- Executive Summary
- Intro Policy Outreach
- Focus Areas Recommendations
- Implementation Strategy
The GreenKeys! team conducted sea level rise modeling to understand the vulnerability of county infrastructure and habitat to flooding and sea level rise.
A key component of GreenKeys! is a comprehensive evaluation of ground elevations above current and future tidewater heights for critical infrastructure. Critical infrastructure includes roads and facilities needed for schools, emergency response, law enforcement, wastewater treatment, water supply, and electrical utilities. In addition, assessments of vulnerable habitat changes were performed using tidewater flooding data and the Sea Level Affecting Marshes Model (SLAMM).
For 2030, the Southeast Florida Regional Climate Change Compact (Compact) recommends a sea level rise planning scenario for a minimum of 3 inches and a maximum of 7 inches for all communities in Monroe, Miami-Dade, Broward, and Palm Beach counties. For 2060, the minimum is 9 inches while the maximum is 24 inches.
However, the base planning year, or the assumed zero elevation point, for sea level rise under all previous Compact scenarios is 2010 for this modeling analysis. The Compact recently changed the baseline from 2010 to 1992, extended the timeline from 2060 to 2100, and included processes that affect the local rate of sea level rise. The result of those changes is 1 additional inch of sea level rise by 2030 and 3 additional inches by 2060, which is due to the additional years included in the forecast.
A building footprint layer is a geographic information systems (GIS) file that outlines the land areas occupied by buildings. It is created manually from high-quality aerial photographs or by using automated methods. It is a common methodology that enables more precise assessments of flood vulnerability for the built environment.
The GreenKeys! team developed a building footprint layer showing visible outlines of critical infrastructure including schools, law enforcement, fire stations, other government buildings, electric and water utilities, hospitals, and disaster response staging areas. Through this procedure, 1,316 structures were digitized into building footprints, including 386 on parcels that the Monroe County Property Appraiser dataset identified as owned by Monroe County.
For a full description of the infrastructure dataset, please see the Monroe County, FL: GIS Vulnerability Assessment for Sea Level Rise Planning report in Appendix C.
The University of Florida GeoPlan Center developed a series of GIS files known as the “Sketch Planning Tool.” The files provide preliminary assessments of sea level rise vulnerability for roads and other transportation systems.
The Sketch Planning Tool is based on a 5-meter horizontal resolution Light Detection and Ranging (LIDAR) Digital Elevation Model (DEM) and is designed for landscape-level vulnerability assessments of road infrastructure. It can be used for general planning purposes but not at the scale of individual sites or road segments.
The results must be corroborated through site-specific information, such as reports of nuisance flooding or site surveys that show road grade surfaces that are below elevation thresholds for flood risks.
The Greenkeys! team used Sea Level Affecting Marshes Model (SLAMM), an advanced land cover and ecosystem change tool, to conduct a detailed analysis of habitat impacts for the entire Florida Keys portion of Monroe County. Unlike other flood vulnerability assessment methods, SLAMM integrates long-term hydrologic functions and ecosystem data to predict future changes to all habitat types, including saltwater marshes, mangroves, and other coastal wetlands already subject to regular tidal flooding.
Under some sea level rise scenarios, coastal wetlands will expand into upland areas as tidal flooding increases. In other scenarios, coastal wetlands decline and transition to open water or non-vegetated mud-flats because wetland plants cannot adapt to rising tides and/or coastal erosion pressures. Full description of the habitat dataset
The Coastal Adaptation to Sea level rise Tool (COAST) software was used to model floods from storms and sea level rise on community assets, including homes and businesses, in Key Largo. An additional set of analyses were performed for Stock Island.
To better understand the costs of not adapting as well as the costs and benefits of implementing various adaptation strategies, the software also calculated cumulative damage to homes and businesses over time, considering both nuisance flooding and Hurricane Wilma-sized storm events. Full discussion of the COAST modeling
While better data could have benefitted some analyses, this would have been costly. Therefore, the team extracted as much information as possible from existing datasets.
Vulnerability Assessment Data
Elevation certificates were found for 35 structures owned by the county. Elevation certificates for additional structures would be helpful for future analyses.
