Earlier this summer we asked readers what topics they want to read about on Balancing the Basin. Here’s one of many questions we received:
“Why there is so much fluctuation of river levels between Thurmond dam and Stevens Creek dam?”
The simple answer is because outflows differ during “peak demand” times for hydropower. Here’s a brief explanation:
The Stevens Creek Dam is located about 13 miles downstream of the J. Strom Thurmond Dam and about 8 miles north of the city of Augusta, Georgia. It is owned and operated by South Carolina Electricity and Gas (SCEG). The impoundment area spans a 12-mile stretch along the Savannah River and an 8-mile stretch of Stevens Creek, totaling approximately 2,400 acres.
The river levels between the Thurmond Dam and Stevens Creek Dam experience normal daily fluctuations ranging from three to five feet. The fluctuations are caused by “peaking” operation at the Thurmond Dam. Peaking power is produced during periods of the day when demand for electricity is highest—generally in the afternoon and early evening.
The Thurmond Dam generally “peaks” one to two times per day. Hourly release rates during peak generation could be as high as 35,000 cubic feet per second (cfs). However, our daily average release rate may be as low as 3,800 cfs (when averaged over a 24-hour period).
The Stevens Creek Dam, on the other hand, holds a steady release rate that averages out over the day to roughly the same amount as Thurmond’s daily average release rate. In other words, the Stevens Creek Dam typically targets Thurmond’s daily average outflow every hour of the day. Therefore, river flows are much smoother and steadier below Stevens Creek.
Although originally constructed solely to generate electricity, the Stevens Creek facility now functions as a re-regulating plant to mitigate the downstream effects of the wide-ranging discharges from the Thurmond Dam. As part of its role to control the effects of the Thurmond Dam, Stevens Creek can still produce hydroelectricity. The Stevens Creek facility, as completed in 1925 with the addition of three more turbine-generator units, continues to provide a yearly average of 94 gigawatt-hours of electricity (source: SCEG website).
As always, we welcome your comments. Thanks for reading Balancing the Basin.
~Tracy Robillard, public affairs specialist