View Full Version : Canals

28th Apr 2012, 18:29
A question I have often pondered over, which I'm sure an esteemed prooner will be along in a jiffy to answer.

I live near the river avon. Given the current drought conditions it has risen about 4 feet this week.

Why do not canals seem to rise and fall in accordance with rainfall in the way that rivers do?


28th Apr 2012, 18:36
Perhaps not a primary reason but the amount of traffic through the locks may account for some of the movement of the water.

28th Apr 2012, 18:52
I think that the canal builders built service reservoirs along the routes of the canals as they were being constructed.I live near the Leeds/Liverpool canal at Apperley Bridge and I am sure the reservoir is on Wrose Top near Shipley.I seem to remember the feeder reservoir had a problem and the canal lost its water level(canal lost its water and the boats grounded)When fault repaired canal refilled.

28th Apr 2012, 18:53
Canals have pumping stations at various points to add water, either from reservoirs or rivers. Locks at the end(s) allow water out. Levels are generally kept constant throughout the boating season. Levels are often dropped in winter to aid maintenance work. Current and forecast drought conditions will likely mean lower average levels this year.

green granite
28th Apr 2012, 19:11
A lot of canals have small weirs to let excess water overflow into a nearby stream, also when the level rises it will overflow the top lock gates and then runs over the top of the lower gates into the lower pound, it's known as "the locks running weir"

28th Apr 2012, 20:12
When I was small the canals were lovely and clear because
no one ever used them so the water never got stirred up.
Nowadays all the barges just make it muddy.

Gertrude the Wombat
28th Apr 2012, 20:42
Why do not canals seem to rise and fall in accordance with rainfall in the way that rivers do?
They're managed.

So are many rivers, come to that, but there seems to be more flexibility in the height of a river - the computers aren't set to adjust the sluices etc so that you get exactly the same height all the time.

Gertrude the Wombat
28th Apr 2012, 20:43
Nowadays all the barges just make it muddy
Unlikely. It's more likely that the boats with engines stir it up.

28th Apr 2012, 20:44
When I was small the canals were lovely and clear because
no one ever used them so the water never got stirred up.
Nowadays all the barges just make it muddy.

But least you can see the sky as the Smog has gone :)

28th Apr 2012, 20:47
Canals aren't actually level. They have a fall of around 4 foot per mile, to avoid stagnation. Plus they get water from else where.

Which is why you can't just anbandon a canal and expect no drainage problems - as was found on the 1930s onwards.

Those old canal designers knew a thing or two!

flying lid
28th Apr 2012, 20:55
Canals were engineered to fit in with adjacent water courses / rivers / streams to do 2 things, top up the canal as needed (when boats go through locks etc), and drain off excess water (ditto as above). Notice many locks have by-washes to help do this. In Wigan the river Douglas feeds the Leeds & Liverpool with a feeder stream running under the old gas works, any excess is drained back into the Douglas a few miles away down towards Liverpool at Gathurst.

Similarly, but on a much larger scale the Manchester Ship canal starts at Salford, where the river Irwell runs in & provides the water supply. The canal then actually joins and leaves the river Mersey between Urmston & Warburton, and at Warrington the course of the Mersey was altered when the ship canal was built. If the Mersey has too much flow then there are huge overflow bypasses at Latchford Locks in Warrington to drain the excess back into the Mersey a couple of miles downstream, past the town.

Some pix here

Latchford Locks,Manchester Ship Canal,4-10 - Derelict Places (http://www.derelictplaces.co.uk/main/showthread.php?t=15110)


It virtually manages itself, wont run out of water (allways pissing down in Manchester !!). A brilliant feat of Victorian engineering. It can never be closed / filled in either, as it is now a part of the Mersey basin water / drainage system.


Sir George Cayley
28th Apr 2012, 21:32
Where a canal has a summit there is a pound (in simple terms a pond) There maybe subsidiary pounds further down the canal.

When a canal descends to a lower level via locks, either single or joined together as a staircase, its operation is a total loss system - top down.

Back pumping is a relatively modern conservation of water method with some notable exceptions such as the Victorian Claverton Station on the K & A.

In low water situations the canal users 'wait turns' to save water. This entails boats traveling up the flight have to wait for an other to travel down. Otherwise the climbing boat 'wastes' a lock full of water equalising the levels.

There are some canals without locks - the Bridgewater Canal from Swinton to Preston Brook and the Cannock Extension Canal. Even these have a flow to avoid stagnation.

Lastly, canals were original existing waters that were canalised. When new navigations had to be dug by navigators (navvies) to keep costs down the locks were just 6'6" wide, hence narrow boat.

On wider canal/river navigations such as the Aire & Calder there isn't this restriction and so barges can be used. Lastly, don't call them longboats :ugh:

Must fly!


29th Apr 2012, 08:00
Clever chaps, those canal builders. There's a minor canal in our village, built by Brindley. It was latterly badly affected by coal miniing subsidence (ironic, as it was built to serve the collieries). To overcome the loss of water this caused, they built a top up feeder in the form of an open drain from a river 2 km away. The feeder runs around a hill, across open fields and under a railway embankment.

It was restored a decade ago and is now navigable again after going out of commercial use in the late 1930s. Amazing to watch British Waterways restore the locks. Because of the above subsidence they even built a brand new lock.

