FLO2D Hydrology

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FLO-2D Hydrology

• Jim O'Brien
• FLO-2D Software, Inc.

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Flood Volume

• If a reviewer doesnt like the FLO-2D results,
  the first thing to check is the hydrology.
• All that FLO-2D does is move the flow around on
  the grid system.

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Simulating rainfall events

• FLO-2D is a combined hydrology and hydraulics
  model. Choices are
• Simulate rainfall and losses (infiltration)
• Any number of inflow flood hydrographs (e.g. at a
  fan apex)
• Rainfall on a flood surface while it is
  progressing over the alluvial fan.

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Hydrology Considerations

• Flood volume (inflow hydrograph rainfall)
  dictates the area of inundation.
• Volume estimate is critical, hydrograph shape is
  more important than peak discharge.
• Narrow peaks attenuate very quickly with overbank
  flows.
• Design events never include surging. There
  should be some sediment bulking.

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FLOENVIR Tools for Storm Modeling

• Spatially Variable Rainfall - Point Rainfall and
  Area Reduction
• Storm Distributions
• Moving Storm

FLOENVIR
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NEXRAD Data

• Use any ASCII data base
• Intersect and interpolate rainfall grid data to
  FLO-2D grid system in GDS
• Use NEXRAD data to replicate storms

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Interpolate Variable Rainfall Depth

• Interpolates temporal rainfall for each FLO-2D
  grid element based on spatially varied rainfall
  data in an ArcInfo ASCII grid file format.
• Data File
• Storm beginning/ending dates and times
• Rainfall time interval (in minutes)
• Storm time intervals
• File name and location.

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Example

• 6/12/2002 1300 6/12/2002 1400 60 2
• C\Models\FLO2D\Raindata2\rain13h.dat
• C\Models\FLO2D\Raindata2\rain14h.dat
• Beginning date of the storm 6/12/2002
• Storm beginning time 1300 hours
• Storm ending date and time 6/12/2002 and 1400
  hours
• Time interval between rainfall data files 60
  minutes
• Two rain grid files are shown above.
• The rainfall file format is the standard ArcInfo
  ASCII grid with the values corresponding to
  rainfall depths. Each file corresponds to a
  rainfall depth at a specific time for rainfall
  grid system.

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RAINCELL.DAT

• Line 1. Beginning date and time, ending date and
  time, time interval (in minutes) and number of
  time intervals.
• Line 2. Grid element number and the total
  rainfall depth at that time. This line is
  repeated for each FLO-2D grid element.
• Successive rainfall data for the entire grid
  system follows for the number of time-interval
  groups. For the example above, there would be
  two sets of rainfall data for the entire grid
  system.
• 6/12/2002 10000 PM 6/12/2002 20000 PM
  60 2
• 1 1.8538
• 2 1.8537
• 1235 2.2709
• 1 1.4794
• 2 1.4791
• 1234 1.6294
• 1235 1.6286

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Soldier Canyon Model

• Rainfall runoff
• Hyperconcentrated sediment flows
• Combined hydrologic and hydraulic model rain on
  the flood
• Details buildings, culvert bridge, variable
  n-values, minor infiltration

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July 31, 2006 Storm
3 Day Meso-convective storm 3.68 inches in 24
hours on July 31 2-year return period
rainfall Saturated basin
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Project Objective

• Delineate the flood hazard
• Hydrology July 31, 2006 Storm Calibration
  Design Storm Selection
• Sediment Loading
• Flood Hazard Mapping with FLO-2D

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Soldier Canyon Model

• Rainfall runoff
• Hyperconcentrated sediment flows
• Combined hydrologic and hydraulic model rain on
  the flood
• Details buildings, culvert bridge, variable
  n-values, minor infiltration

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Tasks to Simulate the July 31, 2006 Storm with
NEXRAD data

• In GDS import DTM points and background images
• Create grid system (100 ft)
• Interpolate elevations to the grid elements
  (22,100 elements)
• Assign outflow nodes
• Add spatial details n-values, buildings
• Convert the NEXRAD data to grid system

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FLO-2D Grid System

• Details
• Buildings
• Streets
• n-values

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NEXRAD Data July 31, 2006 Storm

• Soldier Canyon Watershed

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NEXRAD Data Format
There is a data file for every 15 minutes. Each
cell reports the total rainfall at the end of
that 15 minute interval in mm.
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Convert to FLO-2D RAINCELL.DAT File in the GDS
Import Rain ArcInfo ASCII Grid File
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Interpolate Variable Rainfall
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Generates RAINCELL.DAT
Now the storm is discretized into 22,100 100 ft
square grid elements with rainfall every 15
minutes on every grid element.
Run July 31, 2006 Storm Simulation
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Route Hyperconcentrated Sediment Flow

• Assign sediment concentrations to inflow
  hydrograph
• Match total volume of sediment estimated by
  PCRFCD
• Select fluid matrix parameters for a low viscous
  and yield stress, high dispersive stress

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Bulk the Water Hydrograph at Mt. Lemmon Road
Culvert
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Flood Hazard Delineation
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Flood Hazard Delineation 100-year Flood Event
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FreqPlot Program

• Flood and rainfall frequency program
• Compares 4 distributions in Kings Table

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Whats next?

• Setting Inflow and Outflow Conditions and
  Green-Ampt /SCS Infiltration