Coastal Flooding Short Course

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Coastal Flooding Short Course

• Pacific Disaster Center
• Maui, Hawaii
• June 29-1July 2, 2009

• Jim O'Brien, Ph.D., P.E.
• Reinaldo Garcia, Ph.D.
• FLO-2D Software, Inc.

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• Workshop
• Coastal flooding, river and floodplain flow
  exchange, mud and debris flows

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Notesome slides may have buttons to show flood
simulations that will not work on your computers
because you dont have the data or output files.
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New Features for Version 2009.06

• MODFLOW surface/groundwater interface
• RiverFLO-2D in-channel 2-D model
• Optimized for 64-bit multiple processors
• Levee fragility curves - dam/levee breach erosion
• Two new sediment transport equations
• Enhanced HEC-RAS project data integration
• Watershed delineation
• Many new GDS Mapper Features

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New Features (cont.)

• SCS Curve Numbers
• FreqPlot
• NEXRAD rainfall modeling
• Time depth plots for dam breach
• Project output analysis reporting
• Improved error messaging

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New Features Summary Box
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FLO-2D Model Features

• Physical process model
• Conserves volume and reports on it
• Combined hydrologic and hydraulic model
• Unconfined flooding with no boundary conditions
  or hot starts
• Routes entire hydrograph
• Variable timesteps enable fast simulations

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FLO-2D Products
Shaded color contours with background images
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River Flooding
Rio Grande Model Albuquerque District Corps of
Engineers 173 miles 167,000 grid elements
(250 ft)
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Urban Flooding Hazard Maps
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Urban Flood Hazard Delineation
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Primary Attributes

• 2-D overland unconfined flow in 8-directions
• Channel routing rectangular, trapezoidal or
  cross sections
• Computes channel-floodplain exchange flow
• Floodplain/channel rainfall, infiltration and
  evaporation
• Evaluates development on storage and flow path
• Models street flow and levees
• Simulates sediment transport and mud/debris flows
• Hydraulic structures (bridges, culvert, weirs
  rating tables)

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Channel - Floodplain Interface
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Monroe Creek, Richfield, Utah
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Monroe Creek, Richfield, Utah
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Monroe Creek, Utah

• Channel flooding on an alluvial fan
• 3026 grid elements
• Channel - floodplain flow exchange

Flood
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Rio Grande - Isleta Reach

• Overbank flooding
• Effects of floodwave attenuation

250-yr no levee
250-yr levee
100-yr levee
Annual flood
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Mudflow Simulation Barnard Creek, Centerville,
Utah
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Simple Simulation Barnard Creek, Centerville,
Utah
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Example Barnard Creek, Utah

• Urbanized alluvial fan
• Very steep slopes (streets 10)
• Small debris basin at fan apex
• Street flow conveyances
• Numerous buildings
• Mudflow, water flood and rain

Mud
Water
No Streets
No Buildings
Rain Mud
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Required Data Base

• Digitized topo map or DTM of the flow surface
• Hydrology - rainfall and inflow flood hydrographs
• For Channel Option - cross section surveys

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• When Do I Need a 2-D Model?

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Answer Whenever the flood volume determines the
area of inundation...

• Unconfined flow or distributary flow
• Very flat topography
• Split flow (channel or floodplain)
• Combine hydrologic and hydraulic modeling
• Routing flood hydrograph
• Floodwave attenuation

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Variable Water Surface Elevations Urban Flooding
with Streets and Buildings
Typical HEC-RAS Cross Section
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When flood volume controls the area of inundation
not the peak discharge, the cross section water
surface elevation is highly variable.
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Dam Break or Levee Breach
Jim OBrien FLO-2D Software, Inc.
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Mapper Delineated North Breach
Area of Inundation
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Porting from Version 2007.06 to Version 2009.06

• Add switch IMODFLOW 0 end of line 3 CONT.DAT
• Delete IQDIR from CHAN.DAT (automated)
• New CHANBANK.DAT

• Optional Items
• Levee Fragility Curve Data (LEVEE.DAT and
  BREACH.DAT).
• MODFLOW parameters

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Porting from Version 2007.06 to Version 2009.06

• Sequence
• Add switch IMODFLOW 0 end of line 3 CONT.DAT
• Open GDS or FLOENVIR (load channel) and save the
  data files. Deletes the IQDIR variable and
  creates the CHANBACK.DAT file.
• Open the GDS or FLOENVIR and review the channel
  bank positions.
• ERROR.CHK will list and over- or under- channel
  extensions.

