1. Creating Depth Grid from a DFIRM FEMA Region VIII Mitigation GIS Team Wednesday, February 13, 2013

2. FEMA-MOTF@fema.dhs.gov Overview Floodplain and flood zone overviewFloodplain and flood zone overview Where to find DFIRM dataWhere to find DFIRM data Depth grid basicsDepth grid basics Topography Topography Water surface Water surface Creating a depth gridCreating a depth grid Review and QCReview and QC Exercise – Creating a depth gridExercise – Creating a depth grid

3. FEMA-MOTF@fema.dhs.gov At a minimum, the process determines the Base Flood. Base Flood: NFIP flood of regulation for floodplain management. Defined by law as a flood that has a 1% chance of being equaled or exceeded in a given year. Special Flood Hazard Area (SFHA): Areas subject to the Base Flood (1% chance) or greater, annual change of flooding in any year (aka the “100-year floodplain). Base Flood vs. “100 year” Flood: The base flood is often referred to as the “100 year” flood or a “100 year” event. This is a misnomer because it doesn’t occur only once in 100 years. Floodplain and Mapping Terms

4. FEMA-MOTF@fema.dhs.gov 100-year Floodplain, 100-year Floodway100-year Floodplain, 100-year Floodway 1% Annual Chance (100-yr) FP Zone A (Floodplain only) Zone AE (Floodplain and Floodway) Zone AH/AO (Floodplain only)

5. FEMA-MOTF@fema.dhs.gov 500-year Floodplain/Shaded Zone X (not always 500-year floodplain)/Zone B500-year Floodplain/Shaded Zone X (not always 500-year floodplain)/Zone B <=1 foot of depth <=1 foot of depth 0.2% Annual Chance (500-yr) FP

6. FEMA-MOTF@fema.dhs.gov Zone A Zone A (100-year Floodplain) Zone A (100-year Floodplain) Approximate model (automated or manual) Approximate model (automated or manual) No road crossings included in model No road crossings included in model Topography: 4-ft or greater contour intervals Topography: 4-ft or greater contour intervals No depths or BFEs mapped No depths or BFEs mapped

7. FEMA-MOTF@fema.dhs.gov 7 Zone A (100-year floodplain)

8. FEMA-MOTF@fema.dhs.gov Zone AE Zone AE (100-year Floodplain) Zone AE (100-year Floodplain) Detailed (manual) Detailed (manual) Road crossings included in model Road crossings included in model Topography: 2-ft or less contour intervals Topography: 2-ft or less contour intervals BFEs, Cross sections mapped BFEs, Cross sections mapped In the FIS profiles In the FIS profiles Can have a floodway Can have a floodway

9. FEMA-MOTF@fema.dhs.gov Zone AE (100-year flooplain)

10. FEMA-MOTF@fema.dhs.gov Zone AO Zone AO (100-year Floodplain) Zone AO (100-year Floodplain) Detailed (manual) Detailed (manual) Ponding with 1-3 feet of depth Ponding with 1-3 feet of depth Topography: 2-ft or less contour intervals Topography: 2-ft or less contour intervals Elevations stated on map Elevations stated on map

11. FEMA-MOTF@fema.dhs.gov Zone AO (100-year floodplain)

12. FEMA-MOTF@fema.dhs.gov Zone AH Zone AH (100-year Floodplain) Zone AH (100-year Floodplain) Detailed (manual) Detailed (manual) Ponding with 1-3 feet of depth Ponding with 1-3 feet of depth

13. FEMA-MOTF@fema.dhs.gov Zone V/VE Zone V and VE (100-year Coastal Floodplain) Zone V and VE (100-year Coastal Floodplain) Similar to Zone A and AE, but Coastal (Approximate and Detailed Respectively) Similar to Zone A and AE, but Coastal (Approximate and Detailed Respectively)

14. FEMA-MOTF@fema.dhs.gov Zone V/VE (100-year floodplain)

15. FEMA-MOTF@fema.dhs.gov Zone D – Undetermined Flood Hazard

16. FEMA-MOTF@fema.dhs.gov Zone C and Unshaded Zone X Flood hazards larger event than a 500-year flood (less probability)

17. FEMA-MOTF@fema.dhs.gov DFIRM Database/NFHL Data Available from the FEMA Maps Service CenterAvailable from the FEMA Maps Service Center https://msc.fema.gov/portal https://msc.fema.gov/portal https://msc.fema.gov/portal Click search all products Click search all products

