National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S

U.S. DEPARTMENT OF THE INTERIOR OPEN-FILE REPORT 99-593 U.S. GEOLOGICAL SURVEY Low Moderate High Very High Figure 2. Histograms Figure 3. Bar graph showing the 800 100 showing the frequency of percentage of shoreline along the Ranking of coastal vulnerability index 90 occurrence and cumulative U.S. Atlantic coast in each risk frequency of CVI values for category. The graph also shows the Very low Low Moderate High Very high Low 6,630 km 80 the U.S. Atlantic coast. The total length of shoreline (in VARIABLE 1 23 4 5 600 vertical red lines delineate kilometers) in each risk category. the chosen ranges for low, The total length of mapped shoreline Rocky, cliffed coasts Medium cliffs Low cliffs Cobble beaches Barrier beaches 70 Sand Beaches moderate, high, and very in this study is 23,384 km. Geomorphology Fiords Indented coasts Glacial drift Estuary Salt marsh high risk areas. Moderate 5,332 km Alluvial plains Maine Cumulative Percent 60 Fiards Lagoon Mud flats Deltas 400 Frequency Mangrove 45˚ 50 Coral reefs Frequency 40 High 5,094 km Coastal Slope (%) >0.115 0.115 − 0.055 0.055 − 0.035 0.035 −0.022 < 0.022 Relative sea-level Cumulative Percent − 2.5 − 3.0 − 3.4 New 30 change (mm/yr) < 1.8 1.8 2.5 3.0 > 3.4 Hampshire 200 20 Very High 6,328 km Shoreline erosion/ >2.0 1.0 −2.0 -1.0 − +1.0-1.1− -2.0 < - 2.0 Accretion Stable Erosion Massachusetts accretion (m/yr) New 10 > 6.0 4.1 − 6.0 2.0 − 4.0 1.0 −1.9 < 1.0 York 0 0 5 10 15 20 25 30 35 Mean tide range (m) 0 0 Table 1. Ranking of Connecticut RI Cape Cod Percentage of the U.S. East Coast shoreline in each risk category 8.7 15.6 20.0 56.5 coastal vulnerability Mean wave <0.55 0.55 − 0.85 0.85 − 1.05 1.05 −1.25 >1.25 CVI index variables. height (m) New Jersey Pennsylvania 40˚ New York to New Jersey example North Carolina to Georgia example Maryland Connecticut DE New York Connecticut New York North Carolina North Carolina Virginia LONG ISLAND SOUND 41˚ 34˚ LONG ISLAND SOUND Long Island 41˚ South Carolina 34˚ Long Island South Carolina New Jersey 40˚ EXPLANATION EXPLANATION RISK RANKING North Carolina ATLANTIC OCEAN 32˚ RISK RANKING Georgia Very Low New Jersey Very Low Low Cape Hatteras ATLANTIC OCEAN Low Moderate 35˚ High 40˚ Moderate EXPLANATION EXPLANATION High Very High Mullica River Very High ATLANTIC OCEAN RISK RANKING RISK RANKING Georgia 32˚ GEOMORPHOLOGY GEOMORPHOLOGY Low Low ATLANTIC OCEAN 50 0 50 100 Kilometers 40 0 40 Kilometers Moderate South Carolina Moderate 20 39˚ Cape May High High 75˚ 74˚ 73˚ 72˚ 80˚ 78˚ 76˚ Very High Mullica River Very High Figure 5. Map of the geomorphology variable for the New York to New Jersey region. Figure 9. Map of the geomorphology variable for the North Carolina to Georgia COASTAL VULNERABILITY INDEX region. Like the New York to New Jersey region, geomorphology is still the dominant COASTAL VULNERABILITY INDEX The open-ocean shoreline is composed primarily of high-risk sandy barrier islands, while risk due to geomorphology is lower for lagoons and along the bluffs of northern Long variable influencing the CVI values (see Figure 8). 40 20 0 40 Kilometers 50 0 50 100 Kilometers 39˚ Island. ATLANTIC OCEAN Cape May Georgia 75˚ 74˚ 73˚ 72˚ 80˚ 78˚ 76˚ Figure 4. Map of the Coastal Vulnerability Index for the New York to New Jersey region. Figure 8. Map of the Coastal Vulnerability Index for the North Carolina to Georgia region. EXPLANATION 30˚ Figure 6. Map of the coastal slope Figure 10. Map of the relative sea-level rise variable for the New York to New variable for the North Carolina to Georgia RISK RANKING Connecticut Connecticut New York Jersey region. The coastal slope is New York North Carolina region. The rate of sea-level change is North Carolina Cape Low relatively steep (low risk) throughout lowest at Cape Fear, North Carolina, due to Hatteras much of this area, but is quite low long-term tectonic uplift of the mid- Cape Lookout Cape Canaveral Moderate LONG ISLAND SOUND LONG ISLAND SOUND (high risk) in southern New Jersey. Carolina Platform High. 41˚ 41˚ High 34˚ 34˚ Long Island South Carolina South Carolina Long Island Very High Cape Fear Cape Fear Jones Island Jones Island Florida Figure 11. Map of the mean wave height Cape Romain COASTAL VULNERABILITY INDEX New Jersey variable for the North Carolina to Georgia New Jersey region. The risk due to wave height varies 40˚ 40˚ ATLANTIC OCEAN between the north and south sides of Cape ATLANTIC OCEAN EXPLANATION 200 100 0 200 km EXPLANATION EXPLANATION EXPLANATION RISK RANKING RISK RANKING 32˚ Hatteras and Cape Lookout, and generally 32˚ RISK RANKING RISK RANKING Georgia Scale 1: 6,300,000 Georgia Very Low Very Low ATLANTIC OCEAN Very Low Very Low Low decreases