Locks and Dams

The construction of dams also plays a role in the depth of the Illinois River. In the 1870s the state builds two locks on the Illinois River, one at Henry and one at Cooper’s Creek, increasing the water depth and clearing wooded areas along the banks. These locks double the low water flow by 1880 (Lamb 2001). In the 1890s, the U.S. Army Corps of Engineers build two more locks and dams at La Grange and Kampsville.

The locks and dams are necessary to allow boats to travel from Chicago to Grafton. The natural gradient made such travel impossible (Figure 16).

Figure 16: Illinois River Gradient-Chicago to Grafton (McCarthy 1991)

All of these activities are part of a plan adopted by an Act of Congress on August 11, 1888 to create a navigable waterway between Lake Michigan and the Mississippi River with the capacity for the largest size naval vessels suitable for “defense in time of war,” 14 feet deep and 160 feet wide (Lamb 2001). Engineers contend that only a 7-foot channel was achievable and that no vessels traveling the Mississippi River needed more than a 7-foot depth. The State of Illinois finally begins building the Illinois Waterway in the late 1920s to deepen the channel to 9 feet, with new locks and dams replacing the old ones. These locks and dams have an impact on the Illinois River as water levels increase and the main channel is deepened for navigation. Figure 17 illustrates the affects of the construction of the locks and dams. They create “pools” behind each dam, which dramatically alters the flow of the river; however, as a result of the locks and dams, large boats are able to travel the length of the river.

Figure 17: Creation of Pools with the Construction of Locks and Dams on the Illinois River (McCarthy 1991)