Raster Dataset
Tags
flood-inundation maps, October 1-5, 2015, Charleston, South Carolina, flood, geospatial analysis, elevation, Charleston County, high-water marks, Atlantic Ocean, flooded area
This raster dataset of depth of flood inundation was created to support the development of flood inundation maps for the Federal Emergency Management Agency's (FEMA) response and recovery operations following an October 1-5, 2015 flood event in the community of Charleston, South Carolina on the Atlantic Ocean.
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. The storm caused major flooding in the central and coastal parts 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. During the October 2015 flood event, USGS personnel made about 140 streamflow measurements at 86 locations to verify, update, or extend existing rating curves (which are used to compute streamflow from monitored river stage). Immediately after the storm event, USGS personnel documented 602 high-water marks, noting the location and height of the water above land surface. Later in October, 50 additional high-water marks were documented near bridges for South Carolina Department of Transportation. Using a subset of these high-water marks, 20 flood-inundation maps of 12 communities were created. Digital datasets of the inundation area, modeling boundary, and water depth rasters are all available for download.
The study area covers a 2.3 mile coastal reach in the City of Charleston in Charelston County, SC. Twelve high-water marks were used to define the flood extent.
There are no credits for this item.
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This dataset may be redistributed if it is not edited and is properly referenced. The flood boundaries shown were estimated based on high water marks identified following the flooding event in South Carolina and a digital elevation model. Additional areas may have been flooded and were inaccessable due to hazardous conditions preventing access to flooded areas by the USGS field crews identifying HWMs. Although USGS intends to make this server available 24 hours a day, seven days a week, timely delivery of data and products from this server through the Internet is not guaranteed. The USGS provides these maps "as-is" for a quick reference, emergency planning tool but assumes no legal liability, or responsibility resulting from the use of this information.
Extent
| West | -79.954965 | East | -79.922105 |
| North | 32.805312 | South | 32.767871 |
| Maximum (zoomed in) | 1:5,000 |
| Minimum (zoomed out) | 1:150,000,000 |
A GIS application was used to produce a plane representing the flood-water surface. A raster surface was created with the data points using a Topo to Raster interpolation procedure (http://pro.arcgis.com/en/pro-app/tool-reference/3d-analyst/how-topo-to-raster-works.htm, accessed November 2015), forming the estimated flood surface. A flood-depth grid was made by subtracting the DEM from the flood surface. Areas in which the flood surface elevation was greater than the earth's surface elevation value within the defined study area boundary were included in the flood depth grid. This format allows the GIS data to be overlain on maps and aerial photographs, and to be used for various GIS applications, such as FEMA's Hazards U.S. Multi-Hazards (HAZUS-MH) program (Federal Emergency Management Agency, 2010b) to estimate flood damages. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the dataset in nonproprietary form, as well as in ArcGIS format, this metadata file may include some ArcGIS-specific terminology.
ground condition
See access and use constraints information.
None. This dataset is provided by USGS as a public service.
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This dataset may be redistributed if it is not edited and is properly referenced. The flood boundaries shown were estimated based on high water marks identified following the flooding event in South Carolina and a digital elevation model. Additional areas may have been flooded and were inaccessable due to hazardous conditions preventing access to flooded areas by the USGS field crews identifying HWMs. Although USGS intends to make this server available 24 hours a day, seven days a week, timely delivery of data and products from this server through the Internet is not guaranteed. The USGS provides these maps "as-is" for a quick reference, emergency planning tool but assumes no legal liability, or responsibility resulting from the use of this information.
No formal logical accuracy tests were conducted.
Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
Input data for the water-level surface were obtained from the HWMs identified and leveled by the USGS following the flooding event and verified with high-resolution imagery.
Horizontal accuracy to the input DEM dataset.
Vertical accuracy to the input DEM dataset.
Converted clipped depth grid to a grid of all 1 so a flooded area extent polygon could be created:Raster Calculator (Con("depthclip,1,0))= (wet grid)Edit wetpoly by removing small holes and other outliers due to small variations and artifacts that can not be substaniated by LiDAR data. (Removed 4 cell size or smaller holes within the flooded area) (wetpoly_edit feature class)
Create difference grid between DEM and water surface: Raster Calculator: surface - DEM = (difference grid)
Interpolation Method: Topo to Raster used to create water-surface raster **Boundary extent: boundary feature dataset (Geographic restriction or limit placed on interpolation extent of inital surface. Based on distribution of HWMs in relation to understanding of natural hydrologic flow in region.) ** Environmental Variables: Processing Extent- Snap grid to LiDAR (DEM) **Resulting dataset( surface)
Extracted depth grid to wetpoly_edit for final Depth surface.
