CLIMATE CHANGE AND SEALEVEL RISE IN NORTH CAROLINAS DYNAMIC COASTAL SYSTEM

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CLIMATE CHANGE AND SEA-LEVEL RISE IN NORTH
CAROLINAS DYNAMIC COASTAL SYSTEM!
Stanley R. Riggs, David J. Mallinson, and Stephen
J. Culver Dept. of Geological Sciences East
Carolina University Greenville, NC 27858
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• NATURAL RESOURCES OF THE NORTH CAROLINA
  COASTAL SYSTEM
• BARRIER ISLANDS INLETS
• SHORELINES
• OCEAN
• ESTUARINE
• WATER
• RIVERS
• ESTUARIES
• OCEAN
• WETLANDS
• MARSHES
• SWAMP FORESTS
• FISHERIES WILDLIFE
• HUMAN-ECONOMIC COMPONENT

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SEA-LEVEL RISE BY ITSELF IS A VERY GENTLE
PROCESSIT IS LIKE FILLING YOUR BATHTUB!
STORM EVENTS SUPERIMPOSED UPON SEA-LEVEL
RISE ARE THE CATASTROPHIC FORCES THAT CAUSE
BARRIER ISLANDS TO MIGRATE UPSLOPE!
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THE BASIC FUNCTION OF BARRIER ISLANDS AND
THEIR BEACHES IS TO ABSORB THE OCEANS
ENERGY AT THE AIRSEALAND INTERFACE! BARRIERS
ARE BUILT BY STORMS AND DEPENDENT UPON
STORMS FOR THEIR SHORT-TERM HEALTH AND
LONG-TERM EVOLUTION

