In the USA, excessive rainfall causing sewage discharges into waterways is only a problem with those cities that have combined storm and sanitary sewer systems.
Cities that have separate storm and sanitary sewer systems do not have a problem with that.
In fact, they want to keep the rain water out of the sewer system as much as possible because often they are charged by the sewage authority for treating the excess water (called "infiltration and inflow").
