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Rapid LiDAR-Based Large-Scale Flood-Risk Screening

FFMA Conference 2012
by

Justin Gregory

on 21 October 2013

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Transcript of Rapid LiDAR-Based Large-Scale Flood-Risk Screening

Rapid Large-Scale Flood-Risk Screening
Introduction
Detailed Study
Screening Approach
Example
Application

Public Awareness
Emergency Response
Identify flood prone areas
Prioritize flood control & mitigation projects
Why do we not map or update flood risk?
Cost
Time
Complexity
Why do we map flood risk?
Existing FEMA Floodplain
Gum Swamp Floodplain Analysis
SCALGO
Massive LiDAR Datasets
SCALGO
Flash Flood Mapping
Results
Results
Gum Swamp Watershed
Digital Elevation Model
Current Approach to Mapping Flood Risk
Identify a watershed
Develop a detailed numerical model
5-foot-by-5foot LiDAR based DEM
Model Schematic

Model Schematic
2,000 Nodes & Basins
Average Basin Size 16 acres
Model Development

ICPR Model
Calibrate / Validate Model Results
Floodplain Analysis
Handling Massive LiDAR datasets challenging
Typical Solution
Break dataset up (tiling / chunking)
Generalize
Step 1: Preprocess DEM
Enforce hydraulic features
Fill "noise" in DEM
Gum Swamp Watershed
Step 2: Develop Runoff Response Raster
Gum Swamp Watershed
Step 3: SCALGO flash flood modules
Gum Swamp Watershed
Step 4: Review Flash Flood Mapping
Gum Swamp Watershed
Accuracy Estimates:
Conclusion
Single GIS dataset
Quick to map
Simple to review
All rainfall depths avaliable
Time
Days or Weeks - Not Months or Years
Simple
Cost
Parameterization

500,000 Cross Section Points
120,000 Storage Points
3,000 Weirs
100 Pipes
11,000 Percolation Reaches
6,000 Hydrolgic Response Units
Massive LiDAR Datasets
Alterantive Approach
Develop I/O-effecient raster processing techniques
SCALGO PRODUCTS
SCALGO Model
TIN Construction
Raster interploation
SCALGO Simplify
Depression identification
Depression filling
SCALGO Hydrology
Flow direction
Flow acculmation
Watersheds
Sea level rise
Rapidly assess flood risk for every cell in a raster.
Develop drainage network accounting for flooded depressions
http://scalgo.com/mapserver/?pw=gumswamp&center=29.026408%2C-82.194229&zoom=18&marker=29.008194%2C-82.186325&dynamic_flow=0.254&maps=DEM_m-simplified-10m3-dynflow.tjt
4 Inches Rainfall
8 Inches Rainfall
10 Inches Rainfall
Watershed Evaluation
Inventory Hydraulic Structures
Compared ICPR/SCALGO results 1700 nodes (100-year/24-hour event)
Flood elevation RMSD ~ 1.2 ft
Flood area RMSD ~ 5.9 acres (2.7% error)
QC previous studies
Real-time floodrisk
Future flood risk
Stochastic modeling
Identify hydraulic structures
Applications
Massive LiDAR Datasets
Flow Analysis:
Global SRTM raster (60 Billion cells) - 2 days
Denmark (26 Billion cells) - 1.5 days
St. Johns County 5-foot DEM (1.3 Billion cells) < 2 hours
Other GIS software could take weeks or months if possible
< 5% the costs of detailed flood study
Reduce detailed study cost
Prioritization & Planning
Watershed
Scalable
City
County
Regional
90 m
2 m
2 inches -Rainfall
4 inches -Rainfall
High Priority
Medium Priority
Proposed Screening/Prioritization Approach
Conduct large-scale flood screening analysis
Identify high flood-risk areas
Prioritize flood study areas
Develop detailed numerical models for targeted areas
HEC-HMS/ HEC-RAS
EPA-SWMM
ICPR
FLO-2D
......
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