Floodplain Modeling with LiDAR-Derived Terrain

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Floodplain Modeling with LiDAR-Derived Terrain

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Floodplain Modeling with LiDAR-Derived Terrain

  1. 1. Floodplain Modeling and Delineation with LiDAR-Derived Terrain <ul><li>Wisconsin Dept. of Natural Resources </li></ul><ul><li>Bureau of Watershed Management </li></ul><ul><li>FEMA Risk MAP Program </li></ul>Katie McMahan – GIS Data Manager [email_address] Chris Olds – Floodplain Engineer [email_address]
  2. 2. Presentation Overview <ul><li>LiDAR </li></ul><ul><ul><li>Products </li></ul></ul><ul><li>Terrain </li></ul><ul><ul><li>Required feature classes (surface feature types) </li></ul></ul><ul><ul><li>Process of building </li></ul></ul><ul><ul><li>Possible issues that may arise </li></ul></ul><ul><li>Floodplain delineation </li></ul><ul><ul><li>HEC-GeoRAS geometry to create input feature classes </li></ul></ul><ul><ul><li>HEC-RAS to determine flood elevations </li></ul></ul><ul><ul><li>HEC-GeoRAS mapping to delineate raw floodplain polygons </li></ul></ul><ul><ul><li>Smoothing and merging multiple floodplains </li></ul></ul>
  3. 3. Products received vs. what we use <ul><ul><li>Bare earth </li></ul></ul><ul><ul><ul><li>DEM </li></ul></ul></ul><ul><ul><ul><li>DWG </li></ul></ul></ul><ul><ul><ul><li>LAS </li></ul></ul></ul><ul><ul><ul><li>SHP </li></ul></ul></ul><ul><ul><li>Breaklines </li></ul></ul><ul><ul><ul><li>DWG </li></ul></ul></ul><ul><ul><ul><li>SHP </li></ul></ul></ul><ul><ul><li>Contours </li></ul></ul><ul><ul><ul><li>DWG </li></ul></ul></ul><ul><ul><ul><li>SHP </li></ul></ul></ul><ul><ul><li>Point cloud </li></ul></ul><ul><ul><ul><li>DWG </li></ul></ul></ul><ul><ul><ul><li>SHP </li></ul></ul></ul><ul><ul><ul><li>LAS </li></ul></ul></ul><ul><ul><li>Metadata </li></ul></ul><ul><ul><ul><li>Important elements: </li></ul></ul></ul><ul><ul><ul><ul><li>Projection </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Average point spacing </li></ul></ul></ul></ul>
  4. 4. Terrain Overview <ul><li>TIN-based dataset that is a representation of input feature classes </li></ul><ul><li>Terrain is editable—can remove, add and replace the data referenced </li></ul>
  5. 5. Steps to building terrain <ul><li>Create a File Geodatabase </li></ul><ul><li>The personal geodatabase has a 2GB size limit, too small to handle an entire County’s worth of LIDAR data. </li></ul>
  6. 6. Feature Dataset <ul><li>In ArcCatalog, create a new ‘Feature Dataset’. This will house all data used to and create your terrain. </li></ul><ul><li>Choose the coordinate system the LiDAR data is in; most often a County coordinate system. </li></ul><ul><li>Make sure the linear unit of measurement (ft or meter) is defined correctly for both the projected and vertical coordinate systems </li></ul>
  7. 7. Feature Dataset <ul><li>Import all of the features that will be used to create the terrain into feature dataset. </li></ul><ul><ul><li>LIDAR multipoints (created from LAS files) </li></ul></ul><ul><ul><li>Breaklines </li></ul></ul><ul><ul><li>Hard-clip polygons (usually a buffered polygon of the County boundary) </li></ul></ul><ul><li>Determine Average Point Spacing of bare earth points </li></ul>
  8. 8. Average Point Spacing From LiDAR metadata or using the 3D Analyst Point File Information tool
  9. 9. Average Point Spacing
  10. 10. Bare Earth Multipoints <ul><li>Multipoints should be spatially clustered </li></ul><ul><li>Processing terrain countywide: break down by township or range </li></ul><ul><li>Recent example: </li></ul><ul><ul><li>830 LAS files </li></ul></ul><ul><ul><li>LiDAR points: 2,074,016,000 </li></ul></ul>
  11. 11. LAS to Multipoint
  12. 12. LAS to Multipoint
  13. 13. Breaklines <ul><li>Lines with height recorded at each vertex </li></ul><ul><li>Represents some sort of interruption in the landscape: </li></ul><ul><ul><li>Natural landforms (ridges, valleys) - S </li></ul></ul><ul><ul><li>Edge of pavement - H </li></ul></ul><ul><ul><li>Roadways - H </li></ul></ul><ul><ul><li>**Water lines (streams, rivers, canals, shorelines) - H </li></ul></ul><ul><li>Eliminates interpolation of LiDAR points across the breakline; becomes the edge of the triangles </li></ul><ul><li>Hard line : represents distinct break in the slope </li></ul><ul><li>Soft line : allows the adding of edges without affecting the shape of the surface </li></ul>**Taken from ArcGIS Desktop Help 9.3.1
