|Shields Jr, Fletcher|
Submitted to: Proceedings of the World Environmental and Water Resources Congress Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/20/2011
Publication Date: 5/24/2011
Citation: Shields Jr, F.D., Langendoen, E.J., Thomas, R.E., Simon, A. 2011. Cyclical fluvial response caused by rechannelization. Proceedings of the World Environmental and Water Resources Congress Conference. CD-ROM. Interpretive Summary: Historically, river channel management has often included radical channel straightening and enlargement to alleviate flooding, but these measures frequently cause accelerated erosion upstream and sediment deposition downstream. Watersheds disturbed by channelization are difficult to stabilize, and creative approaches are called for. A case study based on the Yalobusha River in northern Mississippi is used to illustrate problems caused by channelization and rechannelization. The analysis highlights the importance of designing channel systems to convey or store sediment loads from upstream reaches.
Technical Abstract: The Yalobusha River system in northwestern Mississippi was channelized ca. 1967 to enhance channel capacity and alleviate flooding. Design of the channelization project allowed the enlarged, straightened channel to discharge into an unmodified sinuous reach, and the junction between these two geometries featured a sudden reduction (~200x) in sediment transport capacity. A plug of sediment and large wood formed in the channelized reach immediately upstream of the point where the channelized reach terminated, filling the channel, forcing all flows over the banks, flooding low areas upstream and accelerating further deposition. In 2003, following strategic installation of erosion controls throughout the upstream watershed, the action agency decided to rechannelize 4 km of the blocked channel at a cost of $1.13 million. However, the sharp transition between the two geometries was retained. Fluvial response consisted of blockage and avulsion of the new channel less than one year later. This example highlights the importance of maintaining sediment transport continuity in river channel management.