Storm Water Power Generation

Here's a novel idea to generate some more electricity.
Why not build reservoirs to hold water from storm drains and use it for hydro power. Sure this only works when it rains so rainy climates would benefit more. Flat areas would also not work as well because you need greater elevation drops to generate more electricity. Turbines could also be attached where a city's storm water dumps into a large ditch or river.
I have no idea whether this is feasible both from a cost perspective and an engineering one. Would the returns be worth it? Can hydro power turbines take the punishment of periodic operation while being dry the rest of the time? I don't know either of the answers. Perhaps you the reader can help. Please comment.