FIGURE
7-1-1.
Historical maps depicting the evolutionary changes for Croatan Sound and
opening of Roanoke Marshes between Croatan and Pamlico Sounds. Notice the
dramatic changes in inlet location through the barrier islands, the habitat
changes within Croatan Sound due to current scour, and the slow dissection of Stumpy Point Lake by
the receding shoreline. Maps are not to the same scale. PANEL A. Map of Moseley dated 1733. PANEL B. Map of Collet dated 1770. PANEL C. Map of Price and Strother dated 1808. PANEL D. Map of MacRae and Brazier dated 1833. All four maps are
from Cumming (1966).
FIGURE
7-1-2.
Longitudinal cross section along the channel thalweg of Pamlico Creek on the
south, across the interstream divide at Roanoke Marshes, through the channel
thalweg of Croatan Creek, and into the Roanoke
River on the north. This section shows the general antecedent or
paleotopography of the Pleistocene surface and thickness of Holocene sediment
that infilled the channel in response to estuarine flooding by rising sea level
during the past 10,000 years. Figure is modified from Riggs et al. (2000).
FIGURE 7-1-3. Side-scan sonar images of Croatan Sound bottom
showing relict geologic units exposed on the sound floor. All images are about
200 meters in width. PANEL A. A
scour channel located in the center span of the old Croatan bridge (U.S.
Highway 64) shows linear dark gray patterns (areas of low reflectance)
resulting from the exposure of organic-rich mud sediments. These mud sediments
infilled Croatan Creek during estuarine flooding in response to rising Holocene
sea level. Today, these muds are being severely eroded by the modern flow
channel displayed in bathymetric profiles on Figure 7-1-4. Also, notice the linear white sand deposits
(areas of high reflectance) that occur in the lee (south) of each bridge
piling. The broad white reflectance pattern on the north side of the bridge is
the sonar shadow with refraction patterns from the bridge pilings. PANEL B. A shallow, sand-covered
Pleistocene platform on the western side of old Croatan bridge (see bathymetric
profiles on Fig. 7-1-4). The
extensive white pattern is due to the high reflectance character of quartz sand
that dominates the platform tops with sand waves having about 10 meter
wavelengths. Also, notice the linear scarp that has been eroded into an older
mud or peat sediment unit buried below the surficial sand to the east. PANELS C and D. The highly irregular,
mottled pattern is the erosional character of marsh peat that crops out on the
sound bottom along the southwest side of Roanoke Island.
These are the basal remnants of the Roanoke Marshes peat deposits. The peat
deposit is dissected by paleo-tidal creeks (smooth areas) that were backfilled
with soft mud and very fine sand. These channel fill muds erode faster than the
associated peat producing lower depressions. The dark gray pattern of peat,
closest to the center line, grades to white away from the center line, due to
the shadow effect of eroding 3-D peat blocks on the sound floor. The peat
blocks range from 1 to 5 meters across with vertical relief up to 1 meter. See
Figure 7-1-2 for the general
location of these eroded peat remnants of Roanoke Marshes.
FIGURE
7-1-4.
Composite of four bathymetric profiles along the south side of the old Croatan
bridge (U.S. Highway 64). The profiles include a general interpretation and
reconstruction for 1817 based upon old maps (see Fig. 7-1-1), the U.S.
hydrographic Survey profile H257 of 1851, a 1954 N.C. Department of
Transportation profile made during the pre-construction survey along the
proposed bridge location, and an October 1997 profile from Rudolph (1999).
Comparison of these profiles supply the baseline information concerning
shoreline and bathymetric changes along the old Croatan bridge corridor through
time. Figure is modified from Riggs et al. (2000).
FIGURE
7-1-5.
Portion of a satellite image (EOSAT from SPACESHOTS, Inc.) of the Cedar Island area
showing the modern process of drowning across the Carteret Peninsula
interstream divide. The vast Cedar Island Juncas roemarianus marsh (gray color) occurs on the interstream divide
between West Thorofare and Thorofare Bays. With
continued flooding due to rising sea level and shoreline erosion, the marsh
will rapidly disappear and eventually form an open Thorofare Sound. This is a
modern analog for the transition of Croatan Creek to Croatan Bay and finally
Croatan Sound.
FIGURE
8-1-1. Map
shows the location of estuarine shoreline erosion sites in northeastern North
Carolina included in the present study (Chapter
8).
FIGURE 8-2-1.
