EXECUTIVE SUMMARY

This study was performed to investigate the reduction in flood peaks and im-provement in water quality with the Chicago Tunnel and Reservoir Plan (TARP) Phases I and II downstream of Lockport to Peoria. The reduced peak flows and stages will provide some relief from severe flooding, thus reducing flood damage and posing less danger to the levees along the river. This study also investigated the po-tential improvement in water quality of the Illinois River from treatment of essen-tially all combined sewer overflows (CSOs) as envisioned with TARP Phase II. Both hydraulic/hydrologic and water quality analyses were done by using TARP Phase I alone and in conjunction with Phase II. Most of the benefits in the reduction of peak flows downstream of Lockport are due to TARP Phase II, whereas improvements in water quality are due to both phases of TARP. For TARP Phase I simulations, 6,602 acre-feet of tunnel storage were used. For TARP Phase II simulations the volume included the Chicago Underflow Plan (CUP) reservoir storage capacity (46,700 acre-feet). O’Hare System has been exclud-ed from the simulations