  14. 14. Hard Breaklines
  15. 15. Clip Polygon <ul><li>Define boundaries for interpolating a terrain surface with an irregular shape—data that falls outside the polygon is excluded </li></ul><ul><li>Study area boundary </li></ul><ul><li>No height source </li></ul>**Taken from ArcGIS Desktop Help 9.3.1
  16. 16. Build Terrain
  17. 17. Choose Features
  18. 18. Pyramid Type
  19. 19. Terrain Pyramids <ul><li>Levels of detail to improve efficiency—a form of scale dependent generalization (thinning points) </li></ul><ul><li>Z-Tolerance : uses a vertical tolerance in the definition of the terrain resolution at the specified scale (relative to vertical accuracy at full-resolution) </li></ul><ul><ul><li>Used to improve analysis performance through a range of scales </li></ul></ul><ul><li>Window Size : resolution defined by window </li></ul><ul><ul><li>Used for improving interactive display performance (specific vertical accuracies is not a primary concern) </li></ul></ul><ul><li>When exporting rasters or TINs, the entire feature dataset is used (no difference from actual surface). </li></ul><ul><li>**Not necessary for terrain use at constant and large display scale, i.e. raster production for large-scale applications or for data storage purposes; time intensive, no reason to incur the processing cost. </li></ul>
  20. 20. Z-Tolerance <ul><li>Must generate one pyramid no matter which type you choose </li></ul>
  21. 21. Summary of terrain settings
  22. 22. Terrain Overview <ul><li>Coarsest representation of the terrain dataset </li></ul><ul><li>For fast drawing at small scales </li></ul><ul><li>Set only those feature classes that must be represented in the overview to ‘Yes’ </li></ul>
  23. 23. Terrain Overview **Taken from ArcGIS Desktop Help 9.3.1
  24. 24. 3D Analyst Conversion Tool: Terrain to Raster Float will allow the value of the pixel to be in decimal format 5-foot cell size
  25. 25. Conversion to raster <ul><li>Countywide 5-foot grid </li></ul>
  26. 26. <ul><li>3D Analyst license is required; </li></ul><ul><li>Choose LAS over ASCII (if available); </li></ul><ul><li>The data involved should be contiguous; </li></ul><ul><li>Data should be in a projected coordinate system; </li></ul><ul><li>More straightforward to have the z-values in same unit of measure as the x,y values; </li></ul><ul><li>Use data gathered using the same data collection specifications and accuracy requirements. </li></ul><ul><li>Use the fewest feature classes possible; no large single point feature classes. Use a multipoint feature class for large point collections (e.g., anything over 500,000). </li></ul><ul><li>Allow plenty of time for processing large areas of terrain </li></ul>Tips for building terrain
  27. 27. Complications <ul><li>Missing tiles = visual confirmation of the terrain </li></ul><ul><ul><li>requires cooperation with original vendor to gather complete dataset </li></ul></ul><ul><li>Incorrect height values = visual confirmation of the terrain (i.e. giant spikes or dips in elevation) or in floodplain delineation ‘gaps’ </li></ul><ul><ul><li>may result in the need for additional ground truthing or survey cross sections along the stream </li></ul></ul>
  28. 28. Floodplain delineation ‘gaps’
  29. 29. Floodplain Delineation
  30. 30. HEC-GeoRAS
  31. 31. Creating Feature Classes
  32. 32. Creating Feature Classes
  33. 33. Populating Feature Classes
  34. 34. Layer Setup
  35. 35. Layer Setup
  36. 36. Extracting Topological Data
  37. 37. HEC-RAS
  38. 38. Importing GIS data into HEC-RAS
  39. 39. Cross section in HEC-RAS
  40. 40. Cross Section 3D View
  41. 41. Cross section results in HEC-RAS
  42. 42. Flood profile in HEC-RAS
  43. 43. Exporting HEC-RAS results into GIS files
  44. 44. Floodplain delineation using HEC-GeoRAS
  45. 45. Floodplain Delineation Layer Setup
  46. 46. Importing HEC-RAS data
  47. 47. Importing HEC-RAS data
  48. 48. HEC-RAS data back in GIS
  49. 49. Flood Inundation Mapping
  50. 50. Water surface TIN generation
  51. 51. Flood Inundation Mapping
  52. 52. Flood Inundation Mapping
  53. 53. Flood depth grid
  54. 54. Floodplain boundary polygon
  55. 55. Floodplain boundary polygon smoothing
  56. 56. Floodplain boundary polygon smoothing
  57. 57. Merging floodplain feature classes
  58. 58. QUESTIONS?

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