ASSESSING IMPACTS ON SEDIMENTATION DUE TO DAM MODIFICATION ON THE CUYAHOGA RIVER, OH

Humans alter river systems by installing dams for water supply, industry, or agriculture. Dam construction changes base level, slows the water flow and transforms the fluvial environment upstream of the dam into a dam pool that acts as a sediment trap. Dam-induced changes to the fluvial environment can have a negative effect on the native biology, reducing the population of riparian fish, encouraging algal blooms, and often providing a more hospitable environment for invasive species. Therefore, in the past decade, there has been a nationwide change in policy from dam building to dam removal. The Munroe Falls Dam was originally constructed as a log dam in 1817 and was converted into a stone dam in the 1902 as industry expanded. To improve stream flow, water quality and health of biologic communities in the Cuyahoga River, the Munroe Falls Dam will be lowered from 12 ft to 6 ft. This dam modification presents an opportunity to examine the changes in hydrology, sedimentology and geomorphology that will occur upstream and downstream of the dam. Sediment grain size and physical properties have been quantified along three river transects at different distances upstream of the dam. Shallow water river margins in the dam pool have accumulated 1-3 m thick deposits of organic-rich mud. The deep-water thalweg contains up to 1m of low organic content sands. River stage, flow velocity, and suspended sediment concentration were measured 2 km downstream of the dam to assess temporal changes in water and suspended sediment discharge. Suspended sediment discharge increases with an increase in water discharge, which is highest after rainfall events. Measurements of total suspended solids in the Cuyahoga River below the dam indicate normal to excellent water quality, except in turbid overbank slackwater during floods. This study is intended to provide an assessment of baseline conditions for the study of the river after the dam is modified, and to possibly predict some of the changes that may accompany the lowering of the dam.