The River Severn, known by the Romans as Sabrina, today splits into east and west channels at Upper Parting, near Maisemore to the north of Gloucester, and becomes one again at Lower Parting, west of the city. The area between the two channels is known as Alney Island, the location of ancient hams and causeway, modern viaducts and many cows.

While urban Gloucester butts up against the lower course of the east channel, the city's administrative boundary spreads, much like the floodwater that often inundates Alney Island, to the west channel below Over. The eagerness with which the low-lying areas to the north and west of medieval Gloucester flood ensure they remain unmolested by modern Gloucester's urban sprawl.

The Severn has not always looked this way. Over the centuries it has flicked across the landscape around Gloucester like rivulets running down a pane of glass, forming new channels and abandoning old ones. Early documentary evidence is sparse to non-existent, but it is possible to discern the changes in the river over the last 2,000 years or so through geological and archaeological research. Although the conclusions are sometimes contradictory, it is clear that over that period, Sabrina around Gloucester has morphed from one channel to three before settling, for now, on the current two.

Pre-Roman River and the Proto-West Channel Theory

The pre-Roman river was a single channel that followed a less meandering course over ground traversed by today's twisting east channel. Below the area of Sandhurst, where today's east channel makes a tight curve round to the west, the original channel continued south. It was joined in the vicinity of today's Westgate Street car park by the River Leadon flowing in from the west (though at some stage the Leadon changed course, turning south at Over to join the Severn at Lower Parting and leaving a buried channel along its original course).

It was on the bank of this ancient channel of the Severn that the Romans established first a fort then the colony of Glevum, though by that time it's possible the Severn had already spawned a second channel, the forerunner of today's west channel.

The west channel was formed by the natural process of bifurcation, whereby a river overspills its bank on the outside of a meander. One theory is that the new channel was begun in pre-Roman times but flowed roughly along the line of today's west channel from Upper Parting only as far as Over. From Over it followed the buried channel of the former Leadon in a direct line across today's Alney Island, along the future Over Causeway, to meet the original Severn in the vicinity of today's Westgate Street car park.

According to this theory, the new "cross" channel was approximately the size of the original channel by the time the Romans arrived in the 1st century AD and established what would become Gloucester. The area was chosen to control the crossing of the river, and the specific site of the future city was chosen because it required only a single river crossing immediately below the confluence of these two channels of the Severn.

Roman Period

In Roman times the original channel of the Severn flowed farther east than today's river, roughly along the line of today's Lower Quay Street approximately 260 yards (240 metres) outside the Roman west gate. The Romans established a quay on the river there (possibly in a position that would allow them to use the river's tides to propel boats up the cross channel on their way to the Forest of Dean ore mines). Archaeological evidence indicates there was also a bridge at this point.

East Channel

The next episode in the life of the Severn at Gloucester came well after the Romans left Glevum to ruin when they abandoned Britain in the early-5th century. Today's east channel was formed around the 6th or 7th century, when the original channel overspilled its banks in the vicinity of Sandhurst. The new channel basically followed the course of today's east channel, but turned east above, not below, today's Westgate bridges and flowed along the north side of today's Westgate Retail Park, on what would later become known as The Island, before rejoining the original channel.

Saxon and Medieval Period

By the time the Saxons began repopulating Gloucester in the 9th or 10th centuries the original channel outside the old Roman west gate had shifted its course westwards by nearly 150 yards (130 metres). The Saxons established new quays on this channel at St. Oswald's Priory and St. Mary de Lode.

In 1119, some 50 years after the Norman Conquest, construction was begun on a bridge over the original channel, at the point outside today's Westgate Street car park where Westgate Street is now bisected by Royal Oak Road. Later known as Foreign Bridge, it was described in the 16th century as a "bridge on the cheife arme of Severne that runneth hard by the towne, of 7 great arches of stone."

