CSE
Completes Renourishment of Arcadian
Shores (continued
from home page)
Arcadian Shores is a section of South Carolina’s Grand Strand
between North Myrtle Beach and Myrtle Beach. It is home to Hilton Hotel
Resort, Kingston Plantation, and several major residential towers.
While the cities immediately north and south are part of a 50-year
federal beach nourishment project, Arcadian Shores is not included.
However, Horry County, which has jurisdiction over Arcadian Shores,
with funding assistance from the state of South Carolina, has taken the
initiative to maintain and improve the beach.
Ten years ago, Horry County was able to “piggyback”
the first nourishment of Arcadian Shores as the contractor was
completing the project at Myrtle Beach. With a scheduled renourishment
of Myrtle Beach and North Myrtle Beach by the Corps of Engineers in
2008, an opportunity presented itself for renourishment of Arcadian
Shores. The challenge was obtaining permits on relatively short notice
and accomplishing the project within a narrow environmental window.
From start to finish in 11 months
Horry County retained CSE on 23 April 2007 to prepare the design,
secure permits, issue plans to contractors, and oversee construction.
On 30 March 2008, the last of the equipment was removed from the beach
and the 6,000-foot-long project was ready for the tourist season. Going
from initial planning to project completion in less than a year is the
sort of challenge CSE has faced many times. The keys to this
project’s success included:
Timely
condition surveys and
sand budgets for the area by CSE staff.
Identification
of a new borrow
area drawing on work by the US Geological Survey, Coastal Carolina
University scientists, as well as our staff field team.
Timely
review and issuance of
permits by state and federal officials.
Efficient
execution of
construction by the contractor, Great Lakes Dredge & Dock
Company, operating under an exceedingly narrow environmental window for
hopper dredging.
Project Summary
The $4 million Arcadian Shores project
placed ~316,000 cubic yards between Singleton Swash and the Apache
Campground Pier. The new beach added nearly 200 feet of width and
included realignment of the swash to mitigate downcoast erosion.
Construction was via two hopper dredges,
Dodge Island and Padre Island, using a recently discovered deposit 1-3
miles offshore of the project area. Building on a
reconnaissance survey by Coastal Carolina University, CSE obtained 56
borings using our in-house coring system and confirmed sediment quality
to below-operational depths. The high density of cores allowed us to
select dredging corridors having the most compatible sediments for the
beach while avoiding cultural resources, hard bottom, and ongoing
monitoring by state resource agencies.
Hopper Dredge Advantages & Disadvantages
Prior studies along the central Grand
Strand of South Carolina indicated that the best sand tends to be found
in isolated thin sheets overlying an ancient offshore erosional
surface. Such deposits are best suited for hopper dredges which
excavate by sweeping thin layers off the bottom. Natural resource
officials in the Carolinas generally favor hopper dredges because they
tend to leave undisturbed areas for “recruitment”
of benthic organisms. Hopper dredges cut narrow, shallow furrows rather
than broad, deep holes in the bottom. The latter sometimes infill with
finer material, thus changing the bottom characteristics.
The environmental advantages of shallow
cuts via hopper dredge are offset by disadvantages during construction.
Hopper dredges pose more of a threat to sea turtles than cutterhead
dredges. As a result, work is severely restricted to just a handful of
cold-water months under federal regulations. For Arcadian Shores, the
allowable construction window was January through 31 March.
Close Timing for the Project's Completion
CSE’s project team, led by
Bill Forman and Doug Dusini, worked closely with county staff to secure
permits just in time for winter construction. While the last permit
reviews were in progress, CSE prepared final plans and bid packages for
the project. As an example of extraordinary timing and coordinating,
the following schedule was met.
21
February 2008
Plans
available to contractors
28
February 2008
State permit issued
7 March 2008
Contract
issued
6
March 2008
Federal permit
issued
11
March 2008
Construction starts
28
March 2008
Construction ends
31
March 2008
Environmental window for
construction ends
While such close timing is not
CSE’s favored way of accomplishing projects, we are confident
all the beach users and property owners along Arcadian Shores are happy
at the outcome. With a much wider beach in place, they are less
vulnerable to storms and the new beach can accommodate many more beach goers than
before.
Performance Prediction
People ask how long the new beach will
last? CSE predicts “well over ten years” based on
the relatively low erosion rates along South Carolina’s Grand
Strand and the experience after the initial nourishment in 1998. At the
start of the 2008 project, there were 40-60 feet of storm berm
remaining from the first project. So the first nourishment gave a head
start to the second, ten years later. This trend is being repeated at
other Grand Strand beaches under the federal 50-year project.
Renourishment at ~10 year intervals is not only replacing eroded sand,
it is widening the beach even further, keeping seawalls buried, and
allowing a buffer of dunes to soften the shoreline between the ocean
and developed property.
