Prepared in cooperation with the U.S. Environmental Protection Agency–

Great Lakes Restoration Initiative

Hydrology of and Current Monitoring Issues 

for the Chicago Area Waterway System, 

Northeastern Illinois

Scientific Investigations Report 2015–5115

U.S. Department of the Interior

U.S. Geological Survey
Front cover: A USGS crew prepares for an acoustic Doppler current meter discharge measurement on the South Branch of the 

Chicago River, part of the Chicago Area Waterway System. 
Hydrology of and Current Monitoring Issues 

for the Chicago Area Waterway System, 

Northeastern Illinois

By James J. Duncker and Kevin K. Johnson

Prepared in cooperation with the U.S. Environmental Protection Agency–

Great Lakes Restoration Initiative

Scientific Investigations Report 2015–5115

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Sally Jewell, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Duncker, J.J. and Johnson, K.K., 2015, Hydrology of and current monitoring issues for the Chicago Area Waterway 

System, northeastern Illinois: U.S. Geological Survey Scientific Investigations Report 2015–5115, 48 p., http://dx.doi.

org/10.3133/sir20155115.

ISSN 2328-0328 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Chronology of Construction and Regulation for the Chicago Area Waterway System ...........3

Chicago Area Hydrology...............................................................................................................................5

Precipitation...........................................................................................................................................5

Groundwater..........................................................................................................................................6

Surface Water.......................................................................................................................................9

North Shore Channel ................................................................................................................10

North Branch Chicago River ...................................................................................................12

Mainstem Chicago River .........................................................................................................14

South Branch Chicago River ...................................................................................................20

Southeast Fork of the South Branch Chicago River (Bubbly Creek) ................................22

Chicago Sanitary and Ship Canal ...........................................................................................22

Summit Conduit ..........................................................................................................................31

Calumet Sag Channel ...............................................................................................................32

Little Calumet River ...................................................................................................................40

Current Monitoring Issues for the Chicago Area Waterway System .................................................40

Lake Michigan Diversion Accounting ............................................................................................41

Regional Flooding ...............................................................................................................................41

Power Plant Thermal Load Modeling..............................................................................................42

Infrastructure Design ........................................................................................................................42

Waterway Separation ........................................................................................................................45

Summary .......................................................................................................................................................46

References Cited..........................................................................................................................................47

Figures

1. Map showing the Chicago Area Waterway System study area, northeastern Illinois.....2

2. Historical engineering drawings of the map, profile, and cross-sections of the Main 

Drainage Channel for the Chicago Sanitary District of Chicago, from Chicago to 

Joliet, Illinois..................................................................................................................................3

3. Map showing the Tunnel and Reservoir Plan service area, Chicago, Illinois ....................4

4. Schematic drawing of the hydrologic cycle ............................................................................5

5. Maps showing A, pre-diversion, and B, post-diversion surface drainage in Chicago, 

Illinois, and vicinity .......................................................................................................................6

6. Map showing lines of equal precipitation pattern for the 2012 water year, Chicago, 

Illinois, and vicinity .......................................................................................................................6

7. Schematic cross-section diagram showing the elevations of the water table, local 

combined sewer invert, and Chicago Sanitary and Ship Canal water-surface 

elevation in the Pilsen neighborhood on the south side of Chicago, Illinois. .....................7
iv

8. Map showing the potentiometric surface of the deep sandstone aquifers in the 

Chicago area, northeastern Illinois, fall 2007...........................................................................8

9. Graph showing water-surface profile data for the Chicago Area Waterway System, 

Chicago, Illinois, and vicinity during an April 17–18, 2013, storm and the extent of 

drawdown of the water surface at points along the waterway ...........................................9

10. Map showing the Chicago Area Waterway System with the North Shore Channel, 

Chicago, Illinois, and vicinity ....................................................................................................11

11. Graph showing mean daily discharge for the North Shore Channel at Wilmette, 

Illinois, for the 2003 water year, which is the last year of record.......................................12

12. Map showing the Chicago Area Waterway System, including the North Branch 

Chicago River and U.S. Geological Survey streamflow-gaging stations, Chicago, 

Illinois, and vicinity .....................................................................................................................13

13. Graph showing mean daily discharge for the streamflow-gaging station (05536105) 

on the North Branch Chicago River at Albany Avenue, Chicago, Illinois, and vicinity, 

for the 2012 water year..............................................................................................................14

14. Photograph showing the concrete control structure at the confluence of the North 

Branch Chicago River and the North Shore Channel, Chicago, Illinois, and vicinity......15

15. Map showing the Chicago Area Waterway System and the mainstem of the 

Chicago River, Chicago, Illinois ................................................................................................16

16. Data from acoustic Doppler current profiler measurements in the mainstem of the 

Chicago River near Columbus Drive in Chicago, Illinois showing: A, typical low-flow 

water velocity magnitude and B, direction; C, typical high-flow velocity magnitude 

and D, direction; E, reverse flow magnitude and F, direction..............................................17

17. Graph showing gage heights for the Chicago River at Columbus Drive at Chicago, 

Illinois, streamflow-gaging station, hourly precipitation measured at the Chicago 

Lock, and gate settings at the Chicago River Controlling Works during the April 

2013 storm....................................................................................................................................20

18. Map showing the Chicago Area Waterway System including the South Branch of 

the Chicago River and the Southeast Fork of the South Branch of the Chicago River, 

Chicago, Illinois, and vicinity ....................................................................................................21

19. Graphs showing discharge and water-surface profiles for the Chicago Area 

Waterway, Illinois, during the April 17–23, 2013, storm: A, rising storm discharge 

hydrograph and canal drawdown, B, near peak of storm discharge and opening of 

the Chicago River Controlling Works, and C, the effect of flow reversal at the 

Chicago River Controlling Works on the water-surface elevation profile ........................23

20. Data from horizontal acoustic Doppler current profiler (H-ADCP) measurements 

May 25–27, 2009, for Bubbly Creek near 36th Street, Chicago, Illinois: A, water 

velocity, and B, discharge.........................................................................................................25

21. Map showing the Chicago Area Waterway System including the Chicago Sanitary 

and Ship Canal and Calumet Sag Channel, Chicago, Illinois, and vicinity ........................26

22. Graphs showing discharge for the Chicago Sanitary and Ship Canal near Lemont, 

Illinois, for: A, a normal pool elevation with highly unsteady flow conditions, 

April–May 2013, B, a typical dry-weather pattern showing cycle of ponding and 

increased flows, October 12, 2013, and C, a wet weather pattern showing the 

pre-storm drawdown and subsequent flood wave, April–May 2013 .................................27

23. Graph showing mean daily effluent discharge for the Metropolitan Water 

Reclamation District of Greater Chicago–Stickney Water Reclamation Plant, 

Chicago, Illinois, for the 2012 water year................................................................................28

24. Graph showing mean daily discharge for the Chicago Sanitary and Ship Canal near 

Lemont, Illinois, for the 2012 water year.................................................................................28
v

25. Graph showing data from low-, medium-, and high-flow acoustic Doppler current 

profiler measurements in the Chicago Sanitary and Ship Canal near Lemont, Illinois, 

showing: A, low-flow cross-section water velocity contour; B, low-flow plan view 

of depth-averaged velocity magnitude and direction; C, medium-flow cross-section 

velocity contour; D, medium-flow plan view of depth-averaged velocity magnitude 

and direction; E, high-flow cross-section velocity contour; and F, high-flow plan 

view of depth-averaged velocity magnitude and direction.................................................29

26. Photograph showing the entrance to the Summit Conduit and the location of the 

streamflow-gaging station ........................................................................................................32

27. Graph showing mean daily discharge for the Summit Conduit at Summit, Illinois, 

for the 2012 water year..............................................................................................................32

28. Map showing the Chicago Area Waterway System including the Calumet-Sag 

Channel, Chicago, Illinois, and vicinity....................................................................................33

29. Graph showing mean daily discharge at the U.S. Geological streamflow-gaging 

station on the Calumet Sag Channel near Route 83 at Sag Bridge, Illinois, for the 

2012 water year...........................................................................................................................34

30. Graphs showing data from low- and high-flow acoustic Doppler current profiler 

measurements in the Calumet Sag Channel near Route 83 at Sag Bridge, Illinois, 

showing: A, low-flow cross-section water velocity contour, B, low-flow plan view 

of depth-averaged velocity magnitude and direction, C, high-flow cross-section 

velocity contour, and D, high-flow plan view of depth-averaged velocity 

magnitude and direction............................................................................................................35

31. Graph showing mean daily effluent discharge for the Metropolitan Water 

Reclamation District of Greater Chicago Calumet Water Reclamation Plant in 

Illinois for the 2012 water year .................................................................................................37

32. Screen capture and schematic diagrams showing data from acoustic Doppler 

current profiler measurements in the Calumet River near the Thomas J. O’Brien 

Lock and Dam, Chicago, Illinois, showing: A, complex water velocity patterns 

adjacent to the lock and dam, B, circulation patterns in the Calumet River below 

the lock and dam, and C, the complex velocity patterns near the 

Calumet Water Reclamation Plant outfall ..............................................................................38

33. Graph showing daily mean discharge for Tinley Creek near Palos Park, Illinois, 

for the 2012 water year..............................................................................................................41

34. Photograph showing the coal-fired power plant at Romeo Rd along the Chicago 

Sanitary and Ship Canal near Romeoville, Illinois.................................................................43

35. Map showing synoptic water temperature data from the upper Chicago Sanitary 

and Ship Canal collected February 2012 and the sharp increase in water 

temperature at the power plant discharge locations...........................................................44

36. Photograph showing construction of the river walk along the mainstem of the 

Chicago River ..............................................................................................................................45

37. Map showing one of the waterway separation scenarios proposed by the U.S. Army 

Corps of Engineers Great Lakes and Mississippi River Interbasin Study .........................46

Tables

1. Summary of backflow events on the Chicago Area Waterway System, Chicago, 

Illinois, and vicinity, 2000–14 .....................................................................................................10

2. Long-term U.S. Geological Survey streamflow-gaging stations on the North Branch 

of the Chicago River and its tributary streams, Chicago, Illinois, and vicinity .................12
vi

Conversion Factors

Inch/pound to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32 

Datum

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29) and Chicago City Datum (CCD), which is 579.48 feet above NGVD 29.

Elevation, as used in this report, refers to distance above the vertical datum. 

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).
Hydrology of and Current Monitoring Issues for the 

Chicago Area Waterway System, Northeastern Illinois

By James J. Duncker and Kevin K. Johnson

Abstract

The Chicago Area Waterway System (CAWS) consists of 

a combination of natural and manmade channels that form an 

interconnected navigable waterway of approximately 90-plus 

miles in the metropolitan Chicago area of northeastern Illinois. 

The CAWS serves the area as the primary drainage feature, a 

waterway transportation corridor, and recreational waterbody. 

The CAWS was constructed by the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC). Completion 

of the Chicago Sanitary and Ship Canal (initial portion of the 

CAWS) in 1900 breached a low drainage divide and resulted 

in a diversion of water from the Lake Michigan Basin. A U.S. 

Supreme Court decree (Consent Decree 388 U.S. 426 [1967] 

Modified 449 U.S. 48 [1980]) limits the annual diversion from 

Lake Michigan. While the State of Illinois is responsible for 

the diversion, the MWRDGC regulates and maintains water 

level and water quality within the CAWS by using several 

waterway control structures. The operation and control of 

water levels in the CAWS results in a very complex hydraulic 

setting characterized by highly unsteady flows. The complexity leads to unique gaging requirements and monitoring issues. 

This report provides a general discussion of the complex 

hydraulic setting within the CAWS and quantifies this information with examples of data collected at a range of flow 

conditions from U.S. Geological Survey streamflow gaging 

stations and other locations within the CAWS. Monitoring to 

address longstanding issues of waterway operation, as well as 

current (2014) emerging issues such as wastewater disinfection and the threat from aquatic invasive species, is included in 

the discussion.

