Flood Analysis of Scioto River Using HEC-RAS/GIS

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Flood Analysis of Scioto River Using HEC-RAS/GIS

• Converting HEC-2 Data for
• HEC-RAS /ArcView GIS Analysis and Inundation
  Mapping
• (A pilot using Big Darby Creek )

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1873 flood of Athens
No Exact Record Available
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1907 flood - the highest known flood
The estimated peak discharge was 50,000 cfs
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The Joseph Herrold Home Before and After the 1913
Flood
Before...
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Joseph Herrold home after the flood of 1913
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Flood on March 11, 1964 - Ohio University,
Athens
A height of 24.18 feet was recorded on the gage
station
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Pre-processing

• USGS 124,000 DLGs
• AVRas Pre-processing Function
• TIN creation (temporary from DLGs)
• Preparing required themes in ArcView GIS
• Bank lines
• Center line - require a line between banks
• Flow lines - direction of the flow
• X-sections digitized from surveying maps

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Pre-processing (cont.)

• Digitizing provided X-sections using Arc/Info
• Conversion to ArcView GIS
• Labeling stations for X-sections

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Pre-processing

• Creating the HEC-RAS import file (.geo) using
  AVRas
• Temporary TIN
• Center line
• Bank lines
• Flow lines
• X-Sections

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• HEC-2 X-sections

• Preprocessed X-sections

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Geo-referenced X-sections
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Importing GIS and HEC-2 Data

• Separately import GIS geometry file (.geo) and
  HEC-2 data
• Adjust GIS geometry file according to HEC-2 data
• Ground elevations
• X-section lengths
• Run an Avenue script to export X-sections into
  ArcView GIS
• Program written by Nan Shi
• Generate two shapefiles - X-sections and
  elevation points
• Adjust new X-sections referencing streams in GIS

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Cross-Section Cleaning

• Cross-sections lengths adjusted by HEC-2 data
• Position verified by USGS data
• Flow length verified by HEC-2 data

Digitized
Adjusted
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Final DEM Production

• Point elevation data (original HEC-2 data)
• Topographical elevation data (USGS data)
• New TIN created for flood plain delineation

New DEM
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HEC-RAS

• Adding parameters
• Manningsn values
• Ineffective flow areas
• Bridges
• Steady flow data
• Run water surface profile computations
• Model verification

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Model Verification
Original HEC-2
New HEC-RAS
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Post-processing

• HEC-RAS export file
• AVRas post-processing
• Flood plain for 4 profiles
• 17,800 cfs
• 30,800 cfs
• 38,000 cfs
• 58,000 cfs

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Big Darby Flood Delineation
17,800 cfs - green 30,800 cfs - red 38,000 cfs -
blue 58,000 cfs - purple
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Adding AdditionalGeographic Information
17,800 cfs
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Adding AdditionalGeographic Information
30,800 cfs
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Adding AdditionalGeographic Information
38,000 cfs
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Adding AdditionalGeographic Information
58,000 cfs