Chicago's Hydrologic History is one of the primary reasons that early settlers established Chicago at this geographic location. It's hydrologic advantages however also proved to be its biggest challenges.
Where is Chicago Hydro-Geographically?
The City of Chicago and Cook County lie within the Great Lakes Physiographic Province, a glaciated landscape, formed by glacier cycles, through which sands, gravels, and till soils were deposited by the advancing and retreating glaciers. The deposited soils were then distributed by winds and by water, such as rivers and lake currents. The eastern half of Cook County (area in gray), including the City of Chicago, lies in within the Chicago Lake Plain section, composed of a low flat topography, consisting of both glacial clay and sands & gravels along the coastal zone and waterways. The western half of Cook County (area in orange) sits along the Wheaton Valparaiso Terminal Moraine subsection, which forms the topographic watershed divide (the high-ridge) between the Great Lakes and the Mississippi River watersheds.
After the final glacial retreat about 14-15,000 years ago, the Chicago (Lake) Plain was covered by water until about 10,000 years ago (called lake Chicago) when it drained through a low point in the terminal moraine to the west. A wet marshy landscape remained, lined by dunes and sandy gravelly spits along the coastal areas. Prairie streams meandered across the plain, draining the low-plain landscape to the Great Lake to the east. However, the western end of one of the prairie rivers flooded seasonally providing a connection to the river ways to the west (along the present day Sanitary and Ship Canal). This flooded area was called the Chicago Portage; it linked the shortest geographical distance between the Great Lakes and St. Lawrence Seaway to the east, and the Mississippi River system to the west, creating a navigable connection between the routes.
Chicago's natural history, while strategic for cross-navigation of the continent, proved challenging for urbanization of Chicago. The urban ground was very flat and seasonally wet. Without proper sanitation methods, its wastewater (dumped into rivers) was reaching its drinking water source (the Lake). Through a series of hydraulic projects in the mid to late 1800's, the City decided to reverse the flow of the river that carried its waste. By digging a canal to the west, it reversed the flow of the river and therefore its waste westward, hydraulically engineering its way out of its natural watershed.
Over time, the City struggled with the wet nature of the landscape, raising buildings and streets, and piping waste water and rainwater into a combined system. Today the City maintains this westward flow of its combined sanitary-sewer system. Thus, the landscape which historically contained a complex variety of natural hydrologic features such as lakes, streams, marshes, wetlands, and coastal dunes was increasingly drained, flattened, and conveyed into a westward flow as lines in the landscape.
This map depicts the location of the canals and remnant lakes (in dark gray). These water bodies are familiar to 21st century Chicagoans. Depicted (in blue) are the historic footprints of lakes, wetlands, and shorelines that have been altered and disappeared through draining, piping, and canalization.
Of particular interest is the modification to Chicago's primary inland waterway, the Chicago river. The top image gives an excellent idea of what the prairie river looked like prior to canalization. The lower image is of the Chicago River through the downtown Loop, looking westward from the Lakeshore.
Most people don't realize the extent of hydraulic engineering that moves water around Chicago. Chicago has perhaps one of the largest underground water systems in the world, and the Metropolitan Water Reclamation District itself is the largest single user of energy in the State of Illinois to move water through the system.
Why is this?
Chicago's water history has been one of trying to control water coming in and out of the city. Unfortunately it has led to a relentless effort to keep ALL water of the City, quickly moving not just wastewater but also stormwater away. Today the City has a 99% combined sewer system, meaning that wastewater and stormwater and combined into one system, and this piping infrastructure collects, and diverts all water together, first to the treatment plants, then it is discharged to local waterways.
Such a system creates several problems however. Often rainfalls over 2/3" inundates the system, creating flooding and overflows. As a result, Chicago regularly experiences urban flooding, such as street flooding and basement flooding due to sewer backups, inlet restrictors, and overland flooding, and worst of all, combined sewer overflows (CSO) into the rivers and sewage releases into Lake Michigan. There is too much stormwater draining into the system.
Chicago's urban water statistics include the following:
+Chicago withdrawals 1.75 Billion gallons for potable water use from Lake Michigan every day. (Regulated by great lakes binational agreement.) This water is taken in through cribs 2-4 miles off shore, tunneled to the purification plants and distributed across the City by the Department of Water Management.
