Diagram of a sponge city

In conjunction with current flood prevention measures, it is also imperative to start aggressively converting New York into more of a sponge city. A sponge city is a type of urban design that absorbs rainwater until it is slowly filtered through drainage systems. The benefit of a sponge city is that it can reduce flood related damages to infrastructure, while also releasing stored water during times of drought. This full-scale conversion is the necessary next step, since a sponge city shows great resiliency towards floods from heavy storms while also combatting global warming, when compared to the average urban city.

Currently, Manhattan is implementing measures to convert itself to a sponge city, Green roofs which currently cover “less than 0.1% of New York City’s” buildings is a great tool towards the transition for a sponge city. However, green roofs are not only costly to implement, but also too heavy for most roofs to support. Current laws pertaining green roofs state that “all new buildings and alterations of existing buildings where the entire existing roof deck or roof assembly is replaced must provide a sustainable roofing zone covering 100% of the roof”. This gives two options, either implementing a green roof or solar panels. However, this law should be revised to state that new developments must have a combination of green roofs and solar panels. In addition, since solar panels are more effective for high rise buildings, these structures would be suggested to have more solar panels than green roofs. The combination of these two will help decrease energy consumption, and limit the heat island effect that cities face during warmer seasons.

Alongside the re-evaluation of the sustainable rooftop laws, all combined sewer systems should be converted into a separate sewer system. A combined sewer system is problematic because it collects both wastewater and rainwater at the same time. During times of heavy rain, this type of collection method can make this system over exceed in capacity. When it exceeds, it “discharges excess [untreated] wastewater directly to nearby streams, rivers, or other water bodies”. The combination of untreated wastewater, debris, and other toxic materials along with the storm water is a source of pollution to these nearby water bodies. The separate sewer system is also a key element of sponge cities. This is because, in the case of overflow with a sponge city, water will still be filtered into the drainage system and sewer much slower than a non-sponge city. The steadier absorption of rain water will allow more time for the sewage plants to treat the water and remove any debris before it re-enters a nearby water body.

Finally, the use of more developments on various levels of land, particularly around areas that border any water body, is a useful added security towards the flood prevention systems that are currently underway.

Although flood protection barriers are essential toward creating a more resilient New York for the future, having a sponge city will ensure that New York will no longer be threatened by flood related deaths, and flood related building/ infrastructure damages.

Image: Construction of sponge cities underway