GIS Techniques for Floodplain Delineation · 2017. 8. 11. · What’s so Important About...
Transcript of GIS Techniques for Floodplain Delineation · 2017. 8. 11. · What’s so Important About...
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GIS Techniques for Floodplain DelineationDean Djokic ([email protected])
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• What is a floodplain?
• How to get a floodplain?
• What can GIS do for floodplain modeling?
• Simple GIS techniques for floodplain delineation
• Summary
• Q&A
Content
2GIS Techniques for Floodplain Delineation
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What is it All About?
3GIS Techniques for Floodplain Delineation
easy
but, there is no “easy” button,
just hard work.
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What is a Floodplain
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Floodplain Definitions
• “To define a floodplain depends somewhat on the goals in mind. As a topographic
category it is quite flat and lies adjacent to a stream; geomorphologically, it is a
landform composed primarily of unconsolidated depositional material derived from
sediments being transported by the related stream; hydrologically, it is best defined
as a landform subject to periodic flooding by a parent stream. A combination of
these [characteristics] perhaps comprises the essential criteria for defining the
floodplain" (Schmudde, 1968).
• “Any land area susceptible to being inundated by flood waters from any source”
(FEMA).
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Floodplain Definitions
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What’s so Important About Floodplains
• 82% of the world’s population lives in areas with high flood risk (UNDP, 2004).
• ¾ of world population lives within coastal zone
- USA – 16.5 million (5% population) within flood prone coast
• ½ billion people live within flood prone deltas
Mortality risk is expressed within a decile range
with 10 being the most exposed (Decile 10=
est. 300 people/sq. km and decile 9 is around
150 people/sq. km). Source: Mark Pelling,
Visions of Risk, UNDP / ISDR, 2004
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What’s so Important About Floodplains
• Recurring
- Lie, bigger lie, statistics
• Increase in % of aid from Feds due to hurricane/flooding (25% -> 70% since 2005)
- Sandy (2nd most costly), Katrina (1st most costly) ~ $200B
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If We Know Where the Floodplain Is …
• Operations
- Flood prevention (dam and levee operations)
- Emergency management
- Facility management
• Planning
- Design
- Insurance (not everywhere)
- Emergency planning
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How to Get a Floodplain
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How to Get the Floodplain
• Observations
- Water surface elevations
- Flows
- Precipitation (rainfall, snow)
- “Other” (temperature, soil moisture, E/T, …)
• Modeling (H&H)
- Precipitation-runoff
- Real-time
- Planning (design)
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Observations (stage/flow)
• Traditionally through gaging station
- Problems with sensors during floods
• High water marks
- Not real time
• Remote sensing – airborne/satellite
- Problem with sensors and cloud cover,
cost, timeliness
- Some new options with UAVs
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Observations (precipitation)
• Space and time distribution issues
• Traditional rain gages
• Nexrad
• Satellite
• Calibration!!!!
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Observations (other)
• Space and time distribution issues
• Calibration!!!!
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Modeling
• How much water is there?
- Hydrologic modeling (precipitation-runoff modeling), determines for a given storm on a
landscape, how much water will become runoff.
• Where will it go?
- Hydraulic modeling takes the quantity of water and the shape of the landscape and stream
channel and determines how deep and fast the water will be, and what area it will cover.
• Types of modeling
- Real-time (operations, forecasting)
- Long term (planning, design)
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Hydrologic Modeling
• Goal: Find stream discharge, Q, at a location
for a given precipitation event.
• There are many ways to calculate Q.
- Statistical methods
- USGS regression equations (NFF, StreamStats)
- Deterministic/physical modeling
(“rainfall/runoff”)
- HEC-HMS, SMS, …
GIS is used to summarize terrain and hydrologic characteristics of the
watershed for model input. GIS Techniques for Floodplain Delineation 16
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Hydraulic Modeling
• Goal: Predict water surface elevations and velocities for a given discharge in space
and time.
• Input: Terrain geometry with hydraulic characteristics, plus discharge Q and initial
water surface level.