Introduction 

The Chicago Area Waterway System (CAWS) consists 

of a combination of natural and manmade channels that form 

an interconnected navigable waterway of approximately 

90-plus miles (mi) in the metropolitan Chicago area (fig. 1) of 

northeastern Illinois. The CAWS is a principal component of 

the regional hydrology of the Chicago metropolitan area. The 

CAWS functions as an important waterway for both commercial and recreational transportation and as a conduit for 

the discharge of wastewater effluent and stormwater runoff 

from the region. Water levels and flows within the CAWS are 

regulated through a series of control structures operated and 

maintained by the Metropolitan Water Reclamation District of 

Greater Chicago (MWRDGC). The CAWS was constructed in 

response to the growing population and the need for improvements to the natural drainage system in the region. The physiography of the Chicago area prior to settlement consisted of a 

low-lying region with sluggish streams and wetlands.

The primary canals and infrastructure of the CAWS were 

constructed from 1892 to 1939 (Hill, 2000). Since completion 

of the CAWS, water levels and flows within the waterway 

have been maintained on the basis of water levels at various 

points along the waterway. Theoretical equations were used 

to estimate flows at the control structures. Following a 1980 

U.S. Supreme Court ruling (Consent Decree 388 U.S. 426 

[1967] Modified 449 U.S. 48 [1980]), the U.S. Geological 

Survey (USGS) in 1984 installed an acoustic velocity meter 

(AVM) streamflow-gaging station on the Chicago Sanitary and 

Ship Canal at Romeoville, Ill. The AVM streamflow-gaging 

station provided a means for the direct measurement and 

near real-time monitoring of streamflow within the CAWS. 

Analysis of the stage, velocity, and discharge data from the 

AVM streamflow-gaging station at Romeoville revealed 

the complex hydraulic setting that is present throughout the 

CAWS. Since the 1984 installation of the streamflow-gaging 
2 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

Figure 28

waterway section

Figure 21

waterway

section

Figure 18

waterway 

section

Figure 12

waterway 

section

Figure 10

waterway 

section

Figure 15 waterway 

section

Figure 7

waterway

section

Chicago

Sanitary

and

Ship

Canal

Calumet Sag

Creek

Cr

Willow

South Branch

Chicago River

North 

Shore 

Channel

LAKE

MICHIGAN

Des Plaines River

North

Des Plaines River

Grand Calumet R

Calumet R.

River

 Branch 

Chicago 

Channel

Salt

Little Calumet R.

Wilmette Pumping 

Station

Chicago River

Controlling Works

Thomas J. O'Brien

Lock and Dam

Lockport Powerhouse and

Lockport Lock and Dam

Lockport

Controlling

Works

05536995

(Chicago Sanitary 

and Ship Canal

at Romeoville)

05536890

(Chicago Sanitary 

and Ship Canal near Lemont)

05536101

(North Shore 

Channel at 

Wilmette)

05536123

(Chicago River 

at Columbus

Drive at Chicago)

05536358

(Calumet River below

O'Brien Lock and Dam at Chicago)

05536700

(Calumet Sag Channel 

near Rt. 83 at Sag Bridge)

05536118 (North Branch

Chicago River at Grand

Avenue at Chicago)

05536105 

(North Branch Chicago

River at Albany 

Avenue at Chicago)

05536000

(North Branch

Chicago River

at Niles)

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

ILLINOIS

INDIANA

LAKE COUNTY

COOK COUNTY

Map area

ILLINOIS

42°15'

41°45'

41°30'

42°00'

88°15' 88°00' 87°45' 87°30'

Lake Michigan diverted

 watershed

U.S. Geological Survey 

 streamflow-gaging station, 

 identifier, and name

Control structure

EXPLANATION

05536101

(North Shore 

Channel at 

Wilmette)

10 MILES

10 KILOMETERS

5

0 5

0 Base from U.S. Geological Survey, 

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o

 and 33o, 

central meridian -89o

.

Figure 1. The Chicago Area Waterway System study area, northeastern Illinois. (NB, North Branch)
Introduction 3

station at Romeoville, the USGS has worked closely with 

local, State, and Federal partners to advance the understanding 

of the hydrology of the CAWS. The USGS, with support and 

cooperation from the U.S. Environmental Protection Agency–

Great Lakes Environmental Restoration Initiative, compiled 

this report to describe the hydrology of the CAWS.

Purpose and Scope

The purpose of this report is to describe the hydrology 

of the metropolitan Chicago area and the primary hydrologic 

components of the CAWS in quantifiable engineering terms. 

The report was prepared in cooperation with the U.S. Environmental Protection Agency’s Great Lakes Environmental 

Restoration Initiative.

The scope of this report is a description of the primary 

hydrologic components of the metropolitan Chicago area 

and specifically the CAWS. Recent focus on the CAWS with 

respect to a number of issues has highlighted the value of 

waterway data and an understanding of the complex hydrologic and hydraulic setting. This report discusses issues facing 

decision makers at a time when, due to regional economic 

conditions, the level of CAWS monitoring is at a historic low. 

Chronology of Construction and Regulation for 

the Chicago Area Waterway System 

The CAWS was constructed from 1892 to 1939 to serve 

the Chicago region as an integral part of the region’s sanitation 

system and as an important waterway for the transportation of 

bulk goods (fig. 2). The purpose of the CAWS monitoring stations in the early days was initially very specific to operation 

and maintenance of the waterway. Water-level gages along 

the waterway recorded water-surface elevations, which were 

used by engineers to maintain a water-surface slope towards 

Lockport and away from the city of Chicago. Completion of 

the Chicago Sanitary and Ship Canal (CSSC) in 1900 resulted 

in the diversion of water from the Lake Michigan Basin to the 

Illinois River/Mississippi River Basin. A series of legal rulings regarding the diversion resulted in a 1980 U.S. Supreme 

Court decree that mandates the State of Illinois to monitor the 

CAWS as a component of Lake Michigan Diversion Accounting. This decree tasks the U.S. Army Corps of Engineers 

(USACE) to maintain a Lake Michigan Diversion Accounting, 

which relies on the USGS for accurate streamflow monitoring 

in the CAWS. In 1984, the USGS installed an AVM streamflow-gaging station on the CSSC at Romeoville, Ill., to monitor flows for Lake Michigan Diversion Accounting. 

Figure 2. Historical engineering drawings of the map, profile, and cross-sections of the Main Drainage Channel for the Chicago 

Sanitary District of Chicago, from Chicago to Joliet, Illinois. (Figs. 2 and 3 from Hill, 1896)
4 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

As environmental regulations developed in the 1960s 

and 1970s, State and Federal water-quality standards were 

established for the waterway (Copeland, 2010; Hines, 2012). 

The MWRDGC, as the operating agency for the waterway, 

installed a water-quality monitoring network along the waterway. Waterway operation procedures were modified to use the 

information from the water-quality monitoring network and 

incorporate flows to help meet the water-quality standards. 

In 1972 the MWRDGC, in order to comply with waterquality standards, adopted the Tunnel and Reservoir Plan 

(TARP), which is composed of a network of large underground tunnels (11–33 feet [ft] in diameter and referred to as 

“Deep Tunnel”) and several large storage reservoirs that connect to the CAWS (fig. 3). The TARP system presents a major 

change for regional hydrology and provides for flood control 

and the routing of combined sewer runoff in the region. The 

COOK COUNTY

ILLINOIS

INDIANA

Lake

Michigan

Riverside

Evanston

Chicago MAINSTREAM

TUNNEL SYSTEM

O'HARE

UPPER DES PLAINES

TUNNEL SYSTEM

THORNTON

RESERVOIR

CALUMET

TUNNEL

SYSTEM

DES PLAINES

TUNNEL

SYSTEM

Mc COOK

RESERVOIR

O’HARE

RESERVOIR

EXPLANATION

Service area

Water reclamation plant

Completed Deep Tunnel

Storage reservoir completed 

Storage reservoir under construction

Pumping station 

City

87°40'

88°00'

42°00'

41°40'

0 5 10 MILES

0 5 10 KILOMETERS

Figure 3. The Tunnel and Reservoir Plan service area, Chicago, Illinois.
Chicago Area Hydrology 5

Deep Tunnel system provides an outlet for combined sewer 

runoff that otherwise would have overflowed to the CAWS. 

The Deep Tunnel system provides some additional storage but 

is primarily designed to convey the combined sewer runoff to 

storage reservoirs that are under construction. When completed, the TARP system of tunnels and reservoirs will help 

mitigate flooding in the region.

Chicago Area Hydrology

The hydrologic cycle is depicted schematically (fig. 4) 

to outline how the components interact with each other. In 

the relatively flat urban setting of Chicago, the primary features of the hydrologic cycle include engineered structures. 

The engineered drainage system is designed to facilitate the 

rapid removal of excess stormwater from the area to prevent 

overland flooding, combined sewer overflows, and flooded 

basements.

Prior to the start of construction of the CSSC in 1892, the 

natural drainage for much of the Chicago area was towards 

Lake Michigan. The relatively flat, low-lying area that 

composed much of the city was surrounded by wetlands and 

was drained by low-slope sluggish streams. The mouths of the 

Chicago and Calumet Rivers were open to the lake, and shifting sandbars were present that affected the geometry of the 

river mouths. The diversion of water away from Lake Michigan initially began with the completion of the Illinois and 

Michigan Canal in 1848 and continued with the completion of 

the CSSC in 1900 (fig. 5). 

Precipitation

The climate of the Chicago area is classified as a humid 

continental (Changnon and others, 2004). The Illinois State 

Water Survey (ISWS) operates a network of 25 rain gages 

(fig. 6) in the Chicago area for Lake Michigan Diversion 

Accounting (Westcott, 2013). Average precipitation from the 

ISWS network (1990–2012) is 36.77 inches (in.). Long-term 

average annual precipitation for the National Weather Service 

rain gage at Chicago O’Hare Airport is 36.89 in. (1981–2010). 

Most of this precipitation falls in the form of rainfall. Average 

annual snowfall in the Chicago area is approximately 40 in. 

per year (Changnon and others, 2004). 

Figure 4. The hydrologic cycle (U.S. Geological Survey, 2014).
6 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

 





POST-DIVERSION - Circa 1920

PRE-DIVERSION

Lake

Michigan

Lake

Michigan Chicago Rivers

Des Plaines River

Chicago Rivers

Des Plaines River

Calumet 

Calumet 

Rivers

Rivers

Calumet-Sag

Channel

CSSC

0

0

5

5

10 MILES

10 KILOMETERS

EXPLANATION

A

B

Direction of flow

Control structure

 Streamflow-gaging station

Figure 5. A, pre-diversion, and B, post-diversion surface 

drainage in Chicago, Illinois, and vicinity.

Lake

Michigan

COOK

DUPAGE

COOK

WILL

ILLINOIS

INDIANA

25

25

23

25

25

31

31

33

33

31

27

27

29

29

29

29

27

27

27

27

27

27

88°00' 87°40'

42°00'

41°40'

0 5 MILES

0 5 KILOMETERS

EXPLANATION

25 Line of equal

 precipitation,

 in inches

Raingage location

 Figure 6. Lines of equal precipitation pattern for the 2012 water 

year, Chicago, Illinois, and vicinity. (Data are from the Illinois State 

Water Survey dense rain gage network [Westcott, 2013])

Groundwater

The groundwater component of the hydrologic cycle in 

the Chicago area is composed of an interconnected pathway 

of natural subsurface drainage consisting of groundwater flow 

through the soils and bedrock, but it also includes the subsurface sewer system to some extent. Precipitation infiltrates into 

soils and fill material to become shallow groundwater. Shallow 
Chicago Area Hydrology 7

groundwater moves through soils and fill material at varying rates controlled by the physical properties of the material 

(porosity and permeability) and hydraulic gradients (pressure 

head). The soils and fill material may be connected to local 

sewer systems to varying degrees. Many of the local sewers 

in the Chicago area are very old, brick-lined sewers that are 

susceptible to inflow and infiltration. Shallow groundwater 

monitoring wells in Chicago record a varying water-table surface (piezometric surface) that for much of the year is above 

the elevation of the local sewer system (fig. 7).