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UNDERSTANDING THE PRESENT IS THE KEY TO
INTERPRETING THE PAST AND PREDICTING THE
FUTURE! AN EXCELLENT GEOLOGIC RECORD EXISTS
OF PAST CLIMATE CHANGE AND SEA-LEVEL
FLUCTUATIONTHIS IS WHAT BUILT THE NC
COASTAL PLAIN AND CONTINENTAL MARGIN!
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CHANGE IS THE ONLY CONSTANT IN DYNAMIC
COASTAL SYSTEMS!
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NCs MOVING COASTAL ZONE
11,000
200 ft
Today
POST-GLACIAL SEA--LEVEL RISE FLOODS UP AND
ACROSS THE CONTINENTAL SLOPE SHELF
PRODUCING OUR MODERN COASTAL SYSTEM
- 425 ft
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SEA-LEVEL CURVE FOR NORTH CAROLINA
SLOW SEA-LEVEL RISE. AVE 3.3 in/100 yrs
FAST SEA-LEVEL RISE. AVE 30.2 in/100 yrs
MODERATE SEA-LEVEL RISE. AVE 6.4 in/100 yrs
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NORTH CAROLINA SEA LEVEL CURVE
Year (AD)
1200
1300
1400
1500
1600
1700
1800
1900
2000
MSL
0.0
Sand Point Peat Curve
-0.2
1900-2000 AD 19.7 in/100 yrs
-0.4
-0.6
100 BC- 1800 AD 3.3 in/100 yrs
-0.8
Meters Below Present Sea Level
-1.0
1800-1900 AD 12.0 in/100 yrs
-1.2
-1.4
1700s Start of the Industrial Revolution
1900 AD
-1.6
1800 AD
-1.8
1585 First Colonists Settle on Roanoke Island
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NORTH CAROLINA SEA-LEVEL RISE TIDE GAUGE
DATA
DUCK 1.4 ft/100 yr 16.8 in/ 100 yr
PROBLEMS 1. Short Records 2. Incomplete
Records 3. Wilmington 40km Inland 4. Wilmington
Beaufort-- Dredged Channels
1920
2010
Zervas (2004) North Carolina bathymetry /
topography sea level rise project Determination
of sea level trends. NOAA Technical Report NOS
CO-OPS 041.
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DROWNING MAPS FOR THE OUTER BANKS, NC
TODAY MSL
MSL 2 ft
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DROWNING MAPS FOR THE OUTER BANKS, NC
MSL 4 ft
MSL 6 ft
BUT THE COAST DOES NOT EVOLVE THIS WAY!
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GULF OF MEXICO
PRE-STORM BACK-BARRIER SHORELINE
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STORMS AND STORM SURGE ERODE THE LAND
CAUSING SHORELINES TO MIGRATE UPWARD AND
LANDWARD WITH RISING SEA LEVEL! WHAT
HAPPENS TO THE NC COASTAL SYSTEM WHEN
STORMS MAKE LANDFALL?
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ENTIRE OCEAN SHORELINE RECEDES WHILE
BACK-BARRIER SHORELINE GAINS NEW LAND, BUT
AT DIFFERENTIAL RATES!
1
1852
1998
2
3
4
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PEA ISLAND MIGRATION 1852-1998 (146 yrs) 1
LOST 1,370 ft on ocean GAINED 2,870 ft on
estuarine side 2 LOST 1,430 ft on ocean
GAINED 1,370 ft on estuarine side 3 LOST
2,000 ft on ocean GAINED 430 ft on estuarine
side 4 LOST 1,600 ft on ocean GAINED 400
ft on estuarine side 5 LOST 1,500 ft on
ocean GAINED 100 ft on estuarine side
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CHOWAN RIVER ESTUARY HIGH SEDIMENT BANK
PRE-HURRICANE ISABEL 9/18/03
SHORELINE EROSION HURRICANE ISABEL -
80 ft LONG-TERM AVE. - 3
ft/yr
POST-HURRICANE ISABEL 9/18/03
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MARSH SHORELINE EROSION STORM - 85
ft LONG-TERM AVE. - 3 ft/yr
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SEDIMENT SUPPLY IS CRUCIAL FOR HEALTHY
BARRIER ISLANDS IN A RISING SEA
LEVEL! THE BEST SAND IS ALREADY ON THE
BARRIERS!
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BARRIER ISLANDS ARE NOT CREATED EQUAL!
PEAT BEACH WITH MINOR SAND MADD ISLAND
PEAT BEACH WITH MINOR SAND HATTERAS ISLAND
COMPLEX BARRIER ISLANDS HIGH WIDE,
SEDIMENT-RICH WITH BEACH RIDGES--BUXTON WOODS
SIMPLE BARRIER ISLANDS LOW NARROW,
SEDIMENT-POOR ISLANDS
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SEDIMENT-POOR NORTH TOPSAIL ISLAND
SEDIMENT-POOR SOUTH ONSLOW BEACH
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ONSLOW BAY HARDBOTTOMS
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CAPE SHOAL SANDS
OLIGOCENE ROCKS--UNDIFFERENTIATED
MIOCENE PUNGO RIVER FORMATION WITH PLEISTOCENE
CARBONATE HARDBOTTOM CAPS
PLIO-PLEISTOCENE CARBONATE PLATFORM
ALGAL REEFSHELF EDGE
CAPE SHOAL SANDS
SAND/MUD SLOPE
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INLETS AND OVERWASH FANS ARE CRUCIAL FOR
THE SHORT-TERM MAINTENANCE AND LONG-TERM
EVOLUTION OF THE SIMPLE BARRIER-ISLANDS IN
A RISING SEA LEVEL! THEY ADD WIDTH AND
ELEVATION TO THE BACK-BARRIER AS THE
OCEAN SIDE ERODES!
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2
1
3
INLETS A CRITICAL ISLAND BUILDING PROCESS
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OVERWASH FANS A CRITICAL ISLAND
BUILDING PROCESS
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HUMAN INTERACTIONS WITH THE ONGOING
PROCESSES OF CLIMATE CHANGE
AND SEA-LEVEL RISE HOW WILL WE ADAPT TO
THESE CHANGES?
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BARRIER ISLAND NARROWING! BUXTON TO AVON
SEGMENT
1852 SHORELINE
2003 SHORELINE
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1852 SHORELINE
1974 HWY 12
1955 HWY 12
2003 HWY 12
2003 SHORELINE
1999 HWY 12
BARRIER ISLAND NARROWING

• 1. OCEAN SHORELINE RECEDED UP TO 2500 FT
  IN 151 YRS.
• 2. UP TO 76 OF 1852 ISLAND WIDTH HAS
  BEEN LOST.
• 3. AVE. ANNUAL EROSION RATE UP TO - 14
  FT/YR.
• 4. HWY 12 MOVED WEST 4 TIMES SINCE 1955
  WITH NO ISLAND LEFT!

