MULTIDISCIPLINARY MONITORING IN ANTICIPATION OF THE REMOVAL OF SEVERAL LOW-HEAD, RUN-OF-RIVER DAMS - BUSHKILL CREEK, PENNSYLVANIA

A series of low-head run-of-river dams on lower Bushkill Creek in Easton, Pennsylvania are scheduled to be removed during 2019-2020. The dams will be removed to restore the creek to a more natural, free-flowing condition to improve ecosystem function and allow trout, shad and other fish to move freely between Delaware River and Bushkill Creek. Another desired outcome of dam removal in lower Bushkill Creek is the reestablishment of freshwater mussel populations. Because mussel larvae are dependent upon fish hosts for dispersal, dams restrict both mussel and fish distribution.

Beginning in 2010 we began efforts to characterize and study lower Bushkill Creek in anticipation of dam removal. Since then, we have collected monthly data on water quality and macroinvertebrate diversity upstream and downstream of dams and at free-flowing reference reaches of the stream. This past year we conducted timed surveys for freshwater mussels throughout Bushkill Creek. A small number were located at a reference site upstream of all the dams, but mussels were completely absent directly upstream and downstream of the dams. We collected channel bed cores from the pools above dams #1, 2, 3, and 4 for analysis of heavy metal content in legacy sediment. We then conducted associated toxicity assays to determine the singular and interactive effects of cadmium, lead, and copper on the most common macroinvertebrate and freshwater mussel species.

For two years, we have been collecting baseline physical data that will be used to help develop a model of channel response to dam removal. We mapped approximately 5.7 km of Bushkill Creek from the confluence with Delaware River upstream to the bridge at Edgewood Ave in Easton. The stream was separated based on physical characteristics into runs, riffles, pools, and dam-formed pools. We measured a total of 30 channel cross-profiles, and measured bed material grain size distributions to characterize the channel upstream and downstream of each existing dam, as well as at the location of a legacy dam that failed some 75 years ago. In addition we have been developing a photo database including modern as well as historical images of the creek and former mill dams. These data will serve as the baseline for continued detailed monitoring of the channel and biotic response to dam removal.