Tetra Tech evaluated the wet weather performance of three excess flow diversion basins (EFDBs) that the Tulsa Metropolitan Utility Authority (TMUA) operates in the city’s Northside Service Area. This included the hydraulic performance of the facilities and TMUA’s ability to monitor and control diversion in and out of the storage basins.

The TMUA constructed the three basins in the late 1990s to reduce the peak flow conveyed to the Northside Wastewater Treatment Plant. The EFDBs were designed also to prevent sanitary sewer overflows during heavy rainstorms by reducing flows in the main sewers. The EFDBs have not provided the intended benefits.

Tetra Tech extensively tested the diversion and pumping capacity of the EFDBs and identified hydraulic inefficiencies and deficiencies in the EFDB’s pumping facilities.

Using the InfoWorks CS platform, Tetra Tech developed a hydraulic model, including the EFDBs, of a collection system with 942 miles of pipes. Our team used the model to evaluate alternative diversion schemes to improve the facilities’ ability to divert flow into the EFDBs during wet weather events. TMUA selected an alternative that increased diversion capacity without installing in-line gates or control structures and facilitated easier maintenance.

Tetra Tech also updated the Supervisory Control and Data Acquisition (SCADA) system and established additional monitoring points to provide operators with sufficient information to monitor and manage flows.

Based on the collection system modeling, Tetra Tech developed operational strategies to manage flow to the wastewater treatment plant while reducing flow levels in the main interceptors. Various levels of automation were defined and the selected level of automation was programmed into the main computer’s Wonderware software.

The new diversion scheme will save a minimum of $15 million in interceptor costs and reduced capital improvement project funding. The improvement project is currently in the design phase.