Just how good are we at managing water?

[GEEZER]

That's exactly why they have to be almost full. They are laid out on such a shallow (almost flat) grade that they have to be kept full in order for the water to flow. If water is being drawn from the canal at any point, that lowers the canal level below that point and if water is withdrawn from several points, there just isn't enough head to push the water to the farthest downstream points. A lot of this is addressed with water "turns" ie. users must only take water from the canal when it's their turn. Almost all canals are managed that way and I've heard tales of people being shot at, beaten to a pulp and such for taking water out of turn.
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