18. FEMA-MOTF@fema.dhs.gov Topographic Data Best available data and best fitBest available data and best fit USGS National Map (NED) http://nationalmap.gov/USGS National Map (NED) http://nationalmap.gov/http://nationalmap.gov/ Available nationally at resolutions of 1 arc-second (about 30 meters), 1/3 arc-second (about 10 meters)Available nationally at resolutions of 1 arc-second (about 30 meters), 1/3 arc-second (about 10 meters) 1/9 arc-second resolution data is very limited in coverage for most areas of the U.S.1/9 arc-second resolution data is very limited in coverage for most areas of the U.S. LiDAR available through local municipalitiesLiDAR available through local municipalities http://coast.noaa.gov/inventory/ http://coast.noaa.gov/inventory/ http://coast.noaa.gov/inventory/

19. FEMA-MOTF@fema.dhs.gov ~90-meter~30-meter~10-meter~1-meter Raster Resolution Equivalence Less information More information

20. FEMA-MOTF@fema.dhs.gov Raster Resolution Site-Specific – LiDAR or < 3 meter resolutionSite-Specific – LiDAR or < 3 meter resolution County Level Analysis – 10 or 30 meter NEDCounty Level Analysis – 10 or 30 meter NED Time and level of analysis are important when determining the topographic resolution

21. FEMA-MOTF@fema.dhs.gov Depth Grid Process Overview WSEL- DEM = DG

22. FEMA-MOTF@fema.dhs.gov Water Surface Data Cross Sections (Xs) of riverine flooding sources are taken by surveyors and engineers to gather information about the size and geometry of the stream channel and the elevation of the ground. This information is used to accurately model the flood hazards for the stream. Use Cross Sections when available.Cross Sections (Xs) of riverine flooding sources are taken by surveyors and engineers to gather information about the size and geometry of the stream channel and the elevation of the ground. This information is used to accurately model the flood hazards for the stream. Use Cross Sections when available. Base Flood Elevations (BFEs) are the elevation shown on the Flood Insurance Rate Map (FIRM) for Zones AE, AH, A1-30, or VE that indicates the water surface elevation resulting from a flood that has a 1-percent chance of occurring in any given year. In riverine areas, BFEs are plotted as lines at different points along the stream on the FIRM which correspond to elevations in the flood profile in the Flood Insurance Study (FIS) reportBase Flood Elevations (BFEs) are the elevation shown on the Flood Insurance Rate Map (FIRM) for Zones AE, AH, A1-30, or VE that indicates the water surface elevation resulting from a flood that has a 1-percent chance of occurring in any given year. In riverine areas, BFEs are plotted as lines at different points along the stream on the FIRM which correspond to elevations in the flood profile in the Flood Insurance Study (FIS) report

23. FEMA-MOTF@fema.dhs.gov DFIRM to Depth Grid ONLY can be done for areas of detailed study (surveyed zone As – AE, AH, and AO only)ONLY can be done for areas of detailed study (surveyed zone As – AE, AH, and AO only) Use the available cross sections to interpolate the water surface for AE ZonesUse the available cross sections to interpolate the water surface for AE Zones AO Zones – Constant water depthAO Zones – Constant water depth Create unique depth grid for 1, 2, or 3 ft Create unique depth grid for 1, 2, or 3 ft AH Zones – Static BFEAH Zones – Static BFE Create unique depth grid using a constant WSEL Create unique depth grid using a constant WSEL Fill remaining areas with 0.1ftFill remaining areas with 0.1ft

24. FEMA-MOTF@fema.dhs.gov Exercise Create a depth grid based off of the City and County of Denver DFIRM for an area along the South Platte River near Evans Ave and I-25. To do this, the DFIRM Database will need to be downloaded from the FEMA Map Service Center, and the DEM and AOI can be found the FEMA MOTF FTP site. The DEM has been clipped to the area of interest. GO!!!!

25. FEMA-MOTF@fema.dhs.gov Useful Links USGS NED - http://nationalmap.gov/USGS NED - http://nationalmap.gov/http://nationalmap.gov/ Vertcon Conversion -Vertcon Conversion - http://www.ngs.noaa.gov/cgi- bin/VERTCON/vert_con.prlhttp://www.ngs.noaa.gov/cgi- bin/VERTCON/vert_con.prl FEMA Maps Service Center – https://msc.fema.gov/portalFEMA Maps Service Center – https://msc.fema.gov/portalhttps://msc.fema.gov/portal MOTF SOPs – https://content.femadata.com/MOTF/SOPs/MOTF SOPs – https://content.femadata.com/MOTF/SOPs/https://content.femadata.com/MOTF/SOPs/ US Interagency Elevation Invnetory - http://coast.noaa.gov/inventory/US Interagency Elevation Invnetory - http://coast.noaa.gov/inventory/ http://coast.noaa.gov/inventory/