appear to be just a vast expanse of brown mud, but that is definitely not the case. The estuary contains a huge variety of habitats – sandbanks and mudflats, rocky reefs and islands, salt marsh, rockpools and shingle.
Many different fish live in the region, including carp, roach, minnow, eels and brown trout. Some of the furry critters that hang out there are otters, dormice, badgers, polecats, water voles, stoats and mink. Foxgloves, kingcups, yellow iris, bluebells and water lilies make a stunning backdrop for butterflies, newts, frogs, damselflies, and dragonflies.
Worm Reefs?
The reefs in the Severn Estuary are called “biogenic reefs” because they are constructed by worms. Kind of like how a honeybee makes its hive, polychaete worms known as “honeycomb worms” construct a collection of tunnels from sediment and sand particles. These reefs distinguish the region from other estuaries in the southwest of the UK, where such reefs are less likely to be found.
The reef structures provide habitats for many other species. Within secluded tunnels and crevices, you’ll encounter crabs, periwinkles, worms, barnacles and anemones. Subtidal reefs also support colonies of brittle stars and shrimp. Due to their importance in providing habitat and the unique conditions of the estuary, these reefs are protected as part of the Severn Estuary SAC ‘Reefs’ feature.
Discover the Severn for Yourself
On our Cotswolds adventure, we visit 650 acres of wetland reserve along the estuary called Slimbridge. The reserve was established in 1946 by Sir Peter Scott, son of Antarctic explorer Captain Robert Scott. Sir Peter Scott founded the Wildfowl & Wetlands Trust at Slimbridge as a center for science, conservation and public access to nature. He even presented the BBC’s first live television wildlife programs from there!
It was Scott who created the IUCN red list that measures whether species are threatened or endangered. And he was the founding chair of our conservation partner, World Wildlife Fund. He even drew WWF’s original panda logo!
At Slimbridge, Nat Hab travelers are able to witness conservation leadership in action. We learn why wetlands are crucial to Earth’s survival, why they are endangered, and what needs to be done to preserve and restore them.
We believe this extraordinary ecosystem should be championed and cherished. If you are interested in learning more, please watch our recent webinar on the Severn below, and consider joining us on an upcoming nature getaway to the English countryside.
