Seneca Dam
Seneca Dam | |
---|---|
U.S. Army Corps of Engineers | |
Dam and spillways | |
Type of dam | Concrete gravity |
Impounds | Potomac River |
Height | 87 ft (27 m) |
Length | 2,880 feet (880 m) |
Width (crest) | 28 feet (8.5 m) |
Spillways | 27 |
Spillway type | Gated overflow at dam crest |
Reservoir | |
Total capacity | 1,193,000 acre-feet (1.472 km3) |
Surface area | 24,000 acres (9,700 ha) |
Normal elevation | 226 ft (69 m) |
Seneca Dam was the last in a series of dams proposed on the
The earliest proposals for exploitation of
After a new study mandated by Congress in 1936-37, the Corps of Engineers in 1938 proposed a dam for flood control, power generation and water quality improvement, to be located above Great Falls at Riverbend. The scheme was revived following World War II. Opposition to the flooding of the entire river to Cumberland by a chain of dams, and to the inundation of the Chesapeake and Ohio Canal doomed the Riverbend proposal. However, in 1963 the Corps proposed a new plan to improve water quality on the Potomac, which moved water storage off the main stem of the Potomac to its upper tributaries and scaled the Riverbend dam back to a lower dam at Blockhouse Point, near the mouth of Little Seneca Creek, to be called Seneca Dam. This proposal was debated through the 1960s until it was finally abandoned in 1969.
Great Falls dam proposals
Beginning in the 1880s a series of proposals were made to use the
A detailed plan for a major dam on the Potomac at Great Falls was first advanced by the Corps of Engineers in a 1921 report, which proposed a concrete gravity dam which would include a hydroelectric powerplant. Reservoir capacity was projected at 300,000 acre-feet (0.37 km3) for a 24,000-acre (9,700 ha) reservoir with a reservoir at 215 feet above sea level.[1] Power generation capacity was planned at 105 MW[2] and total cost was projected at $18,616,000 in 1921.[3]
Potomac Basin development
By direction of Congress in 1936 and 1937 the Army Corps of Engineers, which manages Washington D.C.'s water supply system, examined possibilities for flood control along the Potomac. The Corps returned with an ambitious
The Corps plan, which would have inundated nearly all of the defunct
In 1958 the Corps again was directed by Congress to study dams, this time to improve water quality in addition to flood control. Tension between legislation for park use and water management use increased, until President
Water quality and supply concerns that had previously been cited as reasons for dam building were addressed by new Federal requirements for stringent sewage treatment, which greatly improved water quality on the lower Potomac, eliminating the need to dilute effluent in reservoirs. Mine waste discharge was also regulated, with dilution provided by the eventual construction of Jennings Randolph Lake on the North Branch of the Potomac by the Corps of Engineers.[7]
Riverbend Dam
The Riverbend Dam was to be a 119-foot (36 m) dam at the westward bend of the Potomac just above Great Falls. Its reservoir was to extend nearly to Harpers Ferry, with branches extending up the Monocacy River past Frederick and major branches on streams in Loudoun County, Virginia. The dam was to incorporate small locks to allow pleasure boats to reach Harpers Ferry. After intense public opposition the Riverbend project was shelved in favor of less ambitious proposals[4]
Seneca Dam
The final proposal for a lower Potomac dam was Seneca Dam. The concept developed in the 1950s and was proposed by the Corps of Engineers in its final form in the 1963 Potomac River Basin Report. Answering objections to the visual intrusion of the Riverbend Dam at Great Falls, Seneca Dam was placed at Blockhouse Point, about 1.6 miles (2.6 km) downstream from the mouth of
The dam was planned as a straight-crested concrete gravity dam with a central overflow spillway regulated by 27 gates. Provision for future power generation was to be included in the south abutment, with water supply provisions on either end of the dam. No lock was to be provided for small craft.[10] For flood control the project was designed to pass 150,000 cu ft/s (4,200 m3/s) of a 400,000 cu ft/s (11,000 m3/s) flood to minimize damage downstream. Drawdown from May to September was expected to be about 5 feet (1.5 m), with another 7 feet (2.1 m) for the rest of the year. The pool would have varied from 38,700 acres (15,700 ha) at maximum flood pool to 24,000 acres (9,700 ha) at full conservation pool, and 9,100 acres (3,700 ha) at minimum pool. Construction was expected to take six years. The reservoir was planned to store 550,000 acre-feet (0.68 km3), of which 50,000 acre-feet (0.062 km3) were allocated for sedimentation. An additional 643,000 acre-feet (0.793 km3) were available for flood storage.[8]
The reservoir was projected to cost more than $100 million in 1962 dollars. The project was opposed by Maryland and Virginia, as well as by conservation organizations and fell out of favor with the Corps of Engineers in 1969.
Roads and railroads were expected to be flooded by the reservoir and would have had to be replaced. The 1963 report described the relocations as "extensive." Road relocations were budgeted at $8,500,000 and railroads at $10,040,000. About 21,000 acres (8,500 ha) of wildlife habitat was expected to be inundated, including the McKee-Beshers and Dierssen wildlife management areas. 13,120 acres (5,310 ha) of replacement habitat was expected to be required to mitigate habitat loss. The project was judged to have little effect on agriculture and forestry. 460 families were expected to be displaced.[8]
See also
References
- ^ Tyler, M.C. (February 14, 1921). Development of Great Falls for Water Power and Increase of Water Supply for the District of Columbia. Government Printing Office. p. 110.
- ^ Corps of Engineers 1921, p. 49
- ^ Corps of Engineers 1921, p. 50
- ^ a b c Mackintosh, Barry (1991). "4: The Parkway Proposition". Chesapeake and Ohio Canal: The Making of a Park. National Park Service.
- ^ "Details Given on Big Dam Project". Hagerstown Morning Herald. AP. March 28, 1945.
- ^ a b Mackintosh, Barry (1991). "5: The Park Campaign". Chesapeake and Ohio Canal: The Making of a Park. National Park Service.
- ^ Garrett County Government, Oakland, Maryland (November 2014). Garrett County Water and Sewerage Master Plan; 2014 Revision (Draft) (PDF) (Report). pp. 2–10. Retrieved 2015-05-31.
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: CS1 maint: multiple names: authors list (link) - ^ .
- ^ Corps of Engineers 1963, p. 28
- ^ Corps of Engineers 1963, Plate 17
- ^ Corps of Engineers 1963, Plates 18, 19