ECU geologists concerned about storm water management

Heavy rains that flooded streets in Greenville recently should alert people to the need for improved planning for storm water management, says a group of East Carolina University geologists.

Professors David Lawrence, Richard Mauger and Richard Spruill said urbanization contributed to Greenville’s flash flood of Oct. 8, when heavy rain from the remnants of Hurricane Josephine caused the city’s Green Mill Run to overflow its banks and pour into streets and parking lots. The storm dumped about three inches of water during a three-to-four hour period.

“It is the kind of thing that I teach students in freshmen geology classes,” said Dr. Spruill, who specializes in the study of ground water in the Department of Geology. His lesson is that urbanization, with its accompanying roof tops, gutters, highways and other paved surfaces, puts large amounts of water into streams and low-lying areas at a rapid rate. Just how much water? A three inch rainfall on a one square mile area would produce more than 52 million gallons of water, the geologists calculate. If the area is covered by concrete or asphalt the water cannot soak into the ground and it will flow quickly to the nearest stream.

“If two to three inches of rain did that to Green Mill Run, then imagine what six inches or more of rainfall will do,” said Spruill. He said rain storms in other parts of the country — most recently in New England — have produced as much as 10 to 18 inches of water in about 24 hours. “It is only a matter of time before we have a massive rain storm here and when it occurs, even 10th Street will be under water,” he predicted.

The scientists said the problem could be relieved by the use of flood control systems that slow down the velocity of the water that drains into the creek. Small dams and holding ponds are the main features of storm water systems that help control flash flooding. They said more of these retention systems are needed in the Greenville area.

“These storm water retention areas could provide the city and the campus with more open spaces and attractive land sites which would be an asset to the community,” Mauger said.

Another way of dealing with the problem, according to Lawrence, is to control development in the flood-prone areas of the city, especially in areas designated as part of the 100-year flood zone. Significant floods of the Tar River have occurred in the past. For example, a large flood in the 1930s inundated the area almost to Third Street on the south side of the river. The rainfall in early October that produced flooding in parts of Greenville was not a particularly large rainfall total, according to the geologists. Instead, they believe the flooding was caused by urbanization (growth in new houses, paved areas and shopping centers) without adequate storm water management.

“My point,” said Spruill, “is that this was not the 100-year flood that produced this. It was more like a 10-year flood. It is going to get worse and people need to be prepared for it,” he said.