ANTHROPOGENIC ALTERATIONS TO SEDIMENT DYNAMICS AND CHANNEL MORPHOLOGY ALONG MILL CREEK, ERIE PA
In the early 19th century, local residents constructed an earthen dam at the current location of Headwaters Park for ice harvesting and recreation. Upstream of the dam, channel aggradation of ~ 2 m had induced ~ 80,000 m3 of valley bottom aggradation. This dam failed catastrophically on August 3rd 1915 after three days of intense rain; the dam was never repaired. Currently, upstream of the dam, Mill Creek has incised a narrow channel into the pond sediments and the sinuosity of the stream channel has decreased through time. Erosion of fine-grained deposits upstream of the dam has initiated downstream floodplain aggradation. Sediment thickness decreases downstream of the dam with the thickest sediments (1.5 m) within 10 m of the dam. Sediments become progressively thinner (0.6 m) farther downstream. The volume of sediments evacuated from the ponded reach is similar to the volume of sediments on the downstream floodplain suggesting the majority of the pond sediments are redeposited in close proximity to the dam. Deposition of fine-grained sediment has changed the channel morphology from a single threaded channel to a multithreaded channel. After initial post-dam aggradation, the channel has incised 1.5 m producing a terrace, which impedes erosion of much of the redeposited pond sediments. Thus, a century after the dam failure the majority of anthropogenic sediments have moved less than 250 meters.