PZ

SMH

EXPLANATION

Fill

Piezometer identifier

Street-level manhole identifier

Material below fill

Sewer shaft

Sewer pipe

Top of well or sewer

Water level

Top of screen

Bottom of screen

570

575

580

585

590

595

Bubbly

Creek

PZ1-BI

SMH-1

Leavitt

SMH-2

Paulina

PZ3s-JH PZ3-JH

SMH-3 PZ2-CE

FEET

PZ4-CC

(Infiltration

Basin)

SMH-1

Leavitt

SMH-2

Paulina

Elevation, in feet above Chicago City Datum

Figure 7. Schematic cross-section diagram showing the elevations of the water table, local combined sewer invert, and Chicago 

Sanitary and Ship Canal water-surface elevation in the Pilsen neighborhood on the south side of Chicago, Illinois.
8 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

The thickness of the glacial till varies across the Chicago 

area (Piskin and Bergstrom, 1975). Silurian-age carbonate bedrock underlies the glacial till throughout the Chicago 

area (Kolata and Nimz, 2010). The Silurian dolomite forms a 

shallow bedrock groundwater aquifer. Sandstone and dolomite 

bedrock of Cambrian and Ordovician age form a deep bedrock 

aquifer (Burch, 2008; fig. 8). 

Figure 8. The potentiometric surface of the deep sandstone aquifers in the Chicago area, northeastern Illinois, fall 2007. (From Burch, 

2008)
Chicago Area Hydrology 9

Beneath the city streets of Chicago lies a vast network 

of sewers that facilitates the drainage of the metropolitan 

area. This network of sewers consists of local and interceptor sewers that convey sanitary and stormwater runoff in 

addition to industrial discharges. Underlying the Chicago 

metropolitan area at a much greater depth (110–330 ft below 

the land surface) is the MWRDGC Deep Tunnel (fig. 3). The 

Deep Tunnel is the tunnel portion of MWRDGC’s TARP. The 

100-plus mi network of four tunnel systems was completed in 

2006 and lies between 70 and 300 ft below the land surface. 

The tunnels were excavated in bedrock and, when the TARP 

project is completed, will drain combined sewer overflows and 

stormwater to three large storage reservoirs. The water in the 

reservoirs will then be pumped to wastewater-treatment plants 

before being treated and discharged to area waterways. 

Surface Water

The dominant features of the hydrology for the Chicago area are the surface-water components that make up the 

CAWS. These consist of a combination of natural channels 

and manmade canals that form the primary surface-drainage 

features. During dry weather, the hydraulic conditions found 

within the CAWS are typically a low-velocity setting with 

water levels maintained by control structures to facilitate navigation. During dry weather much of the waterway is affected 

by diurnal wastewater-effluent discharges. The navigable 

reaches of canal and river channels exhibit very unsteady flow 

characteristics. Many of the flow characteristics described by 

Jackson and others (2011) are found throughout the CAWS. 

Lockages, variable-flow control structures at the lakefront and 

downstream, wastewater-effluent discharges, power-plant and 

industrial withdrawals, and commercial and recreational boat 

traffic all contribute to the unsteady flow characteristics found 

throughout the CAWS. Water-quality conditions during dry 

weather are affected by the large volume of treated wastewater 

effluent in the channel, which can exceed 70 percent of the 

total volume of flow at times.

During wet weather, when storms are forecast for the 

Chicago area, the MWRDGC uses control structures (Lockport Powerhouse and Lockport Controlling Works) near 

the downstream end of the waterway near Lockport, Ill., to 

proactively draw down the water-surface elevation and create storage space within the CAWS channel for the influx of 

stormwater. Navigation depth requirements and the hydraulic 

properties of the CAWS channels limit the amount of drawdown that is possible from the downstream control structures. 

Although the drawdown near the Lockport control structures 

(River mile 291) may reach 10–11 ft below the normal pool 

elevation when all of the control structures are open, the drawdown near Sag Junction (River mile 302) may only be 3 ft, 

and the effect near the lakefront may not be noticeable (fig. 9). 

At times during extreme wet weather, the stormwater 

inflow to the CAWS channel may exceed the channel’s capacity. When this occurs, water levels within the CAWS may 

increase rapidly and approach flood levels. In order to prevent 

flooding, the MWRDGC then opens the lakefront control 

structures and backflows the river water into Lake Michigan. The MWRDGC has backflow capability at each of the 

three lakefront control structures. The MWRDGC maintains 

records of backflow events, backflow duration, and estimated 

backflow volumes. Table 1 shows the MWRDGC record of 

backflow events at the lakefront control structures since 2000.

Lockport (USGS)

Lemont (USGS)

Stickney (USGS)

Grand (USGS) Columbus (USGS)

Chicago Lock (USGS)

Sag Junction(MWRD)

Western (MWRD)

Chicago Lock Lake Michigan(USGS)

Lockport CW (USGS)

Water-surface elevation,

Romeoville (USGS)

in feet above Chicago City Datum

5

4

3

2

1

0

-1

-2

-3

-4

-5

-6

-7

-8

-10

-9

-11

River mile

290 295 300 305 310 315 320 325 330

Figure 9. Water-surface profile data for the Chicago Area Waterway System, Chicago, Illinois, and vicinity during an 

April 17–18, 2013, storm and the extent of drawdown of the water surface at points along the waterway. (MWRDGC, 

Metropolitan Water Reclamation District of Greater Chicago; USGS, U.S. Geological Survey)
10 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

Table 1. Summary of backflow events on the Chicago Area 

Waterway System, Chicago, Illinois, and vicinity, 2000–14. 

[From Metropolitan Water Reclamation District of Greater Chicago (2014)]

Year Number of 

backflows

Total volume

 (in millions of 

gallons)

2000 0 0.0

2001 3 1,189.0

2002 1 1,751.8

2003 0 0.0

2004 0 0.0

2005 0 0.0

2006 0 0.0

2007 1 224.0

2008 2 11,509.9

2009 3 413.6

2010 1 6,534.9

2011 2 2,327.5

2012 0 0.0

2013 1 10,719.5

2014 1 525.0

Several factors influence the frequency and magnitude of 

backflow events. The timing and distribution of precipitation, 

the hydraulic properties of the channels, and the regulation and 

operation of control structures may impact backflows.

The general discussion of CAWS hydrology and flow 

regulation gives an overall view of the complex hydraulic setting and flow characteristics found in the CAWS. The following sections of this report will focus on individual reaches of 

the CAWS and describe in detail some of the hydraulic characteristics of those sections. These descriptions are supported by 

data whenever possible to validate the setting. 

North Shore Channel 

 The North Shore Channel (NSC; fig. 10) is a tributary to 

the North Branch of the Chicago River and receives flow from 

the MWRDGC Wilmette Pumping Station (WPS; a lakefront 

control structure at Wilmette, Ill.) and effluent discharge from 

the MWRDGC Thomas J. O’Brien Water Reclamation Plant 

(OWRP; formerly known as the North Side Water Reclamation Plant). During summer months, in dry weather, the WPS 

diverts lake water into the NSC to dilute the effluent discharge 

from the OWRP. During large storms, the NSC receives 

combined sewer overflows (CSOs) at numerous CSO outfall 

locations along the NSC. Also during large storms, the WPS 

may be used to backflow excess water to the lake to mitigate 

flooding. During winter months, the channel in the vicinity of 

the OWRP outfall is often free of ice cover owing to the effluent discharge.

The USGS operated and maintained a streamflow-gaging 

station (05536101) on the NSC (approximately 1⁄4 mi from 

the WPS) from 2000 to 2003 as part of the Lake Michigan 

Diversion Accounting Program. The streamflow data from 

this gage (fig. 11) provided accurate monitoring of the water 

that was diverted through the WPS; the data also were used 

to calculate flow volume during storm-related backflows to 

Lake Michigan. The data collected during the time that the 

streamflow-gaging station was in operation show unsteady 

flow conditions and periods of reverse flows, which likely 

were the result of the variable input from the NSWRP. The 

range in stage measured at the streamflow-gaging station during the period of data collection was -2.84 to 6.91 ft Chicago 

City Datum (CCD). The range in daily mean discharge during 

this same period was estimated to be from -58 to 245 cubic 

feet per second (ft3

/s). 

Data collection at the USGS streamflow-gaging station 05536101 was discontinued in 2003. The USACE had 

completed a study (USACE, n.d; referred to as “Lakefront 

Accounting”) of monitoring the diversion near the three 

lakefront control structures. The Lakefront Accounting study 

resulted from the U.S. Department of Justice mediation efforts 

to reconcile mid-1990s disputes among Great Lakes states 

resulting from the State of Illinois’ noncompliance with the 

1980 U.S. Supreme Court mandate. In May 2013, streamflowgaging station 05536101 was reestablished with funding 

support from the MWRDGC. The streamflow-gaging station 

provides flow data useful to the MWRDGC for allocation of 

diversion water, maintenance of water-quality standards for 

the NSC, and measurement of backflow volumes. Recent studies on waterway separation by the Great Lakes Commission 

and the Great Lakes and St. Lawrence Cities Initiative (Great 

Lakes Commission, 2012) and the USACE (USACE, 2014) 

have proposed barrier locations that would reroute the OWRP 

effluent discharge directly to Lake Michigan. The complex, 

unsteady flow that would result from the proposed waterway 

separation scheme would warrant monitoring to determine 

flow direction and contaminant loading to the lake that would 

occur if the waterway separation plan were implemented.
Chicago Area Hydrology 11

 

 

Lake Michigan

North Shore Channel

North Branch

Chicago

River

(41

(41

( (14 14

(41

Evanston

Skokie

Chicago

Lincolnwood

Wilmette

Wilmette Pumping Station

05536101

(NORTH SHORE CHANNEL

AT WILMETTE, IL)

05536105

(NORTH BRANCH CHICAGO

RIVER AT ALBANY AVENUE

AT CHICAGO, IL)

0 0.5 1 MILE

0 0.5 1 KILOMETER

Base from U.S. Geological Survey,

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o and 33o

, central meridian -89o.

87°44'

42°06'

42°04'

42°02'

42°00'

41°58'

87°42' 87°40' 87°38'

EXPLANATION

USGS streamflow-gaging station

 and identifier

Pumping station

City boundary

Figure 10. The Chicago Area Waterway System with the North Shore Channel, Chicago, Illinois, and vicinity.

(USGS, U.S. Geological Survey)
12 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

-50

0

50

100

150

200

250

300

Daily mean discharge, in cubic feet per second

2002 2003

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

Figure 11. Daily mean discharge for the North Shore Channel at Wilmette, Illinois, for the 2003 water year, which 

is the last year of record. 

Table 2. Long-term U.S. Geological Survey streamflow-gaging stations on the North Branch of the 

Chicago River and its tributary streams, Chicago, Illinois, and vicinity.

[USGS, U.S. Geological Survey]

USGS station 

number Station name Period of record

05535000 Skokie R. at Lake Forest, IL 1951–present

05535070 Skokie R. near Highland Park, IL 1966–present

05534500 N. Br. Chicago R. at Deerfield, IL 1952–present

05535500 WF N. Br Chicago R. at Northbrook, IL 1951–present

05536000 N.Br. Chicago R. at Niles, IL 1950–present

05536105 N. Br. Chicago R. at Albany Avenue at Chicago, IL 1989–present

05536118 N. Br. Chicago R. at Grand Avenue at Chicago, IL 2002–present

North Branch Chicago River 

The North Branch of the Chicago River (NBrCR) is tributary to the CAWS and joins the NSC (fig. 12); the combined 

streamflow represents most of the flow from the north side of 

Chicago and the northern metropolitan area. The NBrCR is 

composed of a mostly natural channel that is relatively shallow and nonnavigable for motor vessels. During large storms, 

the NBrCR receives CSOs at numerous CSO outfall locations 

along the NBrCR. Dry weather flows consist primarily of 

wastewater effluent from treatment plants and base flow from 

shallow groundwater. 

