What is the effect of heavy rainfall on a combined sewer system?

Heavy rainfall significantly impacts a combined sewer system because it can overwhelm the system's capacity. In a combined sewer system, stormwater and sanitary sewage are transported in the same pipes. During periods of excessive rainfall, the amount of water entering the system increases dramatically, which may lead to situations where the system cannot handle the influx.

As a result, untreated sewage may back up and overflow into neighborhoods, creating public health hazards and environmental concerns. This situation arises because the system is designed to contain a limited volume of water; when that volume is exceeded, the excess may be discharged directly into streets, homes, or local waterways.

Understanding the dynamics of a combined sewer system and the impact of heavy rainfall is crucial for effective management and maintenance planning. This knowledge helps utility operators implement strategic measures to mitigate the risk of backups and overflows during rainy seasons.