Modeling the hydrodynamics of Chicago Area Waterway System (CAWS) and nearshore areas in Lake Michigan: Investigation of different flow behaviors under low and high Lake Michigan level conditions

Since January 2013, the USGS streamgage in Lake Michigan at Chicago Lock (No. 04087440) has recorded a continuous rising of the lake water level. Earlier this year (2020), the instantaneous record of lake level hit +4.5 feet, in reference to the Chicago City Datum (CCD, 0 feet CCD = 579.88 feet above mean tide New York), and the daily-average level has been constantly higher than +3.5 feet, which is 6 feet higher than the lake level in 2013. High lake level has caused sand beach erosion hazards along the lakeshore, and has brought new challenges to the management of the Chicago Area Waterway System (CAWS). Previous works have been focused either on the lake front areas or the waterway system alone. The impact of the rising lake level on the hydrodynamics of the whole system has rarely been studied. In our work, we constructed a combined model of both Lake Michigan and CAWS using the open-source numerical solver TELEMAC, which is the first of its kind to have high-resolution results in both the waterway and the lake. The modeling result indicates that the flow in the Grand Calumet River has been reactivated and constantly contributes over 300 cubic feet per second discharge to the CAWS. In an extreme event, the time window to operate the controlling works, for the flooding pressure relief purpose, has become shorter. The model validation was performed using the USGS streamgage data from 2010 to 2020. The model was also tested using the extreme precipitation event in May 2020 in the City of Chicago. Other impacts of the rising lake level on water quality, sand beach erosion, city water intake and invasive spices prevention management will be investigated as well.