News

Ask Matt ... about drinking water safeguards

By Bill Moss, Published: January 24, 2014

Q. Regarding the recent chemical spill in West Virginia that made Charleston's tap water unsafe to drink, wasn't there once talk about moving the Mills River water intake upstream from the N.C. 280 bridge?

True. The Hendersonville Water Department looked at that in 1990 but the project never got traction probably because of permitting issues. According to City Utilities Director Lee Smith, the project is still on their radar but not in the capital improvements plan. In addition to the Mills River, the city's treatment plant draws raw water directly from two reservoirs in the Pisgah National Forest. Plus, in the event of a chemical spill, the Hendersonville water system can be quickly connected to Asheville's Mills River treatment plant. Smith says, "That should help for short periods of time." The city also has long-range plans to add off-stream storage capabilities in Mills River.

Q. When there is a heavy rainfall event in Transylvania County, how long does it take the French Broad River to crest in Henderson County?
Crest predictions depend on how much rain fell, where it fell, and to a lesser extent the moisture content of the soil. I spoke with NOAA hydrologist Patricia Tanner, who works at the National Weather Service in Greer, S.C. Her office runs "crest-to-crest relationships" based upon data from river gages stationed along the French Broad. The Weather Service also has people in Atlanta who can run computer models to predict where and when flooding will occur. A river crest model for the French Broad would pull data from river gages in Rosman, Blantyre, and Fletcher. The further one goes downstream, the larger the drainage basin. For example, Rosman's basin is 99 square miles but Blantyre's is three times as large.
Now the answer. Based upon a scenario Tanner offered, if the headwaters of the French Broad River in Transylvania County experience a 5-inch rainfall lasting over 12 hours, the runoff would raise the river level in Rosman up to 7 feet. Twelve hours later the downstream gage at Blantyre (at the county line) would show a 16 feet crest. Eight hours after that there would be a 12-foot crest at the bridge at N.C. 191. Finally, four hours after that the river would crest at 10 feet in Fletcher at the NC 280 bridge. The heavy rainfall in Rosman took a day and a half to crest in Fletcher.

Send your questions about a local issue, event, sighting or anything that is puzzling you and the Lightning's intrepid researcher will try to get an answer. Email Matt at: askmattm@gmail.com.