St.Venant equations
GIS is used to summarize terrain and hydraulic characteristics of the
channel for input to a model and post process hydraulic modeling
results (water surface determination).GIS Techniques for Floodplain Delineation 17
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What Do You Need for H&H Analyses
• Definition of the landscape
- Terrain
- Known drainage structures (streams, sinks, lakes)
- Constructed elements (dams, channels, tunnels, …)
- Landscape characteristics
- Land use, soils, vegetation cover, …
• Precipitation
- Rainfall, snowfall, temperature, …
• Boundary conditions
- Water levels, soil moisture content, …
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Easy?
19GIS Techniques for Floodplain Delineation
easy
???
but, there is no “easy” button,
just hard work.
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What Can GIS Do for Floodplain Modeling
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What Can GIS Do for Floodplain Modeling?
• Centralized data storage
• Data preparation for multiple models
• Postprocessing of modeling results
• Integration of modeling results with other data
• Automation of operations (Map to Map)
• Mobilizing technology (once results are available):
- Emergency management
- Notifications
- Vehicle routing
- …
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GIS Database Development
• Develop digital representation of the landscape –
one time process.
- Quality
- Precision
- Labor Intensive
Source: NASA
Source: NASA
GIS Layers/Data
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Arc Hydro: The Backbone
• Arc Hydro data model and tools form the backbone for GIS WR implementation
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• Database design
• Data preparation
• Terrain preparation
• “Watershed” delineation
• “Watershed” characterization
• Parameterization
• Model pre- and post- processing
How “Things” Build Up
Generic
(Arc Hydro)
Semi-generic
Model Specific
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Arc Hydro as Centralized Data Repository Integrates Model Databases
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Simple GIS Techniques for Floodplain Delineation
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Floodplain Delineation Solutions Matrix
• Different levels of complexity are
possible/needed to determine flood
extents
• Simple:
- “Flooding out” based on DEM, stream
centerline, and point data (fixed depth,
incremental depth, observed
measurements, modeled flows at points
and conversion to WSE)
- HAND approach (constant depth of flooding
per reach)
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Floodplain Delineation Solutions Matrix
• Less simple:
- Same as above, but using cross-sections
to control lateral distribution of water
surface elevations along the stream
centerline
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Floodplain Delineation Solutions Matrix
• More complex:
- 1-D hydraulic modeling in operational mode (complexity in data collection)
- 1-D hydraulic modeling in design mode (for fixed flood frequency – design discharges
derived using statistical methods)
- 1-D hydraulic modeling in design mode (for fixed flood frequency – design discharges
derived using deterministic methods)
• Most complex:
- Fully integrated 2-D hydrologic and hydraulic modeling
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Simplified Floodplain DelineationTools
• Support for floodplain analysis
- Real-time (observed, forecasted flows)
- Planning (flood frequency)
• Facilitate landscape characterization for
floodplain analysis
- Streams
- Cross-sections
- Floodplain
• Floodplain delineation
- Points
- Cross-sections
- From models
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Tools
• Organized in several AH
toolsets (most in “H & H
Modeling” and “Utility”)
• ~ 35 tools
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Sample Implementation Use Cases
• DEM only:
- Create synthetic streams from DEM
- “Flood out” WSE along streams in incremental steps
• DEM + cross-sections:
- Use TIN technique for WSE at c-s in incremental steps
• DEM + stream + observed points:
- “Flood out” observed WSE along streams
• DEM + stream + modeled Q at points:
- Build c-s and develop synthetic rating curve at modeled points
- Use synthetic rating curve to get WSE from modeled Q
- Alt 1 – use flood out technique at points
- Alt 2 – use TIN technique at c-s
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Arc HydroDemo
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Summary
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• GIS provides many capabilities to support floodplain delineation.
• Integrated, multi-purpose database for storage of H&H and related data.
• Consistent methodology for spatial data processing and analytical functionality.
• Pre- and post-processing for H&H models significantly reduces time for data
preparation for modeling support.
• Needs approach to GIS as an analytical technology.
• Easy evaluation of alternatives
• H&H model integration and automation
- Operational and change in conditions
Summary
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Q & A
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