Heavy rain fills Beaver Lake, affecting water quality and safety

NWA Democrat-Gazette/DAVID GOTTSCHALK A motorist on a scooter passes Tuesday over a flooded low water bridge on Roosevelt Street in Johnson. Heavy rain Monday night pushed Clear Creek out of its banks. For photo galleries, go to nwadg.com/photos.
NWA Democrat-Gazette/DAVID GOTTSCHALK A motorist on a scooter passes Tuesday over a flooded low water bridge on Roosevelt Street in Johnson. Heavy rain Monday night pushed Clear Creek out of its banks. For photo galleries, go to nwadg.com/photos.

FAYETTEVILLE -- Forecasters have called for more rain this week even as the month's heavy rainfall pushed Beaver Lake to its highest level in four years, making it dangerous for boaters and difficult to clean for the region's tap water.

The National Weather Service on Tuesday said Northwest Arkansas has a roughly 50 percent chance for thunderstorms every day until Sunday, when the chances start to fall.

Beaver Lake

• Area: About 45 square miles

• Water level Tuesday afternoon: 1,129.3 feet above sea level

• Flood level: 1,130 feet

• Water level 1 year ago: 1,120.8 feet.

• Amount of water per foot: Roughly 10 billion gallons

Source: Staff report

High temperatures should reach near 80.

Between 10 and 12 inches of rain have fallen this month, or about twice the normal monthly amount, from Bentonville to Fayetteville, according to the weather service. Storms over the holiday weekend dropped 2 to 4 inches, sending billions of gallons of water gushing through rivers in Benton, Madison and Washington counties toward the lake.

The Army Corps of Engineers opened the lake dam's flood gates Monday for the first time since 2011, releasing seven roaring cascades onto the White River below. The lake's water level rose 2 feet from Saturday to Monday, according to the weather service. It was less than a foot from overflowing the gates for most of Monday and Tuesday.

The dam's pair of hydropower turbines, which provide supplemental power to six states, was churning out hundreds of megawatts of electricity both days when they'd normally generate for only a few hours a day, said Alan Bland, corps park ranger.

"We would much rather generate it out than open the gates, but even the generators couldn't handle it," Bland said.

The corps monitors every stream and river flowing into the lake to tell when the gates need to be opened, Bland said. The gates are strictly a reaction to those stream's levels, he said, meaning the corps won't preemptively open them because of weather predictions.

"There's a chance by this afternoon or tonight sometime we'll lower them," he said Tuesday. "All our water goes to Table Rock (Lake), which had room for us."

He warned boaters the lake was full of trees and other debris "from the dam all the way to Fayetteville."

"It's just really bad right now, so for a couple of weeks there's going to be a boating hazard on the lake," Bland said. "Please be on the lookout and wear that life jacket."

The heavy runoff also means the water coming in is carrying more sediment, said Larry Lloyd, chief operating officer for the Beaver Water District. The district sells water indirectly to most residents in the state's northwest corner.

Measurements of the water's cloudiness, or turbidity, found six times the normal amount of sediment Tuesday, Lloyd said. The district's cleaning process can take care of all of that dirt, but it will require more treatment, he said.

The sudden influx of fresh water also affects the lake's chemistry, making it react differently to acidic compounds used in the treatment, Lloyd said. When that happens, the district switches from an acid to an artificial polymer that's more expensive. Any impact on consumers should be minimal unless the district needs more of that polymer than expected for the year, Lloyd said.

"It's an increased treatment cost and it's more difficult to treat, but it's something we've handled before," he said.

Finally, the extra water could be mixing up the entire lake, Lloyd said. This time of year, the lake typically separates into distinct layers of colder and warmer water. The turnover of those layers in the fall can sometimes cause an odd but harmless taste in tap water.

"Sometimes when you get huge inflows like this, the lake mixes again -- it's like it gets confused," delaying the stratification, Lloyd said.

Heavy rain and flooding has struck from Texas up though the Midwest in recent weeks, including repeated flooding in Arkansas' midsection. At least part of the cause of this month's weather lies more than 2,000 miles away in the Pacific Ocean, said Steve Amburn, meteorologist and science officer for the weather service's office in Tulsa, Okla.

Warmer water than usual, a cyclical circumstance called El Nino, seems to have taken hold along the equator, Amburn said.

How warmer water there could affect weather here is a multi-step process. First, prevailing winds from South America slow, allowing surface water that's usually pushed west to sit still and warm up in the central Pacific. This creates a long, thin trail of warmer-than-normal water, which then fuels thunderstorms.

Correction

A previous version of this story incorrectly stated how El Nino begins. The error has been corrected.

As the storms climb into the atmosphere and condense water vapor into clouds, they release the heat that made them. When there's enough of that heat, the atmosphere in the area expands, like in a hot-air balloon, forming a massive dome. This pushes the high-speed jet stream winding above the United States north, making it curvier while also speeding it up.

As a result, a storm-producing low pressure system sets up in the Southwest, which then aims storms at Texas, Arkansas and the rest of the South.

"It (the jet stream) has kind of been almost stationary here for almost two or three weeks," Amburn said. "Eventually it will move, but it might not be for a little while."

El Nino typically shows itself mostly in the winter. Its name means "the child" in Spanish and refers to the birth of Jesus on Christmas. This one seems to have come early, or perhaps late from last year, Amburn said. The weather service expects it could bring more water and lower temperatures to the southern U.S. through the rest of the year.

"It's getting a head start this year," Amburn said.

Dan Holtmeyer can be reached at dholtmeyer@nwadg.com and on Twitter @NWADanH.

NW News on 05/27/2015

Upcoming Events