STREAM INCISION IN THE COLLINSON ECOLOGICAL PRESERVE, MILAN IL: EFFECTS OF NERBY HIGHWAY CONSTRUCTION?

The Collinson Ecological Preserve, owned by Augustana College, consists of approximately 67 acres of heavily wooded land along the south bluffs of the Rock River Valley, approximately 2 km southeast of Milan, IL. Ravines are eroded into the loess here, with intermittent streams that flow northwest into Mill Creek. Natural outcrops of Devonian limestone (Little Cedar Fm.) exist at low elevations along sections of Mill Creek. Two small hill prairies exist along the western boundary of the preserve.

Several of the ravines in the preserve are experiencing active rejuvenation, identified by down-cutting of 0.3-2 m and numerous knickpoints. The goals of this project are to: 1) determine the cause of the incision by field observations and mapping; 2) establish knickpoint locations for future monitoring; and 3) establish initial “baseline” observations for subsequent studies of the geomorphologic and ecologic effects of the ongoing erosion. The two most probable causes of rejuvenation include either a drop in base level of Mill Creek or an influx of water from sources upstream and outside of the preserve. A newly expanded highway directly southeast and upstream of the field site has been identified as a probable cause of intermittent increased flow into this stream system.