Acknowledgments
Owner: Horry County SC (c/o Steven
Gosnell, Director, Public Works)
Engineer: CSE Columbia SC (c/o Bill
Forman Jr., PE, Doug Dusini, Philip McKee, Trey Hair, and Dr. Tim Kana)
Contractor: Great Lakes Dredges &
Dock Company (c/o Steve Auernhamer)
Beach construction at Arcadian Shores
progressing north to Apache Campground Pier (19 March 2008).
Beach
guest enjoying the afternoon at
Arcadian Shores while the beach is being renourished (19 March 2008).
The renourished beach
at Arcadian Shores after project completion.
Edisto
Beach (continued from home page)
Edisto Beach was first nourished in 1954 using a borrow area in the
marsh directly behind the oceanfront. The 1954 project pumped 854,000
cy of sand, shells, and mud onto the northern two miles of shoreline.
While much of this volume eroded quickly because of its mud content,
enough sand and shells remained trapped between groins to create a
stable beach. Between 1954 and 2005, a minimal beach was maintained,
but it was insufficient to offer any protection during storms. High
tides reached porch steps, so numerous bulkheads and revetments were
installed to prevent further encroachment.
Besides
shells pumped from the salt marsh in 1954, shells from Edingsville
Beach (a washover barrier fronted by marsh outcrops) are transported
downcoast to Edisto Beach, giving its beach a character much different
from other South Carolina beaches. Coarse shell fragments concentrate
in groin fillets, increase the porosity of the beach, and lead to a
steeper profile than normal. As a result, Edisto Beach has one of the
narrowest wet-sand beaches in the state. (Kiawah Island and Hilton Head
Island have intertidal "wet" beaches averaging over 400 ft wide,
whereas Edisto Beach is typically less than 150 ft wide.) Shells and
sharks' teeth have made Edisto Beach a paradise for collectors, but the
resulting steep profile also presents challenges for beach building.
February
2006: before renourishment
June
2006: after renourishment
A
fundamental goal of beach nourishment is to match the sediment grain
size and color of the borrow material with the textures of the native
beach. If this is done, the nourished beach will perform as well as the
native beach, particularly if the project extends for miles along the
coast. (Projects of short length never perform as well because the
bulge of sand produced by nourishment becomes a focus for waves and
erosion.) Another reason to attempt a match of sediment textures is to
create a nourished beach that is indistinguishable from the native
beach.
CSE
initiated a search for nourishment sand off Edisto Beach in 1990. While
huge deposits exist in the shoals of St. Helena Sound, most consist of
silty, fine sand – a material that would alter the character
of Edisto Beach and would be quite unstable as nourishment sand.
Fortunately, CSE was able to identify and confirm one compatible
deposit that closely matches the native sediment texture. This limited
area was used for a small nourishment involving only 150,000 cy in
1995. The borrow area was a dynamic shoal at the edge of a navigable
channel, accessible to ocean-going dredges. The 1995 project
demonstrated the suitability of the borrow source and had the added
advantage of being a renewable resource. Soon after excavations, the
1995 dredged pit infilled with coarse sand.
Sediment
borings by CSE between 2003 and 2005 confirmed an expanded borrow area
in the same vicinity which closely matched the native beach. When the
Illinois anchored for work in late March 2006, the GLD&D crew
knew what to expect. However, most folks at Edisto Beach were caught by
surprise.
February
2006: before renourishment
June
2006: after renourishment
For at
least 40 years, vistas along the beach were interrupted by timber and
rock groins projecting as much as 8 ft above the sand level. People
sitting on the beach were used to seeing only as far as the nearest
groin. The 2006 nourishment almost completely buried the groins. For
the first time in years, crowds several groin cells away looked as if
they were on the same section of beach. And oceanfront property owners
could look over an expanse of dry beach with the satisfaction of
knowing the beach is higher along with their property values.
Many
ask how long Edisto's new beach will last. The answer is not simple
because, in simple terms, Edisto's natural erosion rate varies greatly
from north to south. Before groins were built, the northern end along
the state park eroded at over 10 ft per year (ft/yr). The center of the
island changed very little and the downcoast shoreline actually
accreted over decades.
Groins
(constructed in the 1950s and 1960s) modified shoreline change rates to
the point that natural rates were masked. Now that the groins are
mostly buried, one could expect to see larger fluctuations in erosion
rates, high erosion (ie, >5 ft/yr) at the updrift end of the
project, and accumulation of nourishment sand at the southern
(downcoast) end of the island. If your area of interest is the center
of the island, you will probably see little change over the next
several years. Where erosion occurs, the rate is expected to decline in
relation to the degree of exposure of the groins. In other words, as
the groins are uncovered, they become more effective sand traps.
What's
Next for Edisto Beach?
CSE
will closely monitor the new beach over the next several years. Surveys
will answer the question: "How fast is the beach eroding?"
