Topsail
Island, a 40 km long island, is the second longest barrier within the Onslow
Bay section of North Carolina. The
island is bordered by the New River Inlet to the north and New Topsail Inlet to
the south. The northeast-southwest
barrier orientation exposes the island to frequent winter storms. Prior to 1941, the island then known as Ashe
Island, was used as a stock grazing range, with no development or access to the
mainland. Between 1941 and 1947 the
island was used as a US Military Reservation.
Development began in the early 1950’s several years after the island’s
ownership returned to the private sector.
The island consists of three communities: North Topsail Beach, which
comprises the northern section, Surf City, which covers the central portion of
the barrier and, Topsail Beach, which extends along the southern section of the
island. All three communities were
severely impacted by the recent hurricanes.
Topsail
Island is situated in a chronic overwash zone.
Storms during the period 1944 to 1962, and the late 1980’s were
particularly devastating to the island. Hurricane Hazel (1954) and the Ash
Wednesday storm (1962) caused significant damage along the entire barrier.
During Hurricane Fran(1996) much of the island was overtopped resulting in the
formation of massive and extensive washover topography. The pattern was
repeated again in subsequent storms. Hurricanes Fran (19967), Bonnie (1998),
and Floyd (1999) opened numerous breaches in the barrier particularly along
North Topsail Beach. The elevated water levels that reached 11 feet and the
associated storm waves destroyed several hundred homes. The dune line, roads
and utilities had to be restored numerous times during the past five years at
tax-payers expense.
Development
continues along some sections of the island in places where destruction is sure
to occur during the next storm. We will make a series of two to three quick
stops along each of the three communities to view a variety of management
concerns and discuss the development trends.
Answer
each of the following questions posed at each stop as apart of your laboatory
assignment. Date due 25 September 2001.
Stop 1. North Topsail Beach.
New
River Inlet forms the northern boundary of Topsail Island. The shallow inlet
has migrated within a 3km wide zone.
Its current position marks the southern boundary of this zone. Dredging
operations that began in the 1940's altered the hydrodynamics of the inlet. The
early 1960’s marked the advent of sidecast dredging of the inlet for navigation
purposes. The cumulative effect of the dredging was an increase in the size of
the ebb-tidal delta. The growth of these offshore shoals controlled the
shoreline change patterns on the adjacent beaches.
The erosion/accretion patterns along the inlet’s shoulders have changed appreciably since 1960. During the past 40 years portions of the Topsail Island oceanfront adjacent to the inlet have prograded more than 40 m. In contrast severe erosion has characterized the oceanfront along the Onslow Beach shoulder on the opposite side of the inlet. Accretion associated with the inlet extends along a 1.5km long zone on North Topsail Beach and represents the only segment along the northern end of the barrier experiencing progradation. All of the multi-unit dwellings along the northern end of the island are sited seaward of the 1960 shoreline. The multiple dunes at this site protected most of the structures during the storms from the dramatic structural damage that characterized the beach further south.
North Topsail Beach was considered to be a high-risk development zone prior to the 1996 hurricane season. Almost all of the dunes along the oceanfront with the exception of those near the inlet were leveled as a result of Hurricane Bertha. The small amount of recovery due to natural recovery and artificial profile manipulation did little to improve the beach conditions before Hurricane Fran struck seven weeks later. Recession of the high water line (HWL) along North Topsail Beach due to these two storms ranged from 20-65m. The average overwash penetration associated with Hurricane Fran varied along the beach and ranged from 8m near the prograded dune segment at the north end of the beach to more than 260m in the vicinity of the island breaches.
The shoreface off North Topsail Beach is predominately composed of outcrops with a thin, patchy veneer of sediments. The irregular nature of the offshore limestone platform probably influences the approach of waves and the erosion along the local beaches. The frequency of hardbottoms increases from the southern end of North Topsail Beach to the north. Moderately high-relief (1-1.5m) landward facing scarps are common in this area. Presumably these features and the intervening plateau-like hardbottom areas exerted a major influence on sediment transport during the storms.
Field Notes:
·
Are
the dunes in this area natural? How can you tell?
·
What
accounts for the differences in the nature of the dunes along the northern 5km
of the island?
·
What
are the effects of the frequent overwash events in this area?
·
What
do the numerous outcrops of peat and exposures of relict stump forests along
this section of the island indicate?
·
Can
you determine locations where the island was breached during the storm events?
·
What
is the source of the large limestone clasts and oyster fragments scattered
along the beach?
·
Where
will this community obtain the needed sand resources for the proposed storm
damage reduction and erosion mitigation projects?
·
Should
the State of North Carolina (with the assistance of FEMA) continue to rebuild
the infrastructure in this area?
·
How
can we better regulate the re-development of this area?
·
What
is your the long term prediction for the fate of this section of the island?
