Why only now-a-days Mumbai has started flooding and why not did it flood during the times of British rule? the answer is simple, its because the builders and ministers nexus have reclaimed the creeks in most atrocious way and to add to the woes there is the cancerous growth of slums( or vested vote banks? ).
When Mumbai was formed out of 7 islands the British govt.that time had left lots of creeks unreclaimed so as to let the rain water drain from the main land.
Now what is Bandra-Kurla complex,Garodia Nagar,Back-Bay reclaimation just to name a few - one time creeks I guess,so all this is man-made problem.
So now the only solution for this problem is to stop indiscreet constuction activites and get rid of slums that are occupying the creek regions.( e.g. one on the side of the Mankhurd link road )
