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Why we spill when we spill

January 06, 2016   By Kevin F. Langston in Santee Cooper Lakes

An aerial photo of the Santee Spillway taken during October's spilling operations

While many of us were opening presents on Christmas morning, Santee Cooper was opening floodgates at the Santee Spillway on Lake Marion. It was the third time in as many months that we'd be releasing water into the Santee River.

The Santee Cooper Lakes are part of a 15,000 square-mile watershed that stretches into North Carolina — the second largest watershed east of the Mississippi River. Our lakes are at the end of this line, so when we're under drought conditions it's unlikely we'll get very much water from the reservoirs above us. On the other hand, when it floods, that water is coming our way.

Prolonged rainfall throughout this watershed, combined with spilling operations from upstream reservoirs, brought the latest extreme inflows to lakes Marion and Moultrie. We began this current spill on Dec. 25 at a rate of 20,000 cubic feet of water per second (cfs) and brought it to a peak of 97,000 cfs by Jan. 4. We reduced spilling yesterday to 60,000 cfs and will continue to adjust the volume accordingly.

After a particularly dry summer on the Santee Cooper Lakes, we've conducted three significant spills since South Carolina was first drenched by record-breaking rain in early October. That weather event was described by The Weather Channel as "one of the most prolific rainfall events in the modern history of the United States," and delivered devastating damage to nearly half of the state's 46 counties.

We initiated that first spill on Oct. 4 and continued to release water for 11 consecutive days, peaking at a rate just shy of 85,000 cfs on Oct. 6. We conducted a second spill on Nov. 3, which lasted 27 days and averaged 11,825 cfs per day. This second spill was prompted by the return of widespread rainfall throughout the watershed.

So, why do we spill?

Our lakes are home to three hydroelectric facilities. On Lake Moultrie, there is the 127-megawatt Jefferies Hydroelectric Station and the 84-MW St. Stephen Powerhouse, which is owned by the U.S. Army Corps of Engineers. A smaller, 2-MW unit is located at the Santee Spillway on Lake Marion. Because of these facilities, Santee Cooper's Energy Control Center (ECC) is responsible for monitoring and managing our lake levels. ECC tracks things like current lake elevations, weather conditions and forecasts, and historical lake data to develop daily forecasts, which are then used to determine whether to dispatch the hydroelectric units or release water through the spillway. The ultimate goal is to prevent Lake Marion from exceeding a maximum elevation of 76.8 ft.

The 3,400-ft. Santee Spillway is part of 40 miles of dams and dikes that encircle the Santee Cooper Lakes, and spilling is a normal part of our hydroelectric operations in periods of these extreme inflows. Our dams and dikes have remained secure throughout.

Spilling will continue until further notice, and developments will be noted on our Facebook page and Twitter feed. Information is also be updated each business day on the lakes information line: 1-800-92LAKES.