Transcript Document 7145752

Floodplain Mapping using
HEC-RAS and ArcView GIS
http://www.ce.utexas.edu/stu/tateec
Eric Tate
Francisco Olivera
David Maidment
Outline
 Motivation and Objectives
 HEC-RAS Hydraulic Model
 Stream Cross-Section Mapping
 GIS Data Models
 3-D Terrain Modeling
 Floodplain Mapping
Map-Based Hydrology and Hydraulics
ArcView
Input Data
DEM
ArcView
Flood
plain maps
CRWR-PrePro
HEC-HMS
Flood
discharge
HEC-RAS
Water
surface
profiles
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
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)
Outline
 Motivation
 HEC-RAS Hydraulic Model
 Stream Cross-Section Mapping
 GIS Data Models
 3-D Terrain Modeling
 Floodplain Mapping
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
Normal Water Surface
Flood Water Surface
Floodway
Left Bank Station
Floodway
Main
Channel
Right Bank Station
HEC-RAS: Cross-Section Representation
 Points describe channel
and floodway geometry
 Bank station locations
 Water surface
elevations and
floodplain boundaries
HEC-RAS: Output
Graphical
Text File
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
Outline
 Motivation
 HEC-RAS Hydraulic Model
 Stream Cross-Section Mapping
 GIS Data Models
 3-D Terrain Modeling
 Floodplain Mapping
Stream Centerline Mapping
 Digital orthophotograph
and road coverage
used as a base map
 User defines stream
centerline
 Definition points
identify key stream
cross-sections
Cross-Section Mapping
One to one relationship established between table records
and definition points
Cross-Section Mapping
 Assume straight line
cross-sections
 Proportional aliasing
for cross-section
location
 User input for crosssection orientation
Outline
 Motivation
 HEC-RAS Hydraulic Model
 Stream Cross-Section Mapping
 GIS Data Models
 3-D Terrain Modeling
 Floodplain Mapping
GIS Data Models: Vector
 Points, lines, and polygons
 Typically used for linear feature representation
GIS Data Models: Raster
Digital Elevation Model (DEM)
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 Square grid cells
 Typically used for steadystate spatial modeling and
two-dimensional surface
representation
GIS Data Models: TIN
Triangular Irregular Network (TIN)
 Mesh of equilateral triangles
 Used for three-dimensional surface representation and
drainage analysis.
Outline
 Motivation
 HEC-RAS Hydraulic Model
 Stream Cross-Section Mapping
 GIS Data Models
 3-D Terrain Modeling
 Floodplain Mapping
3D Terrain Modeling: Procedure
Outside Channel: Raster
Inside Channel: Vector
Result: TIN
3D Terrain Modeling: Procedure
 DEM raster to vector
conversion
 Form polygon bounding
the cross-sections
 Delete any DEM points
falling within the bounding
polygon
3D Terrain Modeling
Problem: elevation differences at the end of the cross-section
3D Terrain Modeling
Re-sample cross sections to eliminate elevation differences
3D Terrain Modeling
Build TIN model from re-sampled cross-sections and DEM
Outline
 Motivation
 HEC-RAS Hydraulic Model
 Stream Cross-Section Mapping
 GIS Data Models
 3-D Terrain Modeling
 Floodplain Mapping
Floodplain Mapping: 3D View
Floodplain Mapping: Ultimate Goal
Floodplain Mapping: Plan View
HEC-RAS: Output
Graphical
Text File
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)
Real-time flood mapping
Nexrad radar
rainfall input
Offline
Flood hydrology
analysis system
Real time
Precomputed
flood map
library
Questions?
Comments?
Also thanks to Seann Reed and Brian Adams