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Publication Abstract

Hydrologic and Hydraulic Modeling for Evaluating Alternatives for Managed Connection of the Upper and Lower Cache Rivers Demissie, Misganaw, Elias Bekele, Yanqing Lian, Laura Keefer, 2010  Illinois State Water Survey, Champaign, IL,  ISWS CR 2010-06    Full Text Available

The Cache River basin, located in southern Illinois, has characteristics unique to the State of Illinois and nation, with diverse physical, chemical, and biological features that produced a great diversity of natural communities. Because of these unique characteristics, the Cache River basin contains some high quality bottomland hardwood forests and wetlands that have been recognized nationally and internationally (Ramsar Convention, 2009). However, changes in land-use practices and hydraulic modifications during the last century have significantly threatened the ecological integrity of some of these valuable habitats and wetlands. Therefore one of the key goals of resource managers working in the area is to restore the Cache Riverís natural hydrologic character to a level that can sustain a viable ecology throughout the river corridor.

An essential component of the restoration effort for the Cache River has been the development of detailed hydrologic and hydraulic models to determine water levels associated with proposed restoration measures. These models assist the Cache River Wetlands Joint Venture Partnership (JVP) in the decision-making process of selecting and implementing restoration projects that improve the hydrologic conditions for the natural ecosystem. Hydrologic and hydraulic modeling also allow the JVP to satisfy all regulatory requirements and ensure that natural, agricultural, and social resources are not damaged by flooding induced by modifications to the river system.

Hydrologic and hydraulic models were already developed for the Lower Cache River and are published in a report as a product of Phase I of the project (Demissie et al., 2008). In summary, the Illinois State Water Survey (ISWS) developed calibrated hydrologic and hydraulic models, evaluated the hydrology under current flow conditions and various restoration scenarios, and then compared results to the reference/base condition. The reference/base condition refers to the condition when the hydrology of the Lower Cache River was controlled on the east end by Karnak Levee (composed of two 48-inch gated culverts that prevented flow from Post Creek Cutoff into the Lower Cache River) and on the west end by two in-channel weirs located at Route 37 and west of Long Reach Road, referred to as "Diehl Dam." The current condition is similar to the reference/base condition except for a breach in the Karnak Levee at the former location of the two 48-inch gated culverts. After analyzing all scenarios considered with different combinations of flooding conditions, structural changes, and boundary conditions, the Phase I report conclusions were as follows: ...

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