The History of Coastal Flood
Hazard Assessments in the Great
Lakes
Brian A. Caufield, P.E.,
CFM
June 23, 2016
The Great Lakes
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Some Statistics
 Courtesy of Great Lakes Information Network
 One-fifth of the world’s fresh surface water
 Spread out over the contiguous U.S., would submerge the
country under 9.5 feet of water
 More the 94,000 square miles (larger than New York, New
Jersey, Connecticut, Rhode Island, Massachusetts, Vermont,
and New Hampshire combined)
 10,900 miles of coastline (U.S. and Canada combined)
 3,288 miles in Michigan (only Alaska has more)
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4
Just because an inland body of water doesn’t
make it immune to risk
 Fast moving squall lines can create localized risks
 Passage of low pressure centers act similar to hurricanes
 Central pressures recorded similar to those of a tropical or extratropical storm
 Storms can create:
 Surge
 Waves
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Generalized Coastal Zone Schematic
Wave Runup
Kennedy, Layne. 2010. September 4, 2014. http://laynekennedy.blogspot.com/2010_10_01_archive.html
Overtopping
Green, M. Spencer. AP Photo. 2012. September 4,2014.
http://journalstar.com/ap/business/two-story-waves-on-great-lakes-halt-shipping/article_bcf2bb34-b528-52f5-8cd4-0c57e7ea8922.html
Overtopping
Jackson, Brian. North Ave. Beach. 2012. September 4, 2014.
http://www.suntimes.com/photos/galleries/index.html?story=16046778
Overland Wave Propagation
Unknown. Flooding in Green Bay, WI. 1973. September 4, 2014.
http://greatlakesresilience.org/stories/wisconsin/nor%E2%80%99easter-coastal-storm-flooding-green-bay
Early attempts to identify flood risks
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Waves and Erosion
 Waves
 Leverage USACE Wave Information Study (WIS) 1956-1987
 Local wave height with recurrence interval of 3 years approximately
describes wave action likely to accompany the base flood
 ½ year was used on Lake Ontario due to a different fit for the wave
data on the lake
 Erosion
 Based on FEMA (1989)
 Erosion (in square feet) = 85.6 * Recurrence Interval (in years)
 270 square feet for 3-year recurrence
 190 square feet for 2-year recurrence
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2009 Update
1. Return period lake level
recommended on a
USACE (1988) report, but
additional 20-years of
observations
2. Wave runup is dominant
risk and a response based
approach is desirable
3. Previous wave guidance
included long-term lake
processes
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Updated Water Levels
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Combination of Water Levels and Waves
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Great Lakes Coastal Flood Study
 Kicked off in 2009
 Basin-wide assessment of flood risks
 Updated Guidance
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Crosswalk
December 1990 Storm
Overall Process
Offshore Waves
Still Water Level Levels
Wave Transformation
If Necessary
Shoaling Zone
Erosion
Wave Height
Wave Crest Elevation
Wave Setup
Surf Zone
Coastal Structures
Wave Runup
Wave
Overtopping
Backshore Zone
Flood Hazard Mapping
Study Approach
 Regional Study Approach
 Water level and wave analysis
 Improvement over communitycounty
 Reduces number of boundary
conditions
 Greater consistency in
assumptions
 Local/County Level Activities
 Mapping level tasks performed
at county level
 Nearshore wave transformations
 Wave runup
 Overland wave propagation
Response Based Analysis
 Attempt to consider all (or most) of the complexity of the
contributing processes controlling flooding and derive flood
statistics from the results
 Contributing processes to be considered:
 Water level
 Wave conditions
 Topography
Topography & Bathymetry
Updates to Guidance
Overview and Guidance
on Selection and
Application of Methods
(Instructions for Toolbox)
Detailed Guidance on
Analyzing Coastal Processes
(Toolbox)
Guidance on Use of Results in
Hazard Mapping,
Documentation, and
Reference Information
Guidelines Overview and
Important Contributors to
Coastal Flooding
D.3.1
Waves and Water Levels
D.3.4
Mapping of Hazard
Zones and BFEs
D.3.9
Methodology for Storm
Sampling and Coastal Flood
Frequency Analysis
Wave Setup, Runup and
Overtopping
D.3.5
Study
Documentation
D.3.2
Overland Wave Propagation
D.3.6
D.3.10
Methodology for Analyzing
Coastal Processes
Coastal Erosion
D.3.3
D.3.7
Coastal Structures
References, Notation,
and Acronyms
D.3.8
D.3.11 – D.3.13
Wave Setup
 Description of Wave Setup: localized impacts of water level at the
shoreline during severe storms due to transfer of momentum from
waves to the water column.
Wave Setup Implications for Flood Hazard
Mapping
 Can be a significant contributor to the water level through its
contribution to storm surge and should be included in the
determination of coastal BFEs.
 1-D Surf Zone Model
 Adequately resolve and represent inner surf zone
 Parametric representation
 Direct Integration Method
_

H
'
0
 0.160
H
m0.2
'
0
L0 
0.2
Wave Runup
Limit of Wave Runup
Storm Still
Water Level
Barrier Slope
Breaker Depth
Source: FEMA, 2003
Figure D.3.5-5. Wave Runup Sketch
Wave Runup Approach
 Extract water level and wave pairings from the composite
storm set
 Apply a method to estimate wave runup for each of the
composite storm set pairings
 Conduct a statistical extreme value analysis on the runup
elevations to determine 1-percent-annual-chance
Wave Overtopping
 Overtopping Rate Considerations
for Establishing Flood Insurance
Rate Zones
 Ponding Considerations
Onshore Wave Analysis
Wave Runup
Overland Wave Propagation
Overland Wave Propagation
 How waves interact with landforms
 Elevation
 Obstructions
 WHAFIS
 1977 NAS report
 Version 4.0
Transect
Hybrid Analysis
 WHAFIS is designed for event based analysis
 1-percent-annual-chance water level
 1-precent-annual-chance wave height
 Hybrid




Joint probability approach (Nadal-Carabello et al, 2012)
Water level
Wave height
Wave period
Five Scenarios
 Iso-probability curve
 Maximum water level, associated wave height
 Maximum wave height, associated water level
 Intermediate values
 Computed 1-percent-annual-chance water level
 Computed 1-percent-annual-chance wave height
Coastal Erosion
 Episodic, flood-related erosion due to coastal storm events
 Does not consider long-term erosion hazard areas
 Evaluated prior to wave runup and overland wave
propagation
Erosion Assessment Methods
 1-D surf zone dynamics model
 Requirements
 Cross-shore profile
 Sediment grain size
Coastal Structures
 Evaluation Criteria
 Detailed engineering evaluation (FEMA, 1990)
 Limited data and engineering judgment (USACE, 1989)
Vertical Structures
Sloped Structures
Updates to Guidance
Overview and Guidance
on Selection and
Application of Methods
(Instructions for Toolbox)
Detailed Guidance on
Analyzing Coastal Processes
(Toolbox)
Guidance on Use of Results in
Hazard Mapping,
Documentation, and
Reference Information
Guidelines Overview and
Important Contributors to
Coastal Flooding
D.3.1
Waves and Water Levels
D.3.4
Mapping of Hazard
Zones and BFEs
D.3.9
Methodology for Storm
Sampling and Coastal Flood
Frequency Analysis
Wave Setup, Runup and
Overtopping
D.3.5
Study
Documentation
D.3.2
Overland Wave Propagation
D.3.6
Methodology for Analyzing
Coastal Processes
D.3.3
D.3.10
Coastal Erosion
D.3.7
Coastal Structures
References, Notation,
and Acronyms
D.3.8
D.3.11 – D.3.13
Mapping a Coastal Floodplain
Mapping Example - Ortho
Mapping Example - Terrain
Mapping Example - Mapping Decisions
 Transect 11
 1% Total Water Level – 586.88 feet
 Top of coastal feature – 587.77 feet
 Base Flood Elevation – 587 feet
600
590
580
570
560
-100
100
Profile
300
500
700
1% Total Water Level/BFE
640
 Transect 12
 1% Total Water Level – 591.87 feet
 Top of coastal feature – 624.47 feet
 Base Flood Elevation – 592 feet
620
600
580
560
-100
0
Profile
100
200
1% Total Water Level/BFE
300
Mapping Example - Gutters
Brian Caufield, P.E., CFM [email protected]
www.twitter.com/caufieldba
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