By Ranger Curt
The seven dams on the Potomac River were originally built to divert water into the canal. Dam #4 provided water for 22 miles of the canal, from Milepost 84.6 downstream to Milepost 62.3, just above Harpers Ferry. The water was regulated at the guard lock at Dam #4 to maintain a consistent level of water traveling at two miles per hour down the canal prism.
For the past hundred years Dam #4 has also been capturing the water's power at a facility on the West Virginia side of the river. This hydro-electric gravity dam, built in 1913 and modified in 1994, is 20 feet tall and approximately 800 feet across. It uses a drive belt to transfer power from the river to the turbines. They in turn provide electric power to people in Washington County. True water power!
In 2012, repairs to the Big Slackwater section of the towpath will be completed and visitors will have the opportunity to approach Dam #4 not only from the east, but also from McMahon's Mill and points west. With the completion of this project more visitors will have the chance to experience the Dam #4 rush. Feel the power.
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The roar of the water flowing over Dam #4 is a testament of the power of the Potomac River. The dam is 800 feet long and about 20 feet high.
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Boats entered or exited the canal from the Potomac River just west of Dam #4 and traveled in the Big Slackwater on the river for two miles.
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During times of floods, beams were lowered from the Dam #4 winch house to divert the rush of water down the canal prism and prevent damage to canal structures.
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Across the Potomac River at the south end of Dam #4 is a power plant built by Martinsburg Power Company in 1909. This plant is still operated by Alleghany Power and still uses African sisal rope in ... Read More
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The turbulent waters around Dam #4 provide ideal fishing.







