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11.4 (2050)
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35.8 (2075)
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62.4 (2100)
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>62.4
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Garden, Bush and Long Keys
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High (99th Percentile)
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Loggerhead Key
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High (99th Percentile)
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Elevation NAVD88
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cm
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-14.8 (2015)
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-4.9 (2025)
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26.2 (2050)
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76.6 (2075)
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146.2 (2100)
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>146.2
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1:12,000 1:12,000 1:17,000
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Elevation NAVD88
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cm
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-14.8 (2015)
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-8.1 (2025)
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11.4 (2050)
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35.8 (2075)
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62.4 (2100)
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>62.4
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Garden, Bush and Long Keys
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(Low) 50th Percentile
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1:17,000
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Areas of interest
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Dry Tortugas
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National Park
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Figure 8. Mean sea level elevation maps for Dry Tortugas National Park at Loggerhead, Garden, Bush
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and Long Keys for the median (50th) and high (99th percentile) RCP 8.5 projections. Tides and storm
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surges are not included in this projection.
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3.1.1. General Influence of Sea Level Rise
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Over the next ten years, represented by the 2025 estimates, dramatic change in sea level is not
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anticipated with an expected sea level rise of 7 cm for the low scenario and 10 cm for the high
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projection. These changes will result in more frequent tidal inundation along coastal regions although
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the buttonwood ridge located along the southern peninsula and north shore of Florida Bay should
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remain above mean sea level. This modest increase is not likely to impact the terrestrial portions of
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South Florida or the Dry Tortugas.
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By 2050, local sea levels are expected to increase between 26 and 41 cm. Overall, inundation
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at mean sea level will produce similar impacts for both scenarios with a wider fringe of saltwater
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inundation around the periphery of the peninsula under the high scenario. Expansion of the white zone,
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a low productivity area influenced by the periodic flooding of saltwater [26], is expected to continue.
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Under both projections, mean sea level is expected to reach the elevation of the land surrounding the
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Florida Power and Light Turkey Point nuclear power plant cooling canal system (vertical lines along
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the southwest corner of Biscayne National Park (BNP) in Figure 7).
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By 2075, sea levels are anticipated to increase by 51 and 91 cm for the low and high projections,
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respectively. At these elevations, significant portions of the buttonwood ridge separating Florida
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Bay from the peninsula will be exceeded by mean sea level, and marine conditions can be expected
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to expand into current-day areas of the Everglades that maintain fresh and brackish-water marshes.
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This could signal an important tipping-point in the ecological response of freshwater marshes since
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freshwater basins delineated by the ridge will no longer be viable. Low-lying suburban areas along
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the southeastern peninsula will also be at mean sea level elevation resulting in perennial tidal flooding
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with significantly reduced ability to discharge rain floodwaters by gravity from the urban areas into
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J. Mar. Sci. Eng. 2017, 5, 31 11 of 26
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the sea. Below ground, saltwater intrusion can be expected to reduce aquifer productivity along coastal
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well fields [27].
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In 2100, the projected sea level rise is 77 cm for the low projection and 161 cm for the high scenario.
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Strikingly, in the high scenario, mean sea level can be expected to extend from the southwest peninsula
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to the northeast corner of Everglades National Park along the topographical depression of Shark River
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Slough. It is likely that widespread ecological changes will be evident around South Florida as Florida
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Bay expands. Many of the low-lying islands of Biscayne and Dry Tortugas national parks can be
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expected to become tidally submerged or dynamically redefined. Islands with coral substrate are
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likely to submerge, while sand- or sediment-based islands will become increasingly mobile as tidal
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influences trigger localized erosive and depositional dynamics.
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3.1.2. Infrastructure Inundation
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Figure 9 presents a comparison of projected mean sea level with land elevation surrounding
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infrastructure at Flamingo in Everglades National Park and Fort Jefferson in Dry Tortugas National
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Park where red indicates a building or infrastructure footprint. Conditions at Flamingo are mixed,
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with the low projection forecasting the housing and visitors center to remain above mean sea level to
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2100, but with mean sea levels reaching the boat basin, maintenance yard and water plant by 2100.
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Under the high projection, the housing area is at mean sea level by 2100; the visitor center will be
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partially inundated by 2050; and the maintenance yard and water plant by 2075.
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At Fort Jefferson, the projections indicate that the north coal dock and campground remain above
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mean sea level to 2100, while areas around the ferry dock and the isthmus to Bush and Long Keys
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are expected to be at mean sea level by 2075 under the low sea level rise projection. Under the high
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projection, much of the north coal dock and campground will be at mean sea level by 2075, as will
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much of the land between the ferry dock and moat, although a portion of this will be at sea level by
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2050. The isthmus to Bush Key is expected to be at mean sea level by 2050.
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It is important to note that mean sea level in Florida Bay fluctuates by approximately 30–40 cm
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(12–16 in) in a yearly oceanographic cycle, as well as up to 70 cm (2.3 ft) in daily and monthly tidal
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cycles so that effects of tidal inundation will be observed during high tides several years before the
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projected dates when mean sea level reaches a specific land elevation.
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Figure 9. Sea level rise inundation maps at Flamingo in Everglades National Park (top row) and Fort
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Jefferson in Dry Tortugas National Park (bottom row). Building and infrastructure footprints are
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indicated in red.
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J. Mar. Sci. Eng. 2017, 5, 31 12 of 26
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3.2. Exceedances
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As sea levels rise against a fixed elevation threshold near the mean high water tidal elevation,
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exceedance rate changes will follow Equation (1) experiencing nonlinear growth regardless of whether
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water levels are increasing at a steady or accelerated rate [22]. This is exemplified in Figure 10 at four
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coastal stations across the southern peninsula suggesting a transition from linear exceedance growth
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to exponential growth. Model parameters fit to the middle elevation threshold are shown in Table 4.
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Exceedance model fits suggest a progression of exponential growth initiation times (TG) from
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the eastern end of Florida Bay where freshwater marsh interaction with the coastal region is high, to
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the western side of the Bay where marine conditions prevail with substantial water mass exchange
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with the Gulf of Mexico. Generally, the transition of exceedances near the mean high water tidal
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threshold suggest that the late 20th to early 21st century represents a change of coastal dynamics where
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