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DAM REMOVAL 251 Table II. Several past and proposed dam removals discussed in published work and reviewed here Dam River State Date of Removal Washington Water Power Dam South Fork of the Clearwater River Idaho Removed in 1962 Fort Edward Dam Hudson River New York Removed in 1973 Newaygo Dam Muskegon River Michigan Removed in 1969 Woolen Mills Dam Milwaukee River Wisconsin Removed in 1988 Salling Dam AuSable River Michigan Removed in 1992 Columbia Falls Dam Pleasant River Maine Removed in 1989 Savage Rapids Dam Rogue River Oregon Proposed Edwards Dam Kennebec River Maine Proposed Elwha and Glines Canyon dams Elwha River Washington Proposed Rodman Dam Ocklawaha River Florida Proposed The Fort Edward Dam on the Hudson River was removed in 1973. This removal provides some lessons regarding dam removal and the need for comprehensive pre-removal environmental assessment studies. Fort Edward Dam was a 9.1 m high and 180 m long rock and timber crib dam built in 1817, which was near collapse at the time of removal. The owner, Niagara Mohawk Power Corporation, had received an amendment to their licence from the Federal Power Commission (now the Federal Energy Regulatory Commission) which authorized them to remove the dam. One year after removal, the US Army Corps of Engineers documented sediment/debris blockage of the downstream Champlain Canal which connects the Hudson River with Lake Champlain (FPC, 1977). Other areas of the Hudson River were also obstructed by woody debris and sediment moved downstream after removal of the Fort Edward Dam. It was estimated that 336 300 m3 of sediment had moved downstream in one year after removal of the dam, and that 765 000 m3 remained in the floodplain above the dam after the first year of removal. After two years of hearings it was concluded that Niagara Mohawk had complied with all dam removal authori- zation requirements, except the condition to prevent or control water pollution resulting from removal of the dam. It was also concluded that the pre-removal studies were insufficient and that monitoring of sediments should be initiated. The State of New York appropriated $5 million for the clean-up of the downstream materials eroded following removal of the Fort Edward Dam (FERC, 1978). Before removal of the dam, polychlorinated biphenyls (PCBs) were discharged into the Hudson River just upstream (ca. 6 km) from the dam (Tofliemire, 1986). Water levels in the Hudson River above the dam dropped 4-6m after dam removal, and downstream PCB transport has been monitored since the Fort Edward Dam was removed. Although completed over 20 years ago, the Fort Edward Dam removal provides cogent evidence as to why comprehensive and holistic environmental assessments must be completed before a dam is removed. The 1977 Federal Power Commission ruling on this dam removal found that pre-removal studies must assess the presence and potential movement of sediments and other materials both in the vicinity of the dam and upstream in the reservoir. The judge also found that pre-removal studies must be more precise and unambiguous to determine whether a dam removal should be authorized (FPC, 1977; Lewis, 1992). Sediment movement was also observed following the 1969 removal of the Newaygo Dam on the Muskegon River, Michigan. Removal of this dam resulted in the release of impounded sediment which immediately started migrating through the river channel as a sediment wave (Simons and Simons, 1991). As the sediment conditions before dam removal were unknown, a mathematical model was developed to determine the sediment transport and geomorphic changes that have occurred in the system since dam removal and those expected in the future. The dominant physical processes important to dam removal and incorporated in the model included the flow of water, sediment transport, sediment routing, degrada- tion, aggradation and bed control due to armouring. It was estimated. that about 40% of the original volume of impounded sediment was washed downstream immediately after removal of the dam. The remain- ing sediment is moving downstream as a sediment wave at approximately 1.6 km per year. With time, the