At its meeting on Wednesday, July 21, 1999, the Board of Directors of Fort Smith, Arkansas, selected a size for the expansion of Lake Fort Smith. The new lake will have a normal pool elevation of 911 feet above mean sea level. The current normal pool elevation of Lake Fort Smith is 825 feet.
The board selected from among several alternative designs with normal pool elevations ranging from 885 to 970 feet.
"An analysis of how water yield and construction costs were related to lake size indicated we could get the most for our money at the 911-foot elevation," said Steve Parke, director of utilities. According to Rebecca Kuhr, project engineer for Burns & McDonnell, the balance between required fill for the construction of the dam embankment and the material available from the excavation of the spillway was critical. A reasonable balance was indicated at a normal pool elevation of 911 feet.
Preliminary designs indicate the existing Lake Fort Smith Dam will be raised 101 feet, or about the height of a ten-story building. The surface area of the lake will more than triple, from 418 acres to about 1,390 acres. This expansion will include 338 acres that are currently Lake Shepherd Springs.
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The Lake Shepherd Springs Dam will be removed and the materials used to construct the new dam. The new Lake Fort Smith will hold about 27.5 billion gallons of water, or nearly five times as much as the current Lake Fort Smith and Lake Shepherd Springs combined. Based on the size of the lake's watershed and historic amounts of rainfall, the new Lake Fort Smith should be able to provide 51.2 million gallons of water per day day 49 out of 50 years. This yield is predicted to meet the growing demand for water in the Fort Smith area for about the next 50 years.
What's Next?
The establishment of the lake's new elevation allows the final design process to start and the environmental impact analysis to be completed.
"Designing the spillway will be the next major challenge," said Frank Shorney, project manager for Burns & McDonnell. "The spillway must be wide enough and the dam must be high enough to pass the probable maximum flood without over-topping the dam. At the same time, the spillway must be narrow enough to fit in the available space and not increase downstream flooding from a 100-year storm."
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