Report Shows Removal of Dam Has Had Little Effect on Creek

Removing Good Hope Mill Dam in Cumberland County, PA did not harm the environment as some feared, according to a recent report published by the U.S. Geological Survey (USGS). 

The dam, a 6-foot high 220-foot wide concrete structure on Conodoguinet Creek, was removed to mitigate safety concerns and to provide for passage of native fish, most notably American shad. Concerns about the effects of the dam removal included large fish kills, toxic sediment release, and fear over the Creek drying up. Scientists attribute the lack of significant changes in part to the absence of fine sediment, which dams often trap in large quantities along with toxins. The shape of the channel and habitat that supports aquatic life did not change much after removal because of the low supply of sediment. With respect to water quality, the dam removal changed how some constituents vary throughout the day, but it did not affect the daily maximum or minimum concentrations. Scientists noted a short-term (weeks) change in the community of aquatic organisms living in the vicinity of the dam. Within a year, the community composition became similar to other communities outside the influence of the dam. Changes observed in the fish community were within the scope of natural fluctuations and could not be attributed to removal of the dam.

Although the removal of Good Hope Mill Dam had a successful outcome in the eyes of many, the results may not be the same for dam removal projects elsewhere. The report findings are transferable to other dam removals to the extent that the dam and stream characteristics are similar to those of this study. The Scientific Investigations Report 2005-5226, Effects of Removing Good Hope Mill Dam on Selected Physical, Chemical, and Biological Characteristics of Conodoguinet Creek Cumberland County, Pennsylvania, is available at http://pubs.usgs.gov/sir/2005/5226/. 

For more information about dam removal or natural stream channel design projects, contact F. X. Browne, Inc. at info@fxbrowne.com.