Some time after the construction of Foreign Bridge, and possibly as a consequence of it, the course of the east channel changed slightly. Instead of flowing north of today's Westgate Retail Park to join the original channel above Foreign Bridge, the river began following today's course south of the retail park to join the original channel below Foreign Bridge. The former course persisted as a drainage ditch, and the area on which the retail park now sits, surrounded by water courses, became known as The Island (a feature replicated today by the road gyratory around the retail park).

The new course necessitated a new bridge on Westgate Street beyond Foreign Bridge. The first Westgate Bridge, recorded in the 12th century, was a timber construction, implying that the river then was more akin to a stream. By 1265 the bridge had become a masonry structure of "five great arches", and by 1370 Westgate Bridge had exceeded Foreign Bridge in importance. A fortified gatehouse, rebuilt in the early-16th century, stood at the eastern end. During the English Civil War a drawbridge was installed as part of the city defences in the lead-up to the siege of Gloucester in 1643.

Decline of the Old Severn

The formation of new channels significantly reduced the flow of water along the original channel, which began silting up as a result. From 1370 the channel beneath Westgate Bridge was being referred to as the Great Severn, while the original channel flowing under Foreign Bridge was known as Little Severn, then, from 1529, Old Severn.

The quay on the original channel at St. Oswald's Priory ceased to be used, and by 1390 a new quay had been established on the east channel (which remained in use until the 1960s and is today the river wall on the approach to Gloucester Docks). From the 15th century, as the original channel ran increasingly dry, the arches of Foreign Bridge were progressively blocked up and built against.

West Channel

With the Old Severn on the road to extinction, the last major change was the formation of the west channel as it is today. This occurred in the late-15th century and was likely caused by a severe flood in 1483, in which "...the ryver rose so high that yt overflowed all the countrey adjoyning, insomuch that men were drowned in their beddes, houses with extreme violence were overturned, children were swimming about the fieldes in their cradelles and beastes were drowned on hilles..."

Sources differ as to whether the river broke through at Over (thus changing an already established cross channel) or farther north at Upper Parting (thus establishing the west channel in its entirety for the first time), but the result was the same; the Severn captured the lower course of the River Leadon, which had flowed south from Over to join the east channel at Lower Parting, and established the west channel between Upper Parting and Lower Parting that we know today.

The first record of a bridge over the west channel at Over comes in the 1540s, when it was described as comprising eight arches at the end of Over Causeway, but not yet finished. According to some sources this was the first bridge over the west channel. Other sources which assume a much earlier origin for the west channel report that it was a rebuild of an "ancient" bridge, though they may be confusing the bridge over the river with Over Causeway, which appears in the records for the first time in 1086 and is referred to in historical sources as a Lange Brige and "Gloucester Bridge".

Burial of the Old Severn

By 1712 only one arch of Foreign Bridge remained navigable. The next year the Old Severn was dredged from its confluence with the east channel up to Foreign Bridge and the quay extended along its east bank. The last arch was closed to navigation in 1743.

By the 19th century the Old Severn was known as Dockham Ditch. The stretch below Foreign Bridge was culverted in 1825 (the now grilled entrance to the ditch, where Old Severn once joined the east channel, can be accessed by a short, overgrown path from the north end of the quay). In 1854 the stretch above the bridge was filled in and Priory Road laid down on top (though that road has since been significantly altered).

The line of the Old Severn as it was in its final days is approximately marked today by an alley outside the rear garden fences of houses along Dean's Walk, the stretch of St. Oswald's Road that passes by the King's School Archdeaon Meadow playing field, and the Westgate Street car park. Gradually built over, Foreign Bridge now lies beneath Westgate Street, just outside the car park and extending to the other side of Royal Oak Road.

Navigation

The river in all its forms has long been a trade route, from Roman boats poled along with the tide, through trows designed specifically to navigate the Severn bringing Forest of Dean coal up the river, to the larger brigs that began in 1791 to land at Gloucester Quay cargoes of port, lemon and cork brought up the Severn estuary from Portugal and Spain.

