Modeling the Complex Hydrology and Hydraulics of the Lower Cache River

Abstract

The Cache River is located in the extreme southern part of Illinois, just north of the confluence of the Ohio and Mississippi Rivers. In 1915, a cutoff to the Ohio River was constructed east of Karnak that resulted in sub -dividing the Cache River watershed into the Upper and Lower Cache River watersheds. The Upper Cache River watershed consists of the eastern part of the watershed draining directly to the Ohio River through the Post Creek Cutoff. The Lower Cache River watershed consists of the western part of the watershed draining to the Mississippi River through a diversion channel at the outlet. The Cache River levee was built in 1952 along the west bank of the Post Creek Cutoff to prevent runoff from the Upper Cache River watershed from entering into the Lower Cache River. Because of these and other alterations in the watershed, the hydraulics of the Lower Cache River are very complex. Smaller, local tributaries provide the source of water f or the upper portion of the Lower Cache River. Once water from tributaries enters the upper part of the Lower Cache River, it can flow in an easterly direction towards the Cache River levee or flow in a westerly direction towards the Mississippi River. A combination of several factors determines the directi on of flow in the upper part of the Lower Cache River. Hydrologic and hydraulic models were developed to simulate the hydraulics of the Lower Cache River and to evaluate different alternative measures that can be implemented to reduce or eliminate the unnatural reverse flow in the upper portion of the Lower Cache River. Background