Itchen Navigation: The Locks
This page considers the design and appearance of the locks on the Itchen Navigation when the waterway was in use. The ravages of about 150 years of disuse make it difficult to appreciate these today. Few images exist of the waterway from the days of commercial use and so some features cannot be positively detailed. In addition, the names of some of the features of a lock can vary from waterway to waterway. In this description, the terms commonly used today on the English canal system are used.
We must remember that in the 17th Century what we would today call “civil engineering” was in its infancy - indeed the term was not used until the second half of the 18th Century. Waterway construction tended to be a case of trial and error: if a structure you had built failed, then you would rebuild it more substantially.
Construction of the Navigation seems to have started soon after the passing of the 1665 Act of Parliament although it appears that disputes with landowners and millers led to the passing of about 45 years before regular trade between Northam and Winchester commenced. Thus the structures of the Navigation were built over a considerable period although basic designs are unlikely to have changed significantly over this period.
A lock is a reasonably simple structure to allow boats to proceed up or downhill. In essence, it is a box that can be filled with water or emptied at will using gravity. At each end are gates that can be opened and closed (but only when the water level is the same on either side of a set of gates) to allow boats to enter and leave.
As was usual with river navigation construction at this period, all but one of the locks were built as "turf-sided". This means that the sides of the lock chamber between the top and bottom sets of gates would be constructed with sloping earthen banks, at an angle of about 45°, rather than of the brick or stone walls that were usual in later times. When constructed, these sloping chamber sides were usually lined with a thick layer of turfs where the grass and other plants would be encouraged to grow to help bind the soil together.
It is also very likely that the foot of each turf side would be protected with either a timber or masonry wall to just above the lower water level so that, when filling the lock, the not inconsiderable force of the incoming water did not erode the foot of the chamber side. At Conegar Lock just south of Bishopstoke, such walls made of brick can still be seen.
Some locks on other early river navigations were spanned by one or more “galley beams” or “lintels” that prevented the walls and/or gates of the locks from collapsing inwards (see picture of Spellbrook Lock on the River Stort). It is quite possible that some existed on the Itchen but there is no known evidence that any lintels were ever installed on the Navigation.
On many waterways with turf-sided locks, vertical timbers would have been inserted at intervals along the sides of the lock chamber to prevent boats descending in the lock from settling on the sloping bank although there is no evidence, either documentary or visible on the ground, that locks on the Itchen Navigation had these. Indeed, there is some evidence that members of the crew were accustomed to use shafts (poles) from the lock side to manually keep boats away from these slopes.
Gates and cills
The lock chambers were enclosed by two gates at each end which were constructed of timber which was probably oak. The gates at the lower end or “tail” of a lock are always larger and heavier as they extend to the full depth of the lock whereas those at the upper end or “head” need only be the depth of the waterway upstream. Each gate would be slightly wider than half of the lock’s width so that the pair would form a shallow ‘V’ pointing upstream. This enabled the gates to withstand the water pressure when water levels on either side were not equal and also helped the gates to seal.
At each end of such a lock, the gates would be hung from a substantial framework as, of course, it is important that the gates form a reasonably watertight seal. It is likely that, in common with other 17th Century navigations, this framework would originally have been made of wood but that later, when the wood deteriorated, this was replaced in brick or stone. For example, the brickwork at the head of Twyford Lane End Lock incorporates the date 1749 (about 40 years after this part of the Navigation was built) - probably too soon to be replacing existing masonry.
The vertical timber of a gate furthest from the side of the lock is usually known as the “mitre post”. This must fit snugly together with the same timber of the other gate of the pair to prevent leakage. The vertical timber nearest the lock wall is called the “heel post”. Besides providing the leverage for opening or closing the gate the nearly horizontal “balance beam” also acts as a counter-balance for the weight of the gate. Contemporary pictures of St Catherine Lock on the Itchen show the gates with balance beams (but unusually gates on the River Stort had none - they were originally opened and closed using chains attached to the mitre posts).
Both upper and lower gates, when closed, bed against a “sill” or “cill” at the bottom of the waterway. On the Itchen Navigation, this was sometimes called an “apron”. The inside of the upper cill would be uncovered when the lock is empty, but the whole of the lower one would be permanently under water. The cills on the Itchen were of massive construction in an attempt to ensure that they and their gates were as stable as possible to prevent leaks from developing.
The old type of cill was made of wood. Although the details of construction varied from waterway to waterway, often the foundations of a cill might originally be formed with vertical wooden piles, rammed earth and rubble. Subsequent maintenance may have led to partial or total replacement with brick and/or stone. Over the top of this was often laid a base cill consisting of a block of elm stretching right across the lock and keyed into the lock walls on both sides. Over this would be oak boarding spiked down onto the base cill. This boarding was found at Mansbridge Lock in 1992 during archaeological investigations. On top of this boarding was the structure sometimes known as the “clap cill” against which the bottom beam of the gates would bear when the gates were shut to stop water passing under them.
