It was a 7-foot stone dam that had been constructed to provide a swimming hole, according to the Dam Removal Summary 2023 by American Rivers. Lochner Dam, built to create a swimming hole, is not what most people picture when they think of river restoration. However, that is precisely what happened with the Lochner Dam, which used to exist on Smithtown Creek, a Delaware River tributary in Bucks County, Pennsylvania.
Many removals are driven in part by age-related repair costs. The Manatawny Creek project also reflected local efforts to restore the waterway. The Greater Pottstown Watershed Alliance was among the groups that advocated removing the dam to benefit the waterway and reduce flood risk in the community park. The researchers cautioned that some ecosystem components, including floodplains and riparian vegetation, could take more than a decade to adjust fully after dam removal.
The above-mentioned summary report also states that about 85 percent of more than 90,000 dams registered by the U.S. Army Corps of Engineers are aged 50 or older, during which time more expensive repairs become commonplace. the report identifies the cooperation between the state’s fishery and dam safety program as one of the major reasons for Pennsylvania and Wisconsin being at the top for many years While the removals constitute only about 2 percent of dams across the nation.
They said longer-term monitoring would therefore be necessary to understand the full range of ecological effects.
The ecological effects of dam removal were examined by scientists at another Pennsylvania waterway, Manatawny Creek. By contrast, increased sediment movement reshaped the channel in the former impoundment and downstream. The researchers also recorded substantial changes in the impounded stretch, where bottom-dwelling invertebrates and fish communities shifted from species associated with still water to those adapted to flowing water. Not every effect was welcome. Some downstream fish were affected by the heavy sediment movement and habitat change, though the researchers described the impact as short-term. They also noted that sediments stored behind dams can carry contaminants.
In the 2002 study published in the Journal of the American Water Resources Association, Karen Bushaw-Newton et al. describe the removal of a 2-meter-high dam in lower Manatawny Creek, which is a Schuylkill River tributary in southeast Pennsylvania. The researchers initiated their study in 1999, but most monitoring began in May 2000, before the dam was removed in two stages in August and November. To illustrate this risk, the study cited the 1973 removal of the Fort Edward Dam on New York’s upper Hudson River.
Because the impoundment had a short hydraulic residence time of less than two hours at base flow and rarely experienced temperature stratification, the researchers found that water quality changed little after the removal, partly. Because of concerns about bioaccumulation, pCB-contaminated sediment had settled along about 300 kilometers of the river, and commercial fishing for striped bass and other species had been banned.