Photographs of the Hatteras Overwash site. PANEL
A. Looking east along the north side of the eroding marsh platform. The
outer zone has been totally stripped of marsh grass during winter storms. PANEL
B. Close-up of the peat surface in the outer zone that has been stripped of
marsh grass and is now dominated by green algae. PANEL C. Close-up of
outer edge of eroding marsh platform with a large eroded peat block lying in
the adjacent shallow waters. The marsh grass is Spartina alternaflora.
Photograph is from Murphy (2002). PANEL D. Looking east along the inner
zone of the marsh platform and the adjacent zone of scrub-shrub that occupies
the higher elevation of a more recent overwash fan. Notice the extensive
accumulation of wrack along the inner zone of the Juncus roemarianus
marsh platform. PANEL E. Looking west along the strandplain beach
associated with an overwash fan that occurs to the immediate west of the marsh
platform. Notice the minor amounts of dead submerged aquatic vegetation (SAV)
that has accumulated locally on this summer beach. PANEL F. Same
location as Panel E, but now the fall strandplain beach is covered with an
extensive accumulation of dead SAV.
FIGURE 8-2-2.
The Hatteras Overwash site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ)
with digitized shorelines for 1962 and 1998.
FIGURE 8-2-3.
The Hatteras Overwash site aerial photograph
time slices from 1945, 1962, and 1989. The 1945 photo predates construction of
N.C. Highway 12 and regular maintenance of the associated barrier-dune ridges.
Consequently, this barrier segment is dominated by active overwash processes.
However, in the 1962 post-Ash Wednesday storm photograph, the overwash is
significantly diminished in magnitude. The difference probably reflects the
presence of an elevated N.C. Highway 12 roadbed and reconstruction of the
associated barrier-dune ridge. The 1989 photo shows no overwash due to a major
barrier-dune ridge with increased vegetation growth along the landward side.
FIGURE 8-2-4.
Photographs of the Buxton Inlet site. PANEL
A. Summer photograph looking north along the backside of the marsh platform
with Spartina alternaflora in bright green and Juncus roemarianus
in dark green colors. PANEL B.
Winter photograph looking north along the backside of the marsh platform with
the marsh grasses partially eroded off the peat surface. Notice the scarped
outer marsh edge and the irregular geometry to the marsh shoreline due to
active shoreline erosion processes. PANEL C. Winter photograph looking
south along the marsh platform. Notice that there is some sand available to
form a high water sand berm on top of the marsh platform. PANEL D.
Summer photograph looking north along the backside of the marsh platform.
Notice the abundant sand available to form a major strandplain beach in front
of and temporarily protecting the outer scarped marsh. Also, notice the dead
submerged aquatic vegetation (SAV) that formed wrack berms at three different
previous water levels. Photograph is from Murphy (2002). PANEL E. Winter
photograph looking east across the inner portion of the marsh platform, the narrow
scrub-shrub zone, and the newly constructed barrier-dune ridge on the east side
of the new N.C. Highway 12. Notice the beach berm in the lower right hand
portion of the photo that is composed of a lower sand component and two upper
SAV wrack components. Also, behind the wrack berms is an irregular patch of
rafted wrack within the transition zone vegetation. PANEL F. Looking
east at the newly constructed and vegetated barrier-dune ridge built to protect
the post-Hurricane Dennis (1999) N.C. Highway 12 relocation. These structures
eliminate the overwash and inlet processes that built this portion of the
barrier island and are necessary for maintaining the island for the long term.
Without overwash and inlet processes supplying sand to the estuarine side,
estuarine erosion rates increase causing the barrier to narrow through time.
FIGURE 8-2-5. PANEL A. A 1992 oblique aerial photograph looking north towards Avon and showing three previous locations of N.C.
Highway 12, two of which are “going-to-sea” highways. Notice the small marsh
platforms that occur along the back side of the barrier. The dark vegetation
occurring between the marsh platforms and upland overwash fans, is dense
scrub-shrub growing around the outer lobe of older overwash fans. PANEL B. A
1999 post-Hurricane Dennis aerial photograph (N.C.
Department of Transportation) showing N.C. Highway 12 (#3) “going to sea” and
the newly relocated N.C. Highway 12 (#4). The new highway was built on the west
side of the power lines in the 1992 photograph. However, there is no room to
move the road further west in the future, as the island continues to narrow in
response to shoreline erosion that is taking place on both sides of the
barrier.
FIGURE 8-2-6.
The Buxton Inlet site 1998 Digital Orthophoto Quarter Quardrangle (DOQQ) with
digitized shorelines for 1962, 1974, and 1998.
FIGURE 8-2-7.
