Flooding Vulnerability Assessment Using the COAST Tool and Approach
For the Portland Society for Architecture and the City of Portland, ME
For the Commercial Street Waterfront Area




Estimates of One-Time Damage to Buildings and Real Estate Improvements For a 100year Storm Event, occurring in the Years 2050, 2075 and 2100;
Includes the Effects of a Sea Level Rise Scenario of 2 feet of Rise by 2050, and 4 feet of
Rise by 2100;
Includes Estimates for All Cumulative Expected Monetary Damage to Buildings and Real
Estate Improvements by the Years 2050, 2075 and 2100; and
Indicates which Parcels are Predicted to be Permanently Inundated by Sea Level Rise on
a Daily Basis, if No Action is Taken.
Jonathan T. Lockman AICP
Vice President of Environmental Planning
Catalysis Adaptation Partners LLC
[email protected]
22 October 2013
This project is funded by the
Portland Society for Architecture, in
cooperation with the City of
Portland, ME
I.
Analysis of COAST Results:
Economic Impacts to Assessed Value of Buildings
Portland ME
Table 1-COAST Model Output for Commercial Street Waterfront,
Modeled Water Levels and Vulnerability Assessment Results
For the 100 Year Storm in Years 2050, 2075 and 2100
2075
Predicted
Elevation of
Flood Height
from FEMA
Flood
Storm
Intensity Insurance
Sea Level (return Study, 2012
Rise
period in NAVD88
1
Scenario years)
(ft.)
4 Feet by
100
2100
years
9.5
4 Feet by
100
2100
years
9.5
2100
4 Feet by
2100
Year
2050
100
years
9.5
Model of
Sea
Level Rise COAST Model
Above
Total Flood
MHHW in Elevation for
2013
Each Scenario
Selected
NAVD 88
2
(ft)
(ft.)
COAST Model
Cumulative Expected
Damage
to
the
Value of
COAST Model
All Buildings &
Expected Damage
Improvements
to the Value of
From
All Buildings &
All
Storms,
2013 to
Improvements
Scenario Year,
From
Including Value of
This Single Storm
Properties
Completely
Incident in the
Lost
to
Sea
Level Rise
Scenario Year
3
($ Million)
($ Million)
($ Million)
2.00
11.5
16.0
32.9
8.7
3.00
12.5
25.2
69.6
11.9
4.00
13.5
26.4
111.5
46.4
1
Tidal state is included in FEMA FIS predicted flood elevations for the 100 year storm.
2
COAST Model
Total Value of
All Buildings &
Improvements
Removed from
Inventory Due to
Permanent
Inundation by Sea
Level Rise
From 2013 to
Scenario Year
Elevation of Mean Higher High Water (MHHW) in year 2013 is 4.65 feet (NAVD 88).
This project is funded by the
Portland Society for Architecture.
3
No Discount Rate applied.
The City of Portland’s Commercial Street waterfront is obviously vulnerable to sea level rise and storm
surge damage. COAST estimates $111.5 million dollars in cumulative damage to the value of buildings,
from all storms, (with surge plus sea level rise) for the 87 years between now and the year 2100. Over
the next 37 years, by 2050, $32.9 million dollars in cumulative damage is estimated. This suggests that
some large investments by both the government and private sectors may be justified, with further study.
Furthermore, by the year 2100, $46.4 Million in building value will be located on parcels predicted to be
permanently inundated by the high tide (MHHW) on a daily basis, without any storm surge, if no action
is taken.
Damage estimates for individual parcels are available for each scenario year by querying the COAST model
output.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
3
Page 1 of 11
II.
