Sponge Park
This nice idea isn't new or unique. Stormwater retention for recharge to groundwater or for slow release to surface water (like the Gowanus Canal) has a secondary benefit by improving water quality. Stormwater basins filter out metals and organic contaminants in urban runoff and contaminants can be periodically removed by scarifying the basins during regular maintenance. There is a huge technical problem of inadequate open space to contain a large enough volume to ease the stormwater overload of a combined storm-sanitary sewer in an urban setting like New York City. Constructing sponge parks or other stormwater retention structures would require a much larger land commitment than would be feasible in densely populated cities like New York.
