USACE River Ecosystem Restoration Planning: Lessons Learned from the Illinois River Study

Planning undertaken by the U.S. Army Corps of Engineers for the Illinois River (IL) Basin Restoration Study utilized formulation techniques that could be adapted for other river ecosystem restoration planning efforts. The USACE planning process requires quantification of benefits in order to evaluate the relative merit of alternative approaches. Historically, these benefits have often been quantified in terms of "acres of habitat created or improved". However, when altered abiotic processes or biotic interactions limit ecosystem function to a larger degree than habitat limitation it is necessary to incorporate both spatial and functional considerations to develop meaningful measures of restoration benefit. In the Illinois River system, ecosystem function is generally considered to be limited by a combination of abiotic processes (including sediment transport, water level and water quality), biotic interactions (including lost connectivity and exotic species), and habitat limitation (including deep waters, connected backwaters and floodplains). for the Illinois River Basin Restoration study, developed by the USACE in partnership with the State of Illinois seven overall restoration goals were developed, each addressing one of the identified limiting factors. Each objective was quantified using individually specific criteria, such as tons of sediment delivered to the river, degree of water level fluctuation, miles of connected tributary mainstem and acres of connected backwater multiplied by a depth distribution function. Alternatives were then developed based on differential attainment of the various criteria relative to the level necessary to reach full functionality.