The Buxton Inlet site aerial photograph time
slices from 1962, 1964, 1983, and 2000. In the post-Ash Wednesday nor’easter
storm aerial photo of 1962, notice the extensive overwash zone and the newly
opened Buxton Inlet. In the 1964 photograph, notice the extensive sand body, or
flood-tide delta, that developed on the sound side behind Buxton Inlet. The
Inlet was closed by the U.S. Army Corps of Engineers using sand dredged from
the dark rectangular holes in the flood-tide delta immediately behind the
former inlet. In the 1983 and 2000 photos, notice the two different segments of
N.C. Highway 12 on the left side of the photo that were sequentially relocated
prior to each photograph. Also, notice the numerous and extensive sand mines
(red stars in 2000 photo) that were dredged up to 20 feet deep between 1964 and
1983. The sand was used to close the inlet and for several ocean beach
nourishment projects. The deep holes allow for increased wave action adjacent
to the estuarine shoreline and prevents existing offshore sands from moving
into the back-barrier system, causing increased rates of estuarine shoreline
recession.
FIGURE 8-2-8.
Photographs of the Salvo Day-Use site. PANEL
A. Winter photograph looking north along the outer portion of the peat
platform. Low wind tide has exposed the eroding wave-cut scarp in peat along
the front side of the marsh platform. Notice that the outer zone is stripped of
marsh vegetation by storms and is rapidly colonized by green algae. PANEL B.
Winter photograph looking south along the outer portion of the peat platform
during low wind tide. Notice how different layers of peat are eroded off in a
stair-step fashion and the occurrence of a high water berm composed of dead
submerged aquatic vegetation (SAV) with no sand. PANEL C. Close-up of
the eroding marsh during a low wind tide. Notice the tough modern root mass
forms a sloping overhang (on the left side of the photo) as the softer
underlying peat (visible on the lower right side) is easily eroded. PANEL D.
Close-up of a block of the modern, root-bound, upper peat surface as it begins
to finally crack and break off. PANEL E. Summer photograph of the very
narrow Spartina alternaflora marsh platform in front of a sand upland
dominated by maritime forest and the Salvo cemetery. Notice the occurrence of a
high-water level, thin sand berm perched on top of the marsh platform and a
low-water level, SAV wrack berm without any sand. Photograph is from Murphy
(2002). PANEL F. Winter photograph taken at the same spot as Panel E.
Notice that there are two SAV wrack berms with most of the sand gone that was
associated with the upper sand berm in the previous photo. Also, the marsh
grasses have been mostly stripped off the peat surface due to winter wave
action.
FIGURE
8-2-9. The Salvo Day-Use site 1998 Digital
Orthophoto Quarter Quadrangle (DOQQ) with digitized shorelines for 1962 and
1998.
FIGURE 8-2-10.
The Salvo Day-Use site aerial photograph
time slices from 1962, 1978, and 1983. In the 1962 photograph, notice that even
though N.C. Highway 12 and associated barrier dune ridges were in place prior
to the Ash Wednesday nor’easter storm, the old overwash pattern was
re-established as the cross-island water flowed into Pamlico Sound through the existing
channel structures on either side of the study area. The ongoing process of
estuarine shoreline erosion through time is obvious along the outer edge of the
impoundment in the upper left portion of the photo sequence (1962 to 1983). By
1998 (Fig. 8-2-9) ongoing shoreline
recession has eroded through the adjacent dike and exposed an ever increasing
length of the north-south ditch to the open waters of Pamlico Sound.
FIGURE 8-2-11.
Photographs of Jockey’s Ridge site. PANEL
A. An oblique aerial photograph showing Jockey’s Ridge State Park and the irregular
geometry of the estuarine low sediment bank shoreline. Photograph is from the
Field Research Facility of the U.S. Army Corps of Engineers. PANEL B.
Looking north along the eroding low sediment bank shoreline composed entirely
of sand and covered with various types of grass vegetation. The low wind tide
has exposed the extremely broad and well developed strandplain beach that
consists of an upper portion occupied during high wind tides and a lower
portion occupied during low wind tides. Notice the grassed slump blocks that
have collapsed in front of the wave-cut scarp. PANEL C. Close-up view
looking south along the eroding low sediment bank shoreline and associated
upper strandplain beach. Rapid recession of the wave-cut scarp has required the
observation platform, that was sitting on top of the low sediment bank, to be
repiled and braced. Notice the exposed roots in the wave-cut scarp. PANEL D.
Photo during a low wind tide from a marsh headland and looking east into a
cove. The shoreline is a low sediment bank covered generally by pine trees and
a very broad and well developed strandplain beach. PANEL E. Photo
looking southwest from inside the cove towards the marsh headland of Panel D.
The abundant dead pine trees in the nearshore and on the strandplain beach
demonstrate the active rates of shoreline recession.
