The article linked below asks the question whether Mumbai can really even be flood free and provides certain arguments to claim that making Mumbai flood free is indeed a hard task and a long way off since making it flood resistant is something that's going to be relevant in the future. The article also highlights the impending danger and the increasing trend of the severity of the floods
To this end we could perhaps discuss certain ways wherein we could aim to make the city flood resistant. First, the article talks about the saucer like topology of the city and how rainwater would naturally flow to the centre of the city and collect there. Since 2D modelling of urban floods is only a recent development, rainwater harvesting techniques have seen applications in not only preventing these floods, but also collecting rainwater for future use. Perhaps some RWH techniques could be used since there is a natural stable position for the rainwater to collect.
The article also cites recent construction projects, topsoil erosion and land reclamation which contribute to the increasing severity of floods. It would be nice to discuss certain ways to make these construction projects more environment friendly to the extent that it doesn't contribute to the flooding.