Flash Flood — Alleghany, Virginia

2016-06-23 · near Jerrys Run, Alleghany, Virginia

Event narrative

Flash flooding was first reported in Alleghany County at 215 PM EDT (115 PM EST) as Indian Draft Road (Route 600) was closed. Numerous additional reports and social media reports continued to be received through the afternoon. Numerous small streams flooded including Wilson Creek which overflowed Route 629 (Douthat Park Road). The most serious flooding was along Dunlap Creek with runs through the southwestern portions of the county joining the Jackson River just north of Covington. More than 25 homes were badly damaged in the county most of them along Dunlap Creek which set a new flood of record (see Episode for details). Water was reported over Route 60 from Dunlap Creek in several areas. Two water rescues by boat were performed and several landslides were reported including one that was reported to have closed Pitzer Ridge Road (Route 657) east of Route 18. Three Botetourt County firefighters were injured during flood rescue operations.

Wider weather episode

The synoptic setup for this event featured an upper level ridge over the central U.S. with several strong short-waves topping the ridge and dropping southeast across the Ohio Valley toward the central Appalachians. Satellite imagery showed a deep tap of tropical moisture into West Virginia and a strengthening upper level jet providing additional lift. A warm front was located just north of the area and became a focus for convection in the early morning hours of the 23rd. During the late morning to early afternoon convection continued to train across the same general area of southeast WV and far western VA with hourly rainfall rates of 1.50 to 2 for several hours.

Radar and rain gauge measurements showed as much as 4 to 8 inches (perhaps higher locally) fell in a band across central Alleghany County. The bulk of the rain fell in less than 12 hours between 600 AM and 600 PM EDT. The Governor of Virginia declared a state of emergency in the City of Covington and Alleghany County.

The phenomenal runoff from creeks, streams and overland flow produced an extreme hydrologic response on larger rivers including the Jackson River. The river gage at Covington (CVGV2) rose over 10 feet in 5 hours to reach Flood Stage (17 feet) for the first time since September 2004 (during the remains of Hurricane Jeanne). A River Flood Warning (FLW) was issued at 609 PM as the river was near 15 feet and the crest was only 4.5 hours later at 22.33 feet just below the Major Flood Stage of 23 feet. This was highest stage reached at the Covington gage since the November 1985 flood (23.31 feet) and 2nd highest since the construction of Gathright Dam in 1979. Gathright Dam was built to reduce flooding on the Jackson River but so much rain fell in the watershed below the dam that flooding still occurred at Covington. Numerous homes and several businesses in Covington suffered severe flood damage from the Jackson River. At the same time Dunlap Creek (DLPV2), which drains 162 mi2 of western Alleghany County and empties into the Jackson River in Covington was also rising at an extreme rate, climbing from a stage of around 3 feet (445 cfs) at 200 PM to a record stage of 16.49 feet (30,300 cfs) in a little over 6 hours. The previous record at this gage was 15.65 feet (27,400 cfs) set in June 1972 with the remains of Hurricane Agnes. Hydrological peak stage records at this gage date back to 1929. According to USGS flood frequency reports this flood was likely in excess of a 200-year (0.005 AEP) event on Dunlap Creek. There was extensive flooding along Dunlap Creek with roads and homes flooded and some requiring evacuations. Flooding continued downstream and a few hours later a River Flood Warning was issued for the upper James River including the forecast points at Lick Run (LIRV2) and Buchanan (BNNV2) both of which easily reached flood stage. At Lick Run the crest of 22.84 feet was the 10th highest on record (continuous records since 1925) and the highest since January 1996 (25.03 feet). Per USGS data the 48,000 cfs discharge at Lick Run was roughly a 10-year (.10 AEP) flood event. At Buchanan the 42,900 cfs was merely somewhere between a 2- to 5-year event (0.5 to 0.2 AEP).

View location on OpenStreetMap → (37.7653, -80.2277)

Source: NOAA Storm Events Database, event_id 643488. Narrative written by the NWS forecast office that issued the report.