Officially the county of Avon no longer exists. In the mid-1990s it was replaced by four Unitary Authorities each responsible for all local government tasks in their respective areas. However, although it is no longer in existence as a geopolitical entity, Avon is still very much a county from a birding point of view. There is a large and active community of birders centred on Bristol (the city which holds about 50% of the county’s 1 million population) and consequently Avon is one of the better-recorded counties in the region.
In Britain, Avon holds an in-between position in zoo-geographical terms. We have no real uplands to speak of and thus we lack habitats such as heather moor-land and the large Sessile Oak woods that characterise areas further west such as Devon and Wales- consequently species such as Pied Flycatcher and Ring Ouzel are just passage migrants (even Tree Pipit is almost absent - it occurs in summer in just one area); Red Grouse is absent, and species such as Merlin are winter visitors only. However, there is a strong population of Buzzards in the county, Grey Wagtail and Dipper are well-represented on the county's faster-flowing rivers. On the other hand, the eastern part of the county (which contains the southern parts of the Cotswold Hills) has large areas of arable farmland which hold bird communities more usually associated with eastern England (Quail regularly occurs in one area, Corn Bunting in two, and Red-legged Partridge in several areas). Most of the remainder of the county is a mixture of ridges and valleys with grass fields, hedgerows and mostly small woodlands, with the following exceptions:
(i) most of the south west corner of the county is Levels habitat - mostly uninteresting flat fields with ditches etween them - like a smaller version of the Somerset Levels. Birds such as Reed Bunting and Sedge Warbler are common in this area.
(ii) (the area to the south-west of Bristol contains several large woodlands. In addition to the usual woodland bird community in Avon (woodpeckers, Marsh Tit, Treecreeper, Nuthatch etc.) these often turn up interesting bird records - Lesser Spotted Woodpecker and Hawfinch are periodically reported from Leigh Woods for example (but breeding there is rarely proved)
(iii) the Mendip fringe, which leads up to the upland heath of Blackdown in neighbouring Somerset is interesting. Stonechats, Whinchats, Tree Pipits and Grasshopper Warblers are here, and if we`re lucky, a Nightjar or Dartford Warbler may cross the boundary from Somerset to breed.
(iv) two large lakes, Chew Valley Lake and Blagdon Lake occupy a central position in the southern half of the county. More about these two sites later. There are also a couple of smaller water bodies e.g. Barrow Gurney tanks (3 large concrete bowls which hold waterfowl in winter and get the occasional interesting passage migrant).
Avon's coast isn't really coastline at all - its the eastern shore of one of Britain's largest and most important estuaries, the Severn (and so we don't have things like Red-breasted Merganser, divers, grebes regularly). The estuary has huge numbers of waders, and Avon gets its share of these, with sites such as Clevedon Bay, the Axe Estuary, Severn Beach/New Passage, Portbury Wharf and the Oldbury Power Station area attracting good numbers of species such as Dunlin, Ringed and Grey Plover, Curlew, Redshank. Species associated with sandier shores, such as Sanderling and Bar-tailed Godwit are, however, largely absent in winter from the county.
The estuary also gets good numbers of wildfowl - Mallard, Teal, Wigeon, Shelduck are common (but geese are not regular here, unlike in neighbouring Gloucestershire). Flocks of passerines use the salt-marsh and rocky shores and recent years have seen records of Lapland Bunting, Twite and Shore Larkas well as the more common species such as Linnet, Skylark and Rock Pipit. Among the waders, rare species have been found by a dedicated few observers, including Kentish Plover, White-rumped and Pectoral Sandpipers in recent years. Peregrine, Merlin and Short-eared Owl are all found in winter, although not in large numbers. Hen Harrier is not regular in Avon though. The estuary sees a regular spring passage of Common and Arctic Terns, and Bar-tailed Godwits and Whimbrel also move through in good numbers in spring. Seabird movements in the estuary can be good in most seasons, given the right weather conditions. Pomarine Skua and Leach`s Petrel are the Severn Beach specialities, but more common species such as Gannet, Fulmar, Kittiwake and Arctic and Great skuas are annual.
