Postcard from . . . Denham Deep Lock

THERE’S something immensely satisfying about watching a canal boat negotiating a lock.

Whether that’s because of our fascination with water or the step-by-step ritual of filling the lock chamber and opening sluice gates to raise or lower a vessel, we’ve enjoyed studying the process for centuries.

“Gongoozlers” is what canal folk call those of us who idle on the towpath watching others do all the hard work in this way – but if it was used derisively in the past, nowadays there’s no shame attached to the curious spectators intrigued by the graceful art of lock navigation.

And so it is with a mixture of curiosity and admiration that we are on the towpath on a murky day at Denham Deep Lock watching the owners of The Hatch Shop showing just how to do it in style.

This is the deepest lock on the Grand Union Canal, bringing the canal down by a whisker over 11 feet – nothing dramatic by national standards, perhaps, given that those in Bath and at Sowerby Bridge in West Yorkshire are almost 20ft, but a decent drop nonetheless.

(If you really want to see a lock with a formidable drop, take a glance at the Ardnacrusha Lock on the River Shannon near Limerick, whose two chambers offer a total rise of 100ft, or the world record-breaking 138ft Oskemen lock in Kazakhstan.)

Anyway, Denham Deep Lock may not be able to compete with those figures, but it still offers plenty to distract the casual observer wandering along this section of the Grand Union Canal as it passes through Denham Country Park.

The original Grand Junction Canal, constructed more than 200 years ago, ran from Birmingham to London, some 137 miles and with 166 locks. Nowadays known as the Grand Union Canal, this is the trunk route of the canal system, passing through rolling countryside, industrial towns and peaceful villages as it gives voyagers access to Milton Keynes, Northampton and beyond.

TRUNK ROUTE: the Grand Union Canal PICTURE: Sue Craigs Erwin

Back in Denham, The Hatch Shop is making light work of the lock on its way to Uxbridge. Officially opened back in July but hampered by lockdown restrictions, the pop-up narrowboat shop – complete with Vietnamese rescue dog Sidney – has been moored in London and Oxford, selling a bohemian collection of trinkets and mementoes, from dream catchers and incense burners to cute signs and candles.

With the rear lock gates shut, it’s time to open the sluice gates and allow the boat to slowly slip down to the level of the canal on the other side of the chamber.

That means a little bubbling and boiling as the excess water slips through those atmospheric lock gates, coated with lichen and ferns.

Once the water level inside the chamber has subsided, it’s time to push open the heavy lock gates and move out into the lower level, ready for the onward journey.

With over 1500 locks on the canals, building new lock gates is a year-round job for the Canal and River Trust. Each one is unique, and made to measure by a team of carpenters.

An average lock gate lasts for about 25 years and it could take anything from a fornight to a month to build, using green, sustainably grown oak with steel fitted to strengthen the joints.

Safely out of the chamber, it’s time for The Hatch Shop to resume its journey to Uxbridge, leaving the country park behind.

On a drizzly day in November, it has to be said that this is not the most prepossessing section of the Grand Union, particularly with the roar of traffic from the nearby motorway and a motley collection of vessels in various states of repair dotted along the banks.

The park opens out to the north, towards Denham Quarry and a succession of other attractions in the Colne Valley Regional Park, but the mosaic of rivers, lakes and farmland is not looking at its best at this time of year, and HS2 construction work has left heavy scars on the local landscape too.

Walkers still flock here all year round, but we may have to wait until the spring until the place perks up again and the crowds return to Frans Tea Gardens for a welcoming cuppa by the side of the lock.

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