CORRELATION OF TERRACES IN THE CHAGRIN RIVER VALLEY WITH ANCESTRAL LEVELS OF LAKE ERIE, NORTHEASTERN OHIO

Past lake-level fluctuations can be reconstructed by examining geomorphic evidence of higher lake levels preserved in terraces of the Chagrin River that flows into Lake Erie in northeastern Ohio. Terrace remnants along the Chagrin River are examined and correlated with mapped ancestral beach ridge elevations along the south shore of Lake Erie in Lake County. The Chagrin River drains an area of approximately 267 sq mi (683.9 sq km). The Upper Chagrin is 22.0 mi (35.4 km) long; the main channel length of the river is 23 mi (37.0 km) long. The two main branches of the Chagrin River are the Aurora and the East branches, which are 12 miles (19.3 km) and 15 mi (24.1 km) long, respectively.

Topographic maps and soil surveys of the study area provided insight into the location of terraces above the flood plain of the river. A Trimble GPS unit was used to locate positions of terraces along valley sides, and data were also recorded on topographic base maps. Elevations of terrace remnants were determined by plotting points taken in the field on 2-ft contour maps donated from each county using Arcmap. Profiles of the Chagrin River and its branches, the adjacent uplands, and bedrock topography were produced using the Shaded Bedrock-Topography Map of Ohio, and 10-ft and 2-ft contour maps. Soil and bedrock topographic maps were used to distinguish among terraces eroded into lacustrine sediments, glacial-fluvial deposits, or bedrock. Terrace elevations were plotted on the profiles. Lines of best fit were projected upstream from beach ridges through terrace remnants.

Topographic profiles reveal that there are bedrock-controlled knickpoints, entrenched meanders, and a buried valley within the Chagrin Valley. Most terraces are concentrated in lower parts of the valley, and a few scattered remnants are present in upper regions of the drainage basin. The gradient of the Chagrin River is 12 ft/mi (2.3 m/km), that of the East Branch is 23 ft/mi (4.4 m/km), and that of the Aurora Branch is 16 ft/mi (3.0 m/km). Differences may occur because of origin and bedrock control. Terraces are associated with probable ancestral beach ridges of the Maumee I, Maumee III, Whittlesey, Arkona, Warren, and Elkton levels of ancestral Lake Erie. A large delta having an area of 0.82 sq mi (2.12 sq km) is present in Waite Hill, Lake County and is associated with the Maumee III level.