Crossword Genius

These had been a hindrance, but, finally, water's cascading down, after a bad start, through canal gates (9-6)

Ross

I believe the answer is:

stumbling-blocks

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'these had been a hindrance but finally water's' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'cascading down after a bad start through canal gates' is the wordplay.
I cannot quite see how this works, but
'cascading' could be 'tumbling' (to cascade is to fall or tumble) and 'tumbling' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Irish Times.
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