It's a complicated process that involves a number of different steps, building reservoirs and building barriers. The other important thing to understand is that the reason these barriers exist is that there's a series of canals in the city of Chicago and the whole city sort of developed around these canals. In order to address the water movement between them, they have to adjust a lot of the flood damage and stormwater management in the city of Chicago. That's part of the reason why it's such an expensive solution.
On April 8th, 2014. See this statement in context.