The National Weather Service is proposing to change the flood stage categories for the Dan River at both Paces and South Boston to “be more accurate to the impact it may have,” said Steve Dishman, county emergency services coordinator.
The proposed changes are expected to take effect Thursday.
At the Dan River at South Boston, the definition of “action stage” is rising from 15 feet to 18 feet; the “minor stage” is changing from 19 feet to 22 feet; “moderate stage” is increasing from 25 feet to 29 feet; and the “major stage” is rising from 29 feet to 34 feet.
At the Dan River at Paces, “action stage” is rising from 18 feet to 20 feet; the “minor stage” is rising from 20 feet to 22 feet; the “moderate stage” is rising from 24 feet to 29 feet, and the “major stage” is rising from 27 feet to 35 feet.
“The current levels do not match the definitions,” said Dishman.
Minor flood stage is considered “minimal or no property damage but possibly some public threat” to roadways.
Whereas moderate flood stage affects some structures and roads near the stream and could lead to some evacuations of people and/or transfer of property to higher levels.
The moderate flood stage typically affects the businesses in Riverdale, Dishman explained.
Major flood stage is considered “extensive inundation of structures and roads” and leads to “significant evacuations.”
Tropical Storm Michael crested on Oct. 13 at 31.4 feet, making it the sixth highest on record since continuous record keeping began in 1951.
According to the NWS’ definitions, that “was only a moderate event with some evacuations and structures affected in the Riverdale area,” according to documents on river gauge adjustments.
A USGS gauging station was established in South Boston in August 1900 and updated in 2011.
Since Oct. 1, 2015, the Dan River at South Boston gauge has risen to 19 feet 29 times.
“There is clearly something amiss with minor flood stage at South Boston being reached so frequently,” according to river gauge adjustment documents.
Each time the river reaches minor flood stage, the NWS issues a river flood warning usually within 12 to 36 hours in advance of expected flood state.
“In reality, 19 feet is probably closer to bank full stage than a flood stage,” the river gauge adjustment document states.
The document also states that “low land flooding,” which does not affect roads, is typically reported at 19 to at least 22 feet.
The public can still expect to receive forecasts from the NWS and more often during the flood events, but the number of flood warnings issued should decrease.
“They’ll wait for higher predictions,” said Dishman.
Prior to deciding on these proposed changes, members of Virginia Department of Transportation, public works and emergency management discussed what levels affect roads, buildings and businesses and held a meeting.
More information, and a chance to send in public comment can be found online at https://www.weather.gov/rnk/danriver.