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David KnipeEngineering Section Manager
Automated Zone A Floodplain Mapping
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
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
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
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).
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
Hydrology: Streamstats
hydrology for a stream reach will be completed by using the Purdue
regression equations as
found in the USGS application, Streamstats
!(
!(
!(!(
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
Hydrology: Results
Hydraulic pre processing
three hydraulic data features will need to be
created; stream
centerline, cross sections and overbank
flow paths
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
HEC-RAS import
• File created from Hydraulic script imported into HEC-RAS
HEC-RAS Cross Sections
• Sections as imported represent LiDAR data for each line
Mannings’s N Values
• Automatically derived using relationships based on Anderson Land Use classification and NLCD data (2006)
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
Bridge “modeling”
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
1% annual chance floodplain
• Derived from subtraction of WSEL tin and DEM, with cleaning of edges and elimination of extraneous small shapes
Depth Grids
• New requirement from “RiskMAP” used in HAZUS and for visualization
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
Floodplain Boundary Standard check
• Ensures that floodplain delineations are matching topography
• Standard FEMA evaluation technique
• Points spaced along floodplain boundary at 100 foot interval