The Importance of Managing Sedimentation in the Cache River Wetlands

Sedimentation along the Lower Cache River and the adjoining side channels and wetlands has been recognized as one of the major causes of habitat degradation in the Cache River located in extreme southern Illinois just north of the confluence of the Mississippi and Ohio Rivers. Several factors combine to cause excessive sedimentation in the upper reaches of the Cache River. The first factor is the natural location of the Cache River within the Cache River valley. This relic valley is generally flat with low gradients, and thus lower flow velocities, resulting in higher sedimentation. Another major factor, hydrologic and hydraulic alterations in the Cache River basin over the last century, resulted in a much more complex hydraulics, where flows from tributary streams can now flow in both westerly and easterly directions. This has resulted in sediment from Big Creek, the largest sediment generator, to flow in an easterly direction and settle out in the Cache River wetlands. The third factor is the increased sediment delivery from tributary streams as a result of changes in land-use practices in the watersheds and stream channel alterations along the tributary streams. Data collected over the last 20 years show promising trends: watershed and stream restoration efforts seem to have reduced delivery of sediment to the Lower Cache River.