FIGURE 8-2-12.
The Jockey’s Ridge and Nags Head Woods sites 1998 Digital Orthophoto Quarter
Quadrangle (DOQQ) with digitized shorelines for 1964 and 1998.
FIGURE 8-2-13.
The Jockey’s Ridge site aerial photograph
time slices from 1962, 1971, and 1989. In 1962, the study site behind Jockey’s
Ridge was essentially all active sand dune with very little vegetation. Erosion
of the dune field provided the sand for an extensive strandplain beach. A large
portion of the dune field along Roanoke Sound became vegetated with pine and
scrub-shrub through time, as indicated on the 1971 and 1989 aerial photographs.
This changed the small-scale pattern of the shoreline from a smooth curved
shoreline to the present irregular shoreline with numerous vegetated headlands
and coves (Fig. 8-2-11).
FIGURE
8-2-14. Comparison of barrier
island systems and the estuarine shorelines on aerial photographs from October
1932 and November 1999 for the northern portion of Nags Head including Jockeys
Ridge and Seven Sisters Dune fields. This segment is a complex barrier island
(Fig. 4-5-1B) that is not dominated by overwash. Thus, the back-barrier
estuarine shoreline is not under the influence of oceanic processes. Rather, it
totally responds to estuarine erosion dynamics similar to mainland estuarine
system. PANEL A. This 1932 aerial
photo predates any major shoreface modification such as construction of barrier
dune ridges that would have inhibited the overwash process. However, N.C.
Highway 12 had just been constructed and you can see the original beach houses
built in the late 1800s along the ocean shoreline. Notice the village of Old
Nags Head on the estuarine side of the island.
The Jockey’s Ridge and Seven Sisters back-barrier dune fields are extensive and
very active. The photos were flown after a major nor’easter in March 1932 for
the Beach Erosion Board (1935) as background data for a beach erosion study
(Field Research Facility, U.S. Army Corps of Engineers). PANEL B. This barrier island segment has been dominated by
construction and continuous maintenance of extensive barrier dune ridges since
the late 1930s, along with massive urbanization that has minimized oceanic
processes and allowed for the extensive growth of a major vegetative cover.
Since the estuarine shoreline is dominated by erosion, wherever development
occurs the shoreline has been extensively bulkheaded. However, the shoreline
behind Jockeys Ridge consists of portions of the older back-barrier dune field
that have been partially stabilized by vegetation. Consequently, this area is
now in an erosional mode, resulting in a low sediment bank shoreline with a
well developed sand strandplain beach. The photo was flown by the N.C.
Department of Transportation to evaluate shoreline erosion and the condition of
N.C. Highway 12 following Hurricane Dennis (9/1999).
FIGURE 8-2-15.
The Seven Sisters Dune Field site in a 1932 aerial photograph (Field
Research Facility, U.S. Army Corps of Engineers) with digitized shorelines (blue) and roads (red) from the 1998
DOQQ.
FIGURE 8-2-16.
Photographs of Nags Head Woods site. PANEL
A. Winter photograph looking northeast along the eroding edge of a narrow
marsh platform towards a small segment of low sediment bank dominated by a
maritime forest of pine trees. Notice the irregular erosional geometry of the
marsh peat shoreline. PANEL B. Summer photograph looking the opposite
direction to Panel A, southwest along the eroding edge of a narrow marsh
platform that fronts an upland region dominated by a maritime forest of pine
trees. The outer zone of marsh grass is a mixed assemblage of Spartina
patens and Juncus roemarianus, while the inner zone of tall grass is
Spartina cynusoroides. PANEL C. Close-up winter photograph
looking southwest along the eroding edge of a marsh platform. Notice the two
large eroded peat blocks sticking out of the water just to the right of the
eroding shoreline. PANEL D. Close-up view of an eroding marsh peat
headland along the shoreline in Panel C during a low wind tide. The deeply
undercut modern root zone, slopes steeply into the water. A subsequent storm,
with a high wind tide and wave action, will cause the overhanging block to
break off and produce an offshore peat block as is seen in Panel C. PANEL E.
Close-up view of low sediment bank shoreline that occurs in the distance in
Panel A. The low wind tide has exposed the rippled sand flats of the lower
portion of the strandplain beach. Notice the many trees with the root
structures exposed by the erosional processes. PANEL F. Close-up view of
a dead live oak tree on the lower portion of the strandplain beach. The entire
root system has been exposed through the erosion of the upland soil.
