A flash lock is a type of

lock Lock(s) may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainment * ''Lock ...

for river or

canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...

transport. Early locks were designed with a single gate, known as a flash lock or staunch lock. The earliest European references to what were clearly flash locks were in Roman times.

Development

In England the "gate" was similar to a temporary

needle dam A needle dam is a weir designed to maintain the level or flow of a river through the use of thin "needles" of wood. The needles are leaned against a solid frame and are not intended to be water-tight. Individual needles can be added or remove ...

: a set of boards, called ''paddles'', supported against the current by upright timbers called ''rymers'' which normally kept the level of water above it to navigable levels. Boats moving downstream would wait above the lock until the paddles (and their rymers) were removed, which would allow a "flash" of water to pass through, carrying the boats with it. Upstream boats would be winched or towed through the lock with the paddles removed. Considerable skill was involved both in removing the paddles in a timely manner and navigating the boat through the lock. Flash locks of this type have been documented since at least 1295 C.E. Flash locks were commonly built into small dams or

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

s where a head of water was used for powering a mill. The lock allowed boats to pass the weir while still allowing the mill to operate when the gate was closed. However it could take up to a day or even more to restore the water levels after a boat had passed, so their use was unpopular with the millers. Flash Lock Capstan Wheel

As navigation increased in importance, improvements were made to the basic design, and they came to be known by various names according to where they were located. Thus on the Thames they were called navigation weirs, on the East Anglian rivers they were called staunches, those on the

River Avon, Warwickshire The River Avon () in central England flows generally southwestwards and is a major left-bank tributary of the River Severn, of which it is the easternmost. It is also known as the Warwickshire Avon or Shakespeare's Avon, to distinguish it from ...

were called water gates, and in a number of instances they were called half locks. On the

River Nene The River Nene ( or : see below) is a river in the east of England that rises from three sources in Northamptonshire.OS Explorer Map sheet 223, Northampton & Market Harborough, Brixworth & Pitsford Water. The river is about long, about of w ...

and some of the tributaries of the River Great Ouse, a design using a guillotine gate in a wooden frame was used from the early seventeenth century onwards. The gate was opened by operating a large spoked wheel, connected by chains to a toothed drum. The

pound lock A lock is a device used for raising and lowering boats, ships and other watercraft between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a fixed chamber in which the water lev ...

holds water between two gates, and is considerably easier to navigate. Pound locks have been built in China since 983, in the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

from 1065 and in Britain from the 1560s. Nevertheless, a few flash locks remained after the introduction of pound locks. Flash locks on the Nene continued to be used until they were replaced in a programme of modernisation, which included building new locks, carried out between 1936 and 1941. The last flash lock on the Thames was Hart's Lock (also known as Eaton Lock), which lasted until 1937, while on the Lower Avon, the structure of Cropthorne Water Gate lasted until the reopening of the river to navigation in 1961, although it had not been used for navigation for many years before that. Although slightly different in concept, Thames Lock at Weybridge on the

Wey Navigation The River Wey Navigation and Godalming Navigation together provide a continuous navigable route from the River Thames near Weybridge via Guildford to Godalming (commonly called the Wey Navigation). Both waterways are in Surrey and are owned ...

had an additional single gate some below the lock, which when closed raises the water level above it, allowing boats which would normally foul the cill to work through the lock. It continued in use until 1969, to enable grain barges to use the lock, and although grain traffic stopped in that year, it recommenced in 1981, when the gate was again used. The gate is still used at the lock-keeper's discretion for boats which have a draught exceeding .

Paddle and rymer weirs

Paddles used for the Paddle and rymer weir at Northmoor lock on the River Thames

The weirs which are the remnants of flash locks can still be seen on the

River Thames The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the second-longest in the United Kingdom, after the R ...

though they are not used any more for navigation as regular pound locks were introduced in the eighteenth and nineteenth centuries and the last flash lock removed in 1937. The Environment Agency is now involved in a programme of replacing these, as their manual operation is considered to be dangerous, and involves lifting weights which exceed those recommended by the Manual Handling Operations Regulations 1992. Two or three paddles are stacked between each of the rymers, which slot into a beam placed on the bottom of the river. The paddles are of differing lengths allowing a very fine adjustment of the amount of water flowing through the weir. Four of these weirs were replaced in 2009. Three were on the Thames at

Mapledurham Mapledurham is a small village, civil parish and country estate beside the River Thames in southern Oxfordshire. The large parish borders Caversham, the most affluent major district of Reading, Berkshire. Historic buildings in the area include ...

Molesey Molesey is a district of two twin towns, East Molesey and West Molesey, in the Borough of Elmbridge, Surrey, England, and is situated on the south bank of the River Thames. East and West Molesey share a high street, and there is a second retai ...

and

Radcot Radcot Bridge is a crossing of the Thames in England, south of Radcot, Oxfordshire, and north of Faringdon, Oxfordshire which is in the district of that county that was in Berkshire. It carries the A4095 road across the reach above Radcot ...

, while the fourth was at

Blake's Lock Blake's Lock is a lock situated on the River Kennet in Reading, Berkshire, England. It is on the short reach of the River Kennet which is administered as if it were part of the River Thames and is hence owned and managed by the Environment ...

, the first lock on the

River Kennet The Kennet is a tributary of the River Thames in Southern England. Most of the river is straddled by the North Wessex Downs AONB (Area of Outstanding Natural Beauty). The lower reaches have been made navigable as the Kennet Navigation, which � ...

, which is managed as part of the Thames. Three more of these weirs, at Rushey, Goring and Streatley, have been Grade II listed since 2009, but the EA is proposing to replace most of Rushey, which would be the only full-width example left.

References

Bibliography

* * {{DEFAULTSORT:Flash Lock Locks (water navigation)