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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.

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floodplain mapping using hec ras and arcview gis

Floodplain Mapping using HEC-RAS and ArcView GIS

http://www.ce.utexas.edu/stu/tateec

Eric Tate

Francisco Olivera

David Maidment

outline
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
Map-Based Hydrology and Hydraulics

ArcView

Input Data

DEM

ArcView

Flood

plain maps

CRWR-PrePro

HEC-RAS

Water

surface

profiles

HEC-HMS

Flood

discharge

motivation why map floodplains in gis
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
Objectives
  • Develop procedure to process computed water surface profiles generated from HEC-RAS hydraulic modeling anddraw floodplain maps in ArcView GIS
  • Synthesize a TIN terrain model from HEC-RAS cross-sectional data and a digital elevation model (DEM)
outline6
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping
hec ras background
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

hec ras cross section representation
HEC-RAS: Cross-Section Representation
  • Points describe channel and floodway geometry
  • Bank station locations
  • Water surface elevations and floodplain boundaries
hec ras output
HEC-RAS: Output

Graphical

Text File

hec ras data translation
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
outline11
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping
stream centerline 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
Cross-Section Mapping

One to one relationship established between table records and definition points

cross section mapping14
Cross-Section Mapping
  • Assume straight line cross-sections
  • Proportional aliasing for cross-section location
  • User input for cross-section orientation
outline15
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping
gis data models vector

GIS Data Models: Vector

Points, lines, and polygons

Typically used for linear feature representation

gis data models raster

GIS Data Models: Raster

Digital Elevation Model (DEM)

Square grid cells

Typically used for steady-state spatial modeling and two-dimensional surface representation

gis data models tin

GIS Data Models: TIN

Triangular Irregular Network (TIN)

Mesh of equilateral triangles

Used for three-dimensional surface representation and drainage analysis.

outline19
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping
3d terrain modeling procedure

3D Terrain Modeling: Procedure

Outside Channel: Raster

Inside Channel: Vector

Result: TIN

3d terrain modeling procedure21

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

3D Terrain Modeling

Problem: elevation differences at the end of the cross-section

3d terrain modeling23

3D Terrain Modeling

Re-sample cross sections to eliminate elevation differences

3d terrain modeling24

3D Terrain Modeling

Build TIN model from re-sampled cross-sections and DEM

outline25
Outline
  • Motivation
  • HEC-RAS Hydraulic Model
  • Stream Cross-Section Mapping
  • GIS Data Models
  • 3-D Terrain Modeling
  • Floodplain Mapping
hec ras output29
HEC-RAS: Output

Graphical

Text File

floodplain mapping plan view30
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
Real-time flood mapping

Nexrad radar

rainfall input

Real time

Precomputed

flood map

library

Offline

Flood hydrology

analysis system

questions comments
Questions?Comments?

Also thanks to Seann Reed and Brian Adams