Chew Valley Lake is Avon's most popular birdwatching site. As well as vantage points from two causeways, there are two picnic areas and a public trail, and in addition, four hides which are accessible by permit from Bristol Water. Chew attracts large number of winter wildfowl - Pochard, Great Crested Grebe, Shoveler, Gadwall, Teal, Goosander are here in nationally important numbers, and the lake is also a stronghold for wintering Ruddy Duck, Wigeon, Goldeneye, Coot, Tufted Duck, Mallard Cormorant and Canada Goose. Smew is regularly present (up to 14 in recent winters, making it the best site for this species in south-west England). Rare wildfowl are a frequent occurrence with Green-winged Teal, Blue-winged Teal and Ring-necked Duck recently (Lesser Scaup must surely be next?). Chew also gets its fair share of wildfowl of unknown origin, including regular Ruddy Shelduck each summer, and occasional Red-crested Pochards.
The lake's most important habitat for breeding birds is its reed-bed, which is one of the largest in south-west England. Large numbers of Reed Buntings and Reed & Sedge Warblers breed here, and Cetti's Warblers have colonised in the last five years. Bittern, traditionally a wintering species at Chew, has been staying later in recent years and so perhaps we can look forward to this species becoming a regular breeder here too. Elsewhere around the lake, Great Crested Grebes breed in nationally important numbers, there is a large population of Kingfishers, a Grey Heron colony, and occasionally, Garganey breed successfully, although in most years, we just get passage birds (but in good numbers e.g. flocks of up to 9). Water Rail probably breed each year, and are certainly abundant in winter.
Chew has a huge gull roost, with 30,000 Black-headed Gulls, 10,000 Common Gulls and 1000+ Lesser Black-backed Gulls and a few hundred Herring Gulls (Great Black-backed Gull is usually only present in single figures). Of the rarer species, Med Gull is regular (with annual totals of up to 20, although seldom more than 5 present at once - they peak in early March); Western Yellow-legged Gull is present in small numbers from June through to January, peaking in September at usually about 10 individuals, and Ring-billed Gull is almost annual. Iceland and Glaucous are genuinely rare here though. Surprisingly, none of the rarer gulls on the British list have been found at Chew so far.
However, the lake has made up for this as a rarity hotspot in other ways - in the 1970s, rare waders (particularly Nearctic species in autumn) were turning up at the rate of several per year, but the pace has slowed in recent years. Spotted Crakes, after a lean patch in the late 80s/early 90s, have been regularly seen again in the last few years. With the heavy coverage the lake gets, a few scarce migrant passerines have been recorded e.g. Little Bunting. More of the rare species are picked up by ringers however. Chew Valley Ringing Station operates at the southern end of the lake and has produced records of Marsh and Aquatic Warblers in recent years. The lake has also had its share of outstanding rarities over the years including Greater Sand Plover, Black-winged Pratincole, and over-wintering Gyrfalcon and Britain’s first Pied-billed Grebe (shared with Blagdon Lake).
Blagdon is a smaller and older reservoir, but nevertheless has good populations of most of the species of wildfowl found at Chew. There are no reedbeds though so Blagdon only has small populations of things like Sedge Warbler. Recent rare birds have included Black-winged Pratincole, Red-necked Phalarope, Blue-winged Teal.
Migration at the reservoirs is good - Black, Common and Arctic Terns are a feature of spring along with Little Gulls. Waders in autumn pick the reservoir with the lowest water levels and include good numbers of Common and Green Sandpipers, Ruff, Greenshank, Ringed Plover, Dunlin and regular Spotted Redshank, Little Stint, Curlew Sandpiper and Wood Sandpiper. Passage of hirundines and Swifts is impressive. Yellow Wagtails pass through in small numbers, sometimes overlapping with Water Pipits, which winter here (usually less than 10) and can stay into April by which time they acquire summer plumage. One or two Hobbies visit frequently throughout the summer. Scaup and Long-tailed Duck pass through most springs. Osprey is seen each year and regularly stays for a week or more, but Marsh Harriers are usually frustrating fly-throughs. Little Egrets are now appearing annually at Chew (and on the Severn estuary) in autumn, but we haven’t reached the double-figures counts yet that counties further south have. We wait our turn!
A feature of both Chew and Blagdon (and Barrow Gurney) is that during strong winds, seabirds turn up, having been blown up the estuary. Sabine's Gull and Grey Phalarope are semi-regular, and most of the other British seabirds have put in an appearance at one time or another (except the auks). At least one representative from either the divers or the rarer grebes is to be expected each winter.
