Combined sewer overflow


Have you ever thought about what happens when it rains so heavily that the sewer system can’t cope with it? Exactly, the system will discharge its content at designed or random outlets.

Many cities combine the sewer with the transport of rainwater and created “combined sewers”. In case of storms, combined sewer overflow (CSO) events mean that water from those systems is discharged in an unfiltered way into the environment.

CSO events are serious problems for many cities that rely on a joint infrastructure to manage sanitation and surface runoff. During heavy rains or snow melt, sewers cannot keep up with the load, causing them to overflow and carry sewage, greywater from homes and wastewater from industrial facilities back into the streets. This can lead to an increase in harmful microbes and pollution, which are bad for human and pets health, as well as wildlife in and outside the water.

Fortunately, there are several strategies for creating poo-free streets. Green roofs are a great solution as they increase stormwater retention and detention through permeable surfaces that soak up falling rain and snow. Other stormwater management systems, including bioswales, rain gardens, and rainwater harvesting tanks, can also help reduce CSOs.

Until we find a better way to keep our sewage of the streets even during unpleasant conditions, these structures will remain critically important.

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