Evaluation of Methods to Reduce Backflows from the Chicago Waterway System to Lake Michigan

摘要

A detailed study of seven historic backflow from the Chicago WaterwaySystem (CWS) to Lake Michigan events (including the 2nd and 4th largest since 1965)was done to evaluate changes in waterway operation procedures to determine ifbackflows could be avoided or reduced in volume. The study applied a dynamicwavesimulation model to the CWS at a 15-minute time step combining measuredinflows for the major tributaries, combined sewer overflow (CSO) pump stations, andwater reclamation plants with simulated gravity CSO flows computed by the U.S.Army Corps of Engineers. The simulated CSO inflows were confirmed against adetailed mass balance approach for four storms and the peak flows from the twoapproaches were found to be remarkably similar. It was found that the hydrauliccapacity limitations of the Chicago Sanitary and Ship Canal (CSSC) preventedchanges in operations at the Lockport Powerhouse and Controlling Works fromsubstantially reducing backflows. The maximum discharge through the CSSC isaround 19,500 cfs whereas inflows may peak at 40,000 to 50,000 cfs and flowscannot drain away fast enough to avoid having to allow backflows to Lake Michigan.These backflows cannot be avoided until the reservoirs of the Tunnel and ReservoirPlan (TARP) are completed.