The Sketch Planning Tool does not model effects of sea level rise on bridges. Monroe County GIS data provided point locations to identify bridges, but did not contain the footprint information necessary for more detailed analysis of raw laser measurement data (using LIDAR) to show bridge elevations.
The Florida Keys Aqueduct Authority (FKAA) provided a full set of data showing the locations of water supply lines, pumps, and other distribution infrastructure but aboveground and belowground elevations were not available. GIS data can be used to overlay inundation risks for 2030 and 2060 with the locations of FKAA infrastructure.
However, the data were not sufficient to assess damages due to saltwater corrosion or other sea level rise stressors. Despite this challenge, saltwater intrusion risks to FKAA well fields were assessed using U.S. Geological Survey (USGS) scenarios and updated saltwater intrusion data that correspond closest to the low and high sea level values.
The FKAA provided a dataset of wastewater treatment facilities. However, no data was provided for lift station locations, sewer pipes, or treatment facilities owned by others. With the exception of wastewater treatment plants, data were not sufficient to conduct comprehensive damage assessments.
In Florida, the water management districts and local governments now impose a minimum level of stormwater treatment for all new developments, and the standards that apply to the Florida Keys are the most stringent in the state. The criteria are intended to protect surface waters according to their use classification.
However, much of the development in the Florida Keys occurred prior to this requirement. IBecause they do not allow for natural filtering and cleaning of the water, these old systems have contributed to nearshore water pollution. Policies now seek to retrofit them whenever possible.
As understanding of stormwater runoff increased, water protection policies were enacted. In 1974, the Keys were designated an Area of Critical State Concern (ACSC) and in 1985, the surrounding waters were designated Outstanding Florida Waters (OFW). This required that a county-wide comprehensive water quality monitoring program be established.
In 2001, the county created the Stormwater Management Master Plan. Implementation of the plan is not yet complete and data on stormwater structures and features does not yet exist, except for individual projects or permits.
Improving COAST Modeling Data. Missing or insufficient data has led to several limitations for the COAST modeling results.
Additional data should to be developed to support and reinforce future planning efforts.
Building footprint data provides detailed guidance about where public structures and critical infrastructure are at risk of flooding from rising seas. It is recommended that future flood vulnerability assessments build on this work to develop a more complete digital record of elevation certificates for public facilities. This will promote higher confidence in flood risk assessments and enable creation of building-by-building priorities for retrofitting or rebuilding.
Because tidal flooding from sea level rise develops progressively, issues such as unacceptable loss of access and the vulnerability of an individual structure to tidal flooding will be preceded by many minor, but visible, nuisance flooding events.
For this reason, the team recommends the development and implementation of a geographic database for Monroe County employees (and interested residents) to document the time and location of nuisance flood events that affect parking lots, access roads, and landscapes of public facilities. Coupled with the building footprint layer and associated vulnerability assessment, such documentation will provide a strong basis for implementation of targeted and justified public investments to mitigate tidal flooding vulnerabilities.
Although SLAMM is an advanced ecosystem and land cover change model, caution is warranted in interpreting results. More data on historic land cover changes and field observations are needed for refining and updating the model. The current results do, however, provide a basis for discussing and comparing the magnitude of potential ecosystem changes from sea level rise in the Florida Keys.
GreenKeys! technical methodologies were peer reviewed in conjunction with the county’s planning process. Specific comments were received by the following individuals for refinement of the vulnerability analysis:
The team also received comments and periodic feedback from Jerry Lorenz, PhD, State Research Director, Audubon of Florida. It reviewed related work by Billy D. Causey, PhD, Regional Director, Southeast Atlantic, Gulf of Mexico and Caribbean Region, NOAA Office of National Marine Sanctuaries. Other Monroe County staff also provided numerous comments, especially about the technical foundation for the planning process.
The SLAMM modeling revealed that a higher rate of sea level rise is associated with increased conversion of upland and freshwater- dependent land covers into tidal wetlands and open water habitats. However, an idiosyncratic result is that undeveloped dry land ecosystems show an increase in area by 2030 under the low sea level rise scenario (three inches total sea level rise), while developed dry land ecosystems show a decrease in area. A likely explanation for this discrepancy is that elevations measured by laser (LIDAR) tend to be biased upward where vegetation cover is high.
