FYI about GSI: The Recipe for Green Stormwater Infrastructure Success New research highlights some of the ways planners can increase the social benefits and public acceptance of green stormwater infrastructure. Share Green stormwater infrastructure (GSI) has become an increasingly common way for cities to rely less on traditional "gray" infrastructure such as curbs, gutters, and drains to mitigate flooding and stormwater runoff. GSI is especially useful in legacy cities, usually older and often shrinking in population, with combined sewer systems (CSS) that manage both stormwater and sewage and are easily overburdened during heavy rainfall, forcing polluted waters to divert into nearby waterways.