MONITORING THE EFFECTS OF URBANIZATION ON HEADWARD EROSION AND DOWN-CUTTING RATES, GRAND VALLEY STATE UNIVERSITY RAVINES

Grand Valley State University’s Allendale campus is situated on the upland west of the Grand River valley. Small ravines on the north and east edges of campus drain surface run-off from this upland into the Grand River. Rapid post-1970s campus urbanization has waterproofed natural land surfaces, increasing surface run-off. Much of this run-off is directed into drain pipes at the heads of several campus ravines. Rapid down-cutting, scouring, and headward erosion has resulted in spectacularly fresh exposures of Pleistocene glacial sediments: (1) a lower clay and silt unit, (2) a middle sand (and silt) unit, and (3) an upper till unit. As part of a long-term (1999-2009) Geological Field Methods project, we have mapped these deposits and the related geomorphic features (e.g., gullies, landslides, etc.). Our ultimate goal is to better quantify how increased storm water run-off during urbanization, and the recent move toward “greening” of campus, has affected/affects the ravines system. We estimate long- and short-term down-cutting and headward erosion rates and compare pre-urbanized (natural) values with urbanized values. We track the decade-long history of change recorded on our maps by producing a time-series of digital geologic and geomorphic maps of the campus ravines in the ArcMap GIS environment.