+ Chicago rainfall ranges from 37-40" annually, and rain quantities can vary from a fraction of an inch (the majority of rains) to several inches (the April 2013 rains were the highest in recent years).
+Wastewater (used from the Lake Michigan source), from household, commercial, and industrial uses, is combined with rainwater (collected primarily through downspouts, pavements and street inlets). This combined water moves into a network of 15’ interceptor pipes, leading to the treatment plants. Chicago's Stickney Treatment Plant is the 2nd largest in the world, processing approximately 1B gallons of water per day.
+When a larger rainfall occurs, and the combined water system is at capacity, the Deep Tunnel and Reservoir System, serves as a holding mechanism for water waiting to be treated. The Tunnels are 35’ in diameter (shown in the dark grey) are located 150-250’ below ground. Most tunnels line the major waterways as overflow mechanisms. Some tunnels also lead to the Reservoirs.
+When the Tunnels are at capacity, the combined water is tunneled to regional quarries currently being converting to Reservoirs for holding larger quantities of untreated water.
Statistics and quantities of Chicago's urban water system are shown on the map.
As of 2014, Chicago averaged a combined-sewer overflow weekly, and discharged untreated sewage to Lake Michigan twice annually. Street and basement flooding continue to occur on a regular basis.
Because rainwater is a significant input into the combined system, why not keep rainwater out of it? Are there places we can infiltrate water and keep it in the Lake Michigan watershed?
This excellent question led us to explore the potential to infiltrate water in Chicago, right in neighborhoods, right in industrial areas, and in streets that run through both. In looking back at the hydrologic history and the glacial soils, we located a series of glacial deposits at the surface and subsurface, composed of sands and gravels, capable of infiltrating water, and potentially creating recharge zones for Lake Michigan. Thus, the glaciated landscape of Chicago actually contained one of the keys to unlocking the system.
The U.S. Geologic Survey of 1902 mapped dune sand and sand & gravel soil types that exists in the coastal area, extending approximately 2-3 miles from shoreline. These soils serve to infiltrate, wash and return rainwaters to the Lake. Local infiltration would further benefit those areas, by releasing waters flooding at the surface into the lower soil layers, assisting with passive irrigation for planting, and creating a healthier local microclimate by encouraging hydric and thermal exchange between surface and subsurface.
We can use this soil variability to re-structure the city accordingly, using the capacity of the geologic nature of the City as a robust performance system, managing water in a comprehensive way. By infiltrating water, we are also keeping water out of the combine system, which benefits the whole system.
The image on the left is of sand, dune sand, and gravelly soils (cut from the USGS 1902 survey). The image at right is from a 2009 USGS report specifically identifying areas for infiltration potential - seeking specific hydrogeological characteristics such as porosity and permeability, and depth from ground surface to aquifer capable of moving that water away.
To respond to water issues across the city, this research suggests that there is a network of urban lands where rainwater can be captured and conveyed through passive infiltration features - ranging from garden structures, depressions, and permeable surfaces - such that any design projects that involve the removal of the contact layer between rain water and the underlying permeable units, would induce infiltration.
This means that much of this new contact area will be designed and constructed (rather, deconstructed) as a new vertical interface between urban surface and geologic substrata permeability and transport, increasing the performance potential of both layers.
What are some of the other effects of controlling water at this scale?
In addition to the localized effects of controlling urban water, such as flooding and overflows, there are also continental-scale consequences of controlling water in this way. For Chicago, there are cross-boundary watershed impacts created by Chicago’s urban water systems.
The exertion of hydraulic engineering is directing water away from the Great Lakes, and keeping any rainwater that does fall in Chicago from replenishing the lake. Rapid and vast rainwater collection also dries out the City, instead of allowing water to seeking the ground at a local level in its own watershed. Further, this total amount of water being collected is exported westward through the DesPlaines River, Illinois River, Mississippi River, and to the Gulf of Mexico.
The travel times varying from a couple to several weeks. These westward and southward flows often contain waste materials such as e coli and phosphorus levels, as well as commercial and industrial toxins, which impact water quality downstream. 5% of the hypoxia zone (large region of water containing little to no oxygen) in the Gulf has been attributed to Chicago alone.