The City of Bristol's parks have turned up a few good birds in recent years, including our only Nearctic passerine, a Yellow-rumped Warbler, a Black-throated Thrush and a couple of Yellow-browed Warblers. Other than that the city is pretty poor for birds compared with other cities such as Plymouth or Swansea - the gull flocks hardly ever contain any goodies (with the exception of a Laughing Gull in July 1999!) Other features of note among Avon's avifauna, in no particular order, are:
(i) Tortworth Lake, in the far north of the county, has breeding Mandarins, an offshoot of the populations further north in Gloucestershire.
(ii) several breeding pairs of Peregrine, including a celebrity pair in the Avon Gorge, which are wardened by Bristol Ornithological Club. Raven are being seen more and more regularly and have also established several breeding sites.
(iii) Little Ringed Plover, which have colonised the new Bathampton Oxbow scrape, and are also apparently also now breeding on dry ground next to Bristol airport runway!
(iv) several regular inland sites for Golden Plover in winter.
(v) The complex of woodlands at Inglestone Common/Wetmoor in the north of the county has up to 10 pairs of Nightingale, which elsewhere in the county is only found in small numbers. This is also our only Redstart breeding site.
Absentees as breeding species include Woodcock, Turtle Dove, Willow Tit. If the current rate of decline continues, Tree Sparrow may well join them, although a nest-box scheme operates by the Wildlife Trust for Bristol Bath and Avon may just save the day. Ornithology in Avon is well-served by Bristol Ornithological Club, the county`s main bird study group. There is also an active team of BTO surveyors, managed by Richard Bland and John Tully. Compared to our neighbouring counties, Somerset and Gloucestershire, the bird conservation movement is somewhat under-developed in Avon. For example, we have no RSPB reserves, and only a handful of the Wildlife Trust for Bristol, Bath and Avon`s reserves are important bird sites. Even the English Nature office is based out-of-county.
The county bird report is produced jointly by Bristol Ornithological Club and Bristol Naturalists Society. For further information contact the reports editor, Andy Davies. There is at present no modern avifauna for the county, but a team has started work on the initial stages of a project to produce one sometime in the next millennium. A tetrad survey of breeding birds has been completed, and the results will appear in the book. One of the major tasks will be to try to sort out the old records of rarities though - as with most counties, this might prove problematical - the county list has records of species such as Ivory Gull and Two-barred Crossbill from the last century - it will be interesting to see whether these stand up to scrutiny. I welcome opinions on this county summary from birders both within and outside the county. Please let me know of any errors in or omissions from this summary, and Ill endeavour to correct them.
Avonmouth Sewage Works
Three man-made lagoons and a pool provide feeding and resting areas for many birds. The deeper lagoons attract diving duck such as pochard and tufted duck. The shallower pool, known as Teal Pond, has a thick growth of water plants at its edge and provides plentiful food and cover. There is a bird hide overlooking this pond although access is to Wildlife Trust members only, however the reserve may also be viewed from Kingsweston Lane, Lawrence Weston Road and the access road that joins the two. Permits and maps obtainable from Avon Wildlife Trust. Details to permit holders only.
Blagdon Lake is the smaller cousin to Chew. Has a mile of public footpath along the Southeast side from the east tip near Ubley. Permit holders have access to private paths and two hides, one of which is only just usable, both being in need of repair. [Permits obtainable from Bristol Water, Woodford Lodge, Chew Stoke, BS18 8SH and covers Chew, Blagdon and Barrow Gurney reservoirs. Cost is £1 day rate or £8/year.]
Chew Valley Lake
This reservoir is roughly 4km long and 2.4km wide. The dam is at the northern end and most of the perimeter is naturally vegetated with large reedbeds at the southern end. This is by far the areas most important reservoir for birds and hold internationally important numbers of some wildfowl. Good viewing can be had from the roadside at Heron's Green Bay and Herriot's Bridge. There are five hides but access to these is by permit only. [Permits obtainable from Bristol Water, Woodford Lodge, Chew Stoke, BS18 8SH and covers Chew, Blagdon and Barrow Gurney reservoirs. Cost is £1 day rate or £8/year.]
