The Tulsa Metropolitan Utility Authority (TMUA) operates four flow equalization basins (FEBs) off-line in the Northern Service Area. These FEBs shave off the peak flow conveyed to the North Water Treatment Plant (NWTP) so as not to exceed the available flow capacity during intense wet weather conditions. One other expected benefit for the control of the peak flows is to prevent or minimize the risk of sanitary sewer overflows (SSOs).

The three collection system FEBs have not provided the benefits originally anticipated when they were constructed. Aside from faults in facility equipment and the loss of remote capabilities, it appeared that the existing operation of the FEBs was not optimal to divert the maximum volume when required to protect the NWTP. The FEBs were not used often enough and up to their maximum storage capacities.

As part of the FEBs flow monitoring and SCADA improvement project, Tetra Tech CSO provided the wet weather performance evaluation of the FEBs that included both the hydraulic performance of the facilities and the TMUA's ability to monitor and control diversion in and out of the basins. The deficiencies were characterized and improvements were recommended to allow for the benefits originally intended. The main tasks included:

• Extensive testing of diversion and pumping capacities at the facilities;
• Hydraulic capacity analysis of the sewer network's main component (the four FEBs, main interception trunks, two main lift stations, and the plant’s headworks);
• Hydraulic modeling of the collection system (942 miles of pipes), including the FEBs, using InfoWorks CS;
• Flow responses modeling and controls in the main interception system to evaluate alternative diversion schemes with the goal of improving the facilities' capability of diverting flow out of the collection system during various wet weather events;
• Simulation runs for control scenarios in order to improve storage use;
• Descriptions/recommendations regarding improved control set-ups and opportunities.

The improvement project is currently in the design stage for implementation.