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A program of <u>in situ</u> and laboratory studies was conducted to elucidate the role of the deposited sediments of the Niagara Reservoir in affecting the quality of the flow of the Roanoke River above the headwaters of Smith Mountain Lake. Agronomic analysis techniques were adapted and applied to provide quantitative analysis capability for the sediments. The superficial sediments were observed to constitute a considerable reservoir of nitrogen and phosphorus, which, during the anoxic bottom conditions occurring during the summer months, caused an enhancement of concentrations in the water column. Conversely, during the winter months, the superficial sediments acted as a phosphorus and nitrogen sink, removing both materials from the water column. Laboratory batch and microcosm studies made it possible to quantify the release and removal of nitrogen and phosphorus under aerobic and anaerobic conditions, and to elucidate the factors upon which the exchanges depended. The phosphorus interactions were found to be governed principally by sediment iron and organic matter content. Under aerobic conditions, phosphorus adsorption could be described by the Langmuir Isotherm. The most important nitrogen release mechanism was found to be a cation exchange phenomenon under reducing conditions. Aithough the effective zone of exchange was found to extend only about 2 mm into the sediment surface, the analysis of cores showed the existing profile to be rich in both phosphorus and nitrogen forms, which could be exposed to the water column with sufficient mixing. The deposited sediments of Niagara Impoundment showed a capacity to redistribute the impoundment influent nutrient load, causing an enhance~ ment of the quantities released during the summer months, thus magnifying the impact on the waters of Smith Mountain Lake. The maintenance of aerobic benthic conditions could, at a tremendous energy cost, prevent the sediment releases from occurring. In the long term, sediment nutrients deposited in the past, without proper control, could provide a continuing source of N and P to the waters of Smith Mountain Lake, thereby reducing the effectiveness of upstream control of point and diffuse sources. / Ph. D.

Tidal energy is a clean, sustainable, reliable, predictable source of energy. Recent developments in underwater turbines have made harvesting tidal energy feasible. Determining the power potential available in a given water body can be accomplished by using numerical hydraulic models to predict the flow velocity at a location of interest. The East River in Manhattan has been used here in an effort to develop a modeling methodology for assessing the power potential of a site. Two two-dimensional CFD models, FESWMS and TUFLOW, as well as one one-dimensional model, HEC-RAS, are used to analyze flows in the East River. Comparisons are made between the models and TUFLOW proves to best represent flows in the East River. HEC-RAS provides accurate results; however, the one-dimensional results lack the necessary detail of a two-dimensional model. FESWMS cannot produce results that mimic actual flow conditions in the East River. Using the TUFLOW model, power and energy estimates are made. These estimates show that a two-dimensional model, such as TUFLOW, can be a great tool for engineers and planners developing tidal energy projects. Using the results of this work, a methodology is developed to assess power potential at other sites using publicly available data. / Master of Science

For the last three years, D.C. United and the District of Columbia have been negotiating a site for a new stadium for their soccer club. The owners of United wanted to take a small parcel of the land now known as "Poplar Point", an undeveloped brown-field on the Southeast side of the Anacostia River. The switch from the Anthony Williams to the Adrian Fenty administration in 2007 has proven unkind for the club, which to this day is embroiled in negotiations with the City for the Poplar Point site. While following this debate in the media, I couldn't help but question why United was not pursuing a plot of land on their current site. The club now plays in RFK Stadium, a venue ill-equipped for the sport that costs the club millions of dollars a year because they cannot fill its stands. The site, however, is located on axis with the Capitol, the Washington Monument, and the Lincoln Memorial. My initial research brought me to France in the 18th century. / Master of Science

Since the beginning of civilization rivers are strongly linked to the identity and vitality of cities. they provide water, means of transportation, spaces for urban expansion, and a defined boundary which contributes to the identity of a city. Rivers are often the raison d'etre of cities, and their inhabitants have an intricate relationship with it. Such sites are often a target for impulsive and premature development. in the case of zahle, a city established on the banks of the berdawni river, the area has seen part of its precious asset disappear under an underground parking, forming an artificial barrier, between two urban parts, and a void in the identity of the city. This thesis proposes that urban stitching based on architectural elements can reconnect different parts of the city. how architectural measures can fabricate reminders of a former presence of elements and artifacts, while defining an iconic public architecture, and a modern riverfront with a new urban identity, thus raising the quality of the city. / Master of Architecture

Water edge communities are portals to terra firma. Their role as negotiators between land and water is more important now than ever before due to increasing fluctuations in water height from storm surges and sea level rise. To understand the future of these edge conditions, my research looks to the past at a 1967 report entitled; The Potomac: A Report on Its Imperiled Future and a Guide for Its Orderly Development, authored by pioneers Stewart Udall, Ian McHarg and others. The report approached the ecology and culture of the Potomac River basin through the lens of the 1960s, a time of unprecedented growth. Emerging at the semi-centennial of the original report, my thesis is both an homage and critique, challenging its concepts of order and development, and redefining four of the original eleven principles in the report's concept of the ideal region. The thesis investigation also works within a more actionable scale of intervention, a tributary to the Potomac River. The project develops a transferable approach for other tributaries, exploring Quantico Creek and the town of Dumfries, Virginia, a historic seaport in Prince William County, as a case study for design intervention, and analyzes the historic and ecological conditions that led to the marginalization of the community in the wake of siltation and urban sprawl. The resulting proposal reconnects the community with the creek, and fulfills an intention of the original Potomac Report: to spark inspired realities along the river's 400-mile course. / Master of Landscape Architecture / Water edge communities hold much of the nation's history and are heavily impacted by climate change phenomena. To better understand how to plan and design for these communities, my research re-examines a 1967 report entitled; The Potomac: A Report on Its Imperiled Future and a Guide for Its Orderly Development, authored by some of the most influential designers, planners and conservationists of their era. The report approached the ecology and culture of the Potomac River basin through the lens of the 1960s, a time of large scale development and suburban growth. Fifty years later, my thesis recognizes the aspects of the report that are applicable to planning and design today and recommends changes in the approaches and methodologies of the report for continued use in other communities. The thesis design proposal is at the scale of a small tributary called Quantico Creek in Prince William County, Virginia. The project proposal reconnects the community of Dumfries, VA with Quantico Creek by making it an accessible, public waterfront, and fulfills an intention of the original Potomac Report: to spark inspired realities along the Potomac River’s 400-mile course.