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Paper No. 16-5
Presentation Time: 1:30 PM-5:30 PM
PRE- AND POST-DAM REMOVAL CHANNEL CHANGE IN THE BUSHKILL CREEK, EASTERN PENNSYLVANIA
We have been studying a 3.5 kilometer segment of the Bushkill Creek since 2017 in anticipation of the removal of three run-of-the-river low-head mill-dams. Thee Bushkill Creek has a drainage area of 207 km2 and joins the Delaware River at Easton, PA. The dams are located just upstream of the confluence with the Delaware River and dam removal is designed to reconnect the Bushkill more directly to the Delaware to allow fish to migrate from the river into the stream. Because the project was delayed several years, we had the unique opportunity to monitor the stream for several years prior to dam removal to determine the dynamics of the stream attendant to high discharge, bed-mobilizing storms, with the dams in place, to better contextualize the channel’s response to dam removal. Dam 1, the lowermost dam in the system was removed in July-August 2023 and dam 3 the 3rd dam above the mouth was removed during September-October 2023. We have established monumented cross sections upstream and downstream of each dam and we repeatedly survey the cross sections to evaluate channel change. \Now that two of the dams have been removed our measurements record the channel’s adjustments to a post-dam era where the channel can re-establish a new equilibrium longitudinal profile and hydraulic geometry. Dams 1 and 3 provide interesting contrasts to removal response insofar as subchannel pipelines required bed and bank stabilization in one segment upstream whereas Dam 3 is unencumbered and free to establish a new channel geometry and longitudinal profile. Here we present results of the pre-dam removal channel dynamics at each dam as well as the preliminary post-dam removal engineering and channel adjustments at dams 1 and 3. In addition, we sampled suspended load as dam 1 was being removed and we present that data as well as data from a stream gauge that we installed in 2019 immediately downstream of dam 1 to monitor stage, turbidity, temperature, and conductivity.