Channel Entrenchment Along the Post Creek Cutoff in Southern Illinois

The Post Creek Cutoff was constructed in 1915 by the Cache River Drainage Commission to divert flow from the Upper Cache River to the Ohio River. The construction of the cutoff reduced the stream length from 51 to 8 miles and significantly increased the stream slope. The construction of the cutoff initiated a stream entrenchment process that has resulted in one of the deepest gorges in Illinois. The upstream progression of the streambed entrenchment into the Upper Cache River has created serious problems for some of the most important natural areas in the state, including ponds and wetlands that depend on a certain hydrologic cycle for their existence. The stream entrenchment is creating problems for wetlands and ponds by lowering low-water levels in the stream and increasing the hydraulic gradient between the water levels in the wetlands and ponds and in the stream. This increases seepage and drainage from the ponds and wetlands, disturbing the natural hydrologic balance. Another problem is the formation of lateral gullies to the main channel. As the stream bed becomes deeper, the lateral drainage system is also altered, resulting in new and very deep gullies that increase the drainage from the wetlands and ponds and also erode valuable land.