Severn

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, image = SevernFromCastleCB.JPG
, image_size = 288
, image_caption = The river seen from Shrewsbury Castle
, map = RiverSevernMap.jpg
, map_size = 288
, map_caption = Tributaries (light blue) and major settlements on and near the Severn (bold blue)
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, pushpin_map_size = 288
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, subdivision_type1 = Country
, subdivision_name1 = England and Wales
, subdivision_type2 =
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, subdivision_type3 = Region
, subdivision_name3 = Mid Wales, West Midlands, South West
, subdivision_type4 = Counties
, subdivision_name4 = Powys, Shropshire, Worcestershire, Gloucestershire
, subdivision_type5 = Cities
, subdivision_name5 = Shrewsbury, Worcester, Gloucester, Bristol

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, discharge1_location= Bewdley, Worcs.
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, discharge1_max = max recorded on 1947-03-21
, discharge2_location= Apperley, Glos.
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, discharge3_location= Montford, Shrops.
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, source1 =
, source1_location = Plynlimon, Powys, Wales
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, mouth = Severn Estuary
, mouth_location = Bristol Channel, United Kingdom
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, tributaries_left = Vyrnwy, Tern, Stour, Warwickshire Avon, Bristol Avon
, tributaries_right = Teme, Leadon, Wye
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The River Severn ( cy, Afon Hafren, ), at long, is the longest river in Great Britain. It is also the river with the most voluminous flow of water by far in all of England and Wales, with an average flow rate of at Apperley, Gloucestershire. It rises in the Cambrian Mountains in mid Wales, at an altitude of , on the Plynlimon massif, which lies close to the Ceredigion/ Powys border near Llanidloes. The river then flows through Shropshire, Worcestershire and Gloucestershire. The county towns of Shrewsbury and Gloucester and the City of Worcester lie on its course.

The Severn's major tributaries are the Vyrnwy, the Tern, the Teme, the Warwickshire Avon, and the Worcestershire Stour.

By convention, the River Severn is usually considered to end, and the Severn Estuary to begin, after the Second Severn Crossing, between Severn Beach in South Gloucestershire and Sudbrook, Monmouthshire. The total area of the Estuary's drainage basin is . That figure excludes the area of the River Wye and the Bristol Avon, both of which flow into the Severn Estuary. The Estuary discharges into the Bristol Channel, which opens into the Celtic Sea and from there into the Atlantic Ocean.

Etymology and mythology

The name Severn is thought to derive from a British *''sabrinā'', possibly from an older form *''samarosina'', meaning "land of summertime fallow”.
The name is recorded in the Latinized form ''Sabrina'' in the 2nd century.

The Welsh form of the name is ', first recorded in the 12th-century '' Historia Regum Britanniae''.
Milton's 1634 masque '' Comus'' makes ''Sabrina'' a nymph who had drowned in the river.
In Shrewsbury, there is now a statue of Sabrina in the Dingle Gardens at the Quarry, as well as a metal sculpture erected in 2013.

There is a different deity associated with the Severn Estuary: Nodens, represented as mounted on a seahorse, riding on the crest of the Severn bore.

Geography and geology

The River Severn's current form is the result of a multi-million year history and complex underlying geology but is in part the result of glaciation during the last ice age in the Pleistocene epoch of the Quaternary period. Within Wales, the river runs through a landscape formed in Ordovician and Silurian rocks. As it enters the Shropshire Plain, these lower Palaeozoic rocks are replaced by Permian and Triassic age strata though largely unseen beneath a thick cover of Quaternary deposits. Certain stretches also run across Carboniferous strata as at Shrewsbury and for much of the distance between Ironbridge and Bewdley. Permo-Triassic bedrock then continues until the Severn moves intermittently onto the Jurassic outcrop from Tewkesbury southwards. Only in the SSW-NNE aligned valley either side of Welshpool is there any obvious relationship to geological structure; the valley follows the lines of the Severn Valley Faults. For much of the rest of its course it runs directly across geological structures.

It was first proposed in the 1900s that the former northerly course of the upper Severn was disrupted during the course of the ice age by the blocking of its access to the Irish Sea through Cheshire causing a large lake to develop across much of Shropshire. It was supposed that this lake, named as Lake Lapworth, overtopped its southern margin and rapidly cut down to form the Ironbridge Gorge providing the Severn with a southerly exit to the sea as remains the case today. An alternative theory which has gained favour in recent years does away with Lake Lapworth, suggesting that the upper Severn flowed beneath the icesheet in a bedrock hollow known as the Severn Trench eastwards from Melverley to the Ironbridge Gorge. It is possible that the trench and gorge were cut over successive ice ages.

Tributary rivers

Over its length, there are a large number of tributaries, but the three largest feeding the non-tidal river are the Vyrnwy, the Teme and the Warwickshire Avon. The Wye, the Bristol Avon and the Usk all flow into the estuarine section of the Severn. The main tributaries are described in sequence below.

The first tributary of significance is the Afon Dulas, joining from the south immediately upstream of Llanidloes, with the Afon Clywedog joining in the town. The Afon Cerist, bolstered by the Afon Trannon, and the Afon Carno join as left bank tributaries immediately upstream of Caersws. Mochdre Brook enters on the western edge of Newtown, followed by the Bechan Brook just northeast of the town. The Mule enters at Abermule, and the River Rhiw east of Berriew, followed shortly by the Camlad which rises above Churchstoke and by the Luggy Brook. The left bank Sylfaen Brook enters at Welshpool, and the Bele Brook via the New Cut east of Arddlin.

The River Vyrnwy, which begins at Lake Vyrnwy, flows eastwards through Powys, gathering the waters of the Banwy, Cain and Tanat, before forming part of the border between England and Wales, and joining the Severn near Melverley, Shropshire. The River Perry joins on the left bank above Shrewsbury, while both the Rad Brook and the Rea Brook, which flows northeast from its source at Marton Pool near the Welsh border, join the Severn within the town. The left bank tributary, the River Tern, after flowing south from Market Drayton and being joined by the River Meese and the River Roden, meets the Severn at Attingham Park.

The River Worfe joins the Severn's left bank just above Bridgnorth, before the Mor, Borle and Dowles brooks join on the opposite bank over the next few miles, the last-named draining Wyre Forest. The River Stour rises in the north of Worcestershire in the Clent Hills, near St Kenelm's Church at Romsley. It flows north into the adjacent West Midlands at Halesowen. It then flows westwards through Cradley Heath and Stourbridge, where it leaves the Black Country. It is joined by the Smestow Brook at Prestwood before it winds around southwards to Kinver, and then flows back into Worcestershire. It then passes through Wolverley, Kidderminster and Wilden to its confluence with the Severn at Stourport-on-Severn. The Dick Brook, Shrawley Brook and Grimley Brook enter on the right bank before the River Salwarpe, which runs through Droitwich enters on the opposite (east) bank.

The River Teme flows eastwards from its source in Mid Wales, straddling the border between Shropshire and Herefordshire; it is joined by the River Onny, River Corve and River Rea before it finally joins the Severn on the southern edge of Worcester. Bushley Brook joins just upstream of the confluence of the Warwickshire Avon with the Severn at Tewkesbury. One of several Avons, this one flows west through Rugby, Warwick and Stratford-upon-Avon. It is then joined by its tributary the River Arrow, before joining the Severn. The rivers Swilgate and Chelt also join the Severn's left bank, as do the Hatherley and Horsbere brooks, before it reaches Gloucester. The River Leadon enters the tidal West Channel of the Severn at Over, immediately west of Gloucester. The