For much of the year, we concentrate on stakeholders living on or around our three reservoirs along the Savannah River Basin.
However, for a short period each spring, our focus shifts to the residents in those reservoirs.
Water managers and biologists began coordinating earlier this month to maintain steady reservoir levels to provide largemouth bass with optimal spawning conditions and ensure healthy populations for years to come. These efforts will continue for the next two to four weeks.
“This is the single most important thing the Corps contributes to fisheries management,” said James Sykes, Savannah District fisheries biologist.
Biologists mainly target largemouth bass, which are the primary predators and thus essential to maintaining a balance in fish populations. But largemouth bass are also the number 1 game fish for tournaments in all three reservoirs.
And though it might seem nominal, stable reservoir levels help protect these and other fish at a critical stage in their development.
Timing and temperature
As temperatures begin to rise each spring, Sykes and biologists with the Georgia & South Carolina Departments of Natural Resources monitor the water temperatures and make their rounds looking for spawning activity. The bulk of spawning happens once water temperatures stabilize around 65 degrees, which started in mid-April.
When the time is right, male largemouth bass create nests in shallow water (about 6 inches deep) and attract females. After the females lay their eggs, the males remain to guard the nest.
“We can actually see them on the bed,” Sykes said.
At this stage the males and the eggs they guard face extreme vulnerability.
First, the bass make easy pickin’s for birds of prey as they remain in the same relative position in shallow water while guarding the nest.
Additionally, if the water level decreases too much, they will abandon the nest; if the water level rises too much the development of the eggs gets delayed.
Maintaining the reservoir levels within plus or minus 6 inches gives these fish the best chance for success.
Keeping it level
While the fisheries biologists scour the shorelines for spawning activity, our water managers make their mark on the reservoirs, as well.
“We shift from flow maintenance to elevation maintenance during spawning season,” said Stan Simpson, the senior water manager at Savannah District.
Water managers like Simpson and Kat Feingold, who normally must contend with balancing flood risk reduction, hydropower, water supply and recreation, now strive to keep the pools as level as possible.
On top of that, each spring season provides fresh challenges depending on the amount of rainfall the basin receives.
So far this season, thanks to a wet winter, the upper basin has been sitting pretty.
And while that can bode well for a full pool as the recreation season begins, that also means water managers must remain ready to act quickly as storms push through the region, as has happened in the past few weeks.
In these situations, the water managers project releases based on the forecasts, then remain in daily contact with the Southeastern Power Administration, or SEPA, to adjust the releases as the rainfall actually hits the basin.
For example for Easter weekend, forecasts called for Hartwell to receive about an inch of rain.
Feingold and Simpson projected releases of 5,000 cubic feet per second from Hartwell, along with another 6,000 from Russell and 8,000 from Thurmond.
However, the storm that was supposed to just graze Hartwell, sat on the sub-basin and dumped approximately 3 inches, which caused Hartwell to jump nearly 2 feet in a day, Simpson said.
So over the weekend the water managers made adjustments, sometimes twice in a day, and changed those releases to 15,000 cfs for each reservoir on Saturday, and to 19,000 cfs (Hartwell), 25,000 cfs (Russell) and 19,000 cfs (Thurmond) on Sunday.
“Basically, you’re letting the storms pass through the system,” Feingold said.
“We want to get it back to that target as quickly as possible,” Simpson said, referring to the original level when the spawning season began. (In this case, those targets are 660.5 feet at Hartwell, 475 feet at Russell, and 328 feet at Thurmond.)
Simpson said the fish take precedence during spawning season but there is a limit.
When storms bring too much rainfall, water managers are restricted in the amount of water they can release downstream at Thurmond because releases above 25,000 cfs can cause damage.
Similarly, they treat using the spillways (versus passing water through the generators in the dam) as an absolute last resort because of the potential damage it could cause, as well as wasted potential energy.
In those cases, the reservoir levels can rise to a less than ideal level for fish spawning.
On the other end of the spectrum during droughts, like the basin experienced just a few years ago, water managers do their best to maintain levels at Hartwell and Russell, but are required to release a daily average of 3,800 cfs (at trigger level 3) at Thurmond Dam to ensure downstream stakeholders have access to those resources.
“It’s a juggling act,” Simpson said.
If all goes according to plan the fish hatch, develop into fry and stay together in schools for about a month, Sykes said.
The papa fish no longer guards them, so they must seek shelter among the shoreline plants. This is where fisheries biologists enter the equation again.
For the past 20 years Savannah District has managed an aquatic plant nursery at Russell Lake. This past winter, Thurmond Lake built a nursery, as well.
Biologists focus on two native plant species at the nurseries – water willow and maiden cane, which can both withstand drought and flood conditions.
Each summer, staff and volunteers plant about 5,000 of these species along the shoreline to provide cover for the developing fish.
It’s another small investment that Sykes predicts will pay off big down the road.
“I think it’s going to be a great year and that we’ll have successful spawning levels on all three lakes,” he said.
~ Jeremy S. Buddemeier, Corporate Communications Office