Implementation of three-dimensional eutrophication model of Bubbly Creek, Chicago, Illinois

The Chicago Area Waterways System (CAWS) is a highly branched complex consisting of natural rivers and artificial canals. Known for its flow reversal project done in the early 20th century, the CAWS now links Lake Michigan with the Mississippi watershed, and the water generally flows westward, away from the lake. This is to prevent highly polluted water from entering the lake during storm events which could contaminate Chicago’s main drinking water source. It has been found that during extreme weather events, the water level in the Chicago River can be higher than the water level in the lake, and to prevent flooding in the city, the water has to be allowed to flow back to the lake. This could cause contamination of the drinking water source and the close down of beach areas in the summer months. One of the main sources of contaminants in the CAWS is Bubbly Creek, a highly contaminated channel that joins Chicago River’s South Branch near Ashland Avenue. It served as the disposal area for Chicago’s largest stockyard, Union Stockyard during the late 19th century, and tons of animal remains were deposited onto the river bed everyday. The decomposition of those organic substances has depleted the dissolved oxygen in the water column, and annihilated most aquatic lives. Other issues such as stagnant flow conditions during dry weather season and contaminants brought in by highly polluted flow discharged from Racine Avenue Pumping Station (RAPS) exasperate the degradation of the ecosystem. Extensive studies have been done in the area to study the transport and fate of the contaminants, but a detailed three-dimensional eutrophication model for Bubbly Creek has never been established due to constraints in computational power. With the development of high speed computers and advancement in parallel programming, computational power has increased dramatically, and is no longer a barrier for the development of more complex three-dimensional models. Thus, in this research, a three-dimensional eutrophication model based on the EPA (Environmental Protection Agency) approved three-dimensional model EFDC (Environmental Fluid Dynamics Code) is developed to study the flow and water quality characteristics in Bubbly Creek for the period of May 2009. The validation of the simulation results is done with the help of measured data provided by USGS (U.S. Geological Survey) and MWRDGC (Metropolitan Water Reclamation District of Greater Chicago). It has been found that the water quality in Bubbly Creek is predominantly controlled by combined sewer overflows (CSO) from RAPS. The dissolved oxygen (DO) level in Bubbly Creek could reach near saturation when pumping activity occurs, and would rapidly decrease to near zero after the pumping activity has stopped. The contaminants brought in by the discharge from RAPS not only impair the local ecosystem in Bubbly Creek, but also travel all the way to the downstream boundary at Stickney and deteriorate the DO concentration along the way