Clearing weather forecast precludes predicted opening of Hartwell Dam spillway gates


In the midst of torrential rains earlier this week, the water level in Lake Hartwell rose above full pool, and U.S. Army Corps of Engineers officials began looking at the possibility of opening the spillway gates – an action not taken since 2016, when the gates were opened for flood control for only the fourth time in the lake’s history.


Initially, with continuing intense bands of rain forecasted for this past week, Corps officials indicated the flood gates would possibly have to be opened during the week. However, with rainfall falling short of the forecasted amounts, and the lake level remaining below flood pool, the Corps announced Wednesday that flood gates would likely not be opened before today, Friday Feb. 14.


Now, with a National Weather Service forecast for the Lake Hartwell region predicting little more than isolated showers scattered throughout the coming week, The Corps is putting a hold on any plan to open the spillway gates.


“At this time, we will not be opening the gates any time this long weekend, and it is not looking like will need to until maybe late next week, Corps Senior Public Affairs Officer Billy Birdwell told ConnectLocal.News this morning at 10 a.m. “This far out – five or six days ahead – it’s hard to predict, but at this point, it (opening of the spillway gates) wont happen before late next week.”


Lake Hartwell, as of 5:23 a.m. this morning, Feb. 14, is 663.00 feet above Mean Sea Level – 5 feet above the Feb. 14 “guide curve elevation” - the Corp’s operational target elevation for the specified period – of 657.93 MSL, and 6.38 feet above the the average elevation of 656.62 MSL.


However, even with the 8.57 inches of precipitation in the first 13 days of February – an amount topping the 7.91 inch monthly total for January and the 7.66 inch December total, Lake Hartwell remains below the flood pool level of 665.00 MSL – with 29 percent of the flood storage of 5 inches remaining before the lake is officially termed “flooded.”


FYI



Hartwell Lake, built by the U.S. Army Corps of Engineers, is a man-made lake bordering Georgia and South Carolina on the Savannah, Tugaloo, and Seneca Rivers. The lake is created by Hartwell Dam located on the Savannah River seven miles below the point at which the Tugaloo and Seneca Rivers join to form the Savannah.


Extending 49 miles up the Tugaloo and 45 miles up the Seneca at normal pool elevation, Hartwell Lake comprises nearly 56,000 acres of water with a shoreline of 962 miles. The entire Hartwell “Project” contains 76,450 acres of land and water.


The Savannah River begins 7.1 miles above the Hartwell Dam at the confluence of the Tugaloo and Seneca Rivers and is approximately 315 miles long. The river ends in the Atlantic Ocean near Savannah, Georgia.


Congress authorized Hartwell in 1950 and construction began in October 1955. The project was completed in 1963 at a cost of more than $89 million. Construction of the dam began in 1955 and was completed in 1959.


Hartwell Lake and Dam is the second Corps of Engineers project to be built in the Savannah River Basin. The first, J. Strom Thurmond Lake and Dam, was completed in 1952. A third project, Richard B. Russell Lake and Dam was completed in 1985.


The Hartwell powerplant was completed in 1961; the first generator went on-line at on April 27, 1962.


The 15,840-foot Hartwell Dam is built of more than 880,000 cubic yards of concrete (enough to build a sidewalk from the dam to San Francisco) and more than 3 million pounds of reinforcing steel.


The depth of the lake behind the dam is approximately 180 feet.


The top of the dam is 204 feet above the Savannah River Bed.


On average, the Hartwell Powerplant produces over 468 million-kilowatt hours per year.


Floodgates at the Hartwell Dam have been opened for flood control purposes four times - in 1964, 1965, 1994 and the last time on Jan. 24, 2016. (They have been opened at other times for maintenance and inspection purposes.).


From 5:30 p.m. on Friday, Jan. 22, to 8:30 a.m. on Monday, Jan. 25, the gates released a total of 37,500 cubic feet of water per second, lowering the reservoir 2.07 feet over the weekend.


The spillway, located on top of the dam, contains 12 large gates, each 40 ft. by 35.5 ft., for the quick release of water from the lake. Water can be released at the rate of 5.8 million gallons per minute with all floodgates open one foot (gates can be opened to five feet or more).


The concrete bucket at the toe of the spillway deflects the flow upward to dissipate its destructive energy and prevent erosion of the foundation. The training walls of the concrete structure at each end of the spillway direct the flow into the river channel below the dam. Water released through the floodgates cannot be used to generate electricity.


The lowest lake level on Hartwell Lake is 637.49 ft. msl reached on December 9, 2008. The previous record low at Hartwell Lake was 642.4 ft. msl, reached on December 24, 1981.


The highest lake elevation reached was 665.4 ft. msl reached on April 8, 1964.


The average lake elevation is 657.5 ft. msl.


The normal pool levels vary during the course of the year, and are governed by what is known as the “rule curve”. The rule curve follows the general course of high in the summer, low in the winter. Full pool in the summer is at elevation 660 ft msl, and full pool in the winter is 656 ft msl. The rule curve specifies that the lake should gradually decline from 660 ft to 656 ft between mid-October and early December, hold steady at 656 ft between early December and early January, then gradually increase from 656 ft in early January to 660 ft in mid-April. Between mid-April and mid-October the lake should remain at 660 ft if possible. Obviously this cannot be attained precisely because of heavy rainfall at times and extended periods of drought at other times. However, over the course of more than 40 years the average lake level has followed the rule curve fairly closely, except that the average has declined from 660 earlier in the summer than specified by the rule curve.


(SOURCE: U.S. ARMY CORPS OF ENGINEERS SAVANNAH DISTRICT)

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