In message , at 10:35:43 on Mon, 5 Aug
2019, Martin Brown remarked:

Can the canals not cope with a greater flow of water into them than
was originally intended?

Canals are designed to lose as little water as possible with each lock
movement

True, but...

so they cannot be used to dump water into without seriously damaging
the mechanisms. There is usually a small bypass for any excess.

.... just because they are designed to be as water-efficient as possible
doesn't mean you can't open the paddles at both ends of a lock and quite
safely result in a significant flow. Every now and again a boater does
that by accident, but it's routine to do it to drain a pound for
maintenance, or to bring water through to fill up a drained pound.

--
Roland Perry