david knipe engineering section manager
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Automated Zone A Floodplain Mapping. David Knipe Engineering Section Manager. FEMA floodplain designations. Zone A: has only 1% chance annual flood mapped – could be from any source. Zone AE: has elevation and floodway mapped – from detailed hydraulic model. Why Map Zone A’s?. - PowerPoint PPT PresentationTRANSCRIPT
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David KnipeEngineering Section Manager
Automated Zone A Floodplain Mapping
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FEMA floodplain designations
Zone AE: has elevation and
floodway mapped – from detailed
hydraulic model
Zone A: has only 1% chance annual
flood mapped – could be from any
source
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Why Map Zone A’s?
• New FEMA guidance – all new zones must be model based
• Still 10,000+ stream miles in Indiana that are not model based
• Cost prohibitive to provide detailed zones in all areas
• Need quick, easy and inexpensive way to map quality floodplains
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The Zone A project
• IDNR funded by OCRA / CDGB (not FEMA) to map 3,200 miles of Zone A floodplains
• Modeling exclusively using new LiDAR DEM’s
• Full “RiskMAP” modeling, including 5 profiles, Flood Elevation Points, FBS Points, SFHA boundaries and depth grids
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Zone A tools
• Tools are a set of Python scripts inside of an Arc Toolbox – other tools (such as HEC-GeoRAS) are not needed
• Only stream centerline, cross sections and overbank flow paths need to be created in Arc.
• HEC-RAS model will be considered an approximate model (no bridges, no floodway).
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Stream Selection
Use the CNMS database to determine
stream reaches that were not studied during
the Map Modernization
processClay
Parke
Putnam
Owen
Montgomery
Boone
Hendricks
Vigo
Morgan
Fountain
Monroe
Sullivan
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Hydrology: Streamstats
hydrology for a stream reach will be completed by using the Purdue
regression equations as
found in the USGS application, Streamstats
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Hydrology: Results
• Results from Streamstats service returned as XML file and imported into Excel, plotted on log-log plot
• Final discharges based on best fit line, not actual values (standard Division practice)
• discharges adjusted by defining a split point to improve the fit of the line
• the user to choose either the regression results (50%) or the upper 68% or 90% confidence interval for use in the model
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Hydrology: Results
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Hydraulic pre processing
three hydraulic data features will need to be
created; stream
centerline, cross sections and overbank
flow paths
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Hydraulic processing
• the initial script checks the geometry of the input data for anomalies• the second script pulls elevation data from the DEM and creates a HEC-RAS import file
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HEC-RAS import
• File created from Hydraulic script imported into HEC-RAS
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HEC-RAS Cross Sections
• Sections as imported represent LiDAR data for each line
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Mannings’s N Values
• Automatically derived using relationships based on Anderson Land Use classification and NLCD data (2006)
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HEC-RAS model development
• Cross section points must be filtered (> 500 points)
• Data evaluated for reasonableness and ineffective flow areas
• Discharges added to model from Excel spreadsheet
• Bridges not modeled, but adjusted for using ineffective flow, where necessary
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Bridge “modeling”
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Hydraulic Post Processing
• Run a series of scripts that generate– 1% annual chance floodplain
(S_FLD_HAZ_AR)– Depth grids and WSEL TIN’s for all 5
profiles– Floodplain Boundary Standard check
point– Flood Elevation Points (for INFIP)– Format largely meets DCS standards
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1% annual chance floodplain
• Derived from subtraction of WSEL tin and DEM, with cleaning of edges and elimination of extraneous small shapes
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Depth Grids
• New requirement from “RiskMAP” used in HAZUS and for visualization
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Flood Elevation Points
• Used in INFIP for calculation of RFE at a point
• Created along stream centerline at 50 foot spacing, tagged with 1% flood elevation
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Floodplain Boundary Standard check
• Ensures that floodplain delineations are matching topography
• Standard FEMA evaluation technique
• Points spaced along floodplain boundary at 100 foot interval