Transcript Part 5.b. Automated Zone A Floodplain Mapping

Automated Zone A Floodplain Mapping
David Knipe
Engineering Section Manager
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
process
Fountain
Boone
Montgomery
Parke
Hendricks
Putnam
Morgan
Vigo
Clay
Owen
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