PRELIMINARY CHANNEL RESPONSE TO THE REMOVAL OF THREE DAMS: BUSHKILL CREEK, EASTON, PENNSYLVANIA

The Bushkill Creek a tributary that joins the Delaware River in Easton PA, was used for centuries to power mills by use of low-head dams. However, they have not powered mills for many decades. During the past 15 years, plans began to develop to remove several dams on the lower Bushkill to more fully reconnect the creek to the Delaware an allow fish and eels to migrate upstream into the tributary. In anticipation of dam removal, we have been surveying cross sections upstream and downstream of three dams (designated Dams 1, 2, and 3 moving upstream) in the lower Bushkill since 2017. We have previously reported on the immediate response to the removal of Dams 1 and 3 during the summer of 2023. Here we focus primarily on the removal of dam number 2 during the summer of 2024. Because the channel experienced a high flow event sufficient to mobilize the bed subsequent to the removal of dam 2 in June, the channel has already begun to adjust to the new circumstances. Similar to the channel response to removal at Dams 1 and 2, sediment filling occurred in scour holes immediately downstream of Dam 2 and channel bed erosion occurred immediately upstream of the dam to regrade the channel to smooth the energy profile. The situation at Dam 2 was somewhat different than at Dams 1 and 3 insofar as, the dam-generated pool upstream of Dam 2 at ≈435m was longer than the dam-generated pools upstream of Dams 1 and 3 at ≈250m and ≈365m, respectively. Therefore, there is more channel that can experience change through new flow conditions upstream of Dam 2. A new riffle formed at the location of the dam and extended immediately upstream into the downstream section of the old pool. A very surprising result is that immediately upon dam removal and dewatering of the dam-induced pool above Dam 2, a pool-riffle sequence was revealed within what had appeared to be a continuous dam pool. This implies that despite the obvious and persistent impact of the dam by forming a raised water level above the pool at low flow, apparently, during high-flow channel-forming discharge events, channel-forming events were not impacted by the existence of the dam through the entire length of the low flow pool reach, and a pool-riffle sequence existed in this section of the channel that was masked by the low-flow pool above the dam.