The NBrCR and its tributaries are currently (2014) gaged 

at several locations. Streamflow-gaging station 05536105 near 

the confluence of the NBrCR and the NSC quantifies the flows 

entering the CAWS from the NBrCR (table 2). 
Chicago Area Hydrology 13

94

294

90

190

90

05536000

(NORTH BRANCH

CHICAGO RIVER

AT NILES, IL)

05536123

(CHICAGO RIVER AT

COLUMBUS DRIVE

AT CHICAGO, IL)

05536105

(NORTH BRANCH CHICAGO

RIVER AT ALBANY AVENUE

AT CHICAGO, IL)

05536101

(NORTH SHORE CHANNEL

AT WILMETTE, IL)

05536000

(NORTH BRANCH

CHICAGO RIVER

AT NILES, IL)

05536123

(CHICAGO RIVER AT

COLUMBUS DRIVE

AT CHICAGO, IL)

05536105

(NORTH BRANCH CHICAGO 

RIVER AT ALBANY AVENUE

AT CHICAGO, IL)

05536118

(NORTH BRANCH CHICAGO

RIVER AT GRAND AVENUE

AT CHICAGO, IL)

Wilmette Pumping Station

Chicago

River

Controlling

Works

Lake Michigan North Shore Channel

North

Branch

Chicago

River

Bannockburn

LAKE COUNTY

COOK COUNTY

Lincolnwood

Kenilworth

Chicago

Glenview

Skokie

Northbrook

Niles

Lake

Forest

Highland

Park

Evanston

Park Ridge

Deerfield

Wilmette

Glencoe

Winnetka

Morton 

Grove

Oak Park

Northfield

Lincolnwood

Bannockburn

Harwood 

Heights

Highwood

Kenilworth

Lincolnshire

LAKE COUNTY

COOK COUNTY

EXPLANATION

USGS streamflow-gaging station

 and identifier

Pumping station

City boundary

87°52' 87°48' 87°44' 87°40' 87°36'

42°12'

42°08'

42°04'

42°00'

41°56'

Base from U.S. Geological Survey,

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o and 33o

, central meridian -89o.

0 2 MILES

0 2 KILOMETERS

Figure 12. The Chicago Area Waterway System, including the North Branch Chicago River and 

U.S. Geological Survey streamflow-gaging stations, Chicago, Illinois, and vicinity. 

(USGS, U.S. Geological Survey)
14 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

The USGS streamflow-gaging station (05536105) on 

the NBrCR is approximately 400 ft upstream from a concrete 

control structure that regulates the flow of the NBrCR as the 

flow combines with the NSC. Mean daily discharge at this 

streamflow-gaging station is shown in figure 13. The control 

structure consists of a multilevel concrete weir structure, wing 

walls, and abutment that constrain the flow at low, medium, 

and high stages (fig. 14). The range in stage measured at the 

streamflow-gaging station during the period of data collection 

was 1.00–7.86 ft. Discharge during this same period ranged 

from 3.6 to 3,580 ft3/s. 

The USGS streamflow-gaging station (05536118) on the 

NBrCR at Grand Avenue is approximately 1⁄4 mi upstream 

from the confluence of the NBrCR and the mainstem of the 

Chicago River at Wolf Point (fig. 15). The flow in this reach 

is a combination from the NBrCR and the NSC. The channel 

through this reach is approximately 150 ft wide and 15–20 ft 

deep with vertical sheet piling walls. The range in stage 

measured at streamflow-gaging station (05536118) during the 

period of data collection was –4.32 to 5.00 ft CCD. The range 

in daily mean discharge during this same period was from 

–20 to 14,100 ft3/s. Negative daily mean discharges occur as a 

result of regulation or the effects of upstream and downstream 

(bidirectional) flow from density currents. A vertical string 

of six probes that measured water temperature and specific 

conductance was installed in 2002 to document the density 

currents in this reach. The range in water temperature during 

the period of data collection was 0.0–27.0 degrees Celsius 

( ̊C). The range in specific conductance during the period of 

data collection was 264–5,420 microsiemens per centimeter 

at 25  ̊C.

Mainstem Chicago River 

The mainstem of the Chicago River is a relatively short 

reach of channel (1.6 mi) that connects Lake Michigan to the 

confluence of the North and South Branches of the Chicago 

River (fig. 15). The channel is characterized by vertical 

sheet-pile or concrete walls through the high-rise corridor of 

downtown Chicago. The channel is primarily rectangular in 

cross section with depths in the 15- to 23-ft range when the 

water level is at –2.0 ft CCD. The flow through this reach has 

been monitored since 1996 for the Lake Michigan Diversion Accounting Program and lakefront accounting of direct 

diversions. The AVM data combined with data from a vertical 

string of probes that measured water temperature and specific conductance at the Columbus Drive streamflow-gaging 

station (05536123) were used to define the complexity of 

flows in this reach. Leakage of Lake Michigan water into the 

Chicago River was first quantified using discharge data from 

0

100

200

300

400

500

600

700

800

900

Daily mean discharge, in cubic feet per second

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

Figure 13. Daily mean discharge for the streamflow-gaging station (05536105) on the North Branch Chicago River 

at Albany Avenue, Chicago, Illinois, and vicinity, for the 2012 water year.
Chicago Area Hydrology 15

Figure 14. The concrete control structure at the confluence of the North Branch Chicago River and the North Shore Channel, Chicago, 

Illinois, and vicinity. (Photograph by Shawn Cutshaw, U.S. Geological Survey)

this station, which resulted in the use of several infrastructure 

projects to reduce the leakage. Bidirectional flows, driven by 

density contrasts between the Lake Michigan water and the 

Chicago River water, were also first identified from monitoring at this location (Jackson and others, 2008). Density differences driving the flow primarily arise from salinity differences 

between the NBrCR and the mainstem of the Chicago River; 

water temperature is secondary in the creation of these currents. Deicing salts appear to be the primary source of salinity 

in the NBrCR. These salts enter the waterway in direct 

runoff and in runoff entering the combined sewer system that 

becomes effluent from water-treatment plants. Knowledge of 

the complex flows in this reach helped to account for problematic variability in long-term monitoring of water quality 

in this reach. Water-quality assessments of the Chicago River 

may underestimate (or overestimate) the impairment of the 

river because standard water-quality monitoring practices 

do not account for density-driven underflows (or overflows) 

(Jackson and others, 2008). The range in stage measured at the 

Chicago River at Columbus Drive streamflow-gaging station 

(05536123) during the period of data collection was from 

-4.52 ft to 4.72 ft CCD owing to regulation. The range 

in daily mean discharge during this same period was from 

-2,450 to 1,370 ft3

/s. Typical low- and high-flow velocity 

direction and magnitude data from discharge measurements 

at the streamflow-gaging station are shown in figure 16A–D. 

Velocity magnitude and direction data for a reverse flow event 

are shown in figure 16E–F. 
16 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

05536123

(CHICAGO RIVER AT COLUMBUS

DRIVE AT CHICAGO, IL)

05536118 

(NORTH BRANCH CHICAGO RIVER

AT GRAND AVENUE AT CHICAGO, IL)

Chicago River

Controlling Works

Lake Michigan

Lake Shore Drive

Roosevelt Road

Columbus Drive

Chicago River 05536123

(CHICAGO RIVER AT COLUMBUS

DRIVE AT CHICAGO, IL)

05536118 

(NORTH BRANCH CHICAGO RIVER 

AT GRAND AVENUE AT CHICAGO, IL)

River

South

Branch

Chicago

EXPLANATION

USGS streamflow-gaging station

 and identifier

0 0.25 0.5 MILE

0 0.25 0.5 KILOMETER

Base from U.S. Geological Survey,

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o and 33o

, central meridian -89o.

87°38' 87°37' 87°36'

41°54'

41°53'

41°52'

Wolf

Point

Figure 15. The Chicago Area Waterway System and the mainstem of the Chicago River, Chicago, Illinois. 

(USGS, U.S. Geological Survey)
 17 

0 

A

Riverbed 

0.35 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

Velocity magnitude (streamwise and transverse), in feet per second 

Depth, in feet

5 

10 

15 

20 

100 50 0 

Distance, in feet 

Chicago Area Hydrology Depth-averaged velocities, in feet per second, averaged over total depth 

B

4637590 

0.14 

0.12 

4637585

0.1 

0.08 4637580

0.06 

4637575

0.04 

EXPLANATION 

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction 

448520 448525 448530 448535

UTM Northing, in meters

0.02 

4637570

UTM Easting, in meters 

Figure 16. Data from acoustic Doppler current profiler measurements in the mainstem of the Chicago River near 


Columbus Drive in Chicago, Illinois showing: A, typical low-flow water velocity magnitude and B, direction; C, typical 


high-flow velocity magnitude and D, direction; E, reverse flow magnitude and F, direction.
 

(UTM, Universal Transverse Mercator)
 
18 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois 

0.4 

Riverbed 

Depth, in feet 

Velocity magnitude (streamwise and transverse), in feet per second

5 

10 

15 

20 

0.35 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

0 

0 50 100
 

Distance, in feet
 

C

0 

Depth-averaged velocities, in feet per second, averaged over total depth 

D

4637590 

0.25 

4637585

0.2 

4637580

0.15 

4637575

EXPLANATION 

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction 

448520 448525 448530 448535

UTM Northing, in meters 

0.1 

4637570

UTM Easting, in meters 

Figure 16. Data from acoustic Doppler current profiler measurements in the mainstem of the Chicago River near 

Columbus Drive in Chicago, Illinois showing: A, typical low-flow water velocity magnitude and B, direction; C, typical 

high-flow velocity magnitude and D, direction; E, reverse flow magnitude and F, direction.—Continued 

(UTM, Universal Transverse Mercator) 
Chicago Area Hydrology 19 

E

0 

5 

10 

15 

20 

Depth, in feet 

1.5 

2 

2.5 

3 

3.5 

4 

Velocity magnitude (streamwise and transverse), in feet per second

Riverbed 

0 50 100
 

Distance, in feet
 

F

4637590
 

3.5 4637585


 4637580
 3
 

4637575
 2.5 

EXPLANATION 

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction 

448520 448525 448530 448535


Depth-averaged velocities, in feet per second, averaged over total depth

UTM Northing, in meters 

4637570


2
 

UTM Easting, in meters 

Figure 16. Data from acoustic Doppler current profiler measurements in the mainstem of the Chicago River near 

Columbus Drive in Chicago, Illinois showing: A, typical low-flow water velocity magnitude and B, direction; C, typical 

high-flow velocity magnitude and D, direction; E, reverse flow magnitude and F, direction.—Continued 

(UTM, Universal Transverse Mercator) 
20 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

Even prior to the potential changes associated with 

waterway separation, recent declines in the water level of 

Lake Michigan have been changing the hydraulic setting of 

this reach. At times, record low lake levels can affect the direct 

diversion (by gravity through existing sluice gates) of lake 

water into the river at the Chicago River Controlling Works 

(CRCW; fig. 1). The USGS established river- and lake-level 

gages at the CRCW in August 1997 to evaluate sluice gate 

flow ratings and leakage through the structure. The USACE 

also uses the streamflow data for operations during storms. 

At times, during extreme precipitation events, the water level 

of the mainstem of the Chicago River approaches a threshold flood elevation (+3.5 ft CCD). This elevation triggers a 

response from the MWRDGC and USACE to mitigate imminent flooding by opening the CRCW to backflow the river 

water to Lake Michigan. The backflow occurs as sluice gates 

in the control structure are opened and the river water (at an 

elevation near +3.5 ft CCD) flows by gravity into the lake. If 

opening the sluice gates does not immediately lower the river 

water-surface elevation, the gates to the lock chamber may 

be opened for increased backflow capacity. A large backflow 

event in April 2013 required the use of sluice gates and lock 

chamber gates to mitigate potential flooding (fig. 17). USGS 

field crews made discharge measurements to verify backflow 

capacity and volumes.

Flow in the mainstem of the Chicago River is heavily 

affected by the regulated flows coming through the CRCW. 

These flows include the flow through sluice gates and the 

lockages. The regulated flows are part of the MWRDGC’s 

allocation of Lake Michigan water and are classified as a 

direct diversion. In most years, the MWRDGC uses its allocation between April 1 and October 31 to dilute treated wastewater effluent and maintain the waterway “in a reasonably satisfactory sanitary condition” (U.S. Supreme Court, 1980). The 

direct diversion of Lake Michigan water during the warmer 

months of the year helps to maintain dissolved oxygen levels 

in the waterway. In most years, there is no direct diversion 

during November 1–March 31. During winter months, flow 

in the mainstem of the Chicago River is very low, consisting 

mainly of leakage through the control structures and occasionally through lockage. The mainstem of the Chicago River can 

have variable ice cover during winter months; ice thickness 

generally is greatest close to the lake.

South Branch Chicago River 

The South Branch of the Chicago River (SBrCR) is the 

section of channel from the confluence with the NBrCR and 

mainstem Chicago River at Wolf Point south and southwest 

to the start of the CSSC near South Damen Avenue (fig. 18). 

