NINETY-NINE YEAR SEDIMENT YIELD RECORD OF THE MIDDLE CUYAHOGA RIVER WATERSHED, OHIO

The 17.4 m tall Ohio Edison Dam was constructed in 1912 on the Cuyahoga River, Ohio for hydroelectric power and cooling water storage for a coal-fired power plant. A dam pool sediment volume of 765,000 m³ was calculated from differences between 1918 and 2010 bathymetric maps, and the thickness of cored sediment. Twelve cores provide the nature and spatial variability of the dam pool sediment deposit. Combining the ²¹⁰Pb-dated age model, sediment density and sediment volume analyses allowed changes in mass accumulation rate and sediment yield to be determined. A core-based sediment yield value of 7520 tonnes/yr for the ²¹⁰Pb-dated year 2006 compares well to 7560 tonnes/yr determined using the STEP-L USEPA watershed pollution loading model using year 2006 landcover type. The dam pool sediment deposit was subdivided into three time intervals. The first period (1912 – 1928) is characterized by mud having low amounts of coal combustion products (CCP) and elevated trace metal concentrations. Sediment yield was initially high after the dam was constructed because the Great Flood of 1913 breached the upstream Le Fever Dam releasing its stored sediment as well as being a high discharge event capable of transporting large amounts of sediment. The second period (1928 – 1977) is characterized by mud having abundant CCP, high but variable metals and a generally increasing sediment yield. The third period (1977 – 2011) is characterized by declining CCP and trace metals, reflecting the effectiveness of the Clean Air and Water Acts, as well as declining industrial activity in the watershed. Sediment yield increases dramatically between 2004 to 2008 and again in 2011 as a result of an increase in extreme Cuyahoga River discharge events, and the erosion of upstream sediment following the removal of the Munroe Falls Dam in 2005. The Ohio Edison Dam is being considered for removal as a means of river restoration in the Middle Cuyahoga River. Based on the range of sediment mass accumulation within the Ohio Edison Dam pool since 2001, it is projected that the downstream sediment load will increase by an average of 6,300 tonnes/yr once the Ohio Edison Dam is removed. The increased sediment flux from the Middle Cuyahoga River will increase the need for dredging at the Port of Cleveland and change sedimentary conditions in the Lower Cuyahoga River.