Preliminary results of a dam-removal analysis on brewster creek near st. Charles, Illinois, 2002-2004

The benefits of gradually removing a dam (through multiple notches) are to reduce the total project cost and reduce possible environmental effects by allowing the impounded sediment to slowly move downstream, and a stable stream and revegetated floodplain to form upstream. Notching, in this study of a dam on Brewster Creek, near St. Charles, Illinois, involves cutting a given height (in five 12-18 inch notches over approximately a 9 month period) across the length (or some portion of the length) of the dam. Brewster Creek is a tributary of the Fox River in northeastern, Illinois. Sediment, dissolved oxygen, and geomorphic response are being monitored before, during, and after a gradual (notching) removal of the dam. The study area includes the creek reach immediately below the dam and above the lake. Preliminary data analysis indicate that during and after the removal, the relation between the sediment transported to the study area from upstream and the sediment transported out of the study area remained relatively stable. This preliminary result indicates that the notching system created a fairly slow and predictable sediment transport response to storms, when compared to known upstream sediment loads. This result corresponds to the slow geomorphic response at the site since inception of the notching sequence in 2003. The creek responded to the five notches removed over the course of 9 months by gradually cutting through the former lakebed sediment to establish a meandering channel. Notchings did not appreciably affect dissolved oxygen concentrations in Brewster Creek.