NOTICE TO MARINERS NO. 2/05

Navigation of the River Severn between Sharpness Point and Gloucester.

Small craft safety warning

The River Severn is navigable as far as Sharpness by any vessel that can enter the docks at that place. Above this, between Sharpness Point and Gloucester, the river is uncharted and unsuitable for navigation other than by small craft at or near mean high water springs (MHWS). No aids to navigation are provided in this area, and it is important that anyone wishing to navigate in this area has an appreciation of the natural hazards which may at times be encountered. Such hazards include the strong tidal conditions (described below) and the presence of partially-submerged tree trunks and other debris which are often washed into the river from further upstream during periods of high river flow.

From Sharpness to Epney

The channel between Sharpness and Epney is ill-defined, flowing through drying sandbanks, and it dries in places. Depths vary considerably, with numerous shallow areas. Navigation is thus uncertain and may be dangerous. During spring tide periods, the flow of the incoming tide is strong, covering the sandbanks rapidly which can lead to a risk of small craft being pushed onto the banks and overturned. During spring tides the river level at Epney may rise by up to 4 metres within an hour.

From Epney to Gloucester

Above Epney, the river is constrained by its banks and flows are nearly always downstream except near spring tides. Depths vary considerably, with numerous shallow areas including those at Stonebench and in the Eastern and Western Partings. During spring tides, an in-going stream of up to 1½ hours may be experienced between Framilode and Gloucester from ½ hour to 2 hours after the time of high water at Avonmouth. During spring tides the river level at Minsterworth may rise by up to 2½ metres within an hour and at Llanthony up to 2 metres in a similarly short time.

Overhead Clearances

It should be noted that overhead clearances are limited by bridge crossings of the river in the eastern and western partings.

The Severn Bore

A bore usually occurs when the range of the tide exceeds 13.5m at Avonmouth (9.5m at Sharpness). In the river below the Longney area, sandbanks and shoal areas are swiftly inundated by the rush of the incoming tide. This rush of water may drive boats onto sandbanks, and may well lead to swamping or capsize. Above Longney, where the river

narrows, a wave is formed. This may be as high as 1.5m and travel at up to 13 knots. Whilst the wave may not necessarily be dangerous to boats afloat in the centre of the river, head on to the wave, they are liable to be swamped or stove in if they are close to the bank as the wave breaks with considerable violence.

Following the initial wave, there is a substantial rise in water level for a further hour or so and high tide is also about one hour after the wave has passed. Occasionally, the rising waters have cut off spectators and their vehicles, needing rescue by the police. The danger is particularly great for viewers of the Severn Bore near Stonebench.

Good conduct and safety afloat

In the interests of safety, all river users must:

· wear appropriate lifejackets

· navigate in a responsible manner in accordance with the International Rules for the Prevention of Collisions at Sea

· observe the speed limits

· avoid navigating too close to the river bank to avoid becoming trapped or hurt

In view of the clear additional risks attendant on surfing or boating on the bore, the Trustees strongly discourage surfing or boating in its vicinity.

A full list of Notices to Mariners may be viewed on the Trustees' website:

www.gloucesterharbourtrustees.org.uk

Owners, Agents and Charterers should ensure that the contents of this Notice are

made known to the Masters or persons in charge of their vessels or craft.

M Johnson
Marine Officer

21 January 2005.

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