Planform change and stream power in the Kishwaukee River watershed, Illinois: Geomorphic assessment for environmental management

Effective watershed-scale environmental management and restoration require a sound understanding of the dynamics of fl uvial systems at the watershed-scale and the impact of humans on these dynamics. In Illinois, concern has arisen about the need to implement bank stabilization along meandering rivers, where bank erosion associated with lateral migration is often viewed as a sign of channel instability. Also, many rivers in the state are low-energy fl uvial systems that exhibit limited responses to direct human modifi cation such as channel straightening. From an ecological perspective, the lack of response is problematic owing to its potential long-term alteration of aquatic habitat. This study examines the spatial relationship between the planform dynamics of meandering rivers and stream power in the Kishwaukee River watershed in northern Illinois. The spatial extent of planform change at the scale of drainage network is quantifi ed and related to spatial variations in the magnitude of stream power throughout the watershed. Historical channel change was determined using GIS-based analysis of aerial photography of several reaches scattered throughout the watershed. The results show that the amount of lateral migration per reach is greatest where stream power is highest, but that planform response to channelization is limited regardless of the magnitude of stream power. The fi ndings from this historical analysis of channel change are useful for understanding both the fl uvial dynamics of unmodifi ed meandering rivers and the infl uence of human modifi cation on these dynamics- knowledge that can help guide environmental decision making about the need to implement channel stabilization or restoration measures.