The engineer Ellis F. Chesbrough, in 1866, constructed the first tunnel far enough into the lake that the wood crib that fed it was beyond the flow of sewage into the lake. (DAinfo) Note this was about a decade after Chicago raised its buildings so that it could dump its sewage into the river. (Update: I learned that Ellis was also responsible for the raising of the buildings.)
As the contamination of sewage spread into the lake, longer tunnels and deeper cribs had to be built. The building of the Ship and Sanitary Canal to reverse the flow of the Chicago River and then the building of treatment plants stopped the spread of sewage into the lake. (It has not eliminated sewage in the river and lake, that is why the Tunnel and Reservoir Plan (TARP) is still being built.) But it has reduced the frequency and area of the lake that gets contaminated. Now the primary water supply concern is the threat of terrorist attacks.
The muck of the lake bottom is one of the hardest things to tunnel through. It is easy to remove the material, but it is hard to keep the tunnel open. In muck, most of the work is building a lining to keep the tunnel open compared to the work of removing the material at the head of the tunnel. It is easier to dig through solid rock. Even though it is harder to initially remove the material, you don't have to shore up the sides of the tunnel to keep it open. You just have to line it to prevent leaks and erosion. That is why the TARP project is better known as The Deep Tunnel. Fortunately, Chicago is over a thick bed of dolostone. It even outcrops in some locations such as Lemont, IL. But in other areas, the bedrock is deep below the surface. In some places the TARP tunnels are 350 feet below ground. (Encyclopedia of Chicago) The Dever Crib built in 1935 is a 75 foot diameter steel pipe that goes down to a tunnel 190 feet below lake level. I'm sure that depth then allowed them to dig the tunnel through bedrock. Dolostone is a good rock to dig tunnels through. It is strong enough to support itself but not so strong that it is difficult to remove the material. Also, since we don't have earthquakes near here, the bedrock is competent. That is, it doesn't have a lot of cracks. (The downside of competent bedrock is that earthquakes that are far away can be felt here because there are no cracks to stop the vibrations.)
|Raymond Kunst posted|
Chicago Water Works (Water Crib) 1870s
An article about the Harrison (1898) and Dever (1935) Intake Cribs.
Water was collected and transported through a tunnel 60 feet below the lake surface to the Chicago Avenue pumping station. Chicago's first water tunnel to the original two mile out water cribs of 1865 were completed in 1867. This tunnel of course itself two miles long, dug through clay 60 feet under lake level and was lined to a finished diameter of five feet with two shells of brick.
An intake crib built of timber (the original two-mile crib) was located two miles off shore at the lake end of the tunnel, and the shore end was connected to a new pumping station completed in 1869. This station is the existing Chicago Avenue pumping station. This water system marked the real beginning of Chicago's water works, employing water cribs, huge under-the-lake tunnels, pumping plants, and recently, filtration and purification plants. (BioState)
|Keith King posted|
Chicago, as of 2017, drew over 700 million gallons of water from the lake each day. Around 267 million gallons of that water was exported to other communities. Chicago exported the most water to the DuPage Water Commission, who imported 73 million gallons a day to distribute to over 30 municipalities and water systems in DuPage County.
In all, the Chicago area sources more than 290 billion gallons of water from the lake each year.
Mike Gorogianis Water levels in all the Great Lakes are currently at historical highs. https://www.lre.usace.army.mil/.../Grea.../Water-Level-Data/
Steve Salisbury The volume of water were talking about approximate 3/4 of an inch off the top of the lake a year. This is not measurable compared to the fluctuations in water level.
|Rick Drew Flickr|