FIGURE 8-2-17. The Nags Head Woods site aerial photograph time slices
from 1940, 1964, 1975, and 1983. These photographs show the four major
geomorphic components of this complex barrier island segment. In the 1940
aerial photograph, the modern beach prism and active back-barrier dune field
were essentially uninhabited and only slightly vegetated. These two segments
have since undergone major urbanization along with significant levels of
vegetative stabilization by pines. Nags Head Woods, an older back-barrier dune
field that contains a major maritime forest and abundant inter-dunal
fresh-water lakes, has remained essentially unchanged through the same time
period. The marsh peat platform has accumulated up to 10 feet of peat that is
systematically burying the irregular paleotopography of the Nags Head Woods
dune field in response to ongoing rise in sea level. Notice the long fingers of
maritime forest (red color on the 1983 photograph) growing on the dune sands
that extend across the marsh platform (dark green color). The Nature
Conservancy’s Roanoke Trail follows one of these features to the study site
(red stars).
FIGURE 8-2-18. Photographs of the Duck Field Research Facility site. PANEL
A. An oblique aerial photograph showing the densely vegetated character of
the estuarine shoreline at the Duck site. The narrow, outer and lighter green
colored zone is marsh grass, whereas, the darker zone between the marsh and
N.C. Highway 12, is dense scrub-shrub growing on top of the low sediment bank.
Oblique aerial
photograph is from the Field Research Facility of the U.S. Army Corps of
Engineers. PANEL B. Winter photograph looking north along the
strandplain beach towards the eroded low sediment bank scarp in the distance on
the right side of the photo. Notice the fringing marsh consisting primarily of Juncus
roemarianus in the foreground and Phragmites australis in the
background. In the middle of the strandplain beach is a wrack berm composed of
dead marsh grasses. PANEL C. Summer photograph looking east across the
shoreline to the upland scrub-shrub. The shorter grass in the foreground is Juncus
roemarianus with Phragmites australis in the background.
FIGURE 8-2-19. The Duck Field Research Facility 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized shorelines for 1986, 1992, and
1998.
FIGURE 8-2-20. The Duck Field Research Facility site aerial photograph
time slices from 1986, 1992, 1997, and 2000. Notice how the fringing marsh
along this low sediment bank shoreline fluctuates through time. In 1986, the
fringing marsh occurs only in the southern section of the study area and by
1992 there is no fringing marsh in the study area. A very wide and dense
fringing marsh occurs throughout the entire study area in 1997 and by 2000, the
shallows in front of the access area (red stars) have opened slightly.
FIGURE 8-3-1. Maps of northern Roanoke Island
showing the average annual estuarine shoreline erosion rates by shoreline
segment, shoreline types, types and locations of shoreline erosion control
structures, and the relationship between erosion rates and distance of open
water (fetch) that impact different shoreline segments. Actual erosion rates for any given shoreline segment are dependent
upon the type of shoreline in concert with the fetch and a whole series of
other variables (see chapter 5). PANEL
A. Map shows the average annual estuarine shoreline erosion rate data of
Dolan and others (1972, 1986). The erosion data generally predate the construction
of most erosion control structures. Due to the high erosion rates, much of the
shoreline has now been armored and is now relatively stable but without sand
beaches (Fig. 8-3-2B). The map also shows the location and type of structures,
as well as the distribution of shoreline types used in the present study. PANEL B. Map showing the differences in amount
of fetch around the northern end of Roanoke Island.
FIGURE
8-3-2. Photographs of the
north Roanoke Island site. PANEL A. March 2001 photograph looking east along the
bluff to high sediment bank shoreline of segment 6 (Fig. 8-3-1A). Photo is from
Dough Cemetery at the east end of segment 5 containing the rock revetment. The
eroding bluff shoreline decreases in elevation to a high sediment bank in the easterly
direction. Notice the extensive overhang of the modern root-bound soil mat.
This overhang will ultimately collapse, dropping the associated trees onto the
bluff and strandplain beach where the continuous supply of trees and shrubs
provides an evolving natural debris groin field. The increased size of the
strandplain beach in the distance marks the beginning of segment 7 containing a
wooden groin field. PANEL B. March 2001 photograph looking east along
the rock revetment of segment 5 (Fig. 8-3-1A). The rock revetment was built in
1980 by the U.S. National Park Service to abate the 22.4 ft/yr of shoreline
recession between 1969 to 1975 (Table 8-3-1). Notice that there is no
strandplain beach in front of this rock revetment. PANEL C. June 2001
photograph looking west along eroding sediment banks of segment 6 (Fig.
