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©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Understanding Flood Risk Beyond
the FEMA 100 Year Flood Zones
David Rogers, Vice President Product Development
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Flood Losses: Riverine Floods and Flash Floods Cause Similar % Damage in US
Average % of US Property Damage from River Flooding and Flash Flooding are very similar:
49.1% vs. 50.9%.
Annual Riverine Flood Losses vs. Flash Flooding Losses
in the United States from 1995 to 2012
(Data Source: Office of Climate, Water, Weather Services, NOAA)
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
High Level Solution and Road Map
for Flood Risk Assessment
Flood Risk Assessment
Inland Riverine Floods Inland Flash Floods Coastal Floods Basement Flooding
Flood Model
Riverine Flood Model
FRS
Flood Risk Score
FFRS
Flash Flood Risk Score
H Model
Storm Surge Model
Storm Surge Risk
Score
Basement Flood Risk
Score
FRS
Flood Risk Score
Hurricane Slab Model
Sewer Backup
Risk Score
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
FEMA Flood Zones vs. Storm Surge Inundation
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
River Flooding
Coastal Flooding
Pond and Lake Flooding
Elements of Flood Risk Score (FRS)
Flood Elevation
Flood Frequency
Property Elevation
Distance to Flood
Source
Flood Zone Geometry
Watershed Hydrology
Riverine and Coastal
Hydraulics
Coastal Impact
Levee Impact
Dam Impact
Localized Flood Hazards
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Basic Concept of Flood Risk Scoring
Create comprehensive spectrum of flood risk classifications (above and below 100 -year
flood elevation), up to 5,000-year flood event (10-100 Score)
Compare unknown (targeted property elevation) to known risk point (100-year flood
elevation): deriving risk scores based on elevation variances (elevation difference between
100-year elevations and property elevations)
The challenge is to build the100-year flood surface/profile to cover national rivers, lakes,
coastal zones, and other water bodies
100-Year Elevation
Hydraulic Profile F
req
ue
nc
y
E
leva
tio
n
Lower Flood Frequency
Lower Flood Risk
Higher Flood Frequency
Higher Flood Risk
Higher Repetitive Loss
Elevation
Variance
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
10 Meter National Hydraulic Profiles
DEM
10 Meter Grid Resolution
269 Million Flood Elevation Features
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Flood Risk Score Analysis on the 2008 Midwest
Flood (Cedar Rapids)
The land parcels were
colored by flood risk rating
Flood inundation boundary is
marked by the orange line
and the 100 year and 500
FEMA flood boundaries are
marked by the blue lines.
Property risk aligns with the
inundation boundary.
A large number of properties
beyond X500 were rated as
“Moderate and Higher” risk
300 millions dollars in flood
losses
Rebuilding has occurred in
the same areas with no new
flood protection built.
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
FRS Tom Miller Dam Failure
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Components of Flash Flood Risk Model
– 10
Water Shed Hydrology
Surface Flow Dynamics
Land Use
Soil Infiltration
Vegetation Coverage
Vegetation Changes
Rainfall Intensity
Land Characteristics
Depression Areas
Wildfire Burns
Impervious Cover
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Science Behind the
Flash Flood Risk Score (FFRS)
FRS was based on the FEMA Flood Map. CoreLogic hydrology supports FEMA zones (shaded)
FFRS was based on CoreLogic hydrology, that is more comprehensive and beyond FEMA zones
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
National Rainfall Intensity Frequency
Map
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
2013 Boulder Flood
FEMA flood map was developed based on river miles but not “dry” land. FEMA puts
the site in a X zone and FRS rated this site as “Low” inundation flood risk
FFRS rated the Utah Ball Park as “Extreme” flash flooding risk site (FFRS = 91)
FFRS is a comprehensive tool. A tennis court nearby wasn’t inundated. FFRS rated
the site as Low (FFRS = 19). FFRS accurately captured the flood risk in the area
Tennis Court
Ball Field
Ris
k =
19
Risk = 91
Flash Flooding at Utah Park in Aurora, Co
Very Low Low Moderate High Very High Extreme
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Flash Flooding Risk Map
for San Francisco
San Francisco does not participate in the NFIP. No FEMA flood map is available
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Flash Flooding Event A bicyclist makes his way through water at the intersection of 18th and Dolores streets, San Francisco, CA,
December 2, 2012. 37.76139,-122.42637. Zone N. Catchment Slope: 3.4, Extreme, 93
Pin Point
37.76139,-122.42637
FAC = 723
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Basement Flooding Risk
Basement Flooding
Risk
River Flooding
Heavy Rainfall
Surface Flash
Flooding
Land Surface factors
Sewer System Pattern
Structure Weakness
Coastal Flooding Groundwater Contribution
Structure
Characteristics
Community
Vulnerability
Land Surface Flow
Key contributing factors to rapid
rise of groundwater table:
River Flooding
Coastal Flooding
Flash Flooding
Heavy Rainfall
Structure weakness, groundwater
table, water intrusion
Sewer backup, combined
sewer/storm water system, sewer
location and choke points
Land surface factors: land
depression, soil infiltration, land
use, and forest coverage
Meteorological factor: rainfall
intensity
Land Surface
Characteristics
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Two Different Mechanisms Generating Flooding
Problems Associated with Basements
Directly from rising groundwater table during heavy rainfall:
• Wall crack
• Floor and wall joint
• Floor crack
• Window well
• Mortar joint
• Tie rod
• Floor drain
From sewer systems during heavy rainfall
• Backup from the choke points of sewer systems
• Backup from the sewer main
• Backup from clogged sewer systems
Basement Flood Risk
Score
Basement Structure
Sewer Backup
Both
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
The Sewer System As a Conduit of Flood Risk
Concept of Flood Risk Transfer
©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential
Thank You.
Questions?
19