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HWY 12 GOINGTOSEA
HWY 12 GONETOSEA
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HWY 12
CONSTRUCTED BARRIER- DUNE RIDGES SEVERELY
LIMIT OVERWASH INLET DYNAMICS AND DO
NOT STOP SHORELINE RECESSION! THEY ARE OUT
OF EQUILIBRIUM WITH NATURAL BARRIER
DYNAMICS!
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EROSIONAL HOT SPOTS
OREGON INLET BRIDGE
WHAT ARE THE FUTURES FOR NC HWY 12 AND
ASSOCIATED BARRIER ISLANDS?
HATTERAS FLATS
ALTERNATIVE 4
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RODANTHE
3 POTENTIAL INLET SITEHISTORIC CHICKAMOCOMMIC
INLET
1 POTENTIAL INLET SITE
PINWR 2007
2003
2007
SOUTHERN END OF PEA ISLAND NATIONAL WILDLIFE
REFUGE
NC HIGHWAY 12
2003
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PINWR 2003
IS THIS THE LONG-TERM SOLUTION?
PINWR 2007
PINWR 2003
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IRREGULARLY-FLOODED, WAVE-DOMINATED PLATFORM
MARSHES
PEAT ACCRETION
SHORELINE RECESSION
ECOSYSTEM MIGRATION
SEA-LEVEL RISE
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INHIBITS HABITAT MIGRATION
LOSS OF ECOSYSTEM FUNCTION
FILLING HARDENING WETLAND SHORELINES
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HEALTHY WETLANDS AND GOOD WATER QUALITY ARE
CRUCIAL INGREDIANTS FOR A VIABLE SEAFOOD
INDUSTRY!
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• RESPONSES TO CHANGING COASTAL SYSTEMS
• HARD STABILIZATION
• SEAWALLS, BULKHEADS, ROCK REVETMENTS,
  BREAKWATERS, JETTIES, GROINS, ETC.
• 2. SOFT OR SAND STABILIZATION
• SAND BAGS, BEACH PUSHING, BEACH NOURISHMENT,
  BARRIER-DUNE RIDGES, ETC.
• 3. RELOCATION
• CRITICAL FOR OCEAN-FRONT, HIGH-HAZARD ZONE
  AREAS WITH HIGH EROSION RATES
• 4. RETREAT
• CRITICAL FOR SIMPLE OVERWASH-DOMINATED BARRIER
  ISLAND SEGMENTS THAT ARE SEDIMENT DEFICIENT

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GALVESTON, TX
WHERES THE BEACH?
SEA BRIGHT, NJ
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ALL NC BEACHES ARE ERODING AT LONG-TERM AVE.
RATES UP TO -15 FT/YR! NET
SHORELINE RECESSION 1849-1998 1000 FT (S)
TO 750 FT (N)
1849 SHORELINE
SAND BAGS ARE NO BETTER! WHERES THE
BEACH? SOUTH NAGS HEAD, NC
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INSTITUTE FOR STUDY OF DEVELOPED SHORELINES
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APRIL 1986 BEACH NOURISHED IN 1985
OCT. 1987 ERODED BEACH
X
X
ROCK REVETMENT
X
CAROLINA BEACH, NC ROCK REVETMENT PRE-1985
1985 Nourishment 800,000 Yds3 1988
Nourishment 950,000 Yds3
APRIL 1988 NEW BEACH NOURISHMENT
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NOURISHED BEACHES MAY BE GOOD FOR THE
SHORT-TERM ON SOME ISLANDS IF THERE IS
ABUNDANT HIGH QUALITY SAND AND AMPLE MONEY
AVAILABLE! THEY ARE NOT THE SOLUTION FOR
THE LONG-TERM HEALTH AND EVOLUTION OF
BARRIER ISLANDS IN A RISING SEA LEVEL!
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CAPE HATTERAS LIGHTHOUSEA HARD STAND AND
FINAL RETREAT!
1970
1999
1975
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NEWLY PAVED HIWAY 12
THE PROBLEM! WE HAVE CONSTRUCTED A
PERMANENT HUMAN SUPER-STRUCTURE ON TOP OF
A DYNAMIC AND MOBILE PILE OF SAND!
1932
GOINGTOSEA HIWAY 12
1999
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122 MILES OF N.C. BEACHES WANT NOURISHMENT
PROJECTS 22 MILES OF THE OUTER BANKS
ARE PRESENTLY COLLAPSING!
6mi
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LONG-TERM FUTURE
SHORT-TERM FUTURE
COLLAPSE MAPS OF THE NORTHERN OUTER BANKS,
NC
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GOING, GOING, GONEDAUPHINE ISLAND, ALABAMA
JULY 17, 2001
SEPT. 17, 2004 POST-HURRICANE IVAN
AUG. 31, 2005 POST-HURRICANE
KATRINA
U.S.G.S. PHOTOS
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TO PRESERVE OUR COASTAL RESOURCES AND
MAINTAIN OUR COASTAL ECONOMY, WE MUST
INCORPORATE THE CONCEPT OF CHANGE AND ALLOW
THE ISLANDS TO RESPOND TO THE NATURAL
DYNAMICS!
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PLEISTOCENE LIMESTONE
MODERN SAND
ONSLOW BAY HARDBOTTOMS
MIOCENE MUDSTONE
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SHOREFACE AND INNER SHELF--HIGH RESOLUTION
SEISMIC MAP NEW HANOVER COUNTY, NC
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HISTORIC (RED) AND PRE-HISTORIC (BLUE) INLETS
OUTER BANKS, NC
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• INLET VULNERABILITY OF ISLANDS
• HIGH POTENTIAL
  34
• ANNUAL SCALE
• INTERMEDIATE POTENTIAL 31
• ANNUAL--DECADAL SCALE
• LOW POTENTIAL
  18
• DECADAL SCALE
• VERY LOW POTENTIAL 17
• DECADAL--CENTURY SCALE

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CHANGE IS THE ONLY CONSTANT IN DYNAMIC
COASTAL SYSTEMS!
HORSES OF NEPTUNE WALTER CRANE, 1892