CONYERS - Development upstream of the Yellow River may make flooding like the kind seen Tuesday more likely, according to a Georgia Perimeter College geologist.
A comment heard from several residents affected by flood waters from the Yellow River was that the waters came suddenly and with very little warning. Authorities began evacuating people from danger areas Monday with flood waters rising that night almost immediately after a burst of heavy showers in the area.
John Anderson, Science Department chairman at GPC's Decatur campus, said the overly saturated soil from a week of rains was a factor in the local flooding.
However, for the Yellow River the problem was exacerbated by the amount of development at its head waters in Gwinnett County. With more roof tops and parking lots, the flow of rainwater increases into the river's tributaries.
"The head waters of the Yellow River are pretty much highly urbanized, and so all the rain that fell in Gwinnett County, the head waters of the Yellow River, ran off into the river," Anderson said. "You're channeling a lot more water than what would naturally flow with no impervious surfaces. Streams will become a lot more flashier, or they will rise a lot faster."
A unique facet to steams and rivers in metro Atlanta is that the area is the crossroads of two river basins - the Chattahoochee that flows into the Gulf of Mexico and Ocmulgee that flows into the Altamaha River and Atlantic Ocean.
Anderson explained that almost everything south of College Avenue in Decatur up along Interstate 85 eventually flows into the Yellow River.
"Norcross, Lilburn and Snellville are three major communities inside the Yellow River basin, and as they have expanded and increased parking lots and residential areas, you have a greater chance of more water running off and it all compounds," he said.
The impact downstream comes not only from the sheer volume of water, but also from pollutants carried downstream. Anderson noted that the contents of the septic tank in his backyard in Lilburn began percolating to the surface because the ground had become so saturated.
"If that had been 3 inches in three days, my yard probably would have absorbed all of that, but 3 inches in two hours, it could not handle that," he said.
Jay Jones can be reached at email@example.com.