Stop 2. Surf City.
Surf
City occupies the central 8.7km of Topsail Beach. The majority of the barrier in this vicinity fronts the relict
flood tidal deltas of Stumpy Inlet that opened and closed several times during
the eighteenth and nineteenth centuries.
The finger canals were dredged in the mid to late 1960's across the
marsh that caps the coalesced flood tidal deltas.
Overwash
in this segment of the island during recent storms extended across much of the
low-lying barrier and into the canals. Numerous oceanfront homes and many of
the mobile homes sited on the old wahover fans behind the narrow foredunes were
destroyed. The southern portion of Surf City was less susceptible to
overtopping. The effects of overtopping were greatly reduced due to the topographically
higher foredune and adjacent dune field.
Reconnaissance surveys indicate the shoreface off Surf City beyond the toe of the active beach, is characterized by a very thin, mobile veneer of sand overlying flat limestone hardbottoms. Much of the modern sediment cover consists of thin, graded beds overlying bored and encrusted limestone hardbottoms. This sequence suggests the thin sediment veneer is remobilized frequently.
Field Notes:
·
Is the pattern of development in the Surf City any
different than the area to the north?
·
Why
were the finger canals constructed in this area of the island? Why are there no
finger canals along the northern end of the island?
·
How
would you characterize the dunes in this section of the island?
·
What
are the effects of the frequent overwash events in this area?
·
Why
are there no outcrops of peat along this section of the island?
·
Are
there any potential breaching sites in this area?
·
Has
there been any natural rebuilding of the beach in this section of the island?
·
Does
the community need sand to restore the integrity of the dune and beach? If so
where will it obtain the needed sand resources?
·
Is
there a better argument for the state and federal governments continued efforts
to rebuild the infrastructure in this area after storms?
·
How
can we better regulate the re-development of this area?
·
What is your the long term prediction for the fate of
this section of the island?
Stop 3. Topsail Beach.
New
Topsail Inlet separates Topsail Beach to the northeast and Lea Island to the
southwest. Historic coastal charts and
maps indicate this inlet existed as early as 1738. Since 1738, New Topsail Inlet has steadily migrated to the southwest,
a distance of approximately 10km. Migration rates that ranged from 20 - 35 m/yr
have characterized the inlet over the past 150 years. The orientation-of the
ebb channel has changed on a cyclical basis and as a result has dictated the
patterns of erosion/accretion on the adjacent shorelines.
Extensive
beachfront development on the southern end of Topsail Island began in the early
1950's. The cottages and motels that
date from this period were constructed on the primary dune that paralleled the
southwesterly extending recurved spit.
As New Topsail Inlet migrated, the recurved portion of the dune ridges
also reformed to the southwest in accordance with the position of the
inlet. Migration resulted in a
realignment and erosion of the updrift trailing shoreline. The chronic erosion
that currently characterizes this area stems predominantly from the recession
of the primary recurved dune line as the inlet has migrated. Erosion of oceanfront lots associated with
New Topsail Inlet migration and spit elongation has been accelerated by the
occurrence of numerous storms.
Some
of the most extensive washover fans and terraces developed during the
hurricanes on Topsail Island were mapped in this area of Topsail Beach.
Hurricane Bertha resulted in the overtopping of the southernmost 1.8km of
Topsail Beach and the formation of minor washover topography. Following Hurricane Fran, the most extensive
overwash occurred along the southern 3.4 km of Topsail Beach. Overwash terraces extended 100 to 200m
across the flattened profile. Almost
all of the dunes were eroded. North of
the southernmost 3.4km shoreline stretch, overwash was sporadic. Newly formed washover topography varied
along this segment encompassing the northern portions of Topsail Beach to the
southern limits of the Town of Surf City.
Some stretches showed no evidence of overtopping while other segments
were completely overtopped. This pattern was repeated during Hurricanes Bonnie
(1998) and Floyd (1999)
The Topsail Beach shoreface is characterized as a sediment-starved region where bioerosion and reworking of underlying units provide the primary sources of sediments. A thin patchy veneer of modern sediments covers the flat to low relief Oligocene limestone hardbottoms.
Field Notes:
· Is the pattern of development in the Topsail Beach any different than the other segments of the island?
· What accounts for the differences in the height and width of the dunes along this stretch of the island?
·
Is
there any relationship between the locations of overwash zones and the nature
of the dunes?
·
Are
there potential breaching sites along Topsail Beach?
·
Is
the erosion scenario along the southern 2km of Topsail beach similar to the one
observed along southern section of Figure Eight Island?
·
Is
the prospect for beach nourishment along Topsail Beach better or worse than
areas further north?
·
How
can we better regulate the continued development of this area?
·
What
is your the long-term prediction for the fate of this section of the Topsail
Island?