Gordano Valley National Nature Reswerve - Weston Moor
Fen meadows and reed-fringed pools and ditches are the richest habitats on the reserve. They have rare aquatic plants such as greater bladderwort and an impressive number of insects including the hairy dragonfly. The meadows have many scarce plants such as lesser butterfly orchid along with masses of meadowsweet. A wet woodland provides valuable winter food for finches and a summer breeding site for tawny owls. Reed and sedge warblers are completely dependent upon the reed areas as nesting sites.
Honda Car Site at Avonmouth
There being three large ponds at the back of the Honda car site at Avonmouth, its a very good site with wheatear, green sandpiper, common sandpiper, Heron, Snipe, Raven, Merlin to mention a few. This site is at the end of St Andrews road left into the Cabot Park Industrial Estate, carry on to the first roundabout,with Honda cars on your left,Turn left at this roundabout and stop at the footpath, under the Fish Standards. Take a stroll to the ponds on the path in front of you.
Kingsweston Down is a ridge of grassland sheltered by trees, in summer it is alive with wildflowers and butterflies. Plants include rockrose, harebell, lady's bedstraw and restharrow. A total of 28 species of butterfly have been recorded including common blue, brown argus, purple hairstreak and holly blue. Marbled white are the commonest butterfly species present.
Lawrence Weston Moor
A seemingly forgotten piece of land, this urban oasis is sandwiched between the M5 motorway and housing estates. An extensive area of wet meadows and reedbeds, it is extremely rich in wildlife. The drier fields are hay meadows where plants such as meadowsweet and pepper saxifrage are common, and they are one of the few places in the Bristol area where common meadow-rue can still be found. The wetter meadows have ragged robin, marsh marigold and creeping forget-me-not. Marsh arrowgrass is another rarity found here. These fields are an important area for reed bunting and snipe and reed and sedge warblers are known to breed here.
Weston Big Wood
One of the old Avon county's largest ancient woodlands, Weston Big Wood dates back to the last Ice Age. A network of footpaths criss-cross this wildlife rich wood. Uncommon small-leaved lime trees, oak, hazel and the rare whitebeam are major arboreal features of this woodland. In spring bluebells dominate the wood floor with wood anemones and violets. The presence of herb paris, yellow archangel and the very rare purple gromwell show that this is an ancient wood. Orange tip, speckled wood and purple hairstreak are just some of the butterflies that can be seen. The wood is very good for birds, including woodpeckers, nuthatches, many tits and tawny owls. Bats also roost in the trees and the presence of many setts indicates a large badger population.
34 Cranmoor Green, Pilning, Bristol BS35 4QF
01454 633040 or 07443544962
Number of Species
Number of bird species: 344
County Bird - Pied-billed Grebe Podilymbus podiceps
[…as its logo because it was established in the late sixties around the time when one or two PBGBs overwintered at Chew Valley Lake].
Birding in the Bristol Region
A Celebration: 50 Years of the Bristol Ornithological Club by William Earp | BOC | Paperback | 2017 |
ISBN: 9781527205062Buy this book from NHBS.com
Where to Watch Birds in Somerset, Gloucestershire and Wiltshire
by Ken Hall & John Govett 3rd edition Helm ?Where to Watch? series. 2004 ?14.99p
ISBN: 0713666145Buy this book from NHBS.com
Avon Bird Report
From the County Recorder (see above).
Since about 1990 peregrine falcons have bred in the Avon Gorge. To date they have successfully raised about 20 young having bred almost every year. In 1999 one of the youngsters was captured by a concerned passer-by early one morning and taken to a vet, Dick Best, who checked the bird over and pronounced it fit. The juvenile was then ringed and later released close to the nest site. This is the only juvenile from this site to be ringed so far. The Bristol ornithological Club along with members of the RSPB and the Hawk and Owl Trust have kept a watch on the nest site every year since 1991. This was prompted by a semi-successful attempt in 1990 to destroy the nest site by an unknown faction. A person or persons unknown had climbed down the cliff and destroyed 2 of the 4 young hatched by clubbing them with a snooker cue. Details from John Tully, address below.
BTO Regional Representative
RR. R L Bland, 11 Percival Road Bristol, BS8 3LN
Forums & Mailing Lists
Twitter feed of sightings etc from Bristol Ornithological Club - @bristolbirding retweets and posts on Avonbirds sightings in the old county of Avon giving location and numbers of species. #bristolbirding to join conversation
Guides & Tour Operators
Local birders willing to show visiting birders around their area…
CloudBirders was created by a group of Belgian world birding enthusiasts and went live on 21st of March 2013. They provide a large and growing database of birding trip reports, complemented with extensive search, voting and statistical features.