Mangrove ecosystems showed opposite responses under the two sea level rise scenarios:
These results are consistent with research suggesting that mangrove ecosystems have some capacity for collecting sediments and keeping up with low levels of sea level rise, as well as colonizing into upland areas that become more regularly inundated by tides. However, research also suggests that high rates of sea level rise can overwhelm the adaptive and colonization capacity of mangroves, resulting in major die-backs and significant reductions in area.
Another SLAMM result is the significant decline—53% to 76% by 2030 and 66% to 93% by 2060—in inland freshwater marshes. While covering little land area in the Florida Keys, such marshes are highly important habitat and drinking water sources for critically endangered species, including the Key deer and Lower Keys marsh rabbit.
Freshwater wetlands showed high vulnerability by 2030 at even a low sea level rise scenario, with 28% lost. Under a high sea level rise scenario, there would be large-scale disappearance, with 89% lost. Pineland forests show moderately higher resilience than tropical hammock forests across all the sea level rise scenarios, although the high sea level rise scenario indicates that loss of over 40% by 2060 is possible to likely.
All but two buildings out of 35 show significant exposure of finished first floors to regular tidal flooding (not considering storm surges). Most facilities that show future access issues due to low adjacent land are in the Pigeon Key historic district. Aside from the Pigeon Key historic district, two Monroe County structures show potential exposure of finished first floors to regular tidal flooding:
Three structures within the Key West International Airport (KWIA) complex show potential access concerns. Two buildings, both located at 3491 S. Roosevelt Boulevard, show adjacent grade elevations that indicate vulnerability to nuisance flooding by 2060 under a low sea level rise scenario, or complete inundation by 2060 under a high sea level rise scenario. The KWIA terminal, located at 3491 S. Roosevelt Boulevard, shows potential exposure to nuisance flooding access concerns by 2060 under high sea level rise.
Several Monroe County structures are at risk from an extreme flood event similar to Hurricane Wilma, as amplified by up to two feet of sea level rise in the 2060 high sea level rise scenario. The Bayshore Manor assisted-living retirement home is of most immediate concern due to the social vulnerability of facility residents.
Also of high to moderate concern are two Monroe County Sheriff’s Office structures:
Of moderate future concern are the Roth Building and two nearby structures (Radio Transmission Shop and County Offices) that are owned by Monroe County on Plantation Key in the Village of Islamorada.
Other structures that show risk of current or future flooding from a Hurricane Wilma-sized event are two recreation structures at Clarence Higgs Beach, including a vendor and public restroom structure, and the historic East Martello Tower Museum in Key West.
Results of the flood vulnerability analysis place county-owned facilities in the following categories:
Table 1. Results of the vulnerability analysis for County-owned facilities.
Consultations with county staff identified nine wastewater treatment plants for inclusion in this vulnerability assessment:
Wastewater treatment facilities operated by the municipalities of Key West, Key Colony Beach, Marathon, and Islamorada were not included in this vulnerability assessment.
Results suggest that none of the plants are at risk for regular tidal flooding by 2030 or by 2060 under a low sea level rise scenario. However, results for the 2060 high sea level rise scenario indicate potential ground-level flooding of some structures, including KW Resort Utilities, Key Haven, Bay Point, Duck Key, Cudjoe, Layton, and North Key Largo.
Additionally, visual assessment of each facility’s overlay map suggests that structures and surrounding parcels associated with Key Haven and Bay Point may experience widespread tidal flood risk under the 2060 high sea level rise scenario. According to county staff and FKAA, the Key Haven facility is scheduled for decommissioning soon, mitigating concerns for this facility. The relatively low elevation of the Bay Point Wastewater Treatment Plant suggests that large-scale infrastructure maintenance and upgrade decisions should include potential stressors from sea level rise as a priority design criterion.
