Cor, that's a massive dam - I hadn't really appreciated that you might want to build something that big for the sake of flood management, rather than because you want to store the water for later (e.g drinking water reservoirs).

Does a structure like that aim to produce constant river flow, averaging out the wet and dry seasons? Is this sort of thing only common in places with variable climates?

Ah, thanks - these aren't reservoirs, they're smaller dams for flow management. Makes sense now.

This feels like something you could mitigate by changing the control regime of the dam - if you lower the “full” level, then be would be more spare capacity in the event of a big rainfall event, leading to the same risk of failure as before.