This project is part of the widening and reconstruction of the Central Tri-State (I-294) Tollway. This section of the project involves drainage improvements and bridge replacement at the Tri-State Bridge over Salt Creek.
2IM reviewed an existing HEC-RAS model developed by the Phase 1 Consultant and the DuPage County/FEMA FIS FEQ model of Salt Creek. DuPage and FEMA released draft maps changing the flood plain boundaries and elevations during the study that were developed using FEQ. IDNR-OWR wanted the FEQ model used in the evaluation of the bridge opening. The bridge is located on the Cook-DuPage County line. 2IM was responsible for updating both models to identify a bridge opening that would meet the IDNR-OWR permit requirements. The HEC-RAS model was extended downstream so that both models used a consistent downstream boundary condition. Alternative bridge opening combinations were modeled in both models