Close-Up Illustrations of COAST Model Output for a 100 Year Single Storm Event at Commercial Street,
in the City of Portland, in the Years 2050, 2075, and 2100
Fig. 1-City of Portland: Commercial Street
COAST Model Results, 100 Year Storm in 2050
Total Elevation of Flooding – 11.5 Feet (NAVD 88)
One-Time Storm Damage for This Event:
$16.0 Million
Cumulative Damage Up to This Scenario Year:
$32.9 Million
Value of Buildings on Parcels Lost to Sea Level Rise, by This Scenario Year:
$8.7 Million
Buildings Damaged by Storm Surge from this Single Event (Height of Bar indicates relative damage amount)
Buildings Permanently Inundated due to Sea Level Rise by this Year, if No Action is Taken
Extent of Flooding from this Event
Note: Predicted flood depths and dollar damages for all individual affected parcels are available in Google Earth *.kml files.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 2 of 11
Fig. 2-City of Portland: Commercial Street
COAST Model Results, 100 Year Storm in 2075
Total Elevation of Flooding – 12.5 Feet (NAVD 88)
One-Time Storm Damage for This Event:
$25.2 Million
Cumulative Damage Up to This Scenario Year:
$69.6 Million
Value of Buildings on Parcels Lost to Sea Level Rise, by This Scenario Year:
$11.9 Million
Buildings Damaged by Storm Surge from this Single Event (Height of Bar indicates relative damage amount)
Buildings Permanently Inundated due to Sea Level Rise by this Year, if No Action is Taken
Extent of Flooding from this Event
Note: Predicted flood depths and dollar damages for all individual affected parcels are available in Google Earth *.kml files.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 3 of 11
Fig. 3-City of Portland: Commercial Street
COAST Model Results, 100 Year Storm in 2100
Total Elevation of Flooding – 13.5 Feet (NAVD 88)
One-Time Storm Damage for This Event:
$26.4 Million
Cumulative Damage Up to This Scenario Year:
$111.5 Million
Value of Buildings on Parcels Lost to Sea Level Rise, by This Scenario Year:
$46.4 Million
Buildings Damaged by Storm Surge from this Single Event (Height of Bar indicates relative damage amount)
Buildings Permanently Inundated due to Sea Level Rise by this Year, if No Action is Taken
Extent of Flooding from this Event
Note: Predicted flood depths and dollar damages for all individual affected parcels are available in Google Earth *.kml files.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 4 of 11
Fig. 3a-City of Portland: Commercial Street East
COAST Model Results, 100 Year Storm in 2050
Total Elevation of Flooding – 11.5 Feet (NAVD 88)
One-Time Storm Damage for This Event:
$16.0 Million
Cumulative Damage Up to This Scenario Year:
$32.9 Million
Value of Buildings on Parcels Lost to Sea Level Rise, by This Scenario Year:
$8.7 Million
Buildings Damaged by Storm Surge from this Single Event (Height of Bar indicates relative damage amount)
Buildings Permanently Inundated due to Sea Level Rise by this Year, if No Action is Taken
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 5 of 11
Fig. 3b-City of Portland: Commercial Street East
COAST Model Results, 100 Year Storm in 2075
Total Elevation of Flooding – 12.5 Feet (NAVD 88)
One-Time Storm Damage for This Event:
$25.2 Million
Cumulative Damage Up to This Scenario Year:
$69.6 Million
Value of Buildings on Parcels Lost to Sea Level Rise, by This Scenario Year:
$11.9 Million
Buildings Damaged by Storm Surge from this Single Event (Height of Bar indicates relative damage amount)
Buildings Permanently Inundated due to Sea Level Rise by this Year, if No Action is Taken
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 6 of 11
Fig. 3c-City of Portland: Commercial Street East
COAST Model Results, 100 Year Storm in 2100
Total Elevation of Flooding – 13.5 Feet (NAVD 88)
One-Time Storm Damage for This Event:
$26.4 Million
Cumulative Damage Up to This Scenario Year:
$111.5 Million
Value of Buildings on Parcels Lost to Sea Level Rise, by This Scenario Year:
$46.4 Million
Buildings Damaged by Storm Surge from this Single Event (Height of Bar indicates relative damage amount)
Buildings Permanently Inundated due to Sea Level Rise by this Year, if No Action is Taken
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 7 of 11
III.
Methodology and Assumptions Used for COAST Model Analysis
COAST is a software tool, whose development was funded by the US Environmental Protection Agency,
which is used to predict damages from varying amounts of sea level rise and storm surge. The COAST
software was run for the Portland Society for Architecture and the City of Portland, Maine by Catalysis
Adaptation Partners (CAP), whose principals designed the software, and who use it to help communities
throughout the country. COAST is used to calculate the potential damage from one particular storm in
the future, as well to calculate the accumulated potential damage from all storms that may occur over a
period of years, from today until a point in the future.
For the City of Portland, the first step was to load accurate elevation data into the model. A LiDAR (Light
Detection and Ranging) image of the peninsula area was used, which is a highly accurate map of land
elevations made by taking laser measurements from an airplane. The LiDAR data was provided by the
Maine Geological Survey, of the Maine Department of Agriculture, Conservation and Forestry. Once the
LiDAR image was loaded, the COAST model could identify the height of any piece of land in the study area.
