By Billy Birdwell
Following extensive rain in the upper Savannah River basin and more forecasted, the U.S. Army Corps of Engineers began releasing increased outflows from Hartwell, Richard B. Russell and J. Strom Thurmond lakes on July 8.
Inflows from the recent rainfall pushed elevations into the flood control storage pool at all three reservoirs. On July 8 and 9, the Hartwell sub-basin alone received more than 3 inches of rain, bringing the Hartwell reservoir to the top of its flood storage capacity at 665 ft-msl.
In accordance with our standard operating procedures, we opened the spillway gates at the Hartwell Dam in the early morning hours of July 9 to lower the reservoir below 665 ft-msl, the top of the spillway gates.
As of 3 p.m. on July 9, the elevation at Hartwell Lake was 664.46 ft.msl, at Richard B. Russell, 478.48 ft.-msl, and at J. Strom Thurmond 331.83 ft.-msl.
For the next several weeks, we will release water from the flood storage pools at the Thurmond, Russell and Hartwell dams until all flood storage pools drop to near guide curve for this time of year, or 660 ft.-msl at Hartwell, 475 ft-msl at Russell and 330 ft.-msl at Thurmond.
The flood storage pools are the capacity of the reservoirs above “full pool.” The flood storage pools temporarily store excess storm runoff in the three-lake Savannah River Basin system.
“Our first concern is public safety,” said Corps hydrologist Stan Simpson. “We activated our standard plans for reducing reservoir levels with controlled releases first through our generation turbines. When more rains came Monday night above Hartwell Lake, we needed to increase our releases by passing water through the spillway gates – also part of our standard water management plans.”
“We also must consider the possibility of additional rainfall that could hit our area as tropical storm Chantal approaches the East Coast,” Simpson said. Flood risk reduction is a primary mission of the reservoirs.
Daily average outflows from the Thurmond Dam will be managed to approximately 25,000 cubic feet per second (cfs) averaged over each 24-hour period this week. Water managers issued a revised declaration July 9 calling for increased outflows. During this period of high flow, we will likely issue new declarations frequently.
The Corps of Engineers plans to manage flows at or less than 30,000 cfs at Augusta. However, with downstream inflows, river flows at the New Savannah Bluff Lock and Dam gauge may exceed 30,000 cfs –within river channel capacity. Some minor flooding of docks is expected downstream of Thurmond Dam. Agricultural interests may have some flooding at flows below 30,000 cfs.
With above normal releases, river velocities will be much higher than normal. Boaters, anglers, and others using the river below the Thurmond Dam should exercise extreme caution and should wear a life jacket at all times when on or even near the river. Some low-lying areas could be inundated. Dock owners at all locations should be prepared to adjust their docks if necessary.
The Corps of Engineers has received reports of large debris in the reservoirs and in the Savannah River as well as some inundated signs. Some recreation areas and facilities including boat ramps and courtesy docks have closed due to high water.
The rapid rise in reservoir levels demonstrates why we set guide curves as we did for the reservoirs. Keeping the reservoirs above full pool limits the amount of flood storage we have. For example, from July 4 – 8 Hartwell Lake rose three feet. With some inflows in that period exceeding 33,000 cfs, we saw a rapid rise in spite of discharges in the 10,000 cfs range. Keeping water levels near guide curve allows us to release water in a more controlled way following massive storms.
Spillway gate tests previously scheduled for July 10 at Hartwell Dam and July 11 at Russell Dam and Thurmond Dam remain on schedule.
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