As part of the North Houston Highway Improvement Project (NHHIP), TXDOT required a stormwater pump station capable of managing 100-year, 24-hour design inflows from two directions. The St. Emanuel Pump Station’s dual-inlet configuration and high capacity—over 100,000 GPM—posed significant hydraulic challenges, particularly in meeting ANSI/HI 9.8-2018 standards. Risks included air-entraining vortices, excessive swirl, and pre-rotation near pump intakes, all of which could compromise pump performance and longevity.

Verdantas Flow Labs conducted a detailed physical hydraulic model study at a 1:5.3 geometric scale, supported by complementary CFD simulations. The model included all critical hydraulic features: dual 108-inch influent sewers, a central screening channel, wet wells, pump bays, and sump pits. Testing was conducted in three phases—baseline, modification, and documentation—using dye visualization, swirl meters, pitot tubes, and velocity traverses to evaluate flow patterns, vortex formation, and swirl angles.

Initial baseline testing revealed non-compliance with HI standards, including swirl angles exceeding 30°, and persistent Type II and III subsurface vortices. These findings prompted a series of design modifications:

• Raised bay walls to prevent cross-flow and stabilize approach conditions
• Picket fence flow straighteners to reduce swirl and improve flow symmetry
• Curtain walls to control flow direction and reduce vortex formation
• Fillets and splitters to guide flow axially into pump inlets
• Adjusted baffle wall slot heights to balance flow distribution

Each modification was iteratively tested and refined. Final documentation testing confirmed that all pumps met ANSI/HI 9.8-2018 criteria. Swirl angles were reduced to an average range of 0.5° to 4.2°, with short-term maximums below 7° for all conditions. No unacceptable surface or subsurface vortices were observed, and velocity profiles at pump intakes were within ±10% of the area average, with standard deviations well below the 10% threshold.

This comprehensive modeling effort ensured the hydraulic integrity of one of Texas’s largest stormwater pump stations, supporting reliable performance under extreme storm conditions.