US Flood Risk Modeling annual meeting/6. NAT CAT.pdf · Inland Riverine Floods Inland Flash Floods Coastal Floods Basement Flooding Flood Model Riverine Flood Model FRS FFRS Flood

©2014 CoreLogic, Inc. All rights reserved. Proprietary & Confidential

Understanding Flood Risk Beyond

the FEMA 100 Year Flood Zones

David Rogers, Vice President Product Development


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)


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


FEMA Flood Zones vs. Storm Surge Inundation


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


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


10 Meter National Hydraulic Profiles

DEM

10 Meter Grid Resolution

269 Million Flood Elevation Features


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.


FRS Tom Miller Dam Failure


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


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


National Rainfall Intensity Frequency

Map


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


Flash Flooding Risk Map

for San Francisco

San Francisco does not participate in the NFIP. No FEMA flood map is available


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


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


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


The Sewer System As a Conduit of Flood Risk

Concept of Flood Risk Transfer


Thank You.

Questions?

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Documents

US Flood Risk Modeling annual meeting/6. NAT CAT.pdf · Inland Riverine Floods Inland Flash Floods Coastal Floods Basement Flooding Flood Model Riverine Flood Model FRS FFRS Flood