APPLICATION OF LIDAR IN FLOODPLAIN MAPPING

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APPLICATION OF LIDAR IN FLOODPLAIN MAPPING
Imane MRINI GIS in Water Resources University of
Texas at Austin
Source. Optech,Inc
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PURPOSE OF THIS PROJECT

• Show how LIDAR technology can be used jointly
  with
• GIS and hydraulic models to map the possible
  extent of flooding, and to prove that it could be
  an invaluable tool in flood mapping because of
  its high accuracy.

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WHAT IS LIDAR ?
Acronym for Light Detection And Ranging

• Airborne laser system used to acquire x, y, and z
  coordinates of terrain, and consist of
• Airborne Global Positioning System (GPS)
• Attendant GPS base station
• Inertial Measuring Unit (IMU)
• Light-emitting scanning laser.

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HOW LIDAR WORKS

• Laser pulse rate up to 25,000 per sec.

• Operating altitude 400 - 2,000 meters.

• Swath width up to 1,500 meters
• at 2,000 meter altitude.

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PRECISION OF THE LIDAR DEM
Source.BEG
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LIDAR INSTRUMENT All-Terrain Laser Mapper (ALTM)
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LIDAR FACTS

• Elevation accuracy 10 to 25 cm
• records first and last returns of individual
  pulses and intensity

Applications in ? Flood mapping ? Forest
management ? Coastal management ? Land cover
classification ? Atmospheric pollution monitoring
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DATA PROCESSING Source BEG

• compute a differentially corrected aircraft
  trajectory using a GPS software,
• generate the raw x, y, and z data,
• grid the data to generate an all-points DEM,

(4) filter the raw data and re-grid to generate a
vegetation-removed DEM
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EFFECT OF VEGETATION REMOVAL
After
Before
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FLOODPLAIN MODELING

• Study area Waller creek watershed in Austin,TX
• LIDAR data source Bureau of Economic Geology-
  University of Texas at Austin
• Type of Lidar data 1m DEMs of the all-point and
  bare-earth data as interchange files ( e.00)
• Spatial reference UTM zone 14, datum NAD 1983
• Softwares used ArcGis ( Arctoolbox,
  ArcMap),Arcview , HEC-RASHecGeoRas extension

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STUDY AREA
Waller Creek Watershed
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ALL-POINT LIDAR DATA OF WALLER CREEK
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BARE EARTH LIDAR DATA FOR WALLER CREEK
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FLOOD MODELING PROCEDURE
HEC-GeoRas Preprocessing
Geometric data stream centerlines, riverbanks,
floodplain boundaries, cross-sections along the
streams
ARCVIEW Terrain model processing
Hydraulic modeling
Flood map visualization
HEC-GeoRas Postprocessing
Import file
LIDAR input data 1m grid DEM
Hydrologic modeling
Plan data ( Flow regime)
Flow data from HEC-HMS
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Extracting geometric data

• Use of Spatial Analyst ,3D Analyst and
  Hec-GeoRas extensions
• Using HEC-GeoRas extension and the digitizing
  tool in Arcview, I generated
• - Streamcenterlines
• - Stream banks
• - Flow path centerlines
• - Cross section lines

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STREAM CENTERLINES
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STREAM BANKS
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FLOW PATH LINES
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CROSS-SECTIONS CUTLINES
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DIFFICULTY ENCOUNTERED

• Problem Hec-GeoRas program only works with TINs
• Solution Convert grids to TINs in ArcMap using
  the best vertical accuracy to generate the
  maximum number of triangles in a reasonable
  amount of time

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CONVERTING TINs TO GRID
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EXTRACTED CROSS SECTIONS
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PREPARING THE IMPORT FILE TO HEC-RAS
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DIFFICULTY ENCOUNTERED AT THIS STAGE

• An error message from the Hec-PreRAS program
  during the import file process.

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WORK TO BE DONE MODELING WITH HEC-RAS

• Cross-section extracted
• from the TIN.

• RAS stream geometry.

• Resulting water
• elevations.

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PREVIOUS FLOOD MAPPING WITH TINs (Source. Esteban
Azagra)
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Future work

• Solving the problem of the HecRas import file,
  hopefully before December 6
• Potential ideas to develop
• - Write a program that incorporate grid data in
  the preprocessing for HEC-RAS
• Obtain a more detailed TINs from the grid
  conversion

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ACKNOWLEDGMENT

• Dr. David Maidment, University of texas at Austin
• Becky Smith, Bureau of Economic Geology,
  University of Texas at Austin
• John Andrews, Bureau of Economic Geology,
  University of Texas at Austin