The opening of Gloucester Docks and the Gloucester and Sharpness Canal in the early-19th century spared shipping the tidal dangers of the Severn below Gloucester, but the river remained navigable along both remaining channels above the city. Most traffic would be pulled up the east channel to connect with the Midland canal network and markets in Birmingham and the West Midlands, but the west channel too was used as the last leg in the route from Hereford to Gloucester, a lock at Over Basin connecting the Hereford and Gloucester Canal to the river.

The river, still tidal above Gloucester, was made more dependable for navigation by the installation in 1870 of weirs on the east channel at Llanthony and the west channel at Maisemore. Their purpose was to ensure there would always be a minimum depth of six feet (two metres) of water upriver. Navigation below the weirs was enabled by locks cut the next year across the apices of Alney Island at Llanthony and Maisemore which allowed boats to bypass the weirs.

The Hereford and Gloucester was closed 1881, and the locks at Llanthony and Maisemore were closed 1924 and 1941 respectively. The canal is subject to ongoing restoration by the Herefordshire and Gloucestershire Canal Trust, with Over Basin (but not the lock there) restored in 2000. While Maisemore Lock is now private property, a public footpath passes through the now empty Llanthony Lock (though the land on either side, including the former lock-keeper's cottage, is private property). The east channel remains navigable above Gloucester while the west channel is these days navigated only by surfers riding the Severn Bore upriver.

Bridges Today

The medieval Westgate Bridge was a favourite subject for 18th-century artists but less beloved by a city grown weary of the expense of maintaining the ageing structure. It was replaced in 1816 by a new, single-arched stone bridge. The span of that bridge, not designed to carry the weight of 20th-century military machinery, was replaced with a bailey bridge during the Second World War. The bridge was replaced entirely by the current twin-road and single foot bridges in the 1970s, the construction of which destroyed the archaeological remains of the medieval bridge.

The old bridge at Over, which spanned the river diagonally across today's rail bridge, was maintained and even rebuilt on several occasions. It was finally dismantled when a single-arched stone bridge designed by famous engineer Thomas Telford was built just upriver in 1830. Telford's bridge was, until the opening of the Severn Bridge in 1966, the lowest point at which the Severn was spanned. It was superseded in the 1960s by today's A40 dual carriageway bridge and is preserved now as an English Heritage monument.

The slightly sagging bridge retains its tarmac surface, but the old road either side is now grass embankment and footpath, part of the Gloucestershire Way. A short distance along that way, in the direction of Gloucester, the tarmac of the old road, complete with cats' eyes, makes a brief reappearance, though it temporarily becomes another of fickle Sabrina's channels when high rainfall provokes her into rising again.

Sources

The two main sources used in this article differ in their accounts of the west channel. The pre-Roman cross channel theory appears in The River Severn at Gloucester, published 1978 in the Gloucester and District Archaeological Research Group (GADARG) Review by Fred Rowbotham, whose career as an engineer for the Severn River Authority gave him an intimate knowledge of the river.

The other main source, The Severn Flood-Plain at Gloucester in the Medieval and Early Modern Periods, was published 2006 in Transactions of the Bristol and Gloucestershire Archaeological Society by John Rhodes, Honorary President of Gloucestershire Archaeology (the successor to GADARG). Rhodes references Rowbotham's work, but does not appear to support the existence of the cross channel. Rhodes concludes instead that the west channel was formed in its entirety in the late-15th century when flooding caused the river to break through causeways at both Maisemore and Over.

Various chapters of the Victoria County History encyclopaedia were also consulted: Churcham: Introduction; Gloucester, 1835-1985: Topography; Gloucester: Bridges, gates and walls; and Gloucester: Quay and docks. In discussing the bridges at Over, this general work implies the west channel was already flowing between Upper and Lower Parting in the 11th century. This is repeated in the English Heritage information for Telford's bridge at Over.

Rowbotham specifically addresses what he believes to be the mistaken idea, repeated in other sources, that Roman, Saxon and Norman Gloucester was confronted with multiple channels that required significant bridging. His opinion, broadly supported by Rhodes, that this became a feature of the Severn riverscape around Gloucester only in the later medieval period, is favoured in this article.