Dams decrease stream gradient and flow velocity, and often trap a stream's sediment load. For 188 years, sedimentation in the Munroe Falls dam pool on the Cuyahoga River, Ohio created a sediment record of both natural and anthropogenic variability. A wooden dam, first constructed in 1817, was replaced with a 3.66-m-high stone dam in 1902 to better serve local industrial needs. Before this dam was removed in 2005, a coring and transect profiling study was undertaken to characterize the dam pool sediments. To a distance of 600 m upstream of the Munroe Falls Dam, only similar to 30 cm of sediment overlaid the bedrock in the thalweg, indicating that the deep-water channel was an area of sediment transport. However, in the low-velocity shallow-water margins of the dam pool, up to 3 m of organic-rich, clayey silt had accumulated above pre-dam floodplain deposits. Pastflooding events are recorded in these dam pool sediment deposits by an increase in woody debris and sand. A distinctive lithology having an oily sheen, abundant woody debris, and elevated trace metal concentrations occurs at depth throughout the deposits in the shallow-water margins of the dam pool. Pb-210 dating places the top of this layer at approximately 1918. The 1913 flood in northeast Ohio probably deposited this contaminated layer from washed-out upstream sources. A direct relationship between sediment trace metal (Pb, Zn) and magnetic mineral concentrations demonstrates that magnetic parameters can provide rapid pollution assessment of dam pool sediments.
