Measurements of leakage from Lake Michigan through three control structures near Chicago, Illinois, April-October 1993

A total of 213 measurements of leakage were made at three control structures near Chicago, Ill.--the Chicago River Controlling Works (CRCW), Thomas J. O'Brien Lock and Dam (O'Brien), and Wilmette Pumping Station (Wilmette)--using acoustic Doppler current profilers (ADCP's) and dye-dilution techniques. The CRCW consists of the Chicago Lock and two sets of sluice gates connected by a network of harbor walls. Leakage measurements were made in April, May, July, September, and October 1993 using an ADCP. The mean and standard deviation of leakage measured by the ADCP for the Chicago Lock river gate were 133 and 39 cubic feet per second, respectively. The mean and standard deviation of the leakage measurements at CRCW were 204 and 70 cubic feet per second, respectively. The mean and standard deviation of leakage measurements at O'Brien on September 17, 1993, were 21 and 10 cubic feet per second, respectively. The mean and standard deviation leakage measured at Wilmette using the ADCP were 59 and 8 cubic feet per second, respectively, in April 1993. After the pump bays at Wilmette were sealed in July 1993, the leakage dropped to less than 15 cubic feet per second in September 1993. Discharge estimated by dye-dilution at the Chicago Lock on July 15, 1993, was 160 cubic feet per second, or within 8 percent of the discharge measured with the ADCP. (USGS)