Minne Lusa Stormwater Conveyance Sewer Tunnel and Detention Basin Forebay Hydraulics

The design process for a new multi-facetted project can be complex and require a multi-disciplinary team. For the Minne Lusa Stormwater Conveyance Sewer Tunnel and Detention Basin Forebay consideration of flow capacity, hydraulic transients during filling of the tunnel, air management, and sediment deposition were all required. The objective of hydraulic design effort was to optimize the design for capacity, operations and maintenance, constructability, surge control and capital cost. AECOM and Northwest Hydraulic Consultants (NHC) addressed these design challenges with a suite of design tools including desktop hydraulic design, 1D numerical modeling, hydraulic transient analysis, and physical modeling. The overall effort demonstrated an efficient use of available design tools for developing a safe and robust project.The objectives of the project were to develop a design to significantly reduce untreated combined overflows in Omaha by conveying up to 56.63 m3/s of stormwater via a tunnel to a proposed stormwater detention basin utilizing two existing basins, and provide water quality benefits for the stormwater prior to discharging to the Missouri River. This design approach provided the necessary hydraulic information to develop a very efficient and robust design to divert stormwater out of the combined sewer system, reducing CSO’s and alleviating flooding problems in northeast Omaha. This approach to evaluating complex urban stormwater sewer system and flood control hydraulics is a method that can be used in many flood prone cities.