Fort Mill Times

Data shows Lake Wylie can handle 6 more inches of water. So why won’t it happen for years?

Duke Energy has a plan to raise target lake elevations for three of its largest lakes on the Catawba, including Lake Wylie.
Duke Energy has a plan to raise target lake elevations for three of its largest lakes on the Catawba, including Lake Wylie. Herald file photo

The numbers show, it could do far more good for the Catawba River than it would cause harm. Other numbers show, it won’t be happening soon.

Duke Energy has a plan to raise target lake elevations for three of its largest lakes on the Catawba. The company also has data showing the increases aren’t likely to lead to more flooding. Duke also has a need. Municipal water providers and the company have been meeting for more than a decade now, with considerable time in recent years devoted to pushing out the time line for how long the river can support business, residential and overall community growth in the basin.

Raising summer target levels for lakes Wylie, Norman and James by six inches is a major piece of that puzzle.

“These six inches create 8 billion additional gallons of water available during the summer months,” Mark Oakley, Duke’s licensing project manager, recently told the Catawba-Wateree River Basin Advisory Commission. “If this were the only thing we did, it would extend the yield of the Catawba by a decade.”

Potential impacts

So, why isn’t it happening already? First, Duke didn’t want to increase the target elevations without considering what impacts the move might have.

“The chief concern being, would that extra storage create an exacerbated risk of high water situations up and down the river?” Oakley said.

His company ran the numbers. Lake James, at the headwaters in North Carolina, would face the greatest risk of flooding if it couldn’t release enough water into a saturated system. Duke ran weather and water models out 29,950 days — 82 years — comparing current targets with the new ones. Lake James would be likely to face spillover conditions 17 more days in that span. A figure Oakley said isn’t statistically significant compared to the benefit of higher targets.

Another concern, and one ensuring the targets won’t increase anytime soon, comes downstream. Residents along Lake Wateree were concerned planned improvements to a dam there aren’t done yet. A spillway on Wateree would be finished within eight years of Duke getting its federal hydroelectric license from the Federal Energy Regulatory Commission. Oakley recently told the bi-state advisory group his company hadn’t heard from the U.S. Court of Appeals since March on the status of that license, and doesn’t know when he will.

More than a water quantity issue

Duke applied for a 50-year license, but FERC issued a 40-year one in late 2015. Duke appealed, with millions of dollars in recreation improvements, land conservation and more contingent upon the license length.

The plan now is to raise summer target elevations by Dec. 31, 2025 or when the Wateree spillway is complete — whichever is later. If that projects takes the full eight years after the final license date, it could be some time before the change given that clock hasn’t started yet.

The FERC license itself doesn’t mandate exact target elevations, as long as they fit in between critical low elevations and the full pond elevation where flooding begins. The target for Lake Wylie now is three feet below full pond. So even with another six inches of water, the lake has two-and-a-half feet before it risks flooding.

On Lake Wylie, it’s more than just a water quantity issue. It could be the difference in boats or docks staying afloat during dry weather, rather than resting on the lake bed.

“The additional water volume is not there exclusively for Duke’s use,” Oakley said. “It’s for all uses.”

Not exact science

Maintaining water levels on a major bi-state river with 11 reservoirs isn’t an exact science. Which is part of the reason target elevations typically sit about halfway between critical low and high points. Duke wants to have enough storage to withstand drought conditions, but enough mobility in case major rain events threaten.

Just recently, the company ran water through the system ahead of a hurricane projected to dump rain throughout the basin. When it didn’t, the water level sat a little lower than Duke anticipated.

“Irma turned west,” Oakley said. “It caused us to have to change our plans.”

Running water through the system to prevent flooding is a fairly manageable task for Duke, as long as it operates the basin as a system to avoid deluging any one downstream point. Refilling the lake during drought is another issue. Like anyone else, the company largely has to wait on rain. So higher target elevations could prevent against a greater threat in drought than a more workable one with flooding.

It was drought that started the conversation years ago on extending the yield of the Catawba. A rainfall deficit from 1998 to 2002, just as Duke was gearing up toward its license application in 2006, got experts thinking. By the record drought of 2007-08, Duke and water providers had a drought protocol and other early plans in place to help when weather gets dry.

“It was really a wake-up call,” Oakley said.

Initially, models showed the amount of water needed to sustain economic and population growth in the basin would exceed how much the river actually produces by 2048. Several measures like the raised targets, lowering some water intakes and increased conservation, now have that estimate spanning well into the next century.