Spillway Crest Modifications: Water Supply Embankment Dam

In 1928, the City of Bloomington, Illinois decided that a larger and higher quality supply of water was necessary for industrial growth. The city decided to construct Lake Bloomington, which covers about 525 acres of the Money Creek valley, and at the time of construction, was the second largest artificial body of water in Illinois. In 1957, due to increasing population, the City of Bloomington raised the crest of the Lake Bloomington Dam spillway 5 ft. In 1970, with ever-increasing water supply demands, Evergreen Lake was constructed. Evergreen Lake Dam is an earthfill embankment approximately 67 ft high and 1,780 ft long from abutment to abutment, including a 150 ft wide concrete ogee spillway at the center of the dam. Normal operating procedure for water supply includes the use of both Lake Bloomington and Evergreen Lake as sources of water. When Lake Bloomington falls approximately 5 ft below its normal pool level, a pumping station at Evergreen Lake is activated and pumps water through a transmission main, directly to the water treatment plant. As the level of Lake Bloomington rises back to its normal pool elevation, pumping from Evergreen Lake is discontinued. This operating procedure apparently worked fairly well until the drought of 1987-1988 severely impacted both reservoirs, dropping lake levels as much as a combined 34 ft, and reducing the remaining water supplies to less than 10 months. An emergency water supply measure entailed the construction of a side channel pumping pool on the Mackinaw River, just downstream of the Evergreen Lake Dam. Pumping from the Mackinaw River into Evergreen Lake initiated in January 1990, and was successful in extending the available water supply to the city while the more long-term improvements described in this paper were being designed and constructed.