Avon Wildlife Trust
The Avon Wildlife Trust, the local charity working to protect wildlife, manages 37 nature reserves; provides activities for children through Wildlife Watch, its junior branch; and environmental education for over 4000 school children every year; protects the best areas for wildlife in the region and campaigns on wild places under threat; and encourages everyone to enjoy and care for local wildlife…
Bristol Naturalists' Society
The promotion of education and research into natural history, including geology, with special reference to the Bristol district and the promotion of the conservation of the British fauna and flora and the protection of geological and physiographical sites…
Bristol Ornithological Club
The Bristol Ornithological Club was founded to promote, encourage and co-ordinate the scientific study of ornithology in all its branches in the Bristol area. Whatever your level of birdwatching - as a beginner, just interested with no claim to any special knowledge, or keen with special interests - the BOC can help to increase your knowledge and enjoyment of birds. With regular indoor meetings, featuring expert guest speakers, outdoor trips, to a whole variety of birding sites in the South-west, club holidays in Britain and abroad, a monthly newsletter (Bird News - with all the latest bird sightings) and an annual journal (Bristol Ornithology) there is so much to do and find out about the BOC. Take a look around our website and find out about the top places to birdwatch around Bristol or how to join our club and find out about our forthcoming trips and meetings…
Cam Valley Wildlife Group
Cam Valley Wildlife Group is an independent, volunteer-run, wildlife group based around Midsomer Norton and Radstock. The area covers the towns and villages of Cameley, Camerton, Carlingcott, Chelwood, Chewton Mendip, Chilcompton, Clapton, Clutton, Coleford, Combe Hay, Dunkerton, Emborough, Farmborough, Farrington Gurney, Faulkland, Foxcote, Hallatrow, Haydon, High Littleton, Hinton Blewett, Hinton Charterhouse, Holcombe, Kilmersdon, Litton, Midford, Midsomer Norton, Norton St Philip, Paulton, Peasedown St John, Priston, Radford, Radstock, Shoscombe, Southstoke, Ston Easton, Stratton-on-the-Fosse, Temple Cloud, Timsbury, Tunley, Welton, Westfield, Wellow and Writhlington….
RSPB - Bath & District Local Group
We are a group of 275 members around the Bath area. We hold indoor meetings on the third Wednesday of the month from September to March at the Bath Society Meeting Room, Green Park, Bath, where you can hear illustrated talks given by ornithologists, photographers and other professional speakers. We also have an annual programme of field trips by car or coach to a variety of sites including RSPB reserves… Ann Workman - Meetings are held at: Bath Society Meeting Room, Green Park, Bath, Tel: 01225 428091
The web site for anyone with an interest in the birds of the Severn Beach area on the mid Severn Estuary. Severn Beach is a coastal village in South Gloucestershire and situated at the top corner of the Bristol Channel, England. The web site is dedicated to all birders, past and present, who have visited the patch on a regular basis…
British Birds and Mammals Gallery - Many birds and mammals found in the South West Region are displayed in this gallery and can be viewed with accompanying information on their ecology and behaviour…
University of Bristol - School of Biological Sciences
Chew Valley Lake
Despite the pressures from recreational activities, and sailing in particular, Chew Valley Lake remains excellent for birds and one of the most important sites for waterfowl in south-west England. It is an artificial reservoir covering nearly 500ha and was constructed in the 1950s. Much of the surrounding area is rough grassland with occasional conifer plantations although there are some reedbeds on parts of the shore. Further afield is mainly farmland with patches of deciduous woodland. More than 250 bird species have been recorded here…
Chew Valley Lake Birding
Chew Valley Lake, ten miles south of Bristol, is the largest reservoir in south-west England. This website contains regularly updated news and information on its birds and wildlife…
Narroways Millennium Green Trust
Narroways Hill is a little grassy & wooded ridge dissected by railway lines lying just North of inner-city Bristol. It has always been an open space and as the city has encroached around it, its value as a green sanctuary has increased. When British Rail threatened to sell it to developers in 1997 it caused such a reaction that 800 local people demonstrated to save it, thousands signed petitions & wrote letters and money was raised so it was purchased by Bristol City Council. It became a Millennium Green in the year 2000, with a 999 year lease to keep it free and open to the local people and allow wildlife to thrive. On a warm May day while Slow Worms bask on the railway banks, Marbled White butterflies flit amongst the Knapweed & Scabious and Jays scavenge amongst the treetops. In the evening Pipistrelle Bats emerge…
Bird sightings around Bristol and the old county of Avon… To report anything, e-mail 'firstname.lastname@example.org'. All submissions are passed to the county Recorder…
Barrow Gurney Birds
Welcome to Barrow Gurney Birds – the website dedicated to birdwatching at the Barrow Gurney Reservoirs and environs…
I have an energetic passion for nature and enjoy communicating enthusiastically to a wide range of audiences. Since studying zoology at the University of Bristol (1998 - 2001) I have studied the diet of urban Peregrines and been colour ringing their young. I work on a huge range of activities from taking schools fossil hunting to showing people wildlife from boats. I work for many different organisations, from the British Trust for Ornithology to the National Trust, and in the spring I specialise in teaching birdsong. I also lead groups for Naturetrek on wildlife holidays around the world. I also work closely with the BBC as a consultant, contributor and presenter.
