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

摘要

As part of a dam removal project on Brewster Creek near St. Charles, Illinois, knickpointmigration is being analyzed through detailed surveys and observations. The purpose ofthis paper is to describe the project and document the location of the knickpoint withtime. The project is a pilot gradual-dam-removal study, consisting of cutting five 0.305to 0.457 m vertical notches from June 2003 to February 2004 across the length or someportion of the length of the dam. The dam was approximately 2.438 m high and had a9.144 m wide crest. Before the dam was removed the impoundment was nearly full ofsediment with approximately 0.40 m of water depth throughout. The depositedsediments consisted of 67 to 99 percent silts and clays, and the old streambed wascomposed primarily of sand, gravel, cobble, and stiff cohesive material. Incisionoccurred in the lakebed as a knickpoint was established and developed during and aftergradual dam removal. During the time period between the cutting of the first notch inJune 2003 and the most recent survey in October 2006, the knickpoint migratedapproximately 277 m. The data from this study are currently being used to test thevalidity of existing channel incision models. The study is part of a larger project toassess the erosion dynamics and stream channel evolution resulting from gradual damremoval.