DAM REMOVAL OF THE COLUMBIA DAM IN WESTERN NJ AND ITS EFFECTS ON DOWNSTREAM CHANNEL MORPHOLOGY

The Columbia Dam in western New Jersey is set to be removed over the summer of 2018 as part of The Nature Conservancy’s larger restoration project for the Paulins Kill watershed. The 5.5 m tall dam had a 2.4 km impoundment, was built in 1909, and was originally used for hydropower, although the power plant has been decommissioned since 1916 and the dam no longer provides any useful function. The dam was operated as a run-of-the-river dam, with little control over the outflow over the dam. The purpose of this project is to measure multiple river cross-sections downstream of the dam before and during removal to monitor erosion and/or deposition. The six cross-sections were monumented to allow repeat measurements using a total station. The cross-sections were approximately 20-30 m long with water depths approaching 2 m and covered approximately 700 m of river length. Comparisons between repeat measurements of the same cross-sections allow us to determine where areas have experience deposition and/or erosion. Preliminary analyses suggest little change so far, suggesting that mitigation efforts to reduce deposition have succeeded. The sediment has either remained in the impoundment or was transported to the larger Delaware River, which the Paulins Kill joins immediately downstream of the studied reach. The removal of this dam will allow migratory fish, especially shad, to once again pass into the Paulins Kill River. Currently shad are blocked by the Columbia Dam and congregate at its base in the spring.