Canal water

[44949]

Why are canals short of water, where does it go?

[stewey]

One major reason for the drop in water levels would be evaporation.

[Vagrant]

Another is locks.

[Graham-W]

Locks that transfer boats from canals to rivers ( or vice versa) can loose a lot of water into the river.
Not sure if they are all completely leak free either.

[wildwood]

Nothing to do with thirsty fish then?

[Hymie]

I’m not an expert on canals, but Graham-W’s answer would seem most logical. Having been on only one drunken canal trip with friends – I was amazed at the amount of water transferred with each lock movement. The locks were easy 15m long by 5m wide and maybe 4m deep – that is at least 300 cubic metres of water (or 300,000 litres). The water has to come and go from somewhere. All is either supplied by rivers or lakes, into the canal system.

I believe that the Panama Canal is supplied by a series of lakes close by – without the high rainfall within the locality, the canal could not support the volume of traffic traversing through the canal.

[Hymie]

Forgot to add – of course the water will eventually find its way to the sea.

[New Judge]

Yes, each lock movement effectively deprives the canal of a lock full of water (or at least, a volume equivalent to the lock’s area multiplied by the difference in level that the lock provides).

The Grand Union Canal which runs between London and Birmingham is supplied principally by a reservoir in Welton in Northamptonshire.

The Panama Canal is a slightly bigger beast. It has three sets of locks: there are two on the Pacific side (one of one step and one of two steps) and one three step lock on the Atlantic side. They can each accommodate ships of up to 1,000 feet in length and 100 feet beam. These raise and lower ships between the oceans and the Gatun Lake. The lake, which is artificial and was constructed at the same time as the canal, forms part of the navigation and also supplies the locks with water. It is 85 feet above sea level and my rough arithmetic tells me that for each transition of the canal over fifty million gallons (about 240 million litres) of water is needed. Fortunately the area around the canal benefits from over a hundred inches of rain annually and this is more than adequate for the canal’s needs.

I have been through the Panama Canal on two occasions and it really is a marvel of engineering.

[sddsddean]

Actually Judge, your bit about the Grand Union isn't strictly true. The Braunston summit pound is mainly supplied by Daventry reservoir (nr. Welton) and Drayton reservoir which is also in Daventry, but that summit pound is fairly short (Braunston top to Long Buckby top). There is another, longer summit at Tring. When building the canals, every watercourse, no matter how big, and land drain was diverted to the canal to ensure water supplies. If you drive around the Midlands, nearly every reservoir you see is for the canals. Although everyone sees them now as an old form of transport, in their time they were the greatest thing since sliced bread!, and absolutely reveloutionary. Boat skippers had the same kudos as an airline pilot today. As regards water usage, a narrow lock (7' x 72' x 6' approx) uses around 25,000 gallons a time (1000 bath fulls!). Wide locks use around 50,000 gallons. Since the canals were built there have been various pumping schemes to keep them supplied. The oldest in the world are the Crofton steam pumps on the Kennet & Avon canal, and to this day many of the more popular flights of locks have electric 'back pumping' systems to get water back to the top of the locks.

[piggynose]

yeh, but what a relaxing way to travel, out in the middle of the country, without a care in the world. good memories. i used to work on a canalboat in brum for several years in the 90´s

[New Judge]

Thanks for the additional info, sdd.

I don't know quite as much about the Grand Union as I do about Panama!