Short-term Sediment and Morphologic Response of the Middle Cuyahoga River to the Removal of the Munroe Falls Dam, Summit County, Ohio

Abstract

The removal of the 3.66-m-high Munroe Falls Dam from the Cuyahoga River in Summit County, Ohio, between August and October 2005, follows an accelerating trend to remove dams for the purpose of river restoration. The response of the middle reach of the Cuyahoga River to this dam removal resulted in sedimentologic, morphologic and hydrologic changes. These changes were monitored by measuring transects, discharge and velocity, and collecting bed sediment both pre-removal and post-removal. The overall change to the mean grain size of the channel-floor deposits was characterized by coarsening upstream, and fining downstream of the former dam. The greatest degree of coarsening occurred within 1,000 m upstream of the former dam site. Following dam removal, changes in channel morphology were characterized by approximately 1 m of bed aggradation downstream of the dam site. Upstream, the channel quickly incised to the pre-1817 (pre-dam) substrate within a month of dam removal. Once the pre-1817 substrate was reached, downcutting stopped, and channel-widening became the dominant morphologic response. Prior to dam removal, flow velocity within the impoundment limited sediment transport to suspended load in all but the largest flows of the year. Following removal, reduced cross-sectional area and greater slope, increased flow velocity by 4 to 15 times. Now the river erodes and transports sandsized sediment as bedload even during the low-flow periods. Bedload discharge measurements indicate the largest sediment source is the former impoundment sediment.