USING DAM POOL SEDIMENT AS AN ARCHIVE OF URBAN AND SUBURBAN WATERSHED CHANGE: AN EXAMPLE FROM THE CUYAHOGA RIVER, OHIO

The 20.7 m tall Ohio Edison Dam was constructed in 1912 on the Cuyahoga River near the city of Akron, Ohio. The dam was constructed for hydroelectric power and provided cooling water storage for a coal-fired power plant. During the past ninety-nine years, over 6 m of sediment has accumulated in the dam pool. This ongoing study is assessing if the low-velocity dam pool sediments preserve a record of Middle Cuyahoga watershed sediment-yield variation. Dam pool sediment volume is being obtained from GIS analysis of a 1906 topographic map made prior to dam construction, and bathymetric maps from 1918 and 2010. Ten piston cores were collected to study the nature of the dam pool sediment deposit. ²¹⁰Pb dating is underway and when combined with GIS volume analysis will allow sediment-yield variation to be determined. Down-core loss-on-ignition, magnetic, and sedimentologic profiles reveal changes in sedimentation within the dam pool. Long cores that reached the underlying bedrock contain a basal, clean gravelly-sand interpreted to represent the fluvial environment prior to dam construction. The overlying 5.8 m of sediment is predominately laminated mud. At 5.72 m deep there is a 3.5 cm thick fibrous organic layer interpreted to have been deposited in the large 1913 flood that occurred the year after the dam was built. Between 2.25 and 4.75 m depth, magnetic susceptibility indicates increased magnetic content in the sediment. This section also contains the most numerous silt laminations having high coal fly-ash content. Above 2.25 m depth magnetic content is lower and there are fewer silt laminations. This change in sediment type reflects changes in watershed activity and hence the type of sediment transport to the dam pool. The Ohio Edison Dam is being considered for removal, which will increase sediment input to the Lower Cuyahoga River and the need for dredging at the Port of Cleveland. In order to better understand potential future sediment load conditions, the historic rate must be determined first, especially before the dam removed and the record is lost forever.