Urban stream flooding, stormwater pollution could surge if June’s forecast heavy rains continue (+ video)

If the Columbia area continues to experience a wetter-than-normal June, as some weather experts suggest, it won’t be the Midlands’ three rivers that give the most concern to Congaree Riverkeeper Bill Stangler.

It’s the urban creeks and streams that could see the biggest gush in water levels and pose the most danger during and after heavy rain events, said Stangler, who monitors water quality in the Congaree, Saluda and Broad rivers and the tributaries that flow into them. Those creeks and streams include Rocky Branch in Columbia, Smith Branch in north Columbia, and Twelve Mile Creek in central Lexington County.

Richland and Lexington counties have seen rainfall totals from roughly 2 inches to 6 inches this week, already nearing the monthly average for June.

If soaking conditions continue throughout the month, as National Weather Service experts predict due to the El Nino effect, those urban creeks and streams could see heightened stormwater pollution, which will in turn flow into the three rivers, Stangler said.

“We do have concerns about water quality after big rains like that,” Stangler said. “When it rains like that, it’s not just water that’s going into storm drains and going into our creeks. It’s everything that’s laying around in parking lots and on the streets and in people’s yards ... and that can cause really serious concerns, not just with the trash you see, but also higher bacteria levels in our streams and rivers.”

The urban creeks and streams tend to flood more quickly than the rivers due to large amounts of runoff from surfaces like pavement and rooftops, Stangler said.

Rocky Branch, which flows through downtown Columbia into the Congaree River, flooded the intersection at Main and Whaley streets three times in 48 hours this week, Stangler said.

The creek’s water level spiked to more than 10 feet Wednesday night and 8 feet the previous night, compared to normal levels around 1 or 2 feet.

Those flash floods tend to rise and recede quickly, within an hour or so, and pose a potential danger to drivers and property owners near the flows.

Water levels in all three Midlands rivers were elevated only slightly Thursday afternoon and were nowhere near flood stages, Stangler said.

River levels surged briefly during Wednesday’s overnight storms, Stangler said. But about 12 hours after the deluge, the Congaree River already was receding and flowed about 4 1/2 feet deep, up about a foot from a day earlier, Stangler said. Usually, 10 feet is considered the Congaree’s flood stage, he said.

Wednesday night’s excessive rain caused a number of problems around the Midlands into Thursday, among them:

▪ Flooding in some Five Points businesses

▪ Erosion of the pond dam on Lexington 1 school district office property. Repairs were under way Thursday to strengthen the dam.

▪ Power outages that left more than 1,000 South Carolina Electric and Gass customers without power Wednesday night and into Thursday morning. Power was restored by afternoon.

▪ Flooding of the West Columbia Riverwalk, leaving debris and causing some damage to parts of the park, according to city police officials. The Riverwalk was closed Thursday, with no word on when it might reopen.

▪ A sewer main break in Cayce

▪ Road closures in Springdale, with some slated to remain that way pending repairs.

At Lake Murray, heavy rains generally have a minimal effect on lake water levels, according to Bill Argentieri, the manager of civil engineering who works with hydroprojects for SCE&G. SCE&G manages the nearly 50,000-acre lake originally built for hydropower but now mainly used for recreation and drinking water.

Lake levels Thursday afternoon were only about 2 inches above normal after this week’s rains and far from any concern of overflowing the dam, Argentieri said.

“There are no safety concerns,” Argentieri said.

To gradually bring the lake’s water level down over the next few days, Argentieri said, SCE&G is releasing some water from the lake into the lower Saluda. That means higher than normal water – but still relatively low – flows there and in the Congaree, into which the Saluda flows.

SCE&G activates lights and sirens near the Saluda Dam to warn river users when water levels are about to suddenly swell due to water releases. People also can sign up to receive phone call and email alerts whenever SCE&G releases water into the lower Saluda.

If June continues to see above-normal precipitation and SCE&G continues to release more water into the river to balance levels in the lake, river users could enjoy better conditions for some activities such as kayaking and canoeing on the rivers, Argentieri said. Fishermen, though, may be less pleased to see higher river flows continue, he said.

But there is one consequence of rainy summer that many people would likely appreciate, Argentieri said – “They could quit watering their lawns.”

This story was originally published June 4, 2015 at 8:05 AM.