8-3-1A). The photo shows the amount of recession of the unmodified sediment
bank shoreline (segment 6) since 1980. PANELS D and E. March 2002
close-up views of the wave-cut scarp along segment 6 (Fig. 8-3-1A). Notice that
the bluff is composed entirely of clean sand except in the zone labeled as a
paleosol where a thin layer of sand is bound by organic matter and stained by
iron oxide. Due to the composition, large blocks of sand slump off the bluff
and form a sediment apron along the back side of the strandplain beach (below
the white dashed lines). During subsequent high tides, waves systematically
erode the slump aprons, forming the cuspate scarps and reworking sand into the
strandplain beach.
FIGURE
8-3-3. The north Roanoke
Island site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized
shorelines for 1969, 1975, and 1998.
FIGURE
8-3-4. The north Roanoke
Island site aerial photograph time slices from 1969 and 1994. Crab Claw Spit
formed over time from high rates of sediment bank erosion on the north end of
Roanoke Island and the associated long-shore currents driven by northwest
storms. However, during the latter part of the twentieth century, the amount of
sediment feeding Crab Claw Spit rapidly diminished as most of the north end of
Roanoke Island was stabilized (Fig. 8-3-1A). Loss of the sediment source led to
destabilization, breakup, and rapid eastward migration of the Spit remnants as
demonstrated in the 1994 photo. As the Spit moves, shorelines formerly
protected behind the Spit, become re-exposed to open water and increased rates
of shoreline erosion. The red star marks the same spot on both photographs.
FIGURE
8-3-5. Photographs of the Woodard’s Marina site. PANEL A. Summer photograph looking south into the three common zones that
characterize swampforest shorelines. The photo is taken from within the ghost
swampforest of zone 3 and backed by the dense growth of Spartina
cynosuroides that characterizes the middle zone 2 that is utilized as the
shoreline. Behind the marsh grasses is the dense and living swampforest of zone
1. PANEL B. Winter photograph looking west along the swampforest
shorelines from the same general location as Panel A. PANEL C. Close-up
photo of the shoreline (zone 2) characterized by a small sand berm upon which
supports the dense growth of Spartina cynosuroides. Photograph is from
Murphy (2002). PANEL D. Close-up photo of the cypress trees and
associated knees that are the last survivors within zone 3 as the shoreline of
zone 2 moves landward.
FIGURE
8-3-6. The Woodard’s Marina
site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized
shorelines for 1963 and 1998.
FIGURE
8-3-7. The Woodard’s Marina
site aerial photograph time slices from 1956, 1978, 1989, and 2000. Notice the
dense swampforest vegetation associated with the stream valleys of the many
small drainage systems flowing into Albemarle Sound. A small, classic drainage
system occurs within the boxed area on the 1956 aearial photograph. Notice that
a very prominent cypress headland (red stars) occurs where the main stem of
this stream intersects the Albemarle Sound shoreline. The shoreline within the
cove west of this cypress headland is a low sediment bank that is in agricultural
production. Compare the location of this cove through time as the low sediment
bank recedes more rapidly than the adjacent swampforest shoreline. Due to the
geometry of the drainage system, the length of swampforest shoreline increases
through time at the expense of the sediment bank shoreline, along with a
significant increase in the distance the cypress headland extends into
Albemarle Sound.
FIGURE
8-3-8. Photographs of the Grapevine Landing site. PANEL A. Summer photograph looking north along the swampforest shoreline of the
Alligator drowned river estuary. This swampforest shoreline has been
extensively modified by natural processes resulting in a broad shoreline zone
of marsh and strandplain beaches. The photo shows the southern portion of the
study area, the landing (pier) in the center, and the northern portion of the
study area in the distance. PANEL B. Winter photograph looking south
across the southern portion of the study area from the pier. The outer zone of
marsh grass is generally Juncus, whereas the inner zone occurring within
the swampforest is generally Spartina cynosuroides. PANEL C.
Close-up of strandplain beach within a cove formed by a small headland formed
by a series of stumps and covered with Juncus marsh grass. Photograph is
from Murphy (2002). PANEL D. Close-up of an eroded section of
swampforest with the root systems exposed and Spartina cynosuroides
marsh grass within the existing swampforest. Photograph is by M. Murphy. PANEL
E. Close-up of a strandplain beach within a cove formed by a headland of
swampforest trees that have been recently uprooted. The strandplain beach
consists of a thin, basal bed of quartz sand burying the eroded peat substrate.
The denser quartz sand has been buried by a one-foot thick accumulation of very
light organic detritus. PANEL F. Close-up of the depositional and
erosional sediment structures produced in the organic detritus layer on the
strandplain beach during the last falling wind tide. The coffee-colored water
is visible at the bottom left corner of the photo.
FIGURE
8-3-9. The Grapevine Landing
site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized
shorelines for 1981 and 1998.