The
town would like to obtain federal funding for a "50-year" project (cost
shared among federal, state, county, and municipal sources) and has
entered into discussions with the US Army Corps of Engineers.
Other
alternatives being investigated are extensions to the existing groins.
Longer groins would trap and hold the nourishment sand, increasing the
time before renourishment is needed. If a wider beach can be
maintained, efforts can shift to dune building and better storm
protection.
Even
with the new beach in place, many properties remain vulnerable and will
sustain damages during a hurricane. However, experience has shown that
the damages will be lessened by the presence of a wider beach.
Hunting
Island's eighth nourishment project (continued from home page)
Hunting
Island has been a poster beach for opponents of nourishment because of
the frequency and number of projects attempted. It is one of the places
where one can truly say "this project will only last about three
years." But after all, should more longevity be expected for a beach
that has lost up to 25 feet per year (ft/yr) since the 1940s?
February
2006: before renourishment
June
2006: after renourishment
Hunting
Island's erosion rate is ten times faster than Myrtle Beach's and much
of South Carolina's developed coast. For years, it was the only beach
in South Carolina receiving regular infusions of sand. Eight projects
in 38 years added nearly 5.5 million cubic yards. Yet even with all
this sand concentrated along the 4-mile-long island, today's shoreline
is hundreds of feet landward of the 1960 foredune.
February
2006: before renourishment
June
2006: after renourishment
The
2006 project differs from previous nourishments because it will be
followed by construction of up to six groins. Strategic areas where
groins will be placed are the campground, North Beach at the
lighthouse, and the South Beach recreation area which received all the
2006 nourishment sand. In some places, the new dry beach is 175 ft
wide. Like projects before it, these nourished areas will erode rapidly
until groins are constructed (expected in fall 2006). With groins in
place, the erosion rates will lessen significantly, but will not stop
completely. Hunting Island will require future nourishment even with
groins in place – just not as much or as often.
Turtles
were among the beneficiaries of the 2006 nourishment project. Through
July, 59 nests were recorded with 2 more recorded the first week of
August compared with 90 nests recorded during all of the 2005 nesting
season.
Kiawah's famed Ocean Course saved
in the nick of time (We hope!) (continued
from home page)
Restoration
of the beach along the famed Ocean Course golf resort at Kiawah Island
required closure of a tidal inlet, opening of a new inlet one mile
away, and excavation of 550,000 cy from a ten-year-old barrier beach.
The area of excavations was open ocean a decade ago. But in barely ten
years, a 3-mile-long barrier island/lagoon system formed by way of
shoal bypassing at Stono Inlet. An estimated 5 million cubic yards were
added by natural processes at Kiawah's eastern end. As the bypassing
event progressed, it enclosed a 200-acre lagoon, added 150 acres of
beach/dune/washover habitat, and left a flushing channel in front of
the Ocean Course Club House.
June 2006:
before restoration
July
2006: after restoration
Shoal
bypassing is probably the single most important process along the South
Carolina coast because it controls the sand exchange between inlets and
beaches. Normally, Kiawah receives about 1 million cubic yards during a
shoal-bypassing event. This produces localized accretion and erosion
zones of a scale that are accommodated by healthy development setbacks
established in the 1970s (at the recommendation of Professor Miles
Hayes and others at the University of South Carolina).
The
event in the 1990s that instigated the present project dwarfed all
previous shoal bypasses. Accretion zones moved the shoreline over 2,000
ft seaward (that is more than 250 ft/yr). However, erosion zones
associated with the shoal-bypass cycle were also much larger than
normal. Along the 18th fairway of the Ocean Course, dunes receded at
over 100 ft/yr.
June 2006:
before restoration
July
2006: after restoration
The
2006 project addressed the problem along the Ocean Course by relocating
the new inlet and borrowing sand from the accretion zone. This was a
cooperative plan developed in close coordination among the Town of
Kiawah Island (lead entity), the Kiawah Island Golf Resort Company, SC
DHEC-OCRM, SCDNR, US Army Corps of Engineers, and US Fish &
Wildlife Service (USFWS). CSE was principal designer of the project. A
critical element was protection of the habitat of incipient piping
plovers.
Piping
plovers are a threatened species and receive federal protection.
Although they do not nest in South Carolina, they use certain isolated
spits for roosting and foraging during parts of the year. The new
barrier beach at Kiawah's eastern end provides the type of ephemeral
habitat apparently favored by plovers. Because of its importance, USFWS
required that all work be conducted outside the months when plovers may
be present. This limited the construction window to June and July.
However, because this is also the turtle-nesting season, extra
protection measures for that species were implemented.
Click image
to view renourishment overlay
A
principal goal of this project was to maintain as much washover habitat
as possible while redirecting flows in and out of the lagoon through a
new channel. The project removed sand that otherwise would have formed
high dunes and become vegetated (habitat plovers apparently do not
like). In this way, it bought time for