4 minute read
Kaskaskia River Basin
Modoc, Carlyle, and Shelbyville, Illinois, United States
Promoting revegetation through the use of drawdowns. With a total of 15,126 square kilometers of drainage and a presence in 22 counties, the Kaskaskia River Basin is the main tributary of the Mississippi River, flowing southwest through Illinois. The Jerry Costello Lock and Dam, previously called the Kaskaskia Lock and Dam, is located on the lower end of the basin, about one kilometer from the river. Lake Shelbyville and Carlyle Lake are two multipurpose reservoirs working cooperatively in the basin. Project purposes for each reservoir are flood control, recreation, navigation, water quality, fish and wildlife conservation, and water supply. Several years ago, the U.S. Army Corps of Engineers (USACE)–St. Louis District started to explore changes in waterlevel management that would continue to support flood control and navigation while enhancing wildlife conservation and recreational purposes. USACE St. Louis District successfully implemented 15-centimeter late-summer pool drawdowns at each of the locations in 2021 and 2022 to promote the revegetation of banklines, backwaters, and coves. The district will continue to work with agency partners and host public meetings to discuss project implementation and address questions.
Article Cover: A backwater on the Lower Kaskaskia River. Bands of color help to illustrate how vegetation established in zones as conditions became favorable for germination. (Photo by USACE St. Louis District)
Producing Efficiencies
USACE St. Louis District, Office of Water Control, uses the newer Corps Water Management Systems models to produce daily forecasts with and without precipitation for decision-making and upward reporting. Capable of using 16-day precipitation grids in six-hour increments, this technology enables the office to help plan drawdowns using real-time data and alternatives analysis. Additionally, DigitalGlobe aerial imagery data sets at both normal summer pool and drawdown elevations at each site were used to delineate water lines and calculate area exposed. These data were later combined with predicted seedhead production to estimate the number of waterfowl that could be supported as a result of the drawdowns.
Using Natural Processes
When conditions for the growing season are favorable, the Office of Water Control will draw down the pools throughout the basin at Lake Shelbyville, Carlyle Lake, and the lock and dam to let the aquatic vegetation establish growth. The office will then bring water levels up slowly to ensure that vegetation is not overtopped. Fluctuations at these project sites are a natural occurrence. In 2022, the drawdown on the lower Kaskaskia resulted in approximately 1,009 kilograms of seed per hectare of emergent vegetation. This is comparable to intensively managed moist-soil units, which depend on water-level management and periodic disturbance.
Broadening Benefits
The improved plant production and habitat structure increased the wildlife that can be supported, leading to improved recreational opportunities through nature viewing, hunting, and fishing. A drawdown of pool elevations to 15 centimeters below normal has been used to expose mudflats and banklines, providing shallow hunting areas for waterbirds. As the exposed sediment dries, its structure reduces erosion and allows emergent wetland plants to establish. This vegetation improves water clarity by slowing water movement and trapping sediment and often serves as an important food source for migratory waterfowl.
Promoting Collaboration
The district hosts an annual public meeting at each location to facilitate communication around general project operation, safety, and any additional initiatives, such as the 15-centimeter growing-season drawdown to enhance environmental benefits. Discussion includes a summary of current-year drawdown results and the tentative plan for the coming year, with feedback from local businesses and the public. Coordination calls with USACE operations and the Illinois Department of Natural Resources (the primary agency partner) are initiated as conditions become suitable to begin a drawdown. At season’s end, a call is held to discuss results and any potential future changes.
