Documentation and Analysis of Flash Flood Prone Streams and Subwatershed Basins in Pulaski County, Virginia

1. Documentation and Analysis of Flash Flood Prone Streams and Subwatershed Basins in Pulaski County, Virginia Anthony Phillips Department of Geography Virginia Tech In Cooperation with:

2. Research PurposeStatement • Identify, measure, and analyze areas in Pulaski County that are prone to flash flooding using GIS. • Results tobe compiled in digital form of DVD, as well as in paper form in an operational handbook. • All data to be overlaid in Google Earth and accessible from workstations at the NWS.

3. Research PurposeWhy do we care about flash flooding? • #1 weather-related killer in the United States! • Can occur nationwide, in any environment, but primarily affects these areas in Pulaski County: • River flooding • Small stream flooding • Urban flooding • Dry wash flooding

4. Selecting Flash Flood Prone AreasESRI's ArcGIS • USGS road and stream shapefiles were imported into ArcGIS. • Software was used to select points where roads and streams were within 25’ of each other. • 651 points identified.

5. FieldworkData collected • Following data collected at each road-stream intersect point: • Road name • Road type • Stream name • Stream flow (slow, normal, fast, none) • Distance from road to stream • Angle of depression • Upstream picture • Downstream picture

6. FieldworkCalculating the flood stage for each survey point • Distance from road to stream calculated from eye-level to stream edge. • Standard 50’ measuring tape. • From same location, angle of depression measured from eye-level to stream edge. • Clinometer

7. θ° 6’ 6’ d FS FS= [d x SIN(θ°)] – 6’ Picture by Sarah Prescott

8. Finalizing the DataWhy only 319 points? • Of the 651 points initially plotted by ArcGIS, 319 were fully documented. • The remaining 332 points were either on private roads or were not likely to have flash flooding.

9. Finalizing the DataArcGIS and aerial photography of each subbasin • Final data was imported into ArcGIS. • Each measured point was color-coded to indicate the flood stage height. • Red: <1.5’ • Orange: 1.5 – 3.0’ • Yellow: 3.0 – 5.0’ • Green: 5.0 – 8.0’ • Turquoise: 8.0 – 12.0’ • Blue: >12.0’

10. Finalizing the DataArcGIS and aerial photography of each subbasin • 2007 aerial photography serves as the background for each map. • Additionally, each map includes all roads and streams with their associated names, as well as an inset map of surrounding elevation.

12. Finalizing the DataGoogle Earth • The location and information for each measured point was imported into Google Earth. • Additionally, each subwatershed basin was also imported. • Points used the same color-coded symbology.

14. Results and ConclusionsWhat we’ve learned so far… • The project has been a complete success! • Areas that are susceptible to flash flooding have been fully documented. • All information has been mapped and imported into Google Earth. • Information available to the NWS and County of Pulaski in the form of a handbook and DVD. • Project expanding to include Montgomery County and Virginia Tech Questions?

15. Acknowlegements • Dave Carroll, VT Advisor • Steve Keighton, NWS Science Operations • Peter Corrigan, NWS Hydrologist • Jan Jackson, NWS Senior Forecaster • Bobby Clark, Pulaski County Emergency Manager • Sarah Prescott, Field Assistant • VT McNair SRE Staff