Selected Roadway High-Water Mark Data from Hurricane Joaquin Flooding, October 2015

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As part of the statewide response to the flooding, the USGS and S.C. Department of Transportation (SCDOT) conducted a cooperative study to collect high-water mark (HWM) data at 50 selected road crossings.

The HWM elevations and descriptive data have been posted on the USGS Short-Term Network (STN). The STN is a national-scale application and database designed to support USGS event-based sensor deployments and HWM data-collection efforts. Please visit the project web page for links to the STN.

 Infrared satellite image of the intense rainfall in South Carolina during the morning of October 3, 2015 (from Feaster and othe
Infrared satellite image of the intense rainfall in South Carolina during the morning of October 3, 2015 (from Feaster and others, 2015; National Aeronautics and Space Administration). Black areas show the highest rainfall amounts.(Public domain.)

BACKGROUND

Heavy rainfall occurred across South Carolina during October 1–5, 2015 as a result of an upper atmospheric low-pressure system that funneled tropical moisture from Hurricane Joaquin into the State (fig.1). The storm caused major flooding from the central to the coastal areas of South Carolina. Almost 27 inches of rain fell near Mount Pleasant in Charleston County during this period. U.S. Geological Survey (USGS) streamgages recorded peaks of record at 17 locations, and 15 other locations had peaks that ranked in the top 5 for the period of record. The impacts of this event were widespread across South Carolina. Approximately 410 roads or bridges were closed during the event including 74 miles of I-95 between I-26 and I-20 (Feaster and others, 2015).

APPROACH

Hurricane Joaquin: S.C. Department of Transportation-selected high-water mark locations.
Selected Roadway High-Water Mark Data from Hurricane Joaquin Flooding, October 2015(Public domain.)

As part of the statewide response to the flooding, the USGS and S.C. Department of Transportation (SCDOT) conducted a cooperative study to collect high-water mark (HWM) data at 50 selected road crossings (fig. 2). U.S. Geological Survey personnel visited each site to flag and survey HWMs. The crews flagged marks on both banks, upstream and downstream of bridges (four quadrants of each bridge). Each mark was identified by a unique number, described, and rated for quality. High-water mark information was sought one bridge-width opening upstream from each bridge as well as at or near the downstream bridge exits. If marks at these locations were not available, crews extended their search area several hundred feet further upstream or downstream as necessary. The horizontal coordinates (latitude and longitude) of each mark were determined by Global Positioning System (GPS) equipment relative to the North American Datum of 1983 (NAD 83), and the elevations of these marks were surveyed to North American Vertical Datum of 1988 (NAVD88). At many sites, reliable HWMs were difficult to find because data collection began 3 weeks after the historic flooding, and subsequent rainfall events, wind, or anthropogenic activity had degraded or eliminated any distinct marks. As a result, engineering judgment was used to estimate the peak water-surface elevations for each site or quadrant. The location of the upstream peak elevation was estimated to be one bridge-opening width upstream from the bridge, and the downstream peak elevation was located at the bridge exit.

 

The HWM elevations and descriptive data have been posted on the USGS Short-Term Network (STN). The STN is a national-scale application and database designed to support USGS event-based sensor deployments and HWM data-collection efforts. The URL for the STN website is https://water.usgs.gov/floods/FEV/. The Flood Event Viewer option can be used to inspect data for selected events, and menus at the STN Data Portal can be used to download data by event, state, and more. Please note that the STN uses functionality that is not completely supported by Internet Explorer; the preferred browser is Chrome.

 Hurricane Joaquin Flooding: U.S. Highway 52 at U.S. Geological Survey station 02136000 Black River at Kingstree, SC.
Figure 3 - U.S. Highway 52 at U.S. Geological Survey station 02136000 Black River at Kingstree, SC. (photograph by Dale Skipper, USGS, October 2015). Public domain.

 

REFERENCES

Feaster, T.D., Shelton, J.M., and Robbins, J.C., 2015, Preliminary peak stage and streamflow data at selected USGS streamgaging stations for the South Carolina flood of October 2015: U.S. Geological Survey Open-File Report 2015–1201, 19 p.,