320 - Rainfall Spatiotemporal Variability Effects on Adverse Flow Conditions in Urban Stormwater Systems: A Case Study of the Richmond Tunnel in San Francisco, California

Rapid urban expansion and the increasing frequency and intensity of extreme precipitation events bring new challenges to stormwater drainage systems. One of the underrecognized challenges is transient flow conditions leading to adverse multiphase flow interactions (AMFI), which essentially includes the formation, collapse, compression, and uncontrolled release of entrapped air pockets within stormwater sewers. AMFI forces can cause sewer overflows, displace manhole covers, and damage drainage infrastructure. Conventional methods for designing and evaluating urban water drainage systems commonly use synthetic design storms that have highly idealized spatial and temporal distributions. Design storms neglect fine-scale rainfall characteristics, which we hypothesize are important for AMFI predictions and the activation of air and water interactions. In this study, high-resolution gridded weather radar rainfall data is used to simulate flow conditions in a sewershed in San Francisco using the EPA’s Storm Water Management Model. Flow pressurization and air pocket entrapment are analyzed based on numerical simulations for the Richmond tunnel system in San Francisco under a wide range of stormwater inflows. We hypothesize that the relationship between rainfall spatiotemporal variability and highly dynamic flow transients can help to identify the locations and causes of fast-changing flow conditions that lead to AMFI. This work will aid in the design and operation of stormwater management systems in quickly changing urban landscapes and climate conditions.