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What are my resources?

• Manuals and tutorials/lessons on the CD
• Example projects on the CD
• GUI, GDS and Mapper In-Help
• Power Point presentations
• Technical support (email or phone)
• Website forum chat web page
• Consulting project technical oversight

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Users Manual

• Model theory routing algorithms
• Description of model components
• Parameter sensitivity
• Limitations and assumptions
• Applications
• Model verification

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Data Input Manual

• Data files format and description
• Data limitations and variable ranges
• Output files
• Debugging and troubleshooting guide

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Input Data Manual Format

• FLO-2D reads the data exactly as specified in the
  manual Data Input Section
• Data format
• Data variable description (alphabetical)
• List of instructional comments

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GDS, Mapper and Mapper.NET Manuals

• GDS and MAPPER Manuals
• Simple to use and well illustrated

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Graphical User Interface - GUI

• Self-explanatory with help comments
• Data entry in fields or tables
• Run the model and processor programs

GUI
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Pre-processor Programs

• Frequently used
• GDS creates and edits the grid attributes
• FLOENVIR edits the system attributes becoming
  obsolete
• PROFILES - plots water surface and bed profiles,
  adjusts channel bed elevation and channel depths,
  interpolates slope and cross sections

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Post-processor Programs

• MAXPLOT simple, fast graphical output
• MAPPER mapping tool creates shaded color
  contour plots, animation and much more
• HYDROG - graphically displays a channel
  hydrograph for every channel element
• PROFILES - graphically displays the water surface
  and bed profile

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ASCII Editor

• Editors WordPad, TextPad, UltraEdit
• Files .DAT .BAC .OUT .CHK

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Grid Size Selection
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A common misconception is

• Smaller grid elements increase model flood
  resolution.

Most common problem is
Too many grid elements slow down the model.
How do I choose the grid size?
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Balance three things

• Accuracy of the data base
• Desired results
• Model speed and data editing

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1. Data Base

• Resulting flood maps cant exceed the accuracy of
  the topo maps made with the DTM
• Accuracy of the map contours will not necessary
  improve because you select smaller grid elements

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2. Desired Results

• Unconfined and shallow flooding maps - use
  smaller grid elements
• Frequent return period flooding, smaller
  discharge, distributary flooding
• Large flood inundation use larger grid elements
• 100-year flood fills valley

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Shallow distributary flooding Use smaller grid
elements to improve flood boundary resolution.
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Valley Flooding
Use larger grid elements
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3. Model speed and editing

• 150,000 to 200,000 grid elements with a 10 day
  hydrograph 6 to 12 hours computer run time
• Graphical editing adding channels, streets,
  buildings, spatially variabilty (infiltration,
  n-values) takes time 1-2 weeks

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Grid System Selection

• Qpeak/Asurf lt 1.0 cfs/ft2 (0.3 cms/m2)
• Qpeak peak discharge inflow to one grid
  element
• Asurf surface area of one grid element

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Grid System Selection

• Number of grid elements
• 1,000 15,000 very fast - minutes
• 15,000 - 60,000 moderate hour(s)
• 60,000 - 150,000 slow 2 to 8 hours
• gt150,000 gt 8 hrs - overnight

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Basic steps for starting a FLO-2D project

• Understand the project flood hazard delineation,
  mitigation design, flow hydraulics, rainfall-
  runoff
• Determine basic project area (5 miles x 1 mile)
• Select grid element size (try 50 ft, 200 ft,
  etc.)
• Estimate peak discharge

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Where to get more information

• Web Site www.flo-2d.com
• Email jim_at_flo-2d.com

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Whats coming up?

• Grid System Attributes Graphical Editing with
  the GDS