The I-35 Capital Express Central Drainage Tunnel and Pump Station is taking shape in Austin, Texas, bringing years of hydraulic modeling and design into reality. The stormwater drainage system is a critical component of the larger I-35 Capital Express Central project and includes multiple drop shafts, drainage tunnels, a pump station, discharge structure, and river outfall.  

To support the design, Verdantas conducted computational fluid dynamics (CFD) analyses and physical hydraulic modeling of multiple components within the stormwater system. CFD provided detailed insight into three-dimensional flow behavior and allowed the team to evaluate system performance across a range of potential storm scenarios. The analyses examined critical hydraulic conditions including pump approach flow, energy dissipation, air entrainment and venting, and overall system performance.  

CFD and scaled physical modeling were also used to evaluate the pump station intake against Hydraulic Institute ANSI/HI 9.8-2024 criteria and assess the potential for scour at the Colorado River outfall. Together, the numerical and physical modeling provided complementary tools for evaluating complex hydraulic behavior, verifying design performance, and informing the system before construction.  

As construction progresses, key elements evaluated during the modeling program, including the drop shafts, rectangular pump intake structure, approach tunnel, and screen channels, are now taking shape in the field. The project demonstrates how CFD and physical modeling can be used together to evaluate complex stormwater infrastructure and help move designs from analysis to implementation.

Project Highlights

• Computational Fluid Dynamics (CFD) modeling of multiple stormwater system components  
• Scaled physical hydraulic modeling at the Verdantas Flow Labs Alden Campus 
• Evaluation of pump approach flow and intake performance  
• Analysis of energy dissipation, air entrainment, and system venting  
• Evaluation against Hydraulic Institute ANSI/HI 9.8-2018 pump intake criteria  
• Assessment of potential scour at the Colorado River outfall  
• Evaluation of hydraulic performance across multiple storm scenarios