Hydraulic Calibration of An Unsteady Flow Model for the Chicago Waterway System

The flow and the water-quality processes in the Chicago Waterway System (CWS) are very complex and critical water-quality conditions may result under a wide range of flows. The dominant uses of the CWS are for commercial and recreational navigation and for urban drainage. The water-quality model QUAL2E has been previously developed for water-quality planning and management purposes for the CWS. Due to its applicability only for steady and low flows, QUAL2E cannot solve the problems related to reverse flow of the Chicago River, impact of reduced discretionary diversions from Lake Michigan, changes in runoff and nonpoint source loads resulting from the Tunnel and Reservoir Plan (TARP). The water quality and flow in the CWS change very frequently. So a water-quality model that can simulate water-quality processes under unsteady flow conditions is necessary for water-quality management. The DUFLOW model developed in The Netherlands was selected for simulation of the CWS. The model was run at a 15-min. time step for 8 long periods of complete data during the period August 1, 1998 to July 31, 1999. The main objective of this study is to construct an accurate hydraulic model for unsteady-flow conditions on the CWS so that it could be coupled with water-quality simulation routines and used for water-quality planning and management. Comparison of measured and simulated stage data is good at all locations. The stage simulation agreed with the measured data nearly always within one percent relative to the depth. In case of discharge, simulated flows at the upstream boundaries are substantially less than the measured values. This results because the measured and estimated flows into the CWS were 1.2 to 7. 7% higher than the measured outflow for the CWS. Thus, the flow imbalance was compensated for at the upstream stage boundaries