SEVERN, a river of Wales and England. It rises on the N.E. side of Plinlimmon, on the S.W. border of Montgomeryshire, and flows with a nearly semicircular course of about 210 m. to the Bristol Channel; the direct distance from its source to its mouth is about 80 m. Its Welsh name is Hafren, and its Roman name was Sabrina. Through Montgomeryshire its course is at first in a S.E. direction, and for the first 15 m. it flows over a rough precipitous bed. At Llanidloes it bends towards the N.E., passing Newtown and Welshpool; this part of the valley bearing the name of the Vale of Powis. It receives the Vyrnwy near Melverley, and forms a mile of the Welsh border, and then turning in an E.S.E. direction enters Shropshire, and waters the broad rich plain of Shrewsbury, after which it bends southward past Ironbridge and Bridgnorth to Bewdley in Worcestershire. In Shropshire it receives a number of tributaries, the chief of which is the Tern. Continuing its southerly course through Worcestershire it passes Stourport, where it receives the Stour (left), and Worcester, shortly after which it receives the Teme (right). It enters Gloucestershire close to Tewkesbury, where it receives the Upper Avon (left), after which, bending in a S.W. direction, it passes the city of Gloucester, below which it becomes estuarine and tidal. A high bore or tidal wave, for which the Severn is notorious, may reverse the flow as high up as Tewkesbury Lock (1312 m. above Gloucester), and has sometimes caused great destruction. The estuary merges into the Bristol Channel at the point where it receives on the left the Lower or Bristol Avon, and on the right the Wye.
The source lies at an elevation of about 2000 ft.; the fall from Llanidloes is about 550 ft., from Newtown 365 ft. and from Shrewsbury, 90 m. above Gloucester, 180 ft. The scenery of the upper valley is wild and picturesque, and that of the lower river isat some points very beautiful. The course between the height of the Wrekin and Wenlock Edge (despite the manufacturing towns on the banks at this point), the valley above Bewdley, where the Forest of Wyre borders the left bank, and the fine position of Worcester, with its cathedral rising above the river, may be noticed. The distance from Gloucester to Avonmouth is 44 m., but the upper part of the estuary is tortuous, and, owing to the bores and shifting shoals, difficult of navigation; Qn this account the Gloucester and Berkeley Ship Canal, 1634 m. in length, was constructed, admitting vessels of 350 tons to Gloucester from the docks at Sharpness on the estuary. The navigation extends up to Arley, above Bewdley, 47 m. from Gloucester, but is principally used up to Stourport (43 m.), from which the Staffordshire and Worcestershire canal gives access to the Wolverhampton industrial district and the Trent and Mersey navigation. The Berkeley canal and the Worcester and Birmingham canal are maintained by the Sharpness New Docks and Gloucester and Birmingham navigation company. There is connexion with the Thames by the Stroudwater canal from Framilode on the estuary, joining the Thames and Severn canal near Stroud. The Wye is in part navigable; the Bristol Avon gives access to the great port of Bristol, and the Upper Avon is in part navigable. The Severn is a good salmon river, and is famous for its lampreys, while many of the tributaries afford fine trout fishing, such as the Teme and the Vyrnwy. The drainage area of the Severn is 6850 sq. m., including the Wye and the Bristol Avon, or 4350 sq. m. without these rivers.
Severn Tunnel.—The first bridge above the mouth, of the Severn is that near Sharpness, which carries the Great Western and Midland joint railway between Berkeley Road and Lydbrook junction. But the Severn tunnel, carrying the Great Western railway under the estuary 14 m. below the bridge, forms the direct route between the south of England and South Wales. Before the tunnel was made there was a steam ferry at a point known as “New Passage,” where a ferry had existed from early times. The steam ferry was opened in connexion with the Bristol and South Wales Union railway in 1863, and was subsequently taken over by the Great Western company. Parliamentary powers to construct the tunnel were obtained by this company in 1872, and work began in the following year. The originator of the scheme and chief engineer was Mr Charles Richardson, and Sir John Hawkshaw was consulting engineer. The principal difficulty encountered in the construction was the tendency to flooding, owing both to the river breaking into the works, and, more especially, to the underground springs encountered, one of which when tapped completely flooded the works at a rate of 6000 gallons per minute, and delayed the work for more than a year. In 1879, after this disaster, the contract for the whole work was let to Mr T. A. Walker. The total length of the tunnel is 4 m. 624 yds., of which 214 m. are beneath the river. On the east side the cutting leading to the tunnel has a gradient of 1 in 100, which is continued in the tunnel itself until the deepest part is reached beneath the river-channel known as “ the Shoots," which has a depth of about 60 ft. at low tide and 100 at high tide (ordinary spring). Beneath this the rails run level for 12 chains, after which the ascent of the tunnel and cutting on the west side is on a gradient of 1 in 90. At Sudbrook on the west side there is a pumping and ventilating station. The tunnel was completed in 1886; the time for passenger trains between Bristol and Cardiff was immediately reduced by nearly one half, and the value of the new route was especially apparent in connexion with the mineral traffic between the South Wales coal-field and London and the ports of the south of England.