Posted on Sun, Dec. 02, 2007 - The State website: http://www.thestate.com/local/story/245793.html
Water from the Edisto River is sinking into the underground water table, raising concerns for the future
By JOEY HOLLEMAN - jholleman@thestate.com
Run one gallon of water out of each of two faucets into a bowl. How much water should be in the bowl? One plus one, right? It seems like simple math. But during severe drought, nothing is simple.
Take the Edisto River. Or what’s left of it.
Add the volume of water flowing from the North Fork Edisto and the volume coming from the South Fork Edisto. Then, measure the volume 40 miles downstream from where the forks meet.
The finding?
One plus one doesn’t equal two. Instead, the river is losing 28 percent of its water in those 40 miles. The only explanation is water is flowing from the bottom of the river into the sinking underground water table, said Bud Badr, chief hydrologist with the S.C. Department of Natural Resources. “It’s something I read about in the books, but I’d never seen it (in interior South Carolina) until 2002,” said Badr.
As drought ravages much of the Southeast, the shrinking Edisto has yet to threaten industries or cities that rely on the river. But, Badr says, the river’s plight should prompt South Carolinians to rethink how we use water. A ‘LOSING STREAM’
Why is the Edisto shrinking?
Part of the answer is the state’s underground water supply never truly recovered from the 1998-2002 drought. Also, droughts keep getting worse because of population growth. That growth sucks water from the underground water system. It also covers more land with roofs and roads that quickly lose water instead of allowing it to soak in.
Usually, the downstream volume of the Edisto is much greater than the sum of its two upstream branches. That volume increases as small tributaries join the river and the water table also seeps water into the Edisto. In hydrological terms, that kind of healthy waterway is called a “gaining stream.”
Lately, however, the Edisto has been a “losing stream.” That’s not unusual on small rivers near the coast — like the Combahee and Salkahatchie — or in desert regions out West. But it’s rare on more extensive inland systems like the Edisto. It’s happened before, however, in 2002 on the Lynches River.
Then, near the end of a four-year drought, the Lynches briefly turned into a losing stream, Badr said. However, tropical rains in fall 2002 broke the drought, and things returned to normal on the surface.
But while 2003 was wet, it wasn’t wet enough to fill underground water storage areas. And none of the subsequent years has had above normal rainfall. Water levels in monitored deep wells barely rose back to normal in 2003 and have been sinking since. Those wells reach to large aquifers, pressurized river-like water deposits 50 feet or more below the surface. Because the ground never re-saturated after 2002, the state was ill-prepared when the current drought began in 2006.
Now, the Edisto and the Lynches rivers have become losing streams again — but this time much more quickly than in the past, Badr said.
213 + 224 = 316?
Here’s how that plays out on the Edisto.
For the first three months of November, the average flow on the South Fork Edisto at Bamberg was 213.3 cubic feet of water per second and 224.5 cubic feet of water per second on the North Fork Edisto at Orangeburg. That’s 437.8 cubic feet per second. But 40 miles below the point where the two forks combine, the river registers 316.5 cubic feet of water per second at Givhans.
For those who live on the river, it adds up to lots of sandbars and no room for motorized boats. “There has been no boat traffic on the river lately,” said Ann Shahid, who lives near the river a few miles north of Givhans. “We’re on a deep section, but you can go 100 yards upstream or 100 yards downstream, and it’s nothing but sandbars.”
Jason Hickman, a ranger at Colleton State Park, said conditions were worse during the summer before a couple of tropical systems brushed close enough to rain on the immediate coast. “Four months ago, you could walk a mile and a half upstream from the park in the middle of the river,” Hickman said.
Losing streams aren’t as much of a concern in the thicker, clay-based soil north and west of I-20. However, those areas have received so little rainfall that most streams are at record lows even without losing water to the water table.
Thus far, the shrinking Edisto has created few problems. There’s enough flow in the river to maintain industries along the river and provide for the Charleston Water System, which gets about 10 percent of its water from the Edisto.
But the river’s losing stream status means things could go downhill quickly, Badr warned. “It’s advisable for people who use the water from the river to be aware of the phenomena and manage their water accordingly,” Badr said.
‘WE CAN RUN OUT OF WATER’
Losing streams emphasize a point Badr has been making for years. “We can run out of water,” he said. “It’s a dynamic process. We can’t just keep doing things the way we did 50-100 years ago. He suggests farmers grow more drought-tolerant crops and have more farm ponds. Fewer roofs and fewer paved roads also would help. Water running off hard surfaces — like a roof or road — bypasses the water table, flowing quickly into streams and then into the ocean. “We have plenty of water on the planet,” Badr said. “We just need to think of different ways to do things so we can cope with these more frequent droughts.”
Reach Holleman at (803) 771-8366
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