FIGURE
8-3-10. Photographs of the
Point Peter Road site. PANEL A.
Winter photograph looking west at the former fresh-water swampforest shoreline
that has recently evolved into fresh- to low brackish-water transition zone and
marsh vegetation. Today, the vegetation is dominated by Spartina patens,
Cladium, Baccharis, and Myrica. PANEL B. Close-up
of the highly irregular eroding geometry of the peat shoreline. The small
headlands are held up either by modern Baccharis and Myrica
stumps that occur at the shoreline as it recedes or by larger stumps and logs
that occur in the lower portions of the eroding peat bank. PANEL C.
Close-up of the irregular peat shoreline displaying the tops of the abundant,
large, eroded peat blocks that litter the near-shore area. Notice the irregular
wrack berm on top of the Spartina patens marsh. PANEL D. Close-up
view of erosional wave action that causes the upper and overhanging modern
root-bound layer to oscillate as the softer, decomposing under layer is
actively eroded away. PANEL E. Similar photo to Panel A, but with a
small strandplain beach composed totally of organic detritus eroded out of the
underlying peat bed. The presence and extent of this organic detritus is
extremely variable and dependent upon the season and storm patterns. Notice how
the irregular erosional geometry of the original peat shoreline can be seen on
the landward side of the strandplain beach. PANEL F. Winter photograph
looking north from the same location as Panel E. Now the entire eroding peat
shoreline is buried beneath an extensive strandplain beach composed totally of
organic detritus. This detrital accumulation is over three feet thick at the
waters edge and extends some distance seaward below the waters surface. Notice
the beautiful detailed, and small-scale depositional and erosional sediment
structures that are preserved on this beach as the water rises and falls in
response to the wind tides.
FIGURE
8-3-11. The Point Peter Road
site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized
shorelines for 1969 and 1998.
FIGURE
8-3-12. The Point Peter Road
site aerial photograph time slices from 1969, 1983, 1998, and 2000. Notice that
the impoundment north of Point Peter Road is separated from Pamlico Sound by a
major outer ditch and associated dike. Comparison of land loss along the outer
ditch between the 1969 and 1983 photographs demonstrates the rapid rate of
shoreline recession. The ditch is long gone by 1998 and the impoundment has
reverted to the natural vegetation pattern. Also, notice the major expansion
through time of transition zone and marsh vegetation (light gray-green color on
the 1983 to 2000 photographs) at the expense of the swampforest vegetation (red
color on the 1983 and 1998 photos and dark green on the 2000 photographs). This
is interpreted to be the drowning of these low-lying wetlands in direct response
to ongoing sea-level rise.
FIGURE
8-3-13. Photographs of the
North Bluff Point site. PANELS A and B. Summer photographs looking northeast (A) across
the Outfall Canal to the upland vegetation on the far spoil bank and looking
southwest (B) along the outer edge of the marsh platform. The outer zone of
this platform marsh consists of Spartina alternaflora that grades
landward into a dense growth of Spartina cynosuroides. The latter grass
is growing on a slightly elevated zone of spoil that was deposited along the
outside of the impoundment ditch as indicated on Figure 8-3-13. Notice the
highly irregular shoreline geometry of the rapidly eroding marsh peat
shoreline. Photographs are by M. Murphy. PANELS C and D. Close-up
photographs of the irregular marsh peat shoreline. The peat is about 6 to 7
feet thick at this point with the the wave-cut scarp eroded to depths of 2 to 4
feet below the water surface. Thus, the bottom of the estuary is still in the
soft peat. The estuarine floor gently slopes away from the land to 6 to 7 feet
water depth where the peat has been totally eroded away and the underlying
tight clay forms the esturine floor. Notice the dark coffee color of the water.
FIGURE
8-3-14. The North Bluff
Point site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized
shorelines for 1983 and 2000.
FIGURE
8-3-15. The North Bluff
Point site aerial photograph time slices from 1983 and 1995. The rapid
rate of shoreline recession is indicated by the red star. An entire segment of
the marsh between Pamlico Sound and the outer ditch of the impoundment,
southwest of Outfall Canal Road, has largely disappeared in this 12-year
period.
FIGURE
8-3-16. The Swan Quarter
site 1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized shorelines
for 1956 and 1998.
FIGURE
8-3-17. Photographs of the
Lowland site. PANEL A. Winter photograph looking northeast within the
cove and along a low sediment bank shoreline with Spartina patens,
scrub-shrub, and pond pine growing on the upper surface. Notice the small
strandplain beach that occurs only within the apex of the cove. PANEL B.
