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

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. PURPOSE OF THIS PROJECT

WHAT IS LIDAR ? 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. Acronym for Light Detection And Ranging

HOW LIDAR WORKS Operating altitude: ,000 meters. Laser pulse rate: up to 25,000 per sec. Swath width: up to 1,500 meters at 2,000 meter altitude.

Source.BEG PRECISION OF THE LIDAR DEM

LIDAR INSTRUMENT All-Terrain Laser Mapper (ALTM)

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

DATA PROCESSING Source : BEG (1)compute a differentially corrected aircraft trajectory using a GPS software, (2)generate the raw x, y, and z data, (3)grid the data to generate an “all-points DEM”, (4) filter the raw data and re-grid to generate a “vegetation-removed DEM”

EFFECT OF VEGETATION REMOVAL Before After

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-RAS + HecGeoRas extension FLOODPLAIN MODELING

STUDY AREA Waller Creek Watershed

ALL-POINT LIDAR DATA OF WALLER CREEK

BARE –EARTH LIDAR DATA FOR WALLER CREEK

FLOOD MODELING PROCEDURE HEC-GeoRas Preprocessing LIDAR input data 1m grid DEM ARCVIEW Terrain model processing Plan data ( Flow regime) Geometric data stream centerlines, riverbanks, floodplain boundaries, cross- sections along the streams HEC-GeoRas Postprocessing Flow data from HEC-HMS HEC-RAS steady state simulation Hydraulic modeling Hydrologic modeling Flood map visualization Import file

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

STREAM CENTERLINES

STREAM BANKS

FLOW PATH LINES

CROSS-SECTIONS CUTLINES

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 DIFFICULTY ENCOUNTERED

CONVERTING TINs TO GRID

EXTRACTED CROSS SECTIONS

PREPARING THE IMPORT FILE TO HEC-RAS

DIFFICULTY ENCOUNTERED AT THIS STAGE An error message from the Hec-PreRAS program during the import file process.

RAS stream geometry. Cross-section extracted from the TIN. WORK TO BE DONE : MODELING WITH HEC-RAS Resulting water elevations.

PREVIOUS FLOOD MAPPING WITH TINs (Source. Esteban Azagra)

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

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 ACKNOWLEDGMENT