Flooding and flash flooding across portions of southeast West Virginia and western Virginia during the overnight and early morning hours of March 12-13, 2010 was among the most significant to affect the Blacksburg Hydrologic Service Area (HSA) in years. The flooding, mainly occurring along tributaries and small streams of the Greenbrier and New River basins, was caused by 2 to 3.5 inches of rain which fell in roughly a 6 to 10 hour period during the evening and early morning hours.
The winter of 2009-2010 was one of the wettest and snowiest in recent years in the region and the Winter/Spring Flood Outlooks issued bi-weekly from January through mid-March by the NWS office in Blacksburg repeatedly emphasized the possibility that spring flooding was more likely as a result. The night of March 12-13, 2010 saw the realization of some of those possibilities when major flash flooding occurred across portions of southeast West Virginia and far western Virginia. Although Spring Flood Outlooks are primarily designed to address the likelihood of river flooding the events of March 12-13 were certainly aggravated by the antecedent conditions in place, mainly saturated soils due to the recent melt of a near-record snowpack.
A Flood Watch for the Greenbrier River was issued well in advance of any rainfall, at 330 PM on Tuesday, March 9 primarily due to expected snowmelt and possible heavy rain in the Greenbrier River basin. The Flood Watch was expanded to a much larger area of the western HSA at 426 AM on Friday the 12th as heavy precipitation forecasts gained credibility in terms of amount and location. The 500-millibar (approximately 18,000 feet) chart in Figure 1 below shows and deep cut-off low pressure center over the central U.S. which was forecast to move very slowly the next 24 to 48 hours with complex surface low pressure expected to develop over the southeastern U.S. and track northeastward.
Figure 1. 500-mb heights 1200Z, March 12, 2010
Figure 2. Surface weather map, 06Z, March 13, 2010
Figure 2 above shows the surface weather map at 06Z as an occluded front over the eastern Ohio Valley with low pressure developing right over southwest Virginia along the boundary and heavy rain indicated at Beckley, WV.
Moderate to heavy rains began over the western HSA during the evening hours of the 12th with hourly rates of 0.25” to 0.50” at several IFLOWS gages in the far western counties, increasing to near 1” per hour at several gages. Very high runoff occurred due to the wet soils from recent snowmelt and from actual snowmelt in some areas, combining to produce severe flash flooding and river flooding mainly in the New and Greenbrier river basins. Counties most affected included Mercer and Greenbrier in West Virginia and Giles and Pulaski in Virginia. Figure 3 below shows storm total rainfall amounts, most of which fell in roughly 12 hours during the evening and early morning hours of March 12-13. The 4 to 5-inch amounts estimated by radar in southeastern Bland and far northwest Pulaski counties were unconfirmed by rain gage measurements. Table 1 also below shows rain gage totals which ranged from 2 to 3.5 inches in the most affected areas.
Figure 3. WSR-88D Storm total rainfall, valid time ending 1537Z, March 13, 2010
Table 1 – Top fifteen 24-hour Precipitation amounts: RNK HSA – valid 12Z, March 13, 2010
|PIPW2||BLUESTONE R. AT PIPESTEM||SUMMERS||DCP||3.20|
|MODV2||MEADOWS OF DAN||PATRICK||COOP||2.43|
The heaviest rains fell between about 02z to 06Z with rates that were fairly intense for mid-March, running from 0.2 to 0.5 inches per hour at the height of the storm. Several more intense storm elements produced higher rates including 1.10” in 1 hour from 03Z to 04Z at Stony Fork RAWS and 1.03” at Ellison Ridge IFLOWS about the same time. A Flash Flood Warning was first issued at 9:36 PM (0236Z) for portions of Bland, Giles, Mercer, Monroe and Summers counties. Additional Flash Flood Warnings were issued and extended in time and areal coverage through the early morning hours and later became Areal Flood Warnings as the ‘flash’ portion of the event came to an end. Numerous flood reports were received from spotters and law enforcement agencies through the early morning hours.
Among the larger and gaged river and streams, the hydrologic response was most pronounced along the Bluestone River, East River and Brush Creek in Mercer County, WV and along Walker Creek and Wolf Creek in Giles County, VA. Figure 4 below shows the record (1951-2009 data) flood hydrograph for the Bluestone River at Pipestem (PIPW2), which crested in about 9 hours from the start of the heavier rainfall, with discharge increasing from around 3,500 cfs to over 22,500 cfs over that time period. According to USGS weighted estimates (Wiley, et al., 2000) this peak discharge is very close to the .01 annual chance of occurrence (‘100-year’ flood recurrence interval). The Pipestem stream gage is located just above where the Bluestone River empties into Bluestone Lake and the incredible flow on this river combined with high flows on the Greenbrier River combined to drive the pool elevation at Bluestone Lake up over 37 feet in the next 48 hours from around 1409 to over 1447 feet pool elevation (mean sea level).
On Walker Creek at Bane (BANV2) in Giles County, VA the USGS stream gage crested at 17.92 feet (20,900 cfs), which is the 2nd highest on record since 1939 and 3rd overall (the peak stage/discharge from 1878 was estimated). Wolf Creek (WOLV2), also in Giles County had its 3rd highest measured stage/discharge as well at 13.37 feet (15,200 cfs). Recurrence intervals for the discharge at both these gaging stations was close to or exceeded the .01 annual chance, possibly .005 chance at Wolf Creek , depending on the statistical methodology used (Bisese, 1995).
Figure 4. Stage/Flow Hydrograph, March 12-15, 2010 – Bluestone River at Pipestem (PIPW2)
The flooding caused significant damage to roads and bridges along with home and property damage. The flooding along Wolf Creek in Giles County was significant in several locations including several homes in the town of Narrows and Route 42 was closed in several locations. Walker Creek and other small streams also flooded several homes and closed roads across Giles County. Peak Creek in northwest Pulaski County flooded portions of the downtown area and threatened the 911 center with water. Giles County, VA had damages to at least 20 roads according to Virginia Department of Transportation and Emergency Management reported up to 93 homes in the county affected by flood waters. Two homes were destroyed and 31 received major damage. According to County Emergency Management, damage estimates from Giles County alone approached $2 million while Pulaski County had “only” $65 thousand in damages.
Route 623 in Giles County, VA along Walker Creek – water was
about 6 feet deep on this road at the height of flooding
In Mercer County there were evacuations along the East River near Oakvale and along the Bluestone River near Spanishburg. Greenbrier County had very serious flooding primarily from snowmelt in the Rainelle area. FEMA survey teams were dispatched in southeast West Virginia to both Greenbrier and Mercer counties shortly after the event. In Greenbrier County at least 270 homes were affected by flooding and Mercer County reported some damage to about 100 homes and 60 roads or bridges. Preliminary damage estimates from the West Virginia Department of Highways for state-maintained roads and bridges in Mercer County amounted to approximately $3.6 million, while private property damage approached $1 million.
Road and bridge damage from flooding along the East River, Mercer County, WV
In summary, this was one of the most high-impact flash flood events to affect at least a part of the RNK HSA in the past 5 years with preliminary damages of at least $6 million. Most fortunately no direct injuries or fatalities were reported in the RNK area as a result of the flooding. On the scale of Flash Flood events first developed by Davis (Davis, 2002) and adapted by Jackson and Stonefield (2008) for the RNK HSA, the event would be classified as FS4 or FS5, Severe or Catastrophic. Such events accounted for only 6% all flash flood events from 1994-2007.