from Cape Hatteras southward Low ATLANTIC OCEAN Low Figure 7. Map of the shoreline Low Moderate Moderate Moderate Moderate High into the Georgia embayment. This reflects High High erosion/accretion rate variable for the High Very High Very High Mullica River Very High Very High differences in wave exposure due to 25˚ Mullica River New York to New Jersey region. The RELATIVE SEA LEVEL RISE shoreline orientation, as well as the WAVE HEIGHT SLOPE smaller-scale variations in the CVI EROSION / ACCRETION RATES 50 0 50 100 Kilometers increasing continental shelf width from 50 0 50 100 Kilometers 77˚ 30' 75˚ 72˚ 30' 40 20 0 40 Kilometers values (see Figure 4) are influenced 40 20 0 40 Kilometers 39˚ 39˚ North Carolina to Georgia. primarily by changes in shoreline 80˚ 78˚ 76˚ Cape May Cape May 80˚ 78˚ 76˚ Figure 1. Map of the Coastal Vulnerability Index (CVI) for the U.S. Atlantic coast. The CVI shows the relative vulnerability of the coast to changes due to future rise in sea-level. Areas 75˚ 74˚ 73˚ 72˚ erosion rate. 75˚ 74˚ 73˚ 72˚ along the coast are assigned a ranking from low to high risk, based on the analysis of physical variables that contribute to coastal change. INTRODUCTION RISK VARIABLES erosion. Regional coastal slopes are considered to be very low risk at values >0.2 percent; very high risk consists of regional slopes DISCUSSION most complex and poorly documented variable in this data set. The rates used here are based on a dated, low-resolution data set and <0.025 percent. The rate of relative sea-level rise is ranked using the modern rate of eustatic rise (1.8 mm/yr) as very low risk. Since thus far corrections have been made only on a preliminary level. To best understand where physical changes may occur, large-scale One of the most important applied problems in coastal geology today is determining the physical response of the coastline In order to develop a database for a national-scale assessment of coastal vulnerability, relevant data have been gathered this is a global or "background" rate common to all shorelines, the sea-level rise ranking reflects primarily regional to local isostatic The data underlying the CVI show variability at several spatial scales. The rate of sea-level rise, and tide range vary over a variables must be clearly and accurately mapped, and small-scale variables must be understood on a scale that takes into account to sea-level rise. Prediction of shoreline retreat and land loss rates is critical to the planning of future coastal zone management from local, state and federal agencies, as well as academic institutions. The compilation of this data set is integral to accurately or tectonic effects. Shorelines with erosion/accretion rates between -1.0 and +1.0 m/yr are ranked as moderate. Increasingly higher spatial scale of >100 km. In the case of sea-level rise, this represents the large-scale patterns of isostasy and tectonism present along their geologic, environmental, and anthropogenic influences. strategies, and assessing biological impacts due to habitat changes or destruction. Presently, long-term ( ≥ 50 years) coastal planning mapping potential coastal changes due to sea-level rise. This database is based loosely on an earlier database developed by Gornitz erosion or accretion rates are ranked as correspondingly higher or lower risk. Tidal range is ranked such that microtidal coasts are the Atlantic continental margin of North America (Peltier, 1996; Braatz and Aubrey, 1987). Changes in tide range generally reflect and decision-making has been done piecemeal, if at all, for the nation's shoreline (National Research Council, 1990; 1995). and White (1992). A comparable assessment of the sensitivity of the Canadian coast to sea-level rise is furnished by Shaw et al. high risk and macrotidal coasts are low risk. Mean wave height rankings range from very low (<0.55 m) m to very high (>1.25 m). changes in the configuration of the continental shelf as a whole (e.g., shelf width). Consequently, facilities are being located and entire communities are being developed without adequate consideration of the (1998). In previous and related studies (Gornitz, 1990; Shaw et al., 1998), large tidal range (macrotidal; tide range > 4m) coastlines A second group of variables, consisting of geomorphology and wave height, vary on a ~10 km scale that reflects primarily REFERENCES potential costs of protecting or relocating them from sea level rise-related erosion, flooding and storm damage. Table 1 summarizes the six physical variables used here: 1) geomorphology, 2) shoreline erosion and accretion rates (m/yr), were assigned a high risk classification, and microtidal coasts (tide range <2.0 m) received a low risk rating.

Load more