canals

[laura]

where did all the water come from to fill the canal systems and how was the filling done?

[incitatus]

Streams were diverted into the canals. Each canal has a high point into which water is eeither pumped or diverted from natural water courses. Because of the locks one can fill a canal slowly using very slow water flows.

[aadenny]

Remember that water always flows downhill. Canal builders always calculated where the top ('summit') part of a canal would be (the stretch of the canal between locks is known as the pound, and the top level is the 'summit pound'), and the canal builders had to build a reservoir, higher than that level, to catch the water from the hills above, and store it. As each boat goes downwards through a lock, it will take a lockful of water with it (in English canals, typically 40 - 80,000 gals), and this water has to be replenished from the reservoir above. There is also an inevitable leakeage from the bed of the canal, through lock gates, etc. So any summit pound has to have a catchment area somewhat above it. The highest summit level in the UK, on the Huddersfield Canal, is some 600ft below Saddleworth moor. Some summit levels are rather lower. The summit of the Birmingham canals is fed by the Lickey Hills, near Dudley, only a hundred feet or so above the canal, but it's enough to feed the Birmingham canals in all but the driest months. It helps if the summit pound is long - in effect, the canal then acts as its own reservoir. The main Birmingham canal is many miles long, from Wolverhampton to near Bromsgrove, so can hold a lot of water without relying on the reservoir. On the Kennet & Avon canal the summit pound, near Devizes, is only 3 miles long, so soon runs out of water if the nearest reservoir is dry. Once the summit pound is full, any spare water cascades over to fill the lower pounds, one by one. As each one fills and spills over, the next fills too. So you only need to worry about keeping the summit pound full-to-overflowing, and the rest follow naturally.