Mya-Rose Craig - Birdgirl
A blog by a young birder, birdwatcher, twitcher, naturalist, environmentalist & writer about birds, wildlife, nature, conservation & ringing (banding) who is an Ambassador for World Shorebirds Day, See It Her Way and a Charter Champion for The Charter for Woods, Trees and People
I started birdwatching at the age of 13 when I first began to wear spectacles and realised that the world was colourful! I bought my first camera…
The Bristol Wildlife blog
Last updated 2014 - Bristol is a city in southwest England: with a population of half a million, it’s the largest city in the region, but it is also said to be Britain’s greenest city, with more open spaces than any other city, and a wide range of highly important wildlife sites on its doorstep.…
Birding in the Bristol Region: a celebration
50 years of the Bristol Ornithological Club...
Blagdon Lake Birds
News and information about the Birds & Wildlife of Blagdon Lake in North Somerset, England, UK.
You will find the UK's Cheapest Digital Cameras, Binoculars, Printers, Batteries and other accessory listings from all the major photographic companies on this site. Full accessory lists show that we can supply not just the camera of your choice at the cheapest price but also a full list of accessories…
Bristol Water Birdwatching
Over 270 species of birds have been recorded at Chew, and the lake is the third most important site in Britain for wintering wildfowl. It is designated a Site of Special Scientific Interest (SSSI) and a Special Protection Area (SPA). From late July to February up to 4,000 ducks, of twelve different species, may be present, including internationally important numbers of shoveler and gadwall. Some 400 great-crested grebes gather on the lake in autumn.
A range of cameras and a limited range of binoculars. Mark Williams Tel 01179 734484 Clifton Cameras 82 Alma Rd Clifton Bristol BS8 2DJ…
Forest of Avon
The Forest of Avon will become a unique mix of woodlands, open space, farmland, homes and nature areas - growing more beautiful with the years. The site designated as the Forest of Avon covers an area of 221 square miles. The area stretches north as far as Thornbury and south to Pensford. The eastern boundary takes in Chipping Sodbury; to the west, the Forest reaches the Bristol Channel. At the centre of the Forest of Avon lies the city of Bristol.
Welcome to the Lundy Birds website. Lying astride the mouth of the Bristol Channel, Lundy has long proved to be a magnet for migrating birds, with a long list of major rarities to its name, and is nationally important for its breeding seabirds…
Nailsea Wildlife Wardens
These are some of the Wildlife sites around Nailsea…
North Somerset Bird Of Prey Centre
At the North Somerset Bird Of Prey Centre we offer the chance to watch and interact with some of nature's greatest avian predators. From Hawks and Falcons, to Eagles, Owls and Red Kites. There are opportunities to get up close with these amazing animals, hold them, take photographs and even watch them fly in our own display arena.
The area covered is a ten kilometre coastal strip from the old Severn Bridge, south to the southern end of Chittening Warth. The eastern boundary is formed mainly by the A403, Aust to Avonmouth coast road. The patch is centred on the village of Severn Beach and dominated by the structure of the Second Severn Crossing.