The City of Portland, Oregon has cause to model instances of street flooding in the vicinity of hydraulic drop structures that feed into the Willamette combined sewer overflow tunnel system. Reproducing the events with a collection system model based on the U.S. EPA's Storm Water Management Model (SWMM) requires the representation of friction losses in the vortex generator structures. A modeling study was undertaken to better understand flows and losses in these structures, leading to

more »

... ts to the City's collection system model to benefit the assessment of mitigation alternatives. A conceptual approach to representing the head losses in vortex structure generators within a SWMM-based modeling framework was developed, and the general applicability of the approach was tested through a series of computational fluid dynamics (CFD) model simulations covering a range of flow conditions. The CFD modeling demonstrated that the conceptual approach could represent head losses under the conditions of primary interest, which were fully submerged conditions with the potential to cause surface flooding. When the approach was implemented in SWMM, the observed flooding events were qualitatively reproduced.