Hydraulic modeling and analysis of inline hydrodynamic separator units

Provision C.10 of the Municipal Regional Stormwater Permit Order No. R2-2022-0018, issued by the California Regional Water Quality Control Board requires the City of San José and neighboring jurisdictions to implement trash control measures to reduce trash entering waterways and San Francisco Bay. As such, the City of San José identified and prioritized locations which generate high amounts of trash and determined large full trash capture units, including inline hydrodynamic separators, are a preferred approach to reduce trash entering the waterways. The objectives of this study were to determine an appropriate model development approach using InfoWorks ICM modeling software, present model calibration results to predict the hydraulic performance of inline hydrodynamic separator units, and draw conclusions on the hydraulic design parameters for hydrodynamic separator unit installation projects for urban, residential areas. The model results confirmed that the timing of release of flow after a storm event is dependent on the level of clogging in the inline hydrodynamic separator unit. The calibrated models for two urban systems had shown that hydraulic design of an inline hydrodynamic separator may be performed by modeling the bypass weir which will provide the bare minimum representation of the inline hydrodynamic separator’s hydraulic conveyance opportunity while obtaining the peak hydraulic grade line, regardless of clogging; however, it will not act accordingly after storm events.

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