The LiDAR image for the City was made up of a grid millions of squares, each 2 meters by 2 meters, with
a single elevation value in feet for each square.
The next step was to load the COAST model with the tax map parcels and building values from the City tax
assessment records. Care was taken to make sure that the LiDAR image and the tax map layer were in
the same map coordinate system, and with the same units (feet) for both vertical and horizontal positions.
Then water levels were set up for the creation of simulated storms, with amounts of sea level rise to be
added over time. The starting value of the high tide level of the sea today (MHHW or “Mean Higher High
Water”) was set at 4.65 feet (NAVD 88 units) as determined by the current NOAA tide gauge in downtown
Portland.
The data layers for tax parcels and LiDAR required some special preparation for this project. For some
large lots with multiple building sites, the city’s digital tax assessment parcel map erroneously linked the
total building value for the entire site, to each individual sub-parcel on the entire site. To solve this
problem, CAP dissolved or aggregated many of the sub-lots on such sites, in close coordination with the
City Planning Department. The LiDAR provided by the MGS also needed to be adjusted. When LiDAR
imagery is taken from an airplane, the laser light captures all of the tops of the buildings, as well as all of
the ground surfaces, when it makes a topographic map. Algorithms are applied to remove the buildings
and fill in the resulting holes to make a “bare earth” model of the land surface. When Portland was flown,
this LiDAR processing was done in the typical fashion, but in this processing, many of the piers were
removed, as well as the buildings on them. Given the small budget for this project, there was not an
opportunity to reprocess the original LiDAR to make a new bare earth model with blank piers. Instead,
where there were holes in the data, CAP digitized new pier surfaces by hand, and assigned nearby
elevation values to fill in the holes.
In collaboration with the City, and its hydrology consultant, Robert Gerber, an “exceedance curve” was
established, setting up a prediction of various sized storms and their probability or chances of occurring
in any given year.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 8 of 11
The following values were put into the exceedance curve in the model, for flood heights and their chance
of occurring:
Storm Event
Recurrance
Interval
Probability in Any
Given Year
Surge Height
Above MHHW of
4.65 ft.
(NAVD 88 units)
Overall Elevation
of Flood Waters in
Feet
(NAVD 88 units)
500 Year Storm1
Once every 500 0.002
6.2
10.85
years
Once every 100 0.01
100 Year Storm1
4.85
9.5
years
Once every 50 0.02
50 Year Storm1
4.35
9.0
years
Once every 10 0.10
10 Year Storm1
3.35
8.0
years
1
After consultation with Robert Gerber, taken from the unpublished FEMA Flood Insurance Study for
Cumberland County, 2013.
The COAST model calculates cumulative expected damages from all storms up to a particular date, by
summing up the area under the exceedance curve. The results are conservative, as the damage estimates
do not include wave or wind action on top of the still water predicted flood elevations by FEMA. For
instance, damage from the 100 year storm is based on an elevation of 9.5 feet, which is the predicted
water level from FEMA’s 2013 unpublished Flood Insurance Study (obtained by the City’s hydrology
consultant, Robert Gerber), not including wave setup. For the purpose of generated dollar damages over
a large area, the COAST model uses only a generalized model of flood depths, without the wave or wind
effects which would almost certainly make damage worse in a real storm situation. The model cannot
handle the variability of wave heights that might occur in different parts of the waterfront, given the
limited size of this project’s budget.
As set by the Portland Society for Architecture’s steering committee for this project, the scenarios added
to the model for sea level rise above today’s level were as follows:
By the year 2050, an additional 2 feet.
By the year 2100, an additional 4 feet.
The steering committee selected these values from the Intergovernmental Panel on Climate Change (IPCC)
report, updated Sept 2013, using the middle range sea level rise values.
Now the COAST model had information on:
the elevation of the land;
how high the water is today;
how frequently and how high storm flooding might get in the future including sea level rise; and
a map of all the buildings in harm’s way, with their values for tax purposes.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 9 of 11
The final step was to give COAST a guide to how much damage to expect for each building, depending on
the depth of the flood waters. A “Depth-Damage Function” was used from the US Army Corps of
Engineers. Based on the Army’s damage measurements from years of studying floods, the depth damage
function is a chart with a predicted percent loss of a structure’s worth, depending on the number of feet
of depth of the floodwaters that surround it. A Depth-Damage Function was used from a report: US Army
Corps of Engineers, Water Resources Report Center, Institute for Water Resources, Report 96-R-12, May
1996, “Analysis of Nonresidential Content Value and Depth-Damage Data for Flood Damage Reduction
Studies, Appendix D – Structure Depth-Damage Functions,” page D-1.