In cooperation with this vulnerability assessment and in accordance with FKAA’s ongoing goal to assess “impact thresholds for sea level rise and needed infrastructure,” FKAA officials provided the team with point locations for various types of water supply distribution infrastructure within Monroe County. This includes water storage tanks, system valves, control valves, and cathodic rectifiers associated with the water distribution network, as well as a series of test and sampling stations maintained by FKAA.
Elevations were determined for all points associated with this infrastructure. These values were then used to assign a flood vulnerability score for individual infrastructure points.
Table 2: Summary of MHHW-based future tidal flooding risk to point locations of FKAA infrastructure
This vulnerability assessment is based solely on the ground elevations of specific points, and therefore does not account for additional components that may be especially vulnerable to saltwater flooding. While ground-level exposure to tidal flooding generally increases risks of corrosion and periodic loss of maintenance access, interpretation of specific long-term risks and vulnerability thresholds will require additional site-level information, such as aboveground elevations, presence and condition of saltwater flood-proofing materials, and overall saltwater resistance of components.
The team obtained geographical information for seven electric utility sites deemed critical infrastructure:
The analyses indicate that ground elevations for all of these sites are higher than the threshold for regular (non-storm) tidal flood risk by 2060, under the high sea level rise scenario. Additional site-level evaluations would be necessary to determine above-ground elevations of sensitive components and associated extreme event flood risks for each individual facility.
The Sketch Tool analysis of road vulnerability shows impacts to Monroe County roadways during both nuisance floods in especially high tides as well as daily inundation floods. Because U.S. Highway 1 is the sole road and emergency evacuation route for the Florida Keys, even low-level nuisance flooding is problematic for public safety, health, and welfare. Decreased traffic flow, increased accident risk and higher long-term maintenance costs are all concerns with nuisance flooding. These concerns are magnified with daily tidal flooding, which will slow evacuation times and increase costs for road replacement and eventual elevation measures.
Tolerance for nuisance road flooding impacts is based on numerous variables, but primarily on the amount of traffic. For less-travelled neighborhood roads, shallow nuisance road flooding several times each year may or may not necessarily impose severe traffic constraints, although access to individual homes may be temporarily restricted.
However, even infrequent nuisance tidal flooding on major highways poses additional concerns for public safety, health, and welfare, while also damaging the local economy through the temporary loss of primary transportation routes. Such consequences justify near-term, preventive actions to mitigate these risks.
Full results of the vulnerability assessment
The Coastal Adaptation to Sea Level Rise Tool (COAST) modeling software simulates floods from storm events and sea level rise on community assets, including homes and businesses. The model also calculates cumulative damage to communities over time, from both storm events and sea level rise.
This allows communities to better understand the costs of not adapting to the impacts of storms and sea level rise. Finally, the COAST model calculates the reduced damage (essentially the costs and benefits) of implementing adaptation measures.
Using this data, the COAST model produced a vulnerability assessment of homes and commercial buildings and modeled adaptation actions for Key Largo and for Stock Island. Under a separate contract, the team also performed a vulnerability assessment for the Village of Islamorada. The three adaptation actions modeled were:
Vulnerability Assessment Results
The team evaluated elevating buildings as the most appropriate adaptation strategy. For the purposes of the modeling, all buildings on Stock Island not currently elevated were assumed to be elevated to the 100-year flood height plus three feet. Modeling was based on the assumption that there would be 100% participation by owners of buildings not currently elevated.
The low-cost estimate for elevating buildings and low sea level rise scenario yielded the best (or highest) benefit-cost ratio (3.39). The high-cost estimate for elevating buildings and high sea level rise scenario yielded a lower but still financially efficient benefit-cost ratio (1.41).
Thus, elevating buildings would be a cost-effective adaptation regardless of costs (high vs. low) or sea level rise scenario (high vs. low). However, while this adaptation reduces cumulative damages from storm surges over time, it does not completely protect against sea level rise because supporting infrastructure is still affected.
At community workshops, benefit-cost ratios for the various adaptation strategies were presented to county residents and keypad polling technology was used to evaluate community opinions.
After reviewing model results and participating in the group discussions, residents voted that elevating and floodproofing buildings was their most preferred action. Residents also supported the county pursuing funding sources to help private property owners implement this strategy.