Hypoxia and eutrophication - a closer look at the water quality problems facing the Chicago area waterway system (CAWS) through a 3-D environmental fluid dynamics model

He, Yifan

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https://hdl.handle.net/2142/120399 Copy

Description

Title

Hypoxia and eutrophication - a closer look at the water quality problems facing the Chicago area waterway system (CAWS) through a 3-D environmental fluid dynamics model

Author(s)

He, Yifan

Issue Date

2023-04-25

Director of Research (if dissertation) or Advisor (if thesis)

Garcia, Marcelo H

Doctoral Committee Chair(s)

Garcia, Marcelo H

Committee Member(s)

• Valocchi, Albert J
• Cai, Ximing
• Tinoco, Rafael O
• Melching, Charles S.

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• EFDC
• numerical modeling
• water quality modeling
• eutrophication
• hypoxia
• nutrient

Abstract

With a population exceeding 9 million, the metropolitan area of Chicago generates approximately 1.3 billion gallons of treated wastewater daily. This nutrient-rich water is conveyed through the Chicago Area Waterway System (CAWS) to the Illinois River basin, then to the Mississippi River basin, and eventually to the Gulf of Mexico. Located at the mid-continental divide between the Great Lakes Basin and the Mississippi River Basin, the CAWS is a highly engineered water conveyance system connecting the two basins. Since the renowned flow reversal project’s completion in the early 20th century, water in the CAWS generally flows west towards the Illinois River. However, during extreme weather events, treated and untreated wastewater, along with contaminants from legacy nutrient sources like Bubbly Creek, can be released into Lake Michigan to prevent city flooding. Nutrient influxes from combined sewer overflows (CSOs) and legacy sources threaten the lake’s ecosystem and contribute to nutrient loads released into the Illinois River Basin during extreme rainfall events. Eutrophication, a process characterized by the enrichment of water bodies with nitrogen (N) and phosphorus (P) and subsequent algal mass proliferation, is a natural occurrence in aging aquatic systems such as lakes. However, anthropogenic activities have significantly accelerated eutrophication rates by substantially increasing nutrient loads in ecosystems. Excessive eutrophication has been observed worldwide, leading to undesirable phenomena such as harmful algal blooms (HABs) and depleted dissolved oxygen (hypoxia) in the water column. Although extensive studies have been conducted on nutrient and algae dynamics in lakes, bays, and coastal areas, riverine systems like the CAWS have received far less attention. Previous research in urban river systems focused predominantly on short-term transport and fate of pollutant loads from CSO discharges and Water Reclamation Plant (WRP) effluents during extreme storm events. Few have looked at the nutrient dynamics in the long run under substantially different climate conditions and its relation with algal growth in an urban setting. This dissertation aims to fill this gap and provide a better understanding of how nutrient loadings evolve in the long-term and how they impact eutrophication in the CAWS. An Environmental Fluid Dynamics Code (EFDC) model, supported by the U.S. Environmental Protection Agency (USEPA), was developed as a three-dimensional (3D) representation to simulate the hydrodynamics and water quality characteristics of the CAWS. The model was first calibrated and verified for two consecutive water years (2020/2021) under substantially different weather conditions. It was then applied to examine the water quality impacts of flow reversal events on the CAWS during an extreme event in May 2020. The extent and duration of flow reversals were analyzed, and pollutant loads to Lake Michigan were calculated. Although a notable reduction in lake-ward propagation of contaminated water from Bubbly Creek was observed, untreated sewage still had a profound local influence in Bubbly Creek and the Upper North Shore Channel (NSC) over an extended period. Model results revealed that even during non-extreme rainfall events, effluents from WRPs could form "hydraulic dams” and cause flow reversals. Elevated water surface elevation in the main channel of the CAWS during these periods could push WRP effluents into Bubbly Creek if CSO events do not occur. These phenomena lead to pollutant loads being trapped in relatively stagnant regions in the CAWS, and ultimately resulting in hypoxic conditions. The 3D model was then utilized to identify reaches prone to unnatural algal growth and evaluate various remediation scenarios. Model results suggested that algal growth in the Calumet-Sag Channel system was primarily driven by seeding from the Little Calumet and Grand Calumet River, and limited by light rather than the availability of N or P. Consequently, management practices such as phosphorus reduction from WRP effluents would have a negligible impact on algae concentrations in the CAWS, but their effects on downstream water bodies required further investigation. Source algae removal from the Little Calumet and Grand Calumet River provided most significant algae reduction downstream, but the effectiveness was highly climate dependent and sensitive to lake levels. Finally, the Mid-System Separation alternative proposed by the Great Lakes and Mississippi River Interbasin Study (GLMRIS) report was implemented in the EFDC model. Different scenarios with various augmented flow rates were examined to investigate their impacts on water quality characteristics in the CAWS. In general, the implementation of the proposed alternative would lead to increased pollutant loads to Lake Michigan, and the CAWS would be more prone to hypoxic conditions after storm events. The model’s total diversion accounting suggested that the 3200 cfs diversion limit mandated by the consent decree might be insufficient to maintain adequate dissolved oxygen levels in the CAWS. As decision-makers face increasingly challenging management scenarios, the comprehensive three-dimensional hydrodynamics and eutrophication model presented in this study can provide a valuable tool. The findings and insights from this modeling effort will also assist state and federal agencies in better managing the CAWS and its associated challenges.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Yifan He

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