Thesis advisor: Noah P. Snyder / Dam-influenced streambank morphology has not been studied extensively in rivers in deglaciated landscapes with high densities of colonial-era milldams. Fluvial restoration in the eastern U.S. often focuses on understanding pre-Colonial floodplain processes. Recent work by Walter and Merritts (2008a) in the Piedmont of the U.S. mid-Atlantic region suggests milldams significantly impact sedimentation by creating surfaces composed of post-dam legacy sediment that are often abandoned by the river and function as fill terraces. I analyze channel morphology and sedimentation patterns upstream of two breached dams on the Sheepscot River in mid-coastal Maine using lidar digital elevation models, historical aerial photographs, radiocarbon dating, and hydraulic modeling. In the past several decades, observable channel morphologic changes occurred at the two study sites: Maxcy's Mills dam (built in 1809, it was 2-m high and breached in the late 1950s), and at Head Tide dam (built in the 1760s, it is 4-m high and was partially breached in 1952). The Sheepscot River has a native population of Atlantic salmon, which is a federally listed endangered species. Understanding the existence and transport of legacy sediment has become an important component of habitat restoration efforts in the region. The goal of this investigation is to determine the extent and morphologic function of legacy sediment in order to better understand how historical dam sites affect channel morphology and sediment transport in a post-glacial, low-gradient river system. Field and remote sensing analyses indicate that surfaces (up to 2.65 m high) composed of mud and sand function as floodplains 1 km upstream from Head Tide dam and surfaces 90 cm high continue 2.5 km upstream from Maxcy's Mills. Analysis of seven radiocarbon dates from pieces of tree bark sampled from the stratigraphy (58-187 cm below the surface) of the two study sites suggest up to 1.8 m of sediment upstream of the two study sites was deposited within the past 300 years and is therefore a legacy of the dams. Quantification of the total volume of stored legacy sediment is on the same scale as volumes observed in the mid-Atlantic Piedmont region, leading to the conclusion that post-glacial rivers in northern New England store milldam sediment in similar fashion to streams analyzed in the Walter and Merritts (2008a) study. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

In 2001 the World Commission of Dams concluded that the economic, social and environmental cost of dams has been unacceptably high. As a result, dam removal is emerging as a promising option in addressing these concerns. However, dam removal is a contentious issue sharply divided between biophysical and socioeconomic interests. The purpose of this thesis is to conduct an explanatory case study of Eden Mills, Ontario to investigate the process of dam removal consideration. It was determined that i) safety ii) economics iii) social value and iv) environmental impact were critical variables influencing the decision-making process. Following site analysis, key-informant interviews and a design vignette survey it was determined that Eden Mills pursue dam removal as the social value of the millpond no longer justified the sustained economic and biophysical costs associated with the dam. This process theory can be applied to other dam removal scenarios to facilitate the decision making process.