Close-up of the wave-cut scarp eroded into the low sediment bank overlain by a
thin pocosin peat containing a cover of Spartina patens in the
foreground and pond pine with transition zone scrub-shrub in the background.
The sediment bank is composed of a Pleistocene, tight, slightly sandy clay.
This is the source of the limited sand forming the small strandplain beach in
Panel A. Photograph is by M. Murphy. PANEL C. Summer photograph
looking east along the narrow marsh platform in front of the mineral soils with
their wetland woods consisting predominantly of scrub-shrub, bay trees, and
pond pine. The marsh platform is composed of organic peat that is forming on
top of and pinches out onto the mineral soil that forms the shoreline in Panel
B. Photograph is by M. Murphy. PANEL
D. Summer close-up of the marsh
platform dominated by a narrow outer zone of Spartina patens adjacent to
the water and an inner zone of Spartina cynosuroides that is growing on
a very thin and slightly raised sand and wrack berm. Photograph is by M.
Murphy. PANEL E. Winter photograph looking northwest along the
marsh platform shoreline within the cove. Notice the thick roots of Spartina
cynosuroides that extend out to edge of the eroding marsh peat where the
plants have been stripped off by wave action. PANEL F. Close-up of the
wave-cut scarp and wave-cut platform eroded into the marsh peat. In the
foreground, the tight root-bound upper surface has been eroded off in a
stair-step fashion, whereas, in the background, this root-bound surface is
being undercut forming an overhang.
FIGURE
8-3-18. The Lowland site
1998 Digital Orthophoto Quarter Quadrangle (DOQQ) with digitized shorelines for
1964 and 1998.
FIGURE
8-3-19. The Lowland site
aerial photograph time slices from 1964, 1970, 1983, and 1995. The entire
region within the area of the photograph is wetland. Dense scrub-shrub
swampforest vegetation (red color in the 1983 photograph) lives in standing water
on top of the tight clay soils much of the year. The slightly lower area
surrounding and adjacent to the Oyster Creek drainage system is dominated by
marsh grasses (light blue-green color in the 1983 photograph) living on a marsh
peat substrate that thickens into the drainages. The time series suggests an
expansion of the scrub-shrub swampforest vegetation through time (excluding the
logged areas indicated with white stars) and loss of associated marsh along the
Outer Pamlico River shoreline due to erosion (red stars).
FIGURE 8-4-1. Photographs of the Wades Point site. PANEL
A. September 1979 photograph looking east towards the eroding Wades Point
and a former beach cottage located on the nonhardened low sediment bank
shoreline with upland pine vegetation. Photo is from Hardaway (1980). PANEL
B. A January 2001 photograph from about the same location as Panel A.
Notice the hardened shoreline, lack of upland vegetation, and a relatively new
beach cottage. PANEL C. September 1979 photograph looking west along the
low sediment bank shoreline of the Pamlico River. Photo is from Hardaway
(1980). PANEL D. Close-up of the wave-cut platform eroded into the low
sediment bank shoreline indicated in Panel E. The shoreline is composed of
tight Pleistocene clay with the absence of a strandplain beach due to lack of
sand in the eroding clay sediment. Also, the shallow root systems of the upland
vegetation is totally excavated as demonstrated by the trees along the
shoreline. PANEL E. January 2003 photograph looking north along the
platform marsh shoreline of the Pungo River from Wades Point. The marsh
interior is dominated by Juncus roemarianus with a narrow outer
perimeter marsh dominated by Spartina patens. Locally, there is a narrow
and mixed zone of Phragmites australis and Spartina
cynosuroides that grow on a thin sand and wrack berm that parallels the
shoreline. Notice the highly irregular erosion pattern of the marsh peat in the
foreground and the upland area and associated low sediment bank shoreline in
the distance (see Panel D). PANEL
F. January 2003 close-up photograph of the eroding platform marsh
shoreline. Notice the large peat block in the near shore that has recently
broken off the shoreline.
FIGURE 8-4-7. Photographs of the
Pamlico Marine Lab site. PANELS A and B. March 1978 close-up
photographs of the unmodified and eroding low sediment bank shoreline of the
Pamlico Marine Lab site. Panel A is on the western side and Panel B is on the
eastern side of the lab. Notice the large trees lying along the bank and the
stumps in the near shore, reflecting the receding shoreline. The area
has been generally cleared for the lab, leaving only a few trees along the
bank. PANELS C and D. August 2001 photographs of the modified low
sediment bank shorelines of the Pamlico Marine Lab site. Panel C is on the
western side and Panel D is on the eastern side of the lab. The rock revetment
has temporarily stopped the shoreline recession. Photographs are from the pier by M. Murphy.