Flow through this reach is generally to the south, then southwest into the CSSC; however, at the mouth of southeast fork 

of the SBrCR, locally known as Bubbly Creek, the flow may 

become complex during storms. The high flows discharging from Bubbly Creek are the result of combined sewer 

EXPLANATION

Chicago River

Lake Michigan

Hourly precipitation

South Sluice gates opened

North and South

Sluice gates closed

Sector gates 50% opened

Sector gates

0% opened Sector gates 0% opened

Sector gates 100% opened

Sector gates

100% opened

North Sluice gates opened

-4 8

-3 7

-2 6

-1 5

0 4

1 3

2 2

3 1

4 0

Gage height, in feet above Chicago City Datum

Precipitation at Chicago Lock, in inches per hour

April 2013

17 12:00 PM 18 12:00 AM 18 12:00 PM 19 12:00 AM 19 12:00 PM

Figure 17. Gage heights for the Chicago River at Columbus Drive at Chicago, Illinois, streamflow-gaging station, 

hourly precipitation measured at the Chicago Lock, and gate settings at the Chicago River Controlling Works during 

the April 2013 storm.
Chicago Area Hydrology 21

94

55

290

90

South Damen Avenue

Western Avenue

35th Street

36th Street

Lake Michigan

Chicago River

South

Branch Chicago River

Bubbly

Creek

05536123

(CHICAGO RIVER AT COLUMBUS

DRIVE AT CHICAGO, IL) 05536118

(NORTH BRANCH CHICAGO RIVER AT

GRAND AVENUE AT CHICAGO, IL)

Chicago Lock and

Chicago River

Controlling Works

87°41' 87°40' 87°39' 87°38' 87°37' 87°36'

41°53'

41°52'

41°51'

41°50'

41°49'

0 0.5 1 MILE

0 0.5 1 KILOMETER

Base from U.S. Geological Survey,

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o and 33o

, central meridian -89o.

EXPLANATION

USGS streamflow-gaging station and identifier

Control structure

Figure 18. The Chicago Area Waterway System including the South Branch of the Chicago River and the Southeast Fork of 

the South Branch of the Chicago River (Bubbly Creek), Chicago, Illinois, and vicinity. (USGS, U.S. Geological Survey)
22 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

overflows from the MWRDGC’s Racine Avenue Pumping 

Station (RAPS). These flows enter the SBrCR perpendicular to 

the flow in the SBrCR. Results of hydraulic modeling studies indicate that during high flows from the RAPS, hydraulic mounding may be likely at the confluence and that it is 

possible for a portion of the Bubbly Creek discharge to flow 

upstream to the northeast. A profile of the water-surface elevation for an April 2013 flood (fig. 19A–B) from the MWRDGC 

Lockport Powerhouse to the CRCW (Chicago Lock) reveals 

interesting aspects of the CAWS hydraulic setting. This storm 

produced approximately 4–5 in. of rainfall across much of the 

Chicago area on April 17–18, 2013 (N.E. Westcott, ISWS, 

written commun., 2013). A water-surface profile was produced for this storm event based on USGS and MWRDGC 

streamflow-gaging station data. Animating this profile over 

time shows definite reversal of the water-surface slope as the 

MWRDGC opened the gates (backflow) at the CRCW. With 

the outlet to the lake open and with backflow conditions, the 

water-surface profile shows a hydraulic mound or divide near 

Stickney. This condition persisted for several hours, routing 

the flows from a portion of the upper CSSC, Bubbly Creek, 

and the South Branch and Branches of the Chicago River to 

Lake Michigan. Field discharge measurements document the 

backflows on the mainstem of the Chicago River at Columbus 

Drive, but no discharge measurements have been made to 

verify the mounding or upstream flows in the upper reaches of 

the CSSC or SBrCR. These observations and measurements 

may factor into discussions about locating proposed barriers 

for waterway separation in this reach of the CAWS. 

During winter months, the SBrCR is usually free of ice 

cover. The large amount of effluent in the NBrCR and minimal 

flows from the mainstem would keep ice from forming. Until 

its closing in 2012, the thermal discharge from the Fisk Generating Plant also contributed to keeping this reach free of ice. 

Southeast Fork of the South Branch Chicago 

River (Bubbly Creek) 

The Southeast Fork of the South Branch of the Chicago 

River is more commonly referred to by its local name Bubbly 

Creek (fig. 18). Bubbly Creek received its local name when it 

drained the Chicago Stockyards and areas of the meat packing industry. Today (2014), Bubbly Creek is a relatively short 

reach of channel (1.4 mi) that is primarily stagnant during dry 

weather but receives discharge from the MWRDGC RAPS, 

stormwater runoff, and a few smaller combined sewer overflows during storms. Pumps within RAPS are capable of a 

combined discharge of almost 6,000 ft3/s. During dry weather, 

there is essentially no flow entering Bubbly Creek channel. 

Water within Bubbly Creek rises and falls as levels in the 

CSSC fluctuate. A short-term streamflow-gaging station was 

operated near 36th Street from 2009 to 2010, which deployed 

a side-looking acoustic Doppler velocity profiler (ADCP) to 

record stage and velocity for verification of a hydraulic model 

(fig. 20). During winter months, the Bubbly Creek channel can 

be completely covered by ice.

The USACE is currently (2014) studying the feasibility 

of stream restoration for Bubbly Creek. The stream restoration plans would benefit from additional flow data for Bubbly Creek. Waterway separation scenarios include designs 

to locate a waterway barrier in the vicinity of the mouth of 

Bubbly Creek; the exact location depends on whether or not 

the discharge from RAPS is to go to Lake Michigan or to the 

CSSC. Monitoring of Bubbly Creek would provide measured 

flows for evaluation of waterway separation barriers and mitigation strategies for the effects of these flows on the receiving 

water bodies (SBrCR, mainstem Chicago River, and Lake 

Michigan).

Chicago Sanitary and Ship Canal 

The CSSC consists of approximately 30 mi of manmade 

canal excavated into the bedrock and glacial material from 

Lockport Powerhouse to Damen Avenue in Chicago (fig. 21). 

The CSSC was constructed from 1892 to 1900 and effectively 

reversed the flow of the Chicago River by capturing the flow 

and draining it away from Lake Michigan. The CSSC varies 

in width from approximately 160 to 200 ft and in depth from 

approximately 18 to 22 ft (at normal pool elevation) for most 

of its reach. 

Flow within the CSSC is highly regulated by downstream 

control structures (Lockport Controlling Works, Lockport 

Powerhouse, and the Lockport Lock and Dam) (fig. 22A). During dry weather, water levels are maintained for navigation, 

and discharge through the control structures is regulated to 

balance the inflow to the waterway. At times, power generation at the MWRDGC Lockport Powerhouse is timed to maximize power generation when utility rates are favorable. This 

results in a cycle of “ponding” of water for a period of time 

and subsequent increased flows as water is released through 

turbines (fig. 22B). 

During wet weather, prior to a storm, and in anticipation 

of potential regional flooding, water levels within the CSSC 

are drawn down to increase storage capacity within the channel (fig. 22C). The drawdown is accomplished by opening 

gates at the downstream control structures. These gates continue to be operated during a storm to manage water levels and 

mitigate flood effects. Measured flows recorded at the USGS 

streamflow-gaging stations since 1986 show a maximum discharge for the CSSC of approximately 20,000 ft3

/s.

The MWRDGC Stickney Water Reclamation Plant discharges treated effluent directly to the CSSC near Stickney, Ill. 

(fig. 21). This treatment plant is one of the largest wastewatertreatment plants in the world with a design capacity of 1,200 

million gallons per day (https://www.mwrd.org/irj/portal/

anonymous/stickney). 

During most years, the CSSC is ice free due to the 

thermal loads of the large wastewater-treatment plants, power 

plants, and industrial discharges. During extended periods 

of extreme cold weather, portions of the CSSC above Sag 

Junction have become ice covered. Below Sag Junction, the 

authors have never seen ice cover on the CSSC, even during 

extended periods of subzero air temperatures.
Chicago Area Hydrology 23

Lockport Powerhouse (USGS)

Lemont (USGS)

Stickney (USGS)

Grand (USGS) Columbus (USGS)

Chicago River Controlling

Works and Chicago Lock (USGS) Chicago Lock Lake Michigan

(USGS)

Sag Junction(MWRDGC)

Western (MWRDGC)

Lockport Controlling Works (USGS)

Romeoville (USGS)

Lockport Powerhouse (USGS)

Lemont (USGS)

Stickney (USGS)

Grand (USGS)

Columbus (USGS)

ChicagoLock(USGS)

Chicago Lock 

Lake Michigan(USGS)

SagJunction(MWRDGC)

Western (MWRDGC)

Lockport Controlling Works (USGS)

Romeoville (USGS)

Water-surface elevation,

in feet above Chicago City Datum

5

4

3

2

1

0

-1

-2

-3

-4

-5

-6

-7

-8

-10

-9

-11

River mile

290 295 300 305 310 315 320 325 330

Water-surface elevation,

in feet above Chicago City Datum

5

4

3

2

1

0

-1

-2

-3

-4

-5

-6

-7

-8

-10

-9

-11

River mile

290 295 300 305 310 315 320 325 330

April 2013

17

20

15

10

5

0

18 19 20 21 22

Discharge,

in thousands

of cubic feet

per second

April 2013

17

20

15

10

5

0

18 19 20 21 22

Discharge,

in thousands

of cubic feet

per second

A

B

Figure 19. Discharge and water-surface profiles for the Chicago Area Waterway, Illinois, during the April 17–23, 2013, storm: A, rising 

storm discharge hydrograph and canal drawdown, B, near peak of storm discharge and opening of the Chicago River Controlling Works, 

and C, the effect of flow reversal at the Chicago River Controlling Works on the water-surface elevation profile. (USGS, U.S. Geological 

Survey; CRCW, Chicago River Controlling Works; MWRDGC, Metropolitan Water Reclamation District of Greater Chicago)
24 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois Lockport (USGS)Lemont (USGS) Stickney (USGS) Grand (USGS) Columbus (USGS) Chicago Lock (USGS) Chicago Lock Lake Michigan(USGS) Sag Junction (MWRD) Western (MWRD) Lockport CW (USGS) Romeoville (USGS) Water-surface elevation, in feet above Chicago City Datum

5

4

3

2

0

-1

-2

-3

-4

-5

-6

-7

-8

-10

-9

River mile

290 295 300 305 310 315 320 325 330

April 2013

17

20

15

10

5

0

18 19 20 21 22

Discharge,

in thousands

of cubic feet

per second

C

1

-11

Figure 19. Discharge and water-surface profiles for the Chicago Area Waterway, Illinois, during the April 17–23, 2013, storm: A, rising 

storm discharge hydrograph and canal drawdown, B, near peak of storm discharge and opening of the Chicago River Controlling Works, 

and C, the effect of flow reversal at the Chicago River Controlling Works on the water-surface elevation profile. (USGS, U.S. Geological 

Survey; CRCW, Chicago River Controlling Works; MWRDGC, Metropolitan Water Reclamation District of Greater Chicago)—Continued
Chicago Area Hydrology 25

Gage height is not Chicago City Datum, but range to surface of vertical beam

Top Q

Bottom Q Riverbed 

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

25 26 27

Velocity, in meters per second

Range to surface of vertical beam, in meters

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

May 2009

Cell 1

Cell 2

Cell 3

Cell 4

Cell 5

Cell 6

Cell 7

Cell 8

Cell 9

EXPLANATION

Horizontal acoustic Doppler current meter (H-ADVM) Gage height

A

B

Depth, in feet

4

8

12

16

20

0

10,883 10,979 11,076 11,172 11,268

Ensemble number

Velocity magnitude, in feet per second, referenced to the bottom

0.000 1.000 2.000 3.000 4.000

EXPLANATION

Figure 20. Data from horizontal acoustic Doppler velocity profiler measurements May 25–27, 2009, for Bubbly Creek near 36th Street, 

Chicago, Illinois: A, water velocity, and B, discharge.
26 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

55

294

88

57

355

80 294

55

83

Avenue

Damien

Chicago

Sanitary

Calumet-Sag

Des Plaines

Lockport Powerhouse

and Lockport Lock and Dam

05536890

(CHICAGO SANITARY AND SHIP

CANAL NR LEMONT, IL)

05536995

(CHICAGO SANITARY AND SHIP 

CANAL AT ROMEOVILLE, IL)

05536700 (CALUMET SAG CHANNEL NR RT 83 AT SAG BRIDGE, IL)

05536890

(CHICAGO SANITARY AND SHIP

CANAL NEAR LEMONT, IL)

05536995

(CHICAGO SANITARY AND SHIP 

CANAL AT ROMEOVILLE, IL)

05536700 (CALUMET SAG CHANNEL NEAR ROUTE 83 AT SAG BRIDGE, IL)

Lemont

Lockport

Romeoville

Lockport Powerhouse

and Lockport Lock and Dam

Chicago

Sanitary

and

Ship

Canal

Calumet-Sag

Base from U.S. Geological Survey,

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o and 33o

, central meridian -89o.

