Dam Removal and Knickpoint Migration: Case Study at Brewster Creek near St. Charles, Illinois

As part of a dam removal project on Brewster Creek near St. Charles, Illinois, knickpoint migration is being analyzed through detailed surveys and observations. The purpose of this paper is to describe the project and document the location of the knickpoint with time. The project is a pilot gradual-dam-removal study, consisting of cutting five 0.305 to 0.457 m vertical notches from June 2003 to February 2004 across the length or some portion of the length of the dam. The dam was approximately 2.438 m high and had a 9.144 m wide crest. Before the dam was removed the impoundment was nearly full of sediment with approximately 0.40 m of water depth throughout. The deposited sediments consisted of 67 to 99 percent silts and clays, and the old streambed was composed primarily of sand, gravel, cobble, and stiff cohesive material. Incision occurred in the lakebed as a knickpoint was established and developed during and after gradual dam removal. During the time period between the cutting of the first notch in June 2003 and the most recent survey in October 2006, the knickpoint migrated approximately 277 m. The data from this study are currently being used to test the validity of existing channel incision models. The study is part of a larger project to assess the erosion dynamics and stream channel evolution resulting from gradual dam removal.