By Hugh Fisher
hfisher@salisburypost.com
After months of drought, many were shocked on Aug. 27 when a lake of floodwater formed where Interstate 85 and East Innes Street meet at Town Creek.
Some wondered how such a lake could form so quickly, then just as quickly disappear.
One answer: new development.
More paved space means less open ground for rainwater to seep into and fewer plants or natural contours to slow water down.
And as fields and woods around Rowan County have given way to housing developments and commercial property, the potential for streams to overflow their banks in a heavy downpour has risen.
“When rain occurs, the water is going somewhere,” said Shane Stewart, senior planner for Rowan County Planning and Zoning.
In downtown Salisbury, “there’s very little green space for water to seep in before it reaches streams,” he said.
And when that water hits a bottleneck ó overtaxed storm drains, a narrow channel ó it backs up.
“That whole area around Starbucks, Outback, Subway and so forth ń when the water hits pavement, it’s going to run that much faster. It’s all from the urban impact,” Stewart said.
“That was getting close to what we used to call a 100-year flood,” said Patrick Ritchie, civil engineer and floodplain manager for Salisbury’s Engineering Department.
“It has a 1 percent chance of occurring in any given year. And the levels we saw were close to that. So you would not expect to see that high a rainfall happening very often,” Ritchie said.
Stewart pointed to several other areas around the county where development has increased the potential for floods, among them Grant’s Creek near the Yadkin River.
“Obviously, development pressures around the city, the (N.C.) 150 area and along (U.S.) 29 ó a lot of that contributes to Grants Creek,” Stewart said.
In response to the changing face of Rowan County and the advances in mapping technology, state and local officials are generating new floodplain maps.
The previous maps date from 1980 and are based on U.S. Geological Survey data from aerial photographs and surveys.
The new maps are being made using digital imaging technology that can map the contours of land much more accurately. They also reflect changes due to development over nearly three decades.
Local officials have publicized changes to floodplains, leading some to wonder if their homes will soon be officially inside a floodplain.
The new maps for Salisbury have not yet gotten final approval, Ritchie said. That final certification from the state for city maps is expected “any day now.”
But Rowan County data is official, he said, because there was no preexisting flood elevation data.
The maps can be viewed online at www.ncfloodmaps.com. Shaded areas show city limits, the routes of waterways and the floodplain areas with 1 percent and .2 percent annual chance of flooding.Those terms replace previous designations like “50 year,” “100 year” and “500 year” floods, which planners say are misleading.
“You could have another storm like that tomorrow,” Ritchie said of the flood that filled Town Creek’s basin and shut down traffic on East Innes Street for most of that day in August.
“I think what kind of lulls people to sleep on this is the thought that we were in a drought last year or that they haven’t seen a creek flood in years,” Stewart said.
The better mapping data means some areas not formerly thought to have flood potential are now in floodplains.
“One thing that was very surprising was where Grants Creek feeds into the Yadkin River,” Stewart said.
“There was a huge elevation change. They did have more floodplain on the property.”
Another area of potential concern not far away is Steeple Chase Road in Spencer.
“They had a huge change in elevation,” Stewart said.
But not every floodplain has increased in size. “It’s actually decreased in places,” Stewart said.
Other factors besides ground level can affect the potential for flooding. Silt fills in streambeds, making them shallower, and debris in the flood channel can cause water to spill out onto land.
Closer to Salisbury, Ritchie said most potential trouble spots for flooding are already well known, such as Town Creek.
Yet many of the calls the city receives about flooding are from concerned residents who, after a heavy rainstorm, report slow-draining runoff.
“Any time we get large rains like that and get flooding, we usually do get a flurry of calls,” he said. “And a lot of the ones who are calling with flooding concerns aren’t in areas of designated flood hazard.””As more development occurs around the city, you’ll get more runoff,” Ritchie said. “And more runoff causes floodwaters to be more aggressive.”
One known flood hazard is the Pinehurst Street area, between Mooresville Road and Maupin Avenue. “It does flood, and it did not show up in the flood zone on the flood maps,” Ritchie said.
But a portion of Pinehurst Street will be in the new flood maps.
Outside the city limits, those living in several areas near streams should be aware of the floodplain boundaries.
Stewart did not want to rank them in terms of seriousness, but he said Third Creek near Cleveland could be the worst.
The 1-percent annual chance zone to the north and west of the Cleveland town limits stretches for hundreds of feet outside of the channel, according to the new map data.
Other streams in western Rowan flow into Second Creek, making fast-moving flood waters possible.
“If there’s a structure there, you can have serious problems with the velocity of the water,” Stewart said.
The message from both city and county planners is that property owners, especially those who believe they may be in a flood plain, should arm themselves with knowledge.
Those planning new construction generally find out early on whether their proposed building site lies in a flood zone.
New developments also have to comply with federal stormwater quality guidelines that call, in some cases, for retention ponds to be built.
The purpose of those ponds is to let silt and debris fall out of the rainwater, Ritchie said.
“They are not there to prevent flooding, but they should provide detention that will also benefit,” he said.
And the new map data will help owners of existing property plan for new construction or determine what insurance coverage they may need.
Stewart said county property owners whose land falls within the new floodplain boundaries were notified by mail.
Even so, he said, the existence of a floodplain is “probably one of the last things people think about” when buying a home.
“Folks have had really no change in terms of their curiosity except when we sent out those notices,” Stewart said. “Then they wanted to see.”
Ritchie said he did not know how many homes in the city might be affected by changes in floodplains once the new maps are official.
“It will not be a huge number,” he said.
But residents are welcome to call and ask to see if their property is affected.
“We will pull up the map and check it for them,” Ritchie said.
Stewart echoed the same advice for county residents: “Just check with us. That’s what we’re here for.”
For those who wish to see the unofficial map data for Rowan County, or look at collected maps for other portions of the state, go to www.ncfloodmaps.com.