Channel

Des Plaines

River

DUPAGE COOK

WILL

Sag Junction

MWRDGC Stickney

Water Reclamation 

Plant 

Stickney

414757087490401

(SUMMIT CONDUIT AT SUMMIT, IL)

Lockport Controlling Works

88°04' 88°00' 87°56' 87°52' 87°48' 87°44' 87°40'

41°48'

41°44'

41°40'

41°36'

EXPLANATION

USGS streamflow-gaging station

 and identifier

Control structure

0 1 2 3 4 MILES 5

0 1 2 3 4 KILOMETERS 5

Figure 21. The Chicago Area Waterway System including the Chicago Sanitary and Ship Canal and Calumet Sag Channel, 

Chicago, Illinois, and vicinity. (USGS, U.S. Geological Survey; MWRDGC, Metropolitan Water Reclamation District of Greater Chicago)
Chicago Area Hydrology 27

30

3H 6H 9H 12H 15H 18H 21H 3H 6H 9H 12H 15H 18H 21H 3H 6H 9H 12H 15H 18H 21H 3H 6H 9H 12H 15H 18H 21H

1 2 3

April 2013 May 2013

-500

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5

4H 8H 12H 16H 20H 4H 8H 12H 16H 20H 4H 8H 12H 16H 20H 4H 8H 12H 16H 20H 4H 8H 12H 16H 20H 4H 8H 12H 16H 20H

6 7 8 9 10

October 2012

-2,000

-1,000

0

1,000

2,000

3,000

4,000

5,000

April

2013

May

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 -2,500

0

2,500

5,000

7,500

10,000

12,500

15,000

17,500

20,000

22,500

25,000

Discharge, in cubic feet per second

A

B

C

Figure 22. Discharge for the Chicago Sanitary and Ship Canal near Lemont, Illinois, for: A, a normal pool elevation with highly unsteady 

flow conditions, April–May 2013, B, a typical dry-weather pattern showing cycle of ponding and increased flows, October 12, 2013, and 

C, a wet weather pattern showing the pre-storm drawdown and subsequent flood wave, April–May 2013.
28 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

The daily mean discharge of effluent for the 2012 water 

year is shown in figure 23. The treatment-plant effluent 

discharge greatly increases the flow within the CSSC at the 

MWRDGC Stickney Water Reclamation Plant. Dry-weather 

flows within the CSSC are highly unsteady. 

The USGS operated an AVM streamflow-gaging station at Romeoville, Ill., from 1984 to 2005. The information 

from this gage was used for the State of Illinois’ compliance 

with a U.S. Supreme Court decree (Consent Decree 388 U.S. 

426 [1967] Modified 449 U.S 48 [1980] on Lake Michigan 

diversion. In 2006, construction at the USACE electric fish 

barrier necessitated that the USGS remove the streamflowgaging station and establish a new streamflow-gaging station 

approximately 5 mi upstream near Lemont, Ill. 

The USGS streamflow-gaging station on the CSSC near 

Lemont, Ill., is the primary measurement point for determining the State of Illinois’ Lake Michigan diversion. The mean 

annual flow computed from the data collected at this streamflow-gaging station (fig. 24) is used by the USACE Lake 

Michigan Diversion Accounting Program. 

0

Daily mean discharge, in cubic feet per second

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

500

1,000

1,500

2,000

2,500

Figure 23. Daily 

mean effluent 

discharge for 

the Metropolitan 

Water Reclamation 

District of Greater 

Chicago–Stickney 

Water Reclamation 

Plant, Chicago, 

Illinois, for the 2012 

water year.

0

Daily mean discharge, in cubic feet per second

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Figure 24. Daily 

mean discharge 

for the Chicago 

Sanitary and Ship 

Canal near Lemont, 

Illinois, for the 2012 

water year.
Chicago Area Hydrology 

Water velocity throughout the CAWS, especially in 

the lower reach of the CAWS, is susceptible to the surface 

layer being affected by wind-driven flow. Winds from the 

south or southwest can effectively push the surface layer of 

water against the predominant downstream flow direction; 

in contrast, winds from the north or northeast can provide an 

added push to the surface layer in the downstream direction. 

Discharge measurements and velocity profiles document the 

effects of wind on the water velocities (fig. 25). 

A 0 

5 

0.4 

0.3 

Riverbed 

0 50 100 

Streamwise velocity, in feet per second 

0.2 

10 

0.1 

15 

0 

-0.1 

20 

-0.2 

Depth, in feet 

25 

Distance, in feet 

Depth-averaged velocities, in feet per second, averaged over total depth 

B

4615940 

4615935

 4615930

 4615925

 4615920

 4615915

 4615910

 4615905

EXPLANATION 

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction 

0.2 

0.15 

0.1 

0.05 

UTM Northing, in meters

419810 419815 419820 419825

UTM Easting, in meters 

29 

Figure 25. Data from low-, medium-, and high-flow acoustic Doppler current profiler measurements in the Chicago Sanitary and 

Ship Canal near Lemont, Illinois, showing: A, low-flow cross-section water velocity contour; B, low-flow plan view of depth-averaged 

velocity magnitude and direction; C, medium-flow cross-section velocity contour; D, medium-flow plan view of depth-averaged velocity 

magnitude and direction; E, high-flow cross-section velocity contour; and F, high-flow plan view of depth-averaged velocity magnitude 

and direction. (UTM, Universal Transverse Mercator) 
30 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois 

0.6 

0 

5 

Riverbed 

0 50 100 

Streamwise velocity, in feet per second 

Depth, in feet 

0.5 

10 

0.4 

15 

0.3 

20 

0.2 

Distance, in feet 

C

D

EXPLANATION 

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction 

UTM Northing, in meters

Depth-averaged velocities, in feet per second, averaged over total depth 

419795 419800 419805

 4615900

 4615905

 4615910

 4615915

 4615920

 4615925

 4615930

 4615935 

0.35 

0.4 

0.45 

0.5 

0.55 

UTM Easting, in meters 

Figure 25. Data from low-, medium-, and high-flow acoustic Doppler current profiler measurements in the Chicago Sanitary and 

Ship Canal near Lemont, Illinois, showing: A, low-flow cross-section water velocity contour; B, low-flow plan view of depth-averaged 

velocity magnitude and direction; C, medium-flow cross-section velocity contour; D, medium-flow plan view of depth-averaged velocity 

magnitude and direction; E, high-flow cross-section velocity contour; and F, high-flow plan view of depth-averaged velocity magnitude 

and direction. —Continued (UTM, Universal Transverse Mercator) 
Chicago Area Hydrology 31 

E

0 5.5 

5 5 

Riverbed 

0 50 100 

Streamwise velocity, in feet per second 

4.5 

10 

4 

15 

3.5 

20 

3 

25 

Depth, in feet 

2.5 

Distance, in feet 

F

EXPLANATION 

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction 

UTM Northing, in meters

Depth-averaged velocities, in feet per second, averaged over total depth

3.5 

4 

4.5 

5 

4615900

 4615905

 4615910

 4615915

 4615920

 4615925

 4615930 

419,795 419,800 419,805 419,810

UTM Easting, in meters 

Figure 25. Data from low-, medium-, and high-flow acoustic Doppler current profiler measurements in the Chicago 

Sanitary and Ship Canal near Lemont, Illinois, showing: A, low-flow cross-section water velocity contour; B, low-flow 

plan view of depth-averaged velocity magnitude and direction; C, medium-flow cross-section velocity contour; D, 

medium-flow plan view of depth-averaged velocity magnitude and direction; E, high-flow cross-section velocity contour; 

and F, high-flow plan view of depth-averaged velocity magnitude and direction.—Continued (UTM, Universal Transverse 

Mercator) 
32 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

Summit Conduit

The Summit Conduit is a manmade concrete-lined tunnel 

structure that routes the flows from a drainage ditch on the 

northwest side (right bank) of the Des Plaines River underneath the Des Plaines River and discharges the flow into the 

CSSC (fig. 21). At the time of construction, the drainage area 

consisted primarily of a low-lying portion of the Des Plaines 

River floodplain. The ditch was excavated to permit the floodplain to be farmed. The Summit Conduit structure enables the 

flow within the ditch to be discharged directly into the CSSC. 

As the immediate area developed, the farmland disappeared 

and the drainage area consists of a large quarry operation and 

light industry. A USGS streamflow-gaging station was established at the entrance to the Summit Conduit in 2010 (fig. 26). 

Analysis of discharge data from the streamflow-gaging station 

confirms the regulation of flows within the ditch (fig 27). A 

relatively high sustained base flow and the occasional sudden increase or decrease of water levels are likely related to 

a nearby quarry operation. The limestone quarries in the area 

periodically utilize pumps to dewater sections of the quarries 

as part of routine quarry operations. The pumping is permitted 

through the Illinois Environmental Protection Agency. 

Figure 26. The entrance to the Summit Conduit and the 

location of the streamflow-gaging station.

0

Daily mean discharge, in cubic feet per second

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

10

20

30

40

50

60

Figure 27. Daily mean discharge for the Summit Conduit at Summit, Illinois, for the 2012 water year.
Chicago Area Hydrology 33

Calumet Sag Channel 

The Calumet-Sag Channel consists of approximately 

16 mi of manmade canal connecting the Little Calumet River 

to the CSSC (fig. 28). It was completed in 1922 and widened 

in 1960. The channel is approximately 220–270 ft wide and 

12–16 ft deep at normal pool elevation. The Calumet-Sag 

Channel captures flows from the Little Calumet River, Grand 

Calumet River, and several small tributary streams, including 

Mill Creek, Stoney Creek, and Tinley Creek; the channel 

drains flow away from the natural outlet into Lake Michigan. 

The USACE Thomas J. O’Brien Lock and Dam, constructed 

in 1965, separates the Little Calumet River from Lake Michigan at a point approximately 6.8 mi inland from the lake.

Flows within the Calumet-Sag Channel (fig. 29) are 

highly regulated. Water levels within the Calumet-Sag 

Channel and the lower part of the Little Calumet River up to 

O’Brien Lock and Dam are regulated by downstream control 

294

80

55

94

57

90

294 80

COOK COUNTY

WILL COUNTY

COOK COUNTY

DUPAGE COUNTY

05536890

(CHICAGO SANITARY AND SHIP

CANAL NEAR LEMONT, IL)

05536358

(CALUMET RIVER BELOW O'BRIEN 

LOCK AND DAM AT CHICAGO)

05536700 (CALUMET SAG

CHANNEL NEAR ROUTE 83

AT SAG BRIDGE, IL)

COOK COUNTY

WILL COUNTY

COOK COUNTY

DUPAGE COUNTY

ILLINOIS

INDIANA

Lake Michigan

Des Plaines

River

Calumet-Sag

Channel

Chicago

Sanitary

and

Ship

Canal

Little

Calumet

River

Thomas J.

O'Brien

Lock and

Dam

Lake

Calumet

Tinley Creek

Mill

Creek

Creek

05536700 (CALUMET SAG

CHANNEL NEAR ROUTE 83 

AT SAG BRIDGE, IL) Stoney

Acme

Bend

MWRDGC Calumet Water

Reclamation Plant

0 1 2 3 4 MILES 5

0 1 2 3 4 KILOMETERS 5

EXPLANATION

USGS streamflow-gaging station

 and identifier

Control structure

Base from U.S. Geological Survey,

1:100,000-scale digital data

Albers Equal-Area Conic Projection

Standard parallels 45o and 33o

, central meridian -89o.

87°56' 87°52' 87°48' 87°44' 87°40' 87°36' 87°32'

41°48'

41°44'

41°40'

41°36'

41°32'

Figure 28. The Chicago Area Waterway System including the Calumet-Sag Channel, Chicago, Illinois, and vicinity. 