Created Grid of only inundated areas (positive numbers/wet area): Spatial Analyst Tool: Conditional: Con (Expression: difference "VALUE" >0) (depth grid)
Clipped inundated area grid to extent boundary: Extraction by Mask: depth grid and the mask is the boundary extent= (depthclip grid)
Create a polygon of flooded area:Raster to Polygon=(wetpoly feature class)
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. The storm caused major flooding from the central to the coastal areas of South Carolina (USGS Open-File Report 2015-1201). Digital flood-inundation maps were created by the U.S. Geological Survey (USGS) in cooperation with the Federal Emergency Management Agency (FEMA) to support response and recovery operations following an October 1-5, 2015 flood event. The inundation maps depict estimates of the areal extent and depth of flooding corresponding to high water marks (HWM) identified and surveyed by the USGS between October 7 and October 16, 2015, following the flood event. Water-surface profiles were generated using the TopoToRaster interpolation tool, within ArcGIS and from the elevations surveyed at the HWM. The water-surface profile was combined with a geographic information system digital elevation model grid with a 10ft cell size- derived from light detection and ranging (lidar) data having a 0.5-foot (18.5 cm) vertical and a 3-foot (1 m) horizontal resolution (http://www.dnr.sc.gov/GIS/lidar.html) to generate this depth of flooding surface.The study area covers a # foot reach within the City of Charleston, SC. Twelve HWM were used to define the flood extent.This raster dataset of depth of flood inundation was created to support the development of flood inundation maps for the Federal Emergency Management Agency's (FEMA) response and recovery operations following an October 1-5, 2015 flood event in the community of Charleston, SC on the Atlantic Ocean.A GIS application was used to produce a plane representing the flood-water surface. A raster surface was created with the data points using a Topo to Raster interpolation procedure (http://pro.arcgis.com/en/pro-app/tool-reference/3d-analyst/how-topo-to-raster-works.htm, accessed November 2015), forming the estimated flood surface. A flood-depth grid was made by subtracting the DEM from the flood surface. Areas in which the flood surface elevation was greater than the earth's surface elevation value within the defined study area boundary were included in the flood depth grid. This format allows the GIS data to be overlain on maps and aerial photographs, and to be used for various GIS applications, such as FEMA's Hazards U.S. Multi-Hazards (HAZUS-MH) program (Federal Emergency Management Agency, 2010b) to estimate flood damages. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the dataset in nonproprietary form, as well as in ArcGIS format, this metadata file may include some ArcGIS-specific terminology.ground conditionNone. This dataset is provided by USGS as a public service.Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This dataset may be redistributed if it is not edited and is properly referenced. The flood boundaries shown were estimated based on high water marks identified following the flooding event in South Carolina and a digital elevation model. Additional areas may have been flooded and were inaccessable due to hazardous conditions preventing access to flooded areas by the USGS field crews identifying HWMs. Although USGS intends to make this server available 24 hours a day, seven days a week, timely delivery of data and products from this server through the Internet is not guaranteed. The USGS provides these maps "as-is" for a quick reference, emergency planning tool but assumes no legal liability, or responsibility resulting from the use of this information.Input data for the water-level surface were obtained from the HWM's identified and leveled by the USGS following the flooding event and verified with high-resolution imagery.No formal logical accuracy tests were conducted.Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.Horizontal accuracy to the input DEM dataset.Vertical accuracy to the input DEM dataset.Converted clipped depth grid to a grid of all 1 so a flooded area extent polygon could be created:Raster Calculator (Con("depthclip,1,0))= (wet grid)Create a polygon of flooded area:Raster to Polygon=(wetpoly feature class)Clipped inundated area grid to extent boundary: Extraction by Mask: depth grid and the mask is the boundary extent= (depthclip grid)Extracted depth grid to wetpoly_edit for final Depth surface.Interpolation Method: Topo to Raster used to create water-surface raster **Boundary extent: boundary feature dataset (Geographic restriction or limit placed on interpolation extent of inital surface. Based on distribution of HWMs in relation to understanding of natural hydrologic flow in region.) ** Environmental Variables: Processing Extent- Snap grid to LiDAR (DEM) **Resulting dataset( surface)Create difference grid between DEM and water surface: Raster Calculator: surface - DEM = (difference grid)Edit wetpoly by removing small holes and other outliers due to small variations and artifacts that can not be substaniated by LiDAR data. (Removed 4 cell size or smaller holes within the flooded area) (wetpoly_edit feature class)Created Grid of only inundated areas (positive numbers/wet area): Spatial Analyst Tool: Conditional: Con (Expression: difference "VALUE" >0) (depth grid)See access and use constraints information.