Restoring floodplains and backwater lakes along large rivers by removing levees requires understanding of the tradeoffs between heavy sediment loads along the main stem of the river versus the negative effects of sediment deposition on backwater lakes and wetlands. An opportunity existed to explore this question at a 1600-acre wetland bank site at the confluence of the Illinois and LaMoine Rivers within the LaGrange pool of the Illinois River waterway. Mapping from 1904 shows a large backwater lake (Big Lake) in the same location where one exists at present. By vibracoring of backwater lake sediments and direct measurement of recent sedimentation rates, this project established a depositional history for this site from roughly 1914 to 2017. Radiometric dating (137Cs), coupled with core morphology description, grain size analysis, and analysis of heavy metals in the cores, allowed calculation of a mean sedimentation rate into backwater lakes on the site (Big Lake and Crane Lake) of roughly 0.61 cm/yr from about 1914 to 2004. Direct measurement of sediment deposition in dry land areas of the site yielded estimates of 0.54 cm/yr (2002-2009) and 0.61 cm/yr (2011-2017). When combined with data from a 2006 lakebed survey, these rates would predict infilling of Big Lake completely in about 136 years. However, the re-working of sediments on-site by wave action appears to push sediments away from the lake basin and deposit them in higher elevation and more densely vegetated areas. This wave action results in perpetuating the shallow lake for over a century despite significant inputs of riverine sedimentation.
|Name||TR Series (Illinois Sustainable Technology Center)|
- Illinois River
- LaMoine River
- LaGrange River