29th Apr 2012, 08:23
Part of the Leeds-Liverpool Canal was closed by drought in 2010; the reservoirs keeping it topped up ran low.

29th Apr 2012, 12:13
The River Dee feeds the Llangollen Canal: the water runs down to Hurleston, with bywashes on the locks, and then is used as water supply for Manchester. There are those who take great delight in peeing in the canal at Hurleston at night after getting back from the pub.......

Sir George Cayley
29th Apr 2012, 17:06
That's why I felt drunk after cleaning my teeth !:eek:


29th Apr 2012, 17:14
Max loves'em Are dog's more loyal to their mum's or dad's? - YouTube

Surrounded by the b*ggers round here, a lovely oasis of nature usually.

Great way to get around the place to. Have been able to ride to my many places of work via the canal banks. And they're usually flat to !

29th Apr 2012, 19:06
I know it's not your fault but what's this: 's .. 's .. 's .. ?

In Ingris ze prurial ain't compricated, wee add n s. Not an 's.

Juliet Sierra Papa
29th Apr 2012, 19:53
I remember coming home from school one afternoon and seeing a huge cloud of black smoke a couple of miles away.

A HUGE fire almost completely destroyed Woolworth's £10M warehouse and computer complex in Castleton.
Flames leapt 100ft into the air as 150 firemen from all over the North of England fought the blaze. The fire broke out in the bulk storage department at 4pm on Thursday 8 May 1971, then spread to the loading bay. Half of the Royle Barn Road site's warehouses were burnt down, causing about £3M worth of damage.
Luckily, firemen saved the company's £1M computer section thanks to a fire wall and a lodge containing 574,900 gallons of water. Fire officers were able to use the barrier to form a water curtain between the flames and the rest of the complex.
The 14-acre site was Woolworth's biggest warehousing complex in Britain. The pioneering computer centre served stores throughout the country.

What they did not mention was that the fire brigade was on site for about 10 days and after depleting the lodge of approx half million gals of water continued to dampen down with the contents of the local Canal. This almost completely drained the contents of a +- 3km section ( Between Locks at Oldham rd and Manchester rd) just a small stream running through.

No journo hype either....100 ft flames. Today that would equate to 100 Mtrs and and and....

Didn't realise we had computers in those days.

29th Apr 2012, 20:28
In Ingris ze prurial ain't compricated, wee add n s. Not an 's.

It's possible that something belonging to the dog was more loyal to something belonging to the mum or the dad.

Such as the dog's ballhooks . . .

30th Apr 2012, 10:38
I row on a ship canal, where the water level routinely varies by a foot with probably double that between very high and very low. Almost invariably it’s lower during the week than at weekends. Getting in and out of boats from a fixed pontoon when the level is low is a real pain.

During a very wet spell last year there was concern about potential flooding in lower lying areas ‘downstream’ and water was held back in our stretch, adding another six inches or so to the ‘absolute highest’ level (and completely flooding our pontoon)

Occasionally after a flash downpour the canal fills up with little drownded rats, puffed up like balloons, their little pawses in the air. This is not pleasant.

30th Apr 2012, 11:17
" Didn't realise we had computers in those days. " In those days, they would most likely have been IBM or ICL mainframes.

30th Apr 2012, 11:33
My first contract job was at Woolies there, that was in 1984 though, long after the fire. They used ICL kit.

G&T ice n slice
30th Apr 2012, 13:14
wasn't there a bunch of guys cleaning out a stretch of canal who found a large section of tree-trunk in the bottom. They had a heck of a job getting it out, and once they had there was a sort of gurgling noise and all the water disappeared, much to their bemusement

30th Apr 2012, 13:31

That's right. Was a good long time ago though - 1978. It was on the Chesterfield Canal in Retford: they pulled up the plug that allowed the canal to empty itself into the River Idle, which it crosses on an aqueduct.

There were no records of the plug being there.......no computers in 1777, and everyone knows the only way to keep information is on a computer!

30th Apr 2012, 15:05
Would not the plug have a chain attached (bath) Shirley that would be a give away:p


30th Apr 2012, 15:13
I don't believe it did - it may have had, but 200 years is a long time under water, even for puddled wrought iron, and it would almost certainly have rusted away. They were dredging rubbish, so things with chains on could well have been deemed to be that.

30th Apr 2012, 15:46
Rageng.......... "It was on the Chesterfield Canal in Retford: they pulled up the plug that allowed the canal to empty itself into the River Idle, which it crosses on an aqueduct."

Would not this plug/tree stump have been visible from below the aqueduct?


im from uranus
30th Apr 2012, 15:55
Pic of said plug on this (http://www.chesterfield-canal-trust.org.uk/index.php/gallery/photos/223-retford-drakeholes-and-gringley) page...

30th Apr 2012, 16:20
The chain suggests that it doesn't date from 1777. But I don't know where the outlet into Idle is: if it was in a culvert, it could well be invisible. At that time, the banks of the Idle weren't accessible - they may be now, but I haven't been into that part of Retford since not too long after I left school in 1964.

The canal towpath was out of bounds in those days for us schoolboys: it was too convenient a way of finding a quiet spot for meeting girls from the High School! There weren't any boats, either, to interrupt one.