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Water, Water, Everywhere

In all the time I've spent by or on the canal I've never really thought much about where the water comes from, it's just there. Of course I'm not completely daft and I know that's not the case, canals are man made and the water is only there if we put it there. This makes the water management of canals incredibly complex and indeed the most successful canals are generally those where water management was engineered into them from the beginning (not all were).

Ironically in many cases it was the steam engine that enabled water to be moved to high points on canals which made them viable and of course steam engines which so soon afterwards caused their demise. If it wasn't for Newcomen inventing the first commercially viable beam engine in 1712 then it wouldn't have been possible to pump water to the top of the Grand Junction at Tring Summit. If not for the steam powered water pump then a canal over the Chiltern Hills would never have happened. Thankfully for us it took nearly a hundred years after the first commercial steam engine in 1712 to get the thing to a point where you could put wheels on it and make trains. Canal Mania really did happen by the skin of it's teeth, and thank goodness says I!

But back to water, water, everywhere and where does it come from? Well, assuming the canal you've built isn't too leaky then it's possible to fill it and hey presto you've got as much water as you need. The problem is when you start moving boats around the canal and more specifically up and down hills through locks. It's no real wonder of physics then that all of the water at the highest points ends up at the lowest points. In the case of the Grand Junction with it's broad locks that happens pretty rapidly when a lock's worth of water is about 55,000 gallons.

So for canals it all comes down to the 'lie of the land'. In the case of the Grand Junction Canal it starts of at the River Thames at Brentford (not quite sea level, about 7m), climbs over the Chiltern Hills to reach the heady height of 120m ish, drops down to 80m ish for quite a way before climbing again to Braunston at about 110m ish. Reading the last paragraph the words are screaming for a picture to show what the canal looks like in elevation. Couldn't find one, although I'm sure when Barnes and Jessop surveyed the route in the late 18th century they must have produced one. Anyhow using the wonders of the internet and a good deal of phaffing, pretty much to scale, here it is.

What do think? I know, I'm in danger of turning into a canal nerd (too late screams Ellison!).

So, no problem, just stuff enough water into the system at Tring Summit and Braunston and Bob's your uncle so to speak. When the canal was first built, over 200 years ago, the solution at either end was the same then as it is now. You need a water source at either summit and a reservoir or two (or three or four or more) to manage the supply.

The Tring Summit over the Chiltern Hills was the tricky bit. The water source is easy, it comes naturally from chalk hills in the form of chalk streams fed from aquifiers (water trapped in the chalk coming up as streams, who knew!). The problem at Tring Summit though is that there isn't enough water high enough. The solution is collecting water in a reservoir a bit lower down then pumping it up with a steam engine.

There was a secondary problem in the early days of the Grand Junction which was simply keeping up with growing demand. The early days was all about growing capacity however you could, including buying a water mill so you could use it's water. Interestingly the water supply was measured in 'locks worth', the water mill was 8 locks a day (ish). And of course you need a reservoir, then another, then more until you have four in total, three of which are today called collectively the Tring Reservoirs.

However, none of the reservoirs are at the top of the canal so water had to be pumped up, the capacity for which also had to be grown and was eventually consolidated into the most important pumping station on the Grand Union Canal at Tringford.

The Tringford pumping station pumps water from the reservoirs into the Wendover arm of the Grand Union Canal (same height as the Tring Summit), not surprisingly at Tringford. This unassuming spot is effectively the life blood of the Grand Union Canal which made the new route from London to Birmingham viable. The Pumping Station was refurbished in 2017, using the original Telford designed building. Today it pumps 2,393 million litres of water a year 40 feet up from the reservoirs to the canal. Apparently it doesn't stop much. Now 2,293 million litres of water seems like a lot, and it is, but when you translate that to locks worth per day it's about 30 locks per day, that's 15 locks in either direction. Tringford Pumping Station really is at a pretty unassuming part of the canal and not fantastically photogenic. Anyhow, I did the best I could, the station is very well hidden so here's the pumping station peeping over the bushes and the outlet busily pumping water onto the summit with the added bonus of a small green frog having a wee rest on the cowling.

Although I failed to get a nice picture of Tringford Pumping Station I did get a picture of a boat just going up to Tring Summit at the very photogenic (even on a miserable day, as it was in this picture) lock 46, Cow Roast, looking out towards the summit.

Water supply supply at the Braunston end of the Grand Junction was still challenging, but not nearly as much as Tring. The water supply comes from naturally occurring streams, enough of which are at the right height for the canal. However the same issues of growth and building more reservoirs happened, ending up with one of the best carp fishing lakes in the country, the Drayton Reservoir, feeding into the canal just south of Braunston tunnel. In addition a significantly bigger reservoir, Daventry, was also needed which also feeds into the canal south of the Braunston Tunnel. The scale of water needed on a busy day is huge, the level of water in the Drayton Reservoir can drop by as much as 30cm in a day! However even this wasn't enough so a 're-cycling' scheme was added in 1805 to pump water back up the Braunston locks to save water. My suspicion is this also had an additional bonus of not feeding 'free' water to the Grand Junction's competitive neighbour, the Oxford Canal.

So that's it, there's other water supplies at various points on the Grand Union, but one look at the picture of the canal tells you that our ability to enjoy the Grand Union Canal, as it was over 200 years ago, is brought about by the same sources of water. It comes from streams in Northamptonshire, chalk aquifiers in the Chiltern Hills, a few (rather large) reservoirs and a massive pump in the Hamlet of Tringford (locals will no doubt correct me and say it's Little Tring!).

I wanted to finish with a nice canal picture, so here's the very pretty entrance to a lock. This is lock 14, the top lock at Stoke Bruerne, which has an interesting dog leg as you go in. It so happens myself and Ellison are training to be lock keepers at Stoke Bruerne so maybe lock 14 will feature in a future blog?

More Soon.

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Jul 25, 2023

Just seen you’re training at Stoke Bruerne - may we could meet up one day for lunch or something when you have some free time x

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