Our encounter with a flash lock

Sunday, 03 April 2011 15:02

Flash Lock is a term that I have been coming across a fair bit during my research as we cruise the River Thames. Once upon a time the only way a boat could navigate this river was by using a so called "flash lock".

Since the 1800s we have become used to locks like this one at Northmoor

Millers along the river built weirs to build up water levels to drive their waterwheels. These weirs obstructed boating, but pleased the millers and fisherman as a good head of water was built up above them. The boaters were not so pleased ......

Boating down a "flash lock" was dangerous. Today's "pound" Locks are much safer - provided boaters keep aware and follow the rules. Our day on the river yesterday involved two locks - Shifford and Northmoor. There were a number of other boats out too, including punts from Newbridge.

Electric punt

We chose to go through the middle arch of Newbridge, watched by a few gongoozlers on the Thames Path and in the gardens of the Maybush and Rose Revived pubs.

Newbridge

Passing the summer houses and boat houses after Hart's footbridge - there once was a weir here (Hart's or Ridge weir) - we approached Northmoor Lock.

Chalet

As we tied up to wait for the lock to fill John spotted something he wanted to photograph. Now I know what it was! It was a Paddle and Rymer weir. One of only a few remaining on the Thames, this is a type of weir that is referred to when talking about a "flash lock".

Northmoor paddle and rymer weir

The construction of this type of weir was a large wooden beam across the river bed (sometimes encased in a masonry "cill") which had slots of 4" square, 2' apart. Another beam was fixed above it and above water level; part of this was removable by swinging it or lifting it. 4" square vertical timbers were fixed in the slots and rested on the upper beam. These "rymers" were kept in position by force of water.

Side view of weir showing rymers resting on upper beam - click to enlarge

A number of poles attached to boards (about 2' by 3') were placed against the rymers to hold back the water - the "paddles".

Paddles resting on top of weir

For a boat to pass over, a gap was made by moving about 20' of the upper beam, together with the associated paddles and rymers. The "flash" of water would take downstream boats over the weir. Upstream boats would wait below until the rushing water subsided and were hauled up and over the weir either by manpower, horse power or winch. Clickety click for 1786 diagram of flash lock.

The paddle and rymer weir from downstream

Now - would you like to "ride the flash"? I certainly wouldn't want to in a narrowboat!

Close up of a small "flash"

So back to our cruise. We passed all the static caravans at Bablock Hythe. There were many more people and cars there enjoying the warm weather and a weekend break. We rough moored beyond, just before the beginning of Farmoor Reservoir above the opposite bank. We had started after lunch so it was much later that we normally moor up!

River Thames, Tenfoot Bridge to Farmoor Reservoir
2hours 51 minutes, 8.21 miles, 2 locks