On early navigations, lock gates were hung like field gates on “hooks and rides” (hinges) from a post attached to the lock side but with this system it would have been difficult maintain a watertight seal. Locks in use today use a system whereby the face of the heel post nearest the lock side is rounded to fit the “hollow quoin” in the masonry within which it partially rotates. Inserted in the bottom of the heel post is a round “tan pin” which can rotate in a cup or “pot” set into the cill. The top of the gate is kept in position by a metal “collar” which is fixed to an “anchor” fastened into the masonry at the top of the lock wall. Looking at the remains of the turf-sided locks, it seems highly likely that the lock gates on the Itchen Navigation were hung using hooks and rides.
The distance between the top and bottom sets of gates seems to have varied between about 90 and 100 feet but the top cill was often 10 or more feet long. The top cill is in effect the step in the waterway that the boat overcomes by means of the lock and stability of this part of a lock is crucial. In the 17th Century with little understanding of the forces involved, a massive structure would have been built in an attempt to ensure stability.
To make a lock functional, there must be means of getting water into and out of the lock chamber. On early waterways, this was achieved by means of a sluice, mounted on the upstream side near the bottom of a gate. This sluice could be raised to allow water to pass through a hole in the gate. Today this would normally be called a “gate paddle” but many waterways had their own name for this device. The paddle was connected to an arm or “rod” passing up the gate to a simple, vertical piece of wood with handles and a series of holes which with a peg could be secured in a raised position. Filling the lock would involve raising the paddles in the top gates to allow water from the higher level to pour into the lock using gravity. Similarly, the lock would be emptied into the lower level downstream of the lock. There seems that the top gates of the locks had an open aperture or vent at the top of the gate through which excess water in the pound above could discharge into the lock to help regulate the water levels. To aid this, the normal method of operation on the Navigation was to leave a lock with the top gates closed and the bottom gates open.
Finally, to protect the masonry at the head and tail of the lock from the barges entering or leaving the lock, wooden fendering would often have been fixed to the brick or stonework at about water level. This was achieved with very large iron nails driven through the wood into the wall behind. There is an example of such a nail remaining at the head of Mansbridge Lock on the offside.
These methods of construction had an major advantage: they were relatively cheap. A turf-sided lock tends to leak water through the earthen sides but, although a matter of concern on an artificial canal where water supplies may be limited, on a river navigation where river water was usually fairly plentiful this was a minor consideration. In the 17th Century, bricks were expensive and in southern England suitable building stone was not readily available at reasonable cost. Transporting heavy goods by horse and cart on poor roads was expensive - indeed, this is a major reason why water transport started to be developed at this period.
Thus we find that river navigations such as the River Wey (opened in 1653 from Weybridge to Guildford), the River Kennet (opened in 1723 from Reading to Newbury) and the River Stort (opened from the River Lee to Bishops Stortford in 1769), amongst others, were all originally built with turf-sided locks. In almost all cases these locks were rebuilt over the years with masonry chamber walls. There are just two examples still in use in England: at Garston Lock and Monkey Marsh Lock on the River Kennet section of the Kennet & Avon Canal between Reading and Newbury.
The Allbrook Lock that we see today north of Eastleigh is not turf-sided. The original turf-sided lock was replaced on a new site when the London and Southampton Railway (later to be renamed the London and South Western Railway) was being constructed in about 1837-8. The railway between Northam and Winchester was opened in 1839. The railway embankment came so close to Allbrook Lock that this had to be rebuilt by the railway company at its own expense which partly explains its comparatively good condition today.
The lock was constructed in the style of the day with brick chamber walls and only just long enough for a seventy feet long boat. The gates were hung using hollow quoins and collars (see above). Although the collars are now missing, the anchors for the upper gates remain fastened into the stonework and the hollow quoins are now obscured by modifications to the weir made during the summer of 2003. The widened road bridge at the tail of the lock obscures the gate fixings there. Pictures of the lock can be seen here.
Woodmill Lock is no longer visible having been filled in during road works towards the end of the 19th Century. It was a sea lock with a masonry chamber running east-west. It was last reconstructed in 1829 with bricks. It had the usual two pairs of lock gates pointing upstream to retain water in the non-tidal river, plus a third pair, pointing downstream, to prevent very high tides from flooding the Navigation with sea water. A wooden bridge across the lock was also built at around this time, but by the middle of the century was in poor repair. Pictures of Wood Mill and the site of the lock can be viewed here.