

I think all these measures are designed to slow the flow, spread the storage of the rain across more places so it can cope with the larger downfall in the short-term, buying time for it all to flow away once it has passed.
There are similar ideas in UK with reintroduction of beavers who transform land into spongey floodplains that can tolerate much more rainfall before spilling over.











Reminds me of the ‘totems’ in Inception, except they were to prove to yourself you were not in a dream.