When the COAST tool creates a flood scenario, it looks at an imaginary point at the center of each parcel
polygon, called the “centroid.” The software measures the depth of water at the centroid of each parcel,
and deducts a percent of the building value as damage. In case of multiple buildings on one lot, there
unfortunately was no way to apportion the building value between the separate buildings, because the
municipal tax parcel database aggregates “building value” for all buildings on a lot. The implications are
that if the model shows the centroid of the parcel as flooded, it calculates damage to all of the buildings
on the lot, using the depth-damage function. This may overestimate damage on a site, if in reality the
building or buildings on the lot were not located at the centroid, but rather at some higher ground near
the edge of the parcel.
COAST was then run for the Commercial Street waterfront area of the City of Portland, to calculate the
predicted damage from one-time future storm events, and to sum up cumulative damage for all storms,
up to the years 2050, 2075 and 2100, respectively (37, 62 or 87 years from now). The results are
summarized in table 1 in part one of this report. A google earth map was also created for each town, with
the flooding depth and dollar damage estimate available for each individual flooded parcel, for each
scenario. Google earth files can be loaded and run with Google Earth free of charge on any personal
computer. The google earth files, in *.kml format, can be distributed to property owners or any other
interested parties for use in personal or public planning for sea level rise and storm surge adaptation.
Limitations of the COAST Model





Uniform surge heights for the various predicted storms were entered in to the model. Variation
in the surge height which might actually occur within particular parts of the Casco Bay or Fore
River waterfront was not accounted for.
The effects of waves, wind, and erosion are not considered in the COAST model, as it calculates
damages only using still water flood elevations on the existing terrain.
Values for individual buildings were not available, as the City assessing records combined the
values of all buildings on a particular lot into one number. Damage to buildings was estimated by
multiplying the depth-damage function by the total building value for the lot, at the “centroid,”
or imaginary point at the center of the lot polygon.
Assessing records did not reflect which buildings may have already been flood-proofed. Damage
would be overestimated to these structures.
The Army Corps “Depth-Damage” function may not predict the actual dollar damage to Portland
buildings, given unique characteristics of their age, placement, or construction.
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 10 of 11


IV.
LiDAR data for the “deck” surfaces of the piers was missing from the 2m grid of the image, because
of the processing used to remove buildings from the lidar. CAP needed to digitally fill in missing
elevation data on many of the piers, by using neighboring values in the grid (patching “holes in
the picture”).
The model treated the pier surfaces, extending out over the water surface of the Fore River, as if
they were land surfaces. It was assumed that once any flood waters receded, the piers would
remain undamaged. Damage estimates to the piers themselves were therefore not included in
this study. This study only estimated damage to the value of buildings on the piers.
Possible Next Steps: Evaluation of Adaptation Strategies
In other communities, CAP has developed cost estimates for various adaptation strategies to lessen the
potential damage from sea level rise and surge. These include, but are not limited to, rolling easement
purchases, increasing the heights of bulkheads, and road elevations. Once adaptation strategies are
selected for study by a public process, the COAST tool can be used again to estimate potential damages
with the new adaptation in place, to see how much damage value can be avoided. Then the benefit cost
ratios, indicating the cost effectiveness of each adaptation strategy, can be compared and discussed.
Otherwise, these vulnerability assessment results can be used in any number of ways to help galvanize
and structure important conversations the City. Such conversations could focus on how to begin taking
meaningful action in response to the combined threats of sea level rise and storm surge. These are threats
that extend far beyond simple real estate values analyzed in this project, and that are likely to impact a
wide range of City assets, functions, and values held dear. Visual and numeric outputs from this project,
perhaps in combination with additional modeling the City may wish to undertake, for other vulnerable
assets and/or other candidate adaptation actions, can help guide these conversations and support
innovations in planning and finance that are likely to become mandatory.
For more information on use of the COAST Approach, contact Catalysis Adaptation Partners at
www.catalysisadaption.com .
Catalysis Adaptation Partners LLC
Final Report for Portland, ME
Page 11 of 11