The current system combines sewage and stormwater, which can cause sewage overflows during heavy rains.
"The project will replace as much as one-third of the city's existing impervious cover – about 4,000 acres – with natural or porous surfaces that can intercept stormwater, store it, and then release it at a controlled rate.
Proposals include natural water storage and filtering solutions such as rain gardens (native vegetation planted near waterways), kerbside planters and green rooftops. Porous asphalt, concrete and paving slabs will also be installed in car parks and on streets. Taken together, these technologies should prevent between 5 and 8 billion gallons of wastewater from overflowing each year – that's up to 50% of the total for the area. Other benefits would include the creation of 250 green jobs each year, increased carbon sequestration from the vegetation, and a boost in recreational space."