STREAM RECOVERY POST CHANNELIZATION: A CASE STUDY OF LOW-GRADIENT, AGRICULTURAL STREAMS IN CENTRAL ILLINOIS

Stream channelization, which entails reducing the sinuosity of a stream, widening, and in some cases deepening the stream channel, is a widespread practice in agricultural regions. Channelization efforts in central Illinois have significant impacts on the geomorphology, flow regime, and sediment transport both in, and adjacent to modified reaches. The goal of this study was 1) characterize the changes in stream channels by comparing three streams that are at various stages of recovery post-channelization, 5 years (1900N), 7 years (Frog), and 35 years (Bray), to an unmodified stream reach (Crooked) and 2) estimate a recovery rate. Measured channel slopes within the modified streams were 1 order of magnitude larger than the measured channelized streams in Crooked. The two most recent streams exhibited little geomorphic change since their channelization, while the segment modified 35 years ago experienced bank failure and immature meander development. The lack of redevelopment resulted in sinuosity values lower than that of Crooked, and the reestablishment of meanders similar to Crooked would take an estimated 11,000 years. The distributions of the sediments within all streams were comprised of poorly-sorted sand and pebbles. The distribution of the sediment resembles the source, the glacial diamicton that serves as the surficial sediments. Mobilization of the sediment is frequent, with recorded scour greater than sedimentation. Overall, the channelized segments experienced limited recovery. The segments are still degrading (1900N and Frog) or are transitioning into a threshold stage (Bray).