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Floodplain Mapping using HEC-RAS and ArcView GIS

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Floodplain Mapping using HEC-RAS and ArcView GIS. Eric Tate. Francisco Olivera. David Maidment ... Motivation: Why map floodplains in GIS? ... – PowerPoint PPT presentation

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Learn more at: http://www.ce.utexas.edu
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Tags: arcview | gis | hec | ras | floodplain | gis | mapping | using

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Title: Floodplain Mapping using HEC-RAS and ArcView GIS


1
Floodplain Mapping using HEC-RAS and ArcView GIS
http//www.ce.utexas.edu/stu/tateec
  • Eric Tate
  • Francisco Olivera
  • David Maidment

2
Outline
  • Motivation and Objectives
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping

3
Map-Based Hydrology and Hydraulics
ArcView Input Data DEM
ArcView Flood plain maps
CRWR-PrePro
HEC-RAS Water surface profiles
HEC-HMS Flood discharge
4
Motivation Why map floodplains in GIS?
  • Computer automation results in time and resource
    savings versus manual floodplain plotting
  • Flood insurance rate determination
  • Economic impact analysis and flood early warning
    systems
  • Design of drainage control structures, including
    storm drains, culverts, and bridges

5
Objectives
  • Develop procedure to process computed water
    surface profiles generated from HEC-RAS hydraulic
    modeling and draw floodplain maps in ArcView GIS
  • Synthesize a TIN terrain model from HEC-RAS
    cross-sectional data and a digital elevation
    model (DEM)

6
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping

7
HEC-RAS Background
  • Hydraulic model of the U.S. Army Corps of
    Engineers
  • Input cross-section geometry and flow rates
  • Output flood water elevations

Cross-Section Schematic
8
HEC-RAS Cross-Section Representation
  • Points describe channel and floodway geometry
  • Bank station locations
  • Water surface elevations and floodplain
    boundaries

9
HEC-RAS Output
  • Graphical
  • Text File

10
HEC-RAS Data Translation
  • Data translation from HEC-RAS output text file to
    dbase table
  • Table data includes the river station IDs,
    various cross-section coordinates, reach lengths,
    computed flood elevations

11
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping

12
Stream Centerline Mapping
  • Digital orthophotograph and road coverage used as
    a base map
  • User defines stream centerline
  • Definition points identify key stream
    cross-sections

13
Cross-Section Mapping
One to one relationship established between table
records and definition points
14
Cross-Section Mapping
  • Assume straight line cross-sections
  • Proportional aliasing for cross-section location
  • User input for cross-section orientation

15
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping

16
GIS Data Models Vector
  • Points, lines, and polygons
  • Typically used for linear feature representation

17
GIS Data Models Raster
Digital Elevation Model (DEM)
  • Square grid cells
  • Typically used for steady-state spatial modeling
    and two-dimensional surface representation

18
GIS Data Models TIN
Triangular Irregular Network (TIN)
  • Mesh of equilateral triangles
  • Used for three-dimensional surface
    representation and drainage analysis.

19
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping

20
3D Terrain Modeling Procedure
Outside Channel Raster
Inside Channel Vector
Result TIN
21
3D Terrain Modeling Procedure
  • DEM raster to vector conversion
  • Form polygon bounding the cross-sections
  • Delete any DEM points falling within the
    bounding polygon

22
3D Terrain Modeling
Problem elevation differences at the end of the
cross-section
23
3D Terrain Modeling
Re-sample cross sections to eliminate elevation
differences
24
3D Terrain Modeling
Build TIN model from re-sampled cross-sections
and DEM
25
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping

26
Floodplain Mapping 3D View
27
Floodplain Mapping Ultimate Goal
28
Floodplain Mapping Plan View
29
HEC-RAS Output
  • Graphical
  • Text File

30
Floodplain Mapping Plan View
  • Raster floodplain shows both extent and depth of
    flooding
  • Digital orthophotograph base map allows easy
    comparison of floodplain location with specific
    areas of interest (e.g., infrastructure,
    buildings)

31
Real-time flood mapping
Nexrad radar rainfall input
Real time
Precomputed flood map library
Offline
Flood hydrology analysis system
32
Questions? Comments?
Also thanks to Seann Reed and Brian Adams
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