(USGS, U.S. Geological Survey)
34 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

structures at Lockport (Lockport Lock and Dam, MWRDGC 

Lockport Powerhouse, and Lockport Controlling Works). The 

O’Brien Lock and Dam diverts Lake Michigan water into the 

Little Calumet River during lock operations and direct diversion through sluice gates. 

The range in stage measured at the Calumet River 

downstream from O’Brien Lock and Dam streamflow-gaging 

station during the period of data collection (1997–2003 water 

years) was from -3.01 to 3.64 ft CCD. The range in daily mean 

discharge during this same period was estimated to be from 

844 to 1,069 ft3/s. Velocity data and ADCP discharge measurements downstream from the O’Brien Lock and Dam define a 

complex hydraulic setting (fig. 30). Discharge measurements 

made during the April 2013 backflow event were negative 

(going out to the lake), -7,409 ft3/s through the lock chamber and -5,573 ft3

/s through the sluice gates for a total of 

-12,982 ft3/s. These measurements document the conveyance 

of the channel, and lock and dam structure, during one of the 

relatively rare backflow events.

The USGS installed a short-term streamflow-gaging station on the Calumet-Sag Channel near Route 83 (fig. 21) in 

2011 to characterize the flow contribution of the Calumet-Sag 

Channel to the CSSC (fig. 30). The data at this location were 

collected primarily for a modeling study related to the monitoring of flows for the Lake Michigan Diversion Accounting 

Program. 

Figure 29. Daily mean discharge at the U.S. Geological streamflow-gaging station on the Calumet Sag Channel 

near Route 83 at Sag Bridge, Illinois, for the 2012 water year. Daily mean discharge, in cubic feet per second

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

-500

0

500

1,000

1,500

2,000

2,500

3,000

3,500
Chicago Area Hydrology 35 Streamwise velocity, in feet per second

Distance, in feet

Depth, in feet

A

-0.2

-0.1

0

0.1

0.2

0.3

0 50 100 150

0

5

10

15

Riverbed

EXPLANATION

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction

UTM Easting, in meters

UTM Northing, in meters

Depth-averaged velocities, in feet per second, averaged over total depth

B

421770 421780 421790 421800 421810

 4616485

 4616490

 4616495

 4616500

 4616505

0.05

0.1

0.15

0.2

Figure 30. Data from low- and high-flow acoustic Doppler current profiler measurements in the Calumet Sag Channel 

near Route 83 at Sag Bridge, Illinois, showing, A, low-flow cross-section water velocity contour, B, low-flow plan view of 

depth-averaged velocity magnitude and direction, C, high-flow cross-section velocity contour; and D, high-flow plan view 

of depth-averaged velocity magnitude and direction. (UTM, Universal Transverse Mercator)
36 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois Streamwise velocity, in feet per second

Distance, in feet

Depth, in feet

C

1

1.5

2

2.5

0 50 100 150

0

2

4

6

8

10

12

14

Riverbed

EXPLANATION

Velocity vectors—length and color

 of vectors show magnitude (see

 color scale at right) and orientation

 shows direction

UTM Easting, in meters

UTM Northing, in meters

Depth-averaged velocities, in feet per second, averaged over total depth

D

1.4

1.6

1.8

2

2.2

2.4

2.6

421610 421620 421630

 4616500

 4616510

 4616520

 4616530

 4616540

 4616550

Figure 30. Data from low- and high-flow acoustic Doppler current profiler measurements in the Calumet Sag Channel 

near Route 83 at Sag Bridge, Illinois showing: A, low-flow cross-section water velocity contour, B, low-flow plan view of 

depth-averaged velocity magnitude and direction, C, high-flow cross-section velocity contour, and D, high-flow plan view 

of depth-averaged velocity magnitude and direction. (UTM, Universal Tranverse Mercator)—Continued
Chicago Area Hydrology 37

The flow in the Calumet-Sag Channel is characteristic 

of the unsteady conditions in the CAWS. This reach of the 

Calumet-Sag Channel is also affected by the complex hydraulic setting just downstream at Sag Junction, the confluence 

of the Calumet-Sag Channel and the CSSC. During storms, 

flow at the complex hydraulic setting at the confluence of the 

Calumet-Sag Channel and CSSC forms eddies that collect a 

lot of floating debris, and at times, visible contrasts in sediment loads were observed. A USGS multibeam echosounder 

survey in this reach mapped the change in streambed elevations between the Calumet-Sag Channel (shallower) and the 

CSSC. Discharge measurements made with an ADCP were 

used in this reach to document complex velocity and flow 

direction related to density contrasts between the Calumet-Sag 

Channel and the CSSC.

The discharge hydrograph for the 2012 water year at 

the MWRDGC Calumet Water Reclamation Plant (WRP) is 

shown in figure 31. The bending channel and variable outflow 

of wastewater effluent produce a complex hydraulic setting 

in the reach near Acme Bend. During winter months, the 

Calumet-Sag Channel (fig. 21) can be ice covered over much 

of its length. Barge traffic during winter months breaks the ice 

cover in the navigation channel. 

The regulation of flows, control structures, low water 

slope, and channel characteristics all combine to produce 

a very complex hydraulic setting. The USGS operated and 

maintained an AVM streamflow-gaging station on the river 

side of O’Brien Lock and Dam from 1997 to 2003 as part of 

the Lake Michigan Diversion Accounting program. The AVM 

streamflow-gaging station was located at the end of the lock 

guidewall approximately 1,000 ft from the lock and dam on 

the river side. Flow data from the AVM streamflow-gaging station and ADCP discharge measurements made in the channel 

reach near the lock and dam document the complex hydraulic 

setting (fig. 32A). A series of ADCP discharge measurements 

in the channel reach near the I–94 bridge (fig. 28) were made 

in May 2010 prior to a rapid-response effort for Asian carp 

control (Asian Carp Regional Coordinating Committee, May 

2010). These measurements document the variability of water 

velocity and flow direction in this reach and further document 

the complex hydraulic setting (Jackson and Lageman, 2014; 

fig. 32B–C).

0

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

50

100

150

200

250

300

350

400

450

500

Daily mean effluent discharge, in million gallons per day

Figure 31. Daily mean effluent discharge for the Metropolitan Water Reclamation District of Greater Chicago 

Calumet Water Reclamation Plant in Illinois for the 2012 water year.
38 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

A

Figure 32. Data from acoustic Doppler current profiler measurements in the Calumet River near the Thomas J. O’Brien Lock 

and Dam, Chicago, Illinois, showing: A, complex water velocity patterns adjacent to the lock and dam, B, circulation patterns 

in the Calumet River below the lock and dam, and C, the complex velocity patterns near the Calumet Water Reclamation Plant 

outfall. (WRP, water reclamation plant; from Jackson and Lageman, 2014)
Chicago Area Hydrology 39

B

Grand Calumet 

River

Railroad

bridge

O’Brien Lock 

and Dam

Sluice gates

General circulation

Eddies

Lock bay

±

0 570 1,140 FEET

0 110 220 METERS

EXPLANATION

Depth-average velocity,

 in feet per second

Marinas

General circulation direction

0.00

0.15

0.29

0.44

0.59

0.74

0.88

1.03

1.18

1.32

1.47

1.62

1.76

1.91

2.06

2.21

2.35

2.50

No data

5.00

Figure 32. Data from acoustic Doppler current profiler measurements in the Calumet River near the Thomas J. O’Brien Lock and 

Dam, Chicago, Illinois showing: A, complex water velocity patterns adjacent to the lock and dam, B, circulation patterns in the Calumet 

River below the lock and dam, and C, the complex velocity patterns near the Calumet Water Reclamation Plant outfall. (WRP, water 

reclamation plant; from Jackson and Lageman, 2014)—Continued
40 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

C

Calumet Water 

Reclamation Plant (WRP)

outfall

Acme Bend

Sidestream elevated 

pool aeration (SEPA)

 station

Industrial

outfall

General 

circulation 

May 21-22, 2010

Calumet WRP outfall

discharge

465-564 

cubic feet 

per second

(ft3

/s)

Stagnation line 

Railroad bridge

±

0 500 1,000 FEET

0 100 200 METERS

EXPLANATION

Depth-average velocity,

 in feet per second

0.00

0.08

0.17

0.25

0.33

0.42

0.50

0.58

0.67

0.75

0.83

0.92

1.00

1.08

1.17

1.25

1.33

1.42

No data

1.50

General circulation

 direction

April 29, 2005

March 30, 2002

February 17, 2005

Outfall 

discharge

300 ft3

/s

Outfall 

discharge

555 ft3

/s

Outfall 

discharge

414 ft3

/s

April 29, 2005

March 30, 2002

February 17, 2005

Outfall 

discharge

300 ft3

/s

Outfall 

discharge

555 ft3

/s

Outfall 

discharge

414 ft3

/s

Figure 32. Data from acoustic Doppler current profiler measurements in the Calumet River near the Thomas J. O’Brien Lock and 

Dam, Chicago, Illinois showing: A, complex water velocity patterns adjacent to the lock and dam, B, circulation patterns in the Calumet 

River below the lock and dam, and C, the complex velocity patterns near the Calumet Water Reclamation Plant outfall. (WRP, water 

reclamation plant; from Jackson and Lageman, 2014)—Continued
Current Monitoring Issues for the Chicago Area Waterway System 41

Little Calumet River 

The Little Calumet River watershed upstream from 

the confluence with the Calumet-Sag Channel drains to the 

Calumet-Sag Channel. After completion, the Calumet-Sag 

Channel intercepted the flow from the Little Calumet River 

and diverted the flow away from Lake Michigan. 

During dry weather, the flows are affected by wastewatereffluent discharge from the Thorn Creek Sanitary District 

treatment plant (not shown) along the tributary Thorn Creek. 

The Little Calumet River receives stormwater runoff from 

the heavily urbanized parts of the watershed and combined 

sewer overflows during wet weather. During winter months, 

the Little Calumet River is often completely ice covered. The 

southwest-northeast orientation of the channel of the Little 

Calumet River at the confluence with the Calumet-Sag Channel contributes to the complex hydraulic setting in this reach. 

The USACE constructed several flood control projects 

in the Little Calumet River drainage basin. A control structure 

near the mouth of Hart Ditch (not shown) regulates the flows 

and restricts westward flow during large storms. A natural 

drainage divide in the area around the mouth of Hart Ditch 

produced variable flow directions in this reach of the channel 

prior to the flood control projects. The Little Calumet River is 

gaged at four locations along the main channel and at multiple streams tributary to the Little Calumet River. The main 

channel streamflow-gaging stations are located at South Holland, Ill., and at Hammond, Highland, and Munster, Indiana. 

Several small tributary streams flow into the CalumetSag Channel, including Tinley Creek, Stoney Creek, and Mill 

Creek. During dry weather the combined flows of these tributaries represent a relatively small fraction of the flow within 

the Calumet-Sag Channel. Daily mean discharge for Tinley 

Creek is shown in figure 33. 

Current Monitoring Issues for the 

Chicago Area Waterway System

The CAWS is presently a focal point for several important issues that require an understanding of the complex 

waterway, such as 

• Lake Michigan Diversion accounting, 

• long-term regional water supply, 

• invasive species, 

• waterway separation, 

• regional waterway transportation, and

• local and regional flood control issues.

Daily mean discharge, in cubic feet per second

2011 2012

Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept.

0

50

100

150

200

250

Figure 33. Daily mean discharge for Tinley Creek near Palos Park, Illinois, for the 2012 water year.
42 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

As of 2014, the purpose of CAWS monitoring has expanded 

to address many issues beyond the monitoring needs of 

1900. The demands on the CAWS have increased over time. 

Navigation and wastewater discharge regulations have become 

increasingly stringent and require more detailed monitoring 

to effectively meet the regulatory needs. Waterway operations 

must balance increasing demands for water quality, commercial and recreational navigation, regional flood control, and 

newer issues such as wastewater disinfection and the threat 

from aquatic invasive species. Overall there continues to be 

a regional recognition of Lake Michigan water as a valuable 

resource. These needs emphasize that, more than ever before, 

there is an increased need for CAWS monitoring.

There are several issues pertinent to the CAWS that are 

dependent upon or directly benefit from accurate waterway 

monitoring data. A primary reason for monitoring flows within 

the CAWS is to maintain compliance with the U.S. Supreme 

Court decree on Lake Michigan Diversion accounting. Monitoring water levels at various points within the CAWS insures 

appropriate depths for navigation within the waterway. The 

waterway is also a critical component of a regional floodcontrol program, which is dependent on waterway monitoring. The monitoring of flow within the waterway is a critical 

component to maintaining compliance with State and Federal 

water-quality standards. Flow monitoring provides critical 

information for several power plants and industries located 

along the CAWS that use the CAWS for cooling water.

Lake Michigan Diversion Accounting 

The USGS streamflow-gaging station (05536890) on the 

CSSC near Lemont, Ill., functions as the primary measurement 

point for Lake Michigan diversion accounting. Long-term 

monitoring of the CAWS at this location meets the requirements of the 1980 U.S. Supreme Court decree (Consent 

Decree 388 U.S. 426 [1967] Modified 449 U.S. 48 [1980])

and provides a long-term continuous record of discharge for 

the CAWS. The value of the long-term streamflow-gaging 

station is that it allows engineers and scientists to analyze the 

flow records for trends. Implementation of water-conservation 

measures and repairs made to the critical infrastructure in the 

Chicago area can be detected in the flow records when they 

are evaluated over an extended period. The single streamflowgaging station at the lower end of the CAWS (fig. 1; Romeoville 1984–2006, then Lemont 2006–present) records the 

cumulative effects of changes within the hydrology of the 

entire Chicago area.

The 1980 U.S. Supreme Court decree mandates that the 

USACE Lake Michigan Diversion Accounting Program be 

reviewed by an independent technical review committee every 

5 years. The technical review committees recognized that 

data from the single streamflow-gaging station at Romeoville/

Lemont were not adequate to address questions regarding the 

distribution of flows near the lakefront structures and leakage 

through the lakefront control structures. The committee was 

also interested in a simpler approach to diversion accounting 

that did not rely on complex modeling to complete the annual 

computations. An alternative monitoring network to the Romeoville streamflow-gaging station was proposed by the Third 

Technical Review Committee on Lake Michigan Diversion 

(Espey and others, 1994). These recommendations resulted in 

the installation of three additional AVM streamflow-gaging 

stations in close proximity to the lakefront control structures. 

These streamflow-gaging stations (fig. 1) are located at (1) 

North Shore Channel at Wilmette, Ill., (2) Chicago River at 

Columbus Drive at Chicago, Ill., and (3) Calumet River below 

O’Brien Lock and Dam at Chicago, Ill. Streamflow data collected at these three gaging stations helped define the distribution of direct diversion flow within the CAWS, seasonal timing of direct diversion into the CAWS, and detailed timing and 

flow of storm-related backflow events. Although the USACE 

Lake Michigan diversion accounting program has ended the 

alternative monitoring network concept, the data collected 

from the three streamflow-gaging stations has contributed to a 

better understanding of the CAWS.

Regional Flooding 

As the primary outlet for stormwater in the region, flow 

within the CAWS is managed by the MWRDGC to prevent 

flooding during storms. The CAWS is an important component 

of MWRDGC’s regional flood control program. As storms 

approach the region, the MWRDGC actively manages water 

levels within the CAWS to provide for more channel storage of stormwater within the channel. The MWRDGC TARP 

system of sewers, tunnels, and reservoirs works together to 

capture stormwater and combined sewer flows. During large or 

intense storms, the capacity of the system is exceeded and the 

excess flow is diverted directly to the CAWS. Control structures at Lockport, the Wilmette Pumping Station, the CRCW, 

and the T.J. O’Brien Lock and Dam are used to prevent flooding. As new TARP reservoirs are completed, the hydrology of 

the CAWS is likely to change to reflect the additional storage 

and delayed release of reservoir water to the CAWS. The near 

real-time data from the AVM streamflow-gaging stations on 

the CAWS is used to monitor the water levels within the system and evaluate the routing of flood hydrographs. Operators 

at the control structures use the data during floods for operation of water-level control. The USGS has worked closely 

with the USACE and the MWRDGC to provide near real-time 

data for waterway operations. 

Discharge data are also critical for the calibration of 

hydraulic models that engineers use in regional flood control 

projects. The USACE has recently completed (2011) the flood 

protection features for a major flood control project along the 

Little Calumet River. The levees, floodwalls, pump stations 

and flow control structures will provide 200-year level of flood 

protection to more than 9,500 homes and businesses in the Little Calumet River watershed and prevent nearly $11 million in 

average flood damage. Flood control projects like the USACE 

Little Calumet River Project rely on accurate waterway gage 

data for the design of flood control measures.
Current Monitoring Issues for the Chicago Area Waterway System 43

Power Plant Thermal Load Modeling

Several major coal-fired power plants (Midwest Generation Plants-Will County, Fisk, and Crawford) are located 

along the CAWS and rely directly on the volume of flow in 

the CAWS for cooling water (fig. 34). Two of the three power 

plants (Fisk and Crawford) have recently closed or are in the 

processing of closing operations (as of 2014). Each of these 

plants operate or operated as “once-through” cooling systems 

where water is withdrawn directly from the waterway, absorbs 

heat from cooling coils, and is returned to the waterway. The 

water withdrawals of these plants directly impact the local 

flows within the CAWS. The USGS studied this reach in detail 

in 2010 (Jackson and Lageman, 2014) using Rhodamine dye 

as a tracer. The dye data defined a low-velocity stagnant 

zone of water between power plant intake and return channel. The thermal loading from these withdrawals also impacts 

the water-quality conditions throughout the CAWS. A sharp 

increase in water temperature is observed at the warm water 

power plant discharge location (fig. 35), and elevated water 

temperatures are observed downstream from the power plants. 

Power plant operators currently rely on the real-time flow data 

from the USGS AVM gaging station on the CSSC near Lemont gaging station to meet waterway thermal regulations. 

Infrastructure Design 

Flow data are routinely used by engineers to design infrastructure components along waterways. Bridge piers, loading 

terminals, outfalls, and other structures that extend into the 

water require water level and flow data for proper design. 

Increased demands for recreational use of the CAWS brings 

more people in close contact with the waterway, from new 

river-walk paths and facilities to new boathouses for humanpowered craft; the associated facilities and structures that are 

built along the waterways are designed and constructed using 

water level and flow data (fig. 36).

Figure 34. The coal-fired power plant at Romeo Rd (135th Street) along the Chicago Sanitary and Ship Canal near Romeoville, Illinois.
44 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois Lake Michigan Channel

and Ship Canal

Chicago

River

COOK

WILL

DUPAGE

North Branch

River Des Plaines

Cal-Sag

Chicago

Sanitary

EXPLANATION

Sampling location on the  Chicago Area WaterwaySampling location shown

87°38' 87°40' 87°42' 87°44' 87°46' 87°48'

41°54'41°52'41°50'41°48'

EXPLANATION

Temperature,in degrees Celsius

5.01 to 6.006.01 to 7.007.01 to 8.008.01 to 9.009.01 to 10.0010.01 to 11.0011.01 to 12.0012.01 to 13.0013.01 to 14.0014.01 to 15.0015.01 to 16.00

0 2 1 MILES0 2 1 KILOMETERS

Orthography from the USDA Farm Service Agency, Aerial Photography Field Office 2012 National Agriculture Imagery Program (NAIP) Natural Color Imagery for Illinois, accessed in 2014 at http://gis.apfo.usda.gov/arcgis/services

Figure 35. Synoptic water temperature (near surface) data from the upper Chicago Sanitary and Ship Canal collected February 2012 and the sharp increase in water temperature at the power plant discharge locations.
Current Monitoring Issues for the Chicago Area Waterway System 45

Figure 36. Construction of the river walk along the mainstem of the Chicago River.
46 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

Waterway Separation

Construction of the CAWS provided an important waterway link between the Lake Michigan Basin and the Illinois 

River/Mississippi River Basin. While this link is important to 

transportation of bulk goods in and out of the region and the 

reduction of wastewater discharge to Lake Michigan, it also 

is an open pathway for the movement of aquatic invasive species. In 2002, the USACE constructed an electric fish barrier 

in the lower reaches of the CAWS to prevent the movement 

of invasive species through the waterway. Recent movement 

of several species of Asian carps up the Illinois River (not 

shown) towards the CAWS spurred discussions on a complete 

waterway separation of the CAWS to permanently sever the 

waterway link between Lake Michigan and the Illinois River/

Mississippi River Basins. A major concern for separating the 

waterways is the threat that invasive Asian carps may pose to 

the sport fishing industry in the Great Lakes. Concurrent studies by the Great Lakes Commission (Great Lakes Commission, 

2012) and the USACE (U.S. Army Corps of Engineers, 2014) 

are evaluating the feasibility and technical issues of waterway 

separation. Several separation scenarios and separation locations have been evaluated (fig. 37). The physical placement 

of a barrier or multiple barriers in the waterway represents a 

radical change in the hydraulics and hydrology of the CAWS. 

Each scenario and location has positive and negative aspects 

with regards to transportation, flooding, water quality, and 

costs. The effects of the barriers at different scenario locations 

will be addressed through engineering studies using hydraulic 

model simulation. Addressing the data requirements for proper 

calibration of the hydraulic models is just one type of shortterm use of waterway data. 

EXPLANATION

Project

Mitigation

Project and mitigation

Conveyance tunnel

Water reclamation 

plant outfall tunnel

Sediment remediation

Buffer response zone

Water reclamation

plant

Mid-system separation CAL SAG 

open control technologies with 

buffer zone

Alternative features

Figure 37. One of the waterway separation scenarios proposed by the U.S. Army Corps of Engineers Great Lakes and Mississippi River 

Interbasin Study. (From U.S. Army Corps of Engineers, 2014; GLMRIS, Great Lakes and Mississippi River Interbasin Study; ANS, aquatic 

nuisance species; CAL SAG, Calumet Sag Channel; WRP, water reclamation plant)
Summary 47

Summary 

The hydrology of the Chicago Area Waterway System 

(CAWS) can be characterized as a low-slope natural drainage 

system that has been highly modified to facilitate the drainage of a large metropolitan area. The construction of manmade canals, water-control structures, tunnels, and reservoirs 

to interrupt the natural drainage patterns and convey water 

away from Lake Michigan has produced a complex regulated 

hydraulic setting. This report describes the hydraulic characteristics of the different reaches of the CAWS and presents 

examples of the flow measurement data over a wide range of 

flow conditions. Examples of flow measurement data through 

a range of flow conditions including low, medium, high, and 

in some locations, reverse flow are presented. The unsteady 

flow characteristics found throughout the CAWS are evident in 

the data and presented graphically. The detailed hydraulic data 

collected by the U.S. Geological Survey at streamflow-gaging 

stations throughout the CAWS provide engineers and scientists with an understanding of how this complex waterway 

system operates and contribute to a more efficient operation 

of the CAWS. The use of hydroacoustic flow measurement 

instruments like acoustic velocity meters and acoustic Doppler current profilers has advanced the understanding of the 

complex hydraulic setting characteristic of many reaches of 

the CAWS. The implementation of near real-time telemetry to 

streamflow-gaging stations on the CAWS helps to reduce the 

amount of missing record in the operation and maintenance 

of the streamflow-gaging stations. The many issues affecting 

the CAWS reinforce the need for detailed hydraulic data to 

understand the complex hydraulic setting. 

Since its construction in 1900, the CAWS has served 

several important functions for the Chicago region, including 

a long-term regional water supply/wastewater diversion function that provides municipal water supply for approximately 

9 million people and helps maintain water quality in Lake 

Michigan, a regional waterway for transportation, and local 

and regional flood control. Recently, the CAWS has become 

the focal point for several important regional issues. Proposed 

changes to the State of Illinois’ diversion of Lake Michigan 

water, water supply needs for projected growth in the population of the Chicago metropolitan area, protection from and 

control of invasive species that threaten the ecology of both 

the Great Lakes and Illinois River, regional flood control 

functions, infrastructure design, and cooling water demands 

for power plants are just some of the issues that currently or 

will potentially impact the CAWS in the near future. Increased 

levels of waterway monitoring can provide scientists and engineers a better understanding of CAWS hydrology and the data 

to address current and future uses for the CAWS.
48 Hydrology of and Current Monitoring Issues for the Chicago Area Waterway System, Northeastern Illinois

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http://dx.doi.org/10.3133/sir20155115