This document discusses the history of coastal flood hazard assessments in the Great Lakes region. It provides statistics on the size and coastline of the Great Lakes. While inland, the Great Lakes can experience risks from storms similar to hurricanes, including surge, waves, and overtopping. The document outlines the processes considered in coastal flood analyses, such as wave setup, runup, overtopping, and overland wave propagation. It describes the Great Lakes Coastal Flood Study initiated in 2009 to conduct a basin-wide flood risk assessment and update guidance. The study uses a regional approach to analyze water levels, waves, and other processes to map flood hazards.
3. 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)
3
5. 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 extra-
tropical storm
Storms can create:
Surge
Waves
5
7. Wave Runup
Kennedy, Layne. 2010. September 4, 2014. http://laynekennedy.blogspot.com/2010_10_01_archive.html
8. 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
9. Overtopping
Jackson, Brian. North Ave. Beach. 2012. September 4, 2014.
http://www.suntimes.com/photos/galleries/index.html?story=16046778
10. 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
12. 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
12
13. 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
13
20. Overall Process
Offshore Waves Still Water Level Levels
Wave Transformation
If Necessary
Flood Hazard Mapping
Wave Height
Wave Crest Elevation
Wave Runup
Wave
Overtopping
Erosion
Shoaling Zone
Surf Zone
Backshore Zone
Coastal Structures
Wave Setup
21. Study Approach
Regional Study Approach
Water level and wave analysis
Improvement over community-
county
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
22. 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
24. Updates to Guidance
D.3.1
D.3.2
Overview and Guidance
on Selection and
Application of Methods
(Instructions for Toolbox)
Detailed Guidance on
Analyzing Coastal Processes
Guidance on Use of Results in
Hazard Mapping,
Documentation, and
Reference Information
D.3.3
Waves and Water Levels
D.3.4
Wave Setup, Runup and
Overtopping
D.3.5
Overland Wave Propagation
D.3.6
Coastal Erosion
D.3.9
Study
Documentation
D.3.10
References, Notation,
and Acronyms
D.3.11 – D.3.13
Guidelines Overview and
Important Contributors to
Coastal Flooding
Methodology for Storm
Sampling and Coastal Flood
Frequency Analysis
Overview and Guidance
Application of Methods
(Instructions for Toolbox)
(Toolbox)
Guidance on Use of Results in
Hazard Mapping,
Documentation, and
Reference Information
Methodology for Analyzing
Coastal Processes
Mapping of Hazard
Zones and BFEs
Study
Documentation
Coastal Structures
D.3.8
D.3.7
25. 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.
26. 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
2.0
0
'
0
2.0
'
0
_
160.0
LH
m
H
27. Wave Runup
Figure D.3.5-5. Wave Runup Sketch
Barrier Slope Breaker Depth
Limit of Wave Runup
Storm Still
Water Level
Source: FEMA, 2003
28. 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
33. 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
34. 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
35. 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
36. Erosion Assessment Methods
1-D surf zone dynamics model
Requirements
Cross-shore profile
Sediment grain size
37. Coastal Structures
Evaluation Criteria
Detailed engineering evaluation (FEMA, 1990)
Limited data and engineering judgment (USACE, 1989)
40. Updates to Guidance
D.3.1
D.3.2
Overview and Guidance
on Selection and
Application of Methods
(Instructions for Toolbox)
Detailed Guidance on
Analyzing Coastal Processes
Guidance on Use of Results in
Hazard Mapping,
Documentation, and
Reference Information
D.3.3
Waves and Water Levels
D.3.4
Wave Setup, Runup and
Overtopping
D.3.5
Overland Wave Propagation
D.3.6
Coastal Erosion
D.3.9
Study
Documentation
D.3.10
References, Notation,
and Acronyms
D.3.11 – D.3.13
Guidelines Overview and
Important Contributors to
Coastal Flooding
Methodology for Storm
Sampling and Coastal Flood
Frequency Analysis
Overview and Guidance
Application of Methods
(Instructions for Toolbox)
(Toolbox)
Guidance on Use of Results in
Hazard Mapping,
Documentation, and
Reference Information
Methodology for Analyzing
Coastal Processes
Mapping of Hazard
Zones and BFEs
Study
Documentation
Coastal Structures
D.3.8
D.3.7