Procedure to determine direct diversions from Lake Michigan

Abstract

Illinois diverts water from Lake Michigan to the Chicago River and Canal System in three primary ways: (1) diversions for municipal water supply, (2) storm water diverted away from the lake, and (3) direct diversions primarily for water quality purposes. The U.S. Supreme Court has ruled that the total average diversion must not exceed 3200 cfs. Since the stormwater diversion is uncontrollable, by reducing the amount necessary for direct diversion, the diversion available for municipal use can be increased. An optimization procedure, utilizing an efficient network algorithm, is developed to determine the average monthly flowrates at the three diversion points on Lake Michigan. The algorithm minimizes the total amount diverted that is necessary to maintain the dissolved oxygen standard in the waterway system. The procedure is applied to evaluate direct diversion needs under existing conditions and after installation of ten instream aeration stations. Results show the need for large diversions during the summer months and primarily at one diversion point. The installation of instream aerators reduces the need for direct diversions by approximately 25 percent.