floodplain mapping using av-ras

Floodplain Mapping Using AV-RAS

Esteban Azagra and Francisco Olivera, Ph.D.Center for Research in Water Resources

University of Texas at Austin

Objective

• AV-RAS is a system of ArcView tools developed in Avenue -- the ArcView programming language -- that:

• extracts hydrologic data from digital terrain data, and

• maps the HEC-RAS results back on the digital spatial data

Floodplain Mapping Approach

CRWR-PrePro AVRasWatersurfaceprofiles

ArcView

Geometricdata

ParametersSchematic

Flowdischarge

HEC-HMS HEC-RAS

Digital Spatial Data

ArcView

HEC-RASHEC-HMS

• Digital spatial data required:

• Digital elevation model (DEM).

• Vector stream network.

• Land use / land cover

• Soils

Streams and Watersheds

ArcView

HEC-RASHEC-HMS

• CRWR-PrePro is used for:

• Stream and watershed delineation.

• Determination of stream and watershed hydrologic parameters.

HEC-HMS: Flow Determination

ArcView

HEC-RASHEC-HMS

HMS-RAS ConnectionHMS Junctions RAS Cross-sections

ArcView

HEC-RASHEC-HMS

HMS-RAS Connection

ArcView

HEC-RASHEC-HMS

(0500, 3559.6)

HMS Hydrograph

RAS Flow Data

Digital Terrain Model: TIN

ArcView

HEC-RASHEC-HMS

• Observed points and breaklines for constructing a triangular irregular network (TIN).

•TIN components:- nodes- edges- triangles

Digital Terrain Model: TIN

ArcView

HEC-RASHEC-HMS

• 3D display of a TIN.

Digital Terrain Model: TIN

ArcView

HEC-RASHEC-HMS

Digital Terrain Model: TIN

• Embedding Buildings into the TIN.

ArcView

HEC-RASHEC-HMS

Cross Sections

• Stream centerline.• Banks.• Flow paths.• Cross sections.

ArcView

HEC-RASHEC-HMS

• Bridges are not captured by the TIN: cross sections should NOT be defined at the bridges.

ArcView

HEC-RASHEC-HMS

Cross Sections

Hydraulic Modeling with RAS

• RAS stream geometry.

• Cross-sections extracted from the TIN.

ArcView

HEC-RASHEC-HMS

Hydraulic Modeling with RAS

• Water surface elevations.

ArcView

HEC-RASHEC-HMS

Floodplain Mapping

ArcView

HEC-RASHEC-HMS

• Floodplain for 500 cfs.

Floodplain Mapping

• 2-D floodplain animation (500 – 5,000 cfs).

Floodplain Mapping

• 2-D representation of the Central Park detention pond.

Floodplain Mapping

• 3-D floodplain animation.

Limitations

• Bridge and culvert data has to be entered by hand.

CS 9658

490

495

500

505

510

515

520

525

0 20 40 60 80 100 120 140 160

Distance along cross-section (ft)

Ele

vati

on a

bov

e M

LS

(ft

)

Field data

Data extracted from the TIN

Limitations

• The accuracy obtained from TIN data might not be good enough.

Solutions

Source: digital representation of NYCgenerated by ASI and published by ESRI.

• New technologies (i.e. LADAR) are improving the quality of the digital terrain representations.

Source: digital representation of NYCgenerated by ASI and published by ESRI.

Solutions

• New technologies (i.e. LADAR) are improving the quality of the digital terrain representations.

Conclusions

• Automation of floodplain delineation results in time and resource savings.

• The lack of subjectivity provides standardized results.

• Applications include:• Design of control structures (detention

ponds, culverts, bridges, …).• Flood insurance rate determination.• Real-time flood emergency mapping.

• The accuracy of the digital terrain model has to be improved.

• Some field data will be still required.