Preparing the San Francisco Sewer System for the Looming Compound Challenge of Climate Change Induced Rainfall, Extreme Tides, and Sea Level Rise

San Francisco’s (City) combined sewer system collects and treats most of the City’s dry-weather flow and stormwater. When larger magnitude rainfall events occur, a portion is discharged to the San Francisco Bay or Pacific Ocean at outfalls. Climate change may induce increases in precipitation magnitude as well as increased shoreline water levels caused by a combination of sea level rise and extreme tides. Higher water levels will require additional backflow prevention which will further hydraulically constrain system relief in wet weather. The City has analyzed various combinations of these stressor variables along with anticipated changes over time to the collection system network assets. The analysis evaluated the severity of consequences caused by higher shoreline water levels across different magnitude storm events and the extent to which system operation may be compromised. Based on the analysis, the City is better informed as to estimates of additional pumping, storage, and operational flexibility that may be needed.