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Holtwood Dam (also Holtwood Hydroelectric Dam, Holtwood Hydroelectric Plant, McCalls Ferry Dam) is the oldest of three major dams built across the lower Susquehanna River, and the middle location of the three. It was constructed as the McCalls Ferry Dam between 1905 and 1910 by the Pennsylvania Water & Power Company. The dam was renamed Holtwood in honor of two company executives.〔(【引用サイトリンク】title= The Conestoga Area Historical Society - Martic Township )〕 PW&P merged with the current owner of the dam, Pennsylvania Power & Light (PPL), in 1955. ==Holtwood hydroelectric plant== The Holtwood Hydroelectric Plant produces 109 Megawatts of power, using 10 turbine driven generators. The dam consists of a main concrete dam, which is mostly one continuous spillway, with a power house at the eastern end. The water level is raised by wooden flash boards and inflatable dam sections.〔(【引用サイトリンク】title= Lake Aldred Water Level to Drop for Holtwood Dam Maintenance )〕 The western end of the dam has the original, and ineffective, fish ladder. In the mid 1990s, construction started on a fish lift. The fish lift and dam were damaged by heavy rain and rapid snowmelt from the severe 1996 flood in January of that year. The new fish lift was completed in time for the 1997 season〔(【引用サイトリンク】 title= How Fish Lifts Work )〕 and began lifting american shad and other migratory fish species. The Kingsbury thrust bearing of Holtwood's Generator No. 5 is designated an International Historic Mechanical Engineering Landmark. Previously used roller bearings would last about 2 months under the generator's 220 ton load, but the Kingsbury bearing has been in use since 1912. The impounded water, Lake Aldred, was originally dredged for anthracite coal silt, or ''fines'', washed downstream from the coal mining regions of Pennsylvania. This coal was used in the adjacent Holtwood Steam Generator station. When Safe Harbor Dam was built upstream, its impoundment was then "mined" for coal as well. More efficient primary mining upstream reduced the availability of fines, and 1972 environmental laws made the dredging impractical, so coal was brought in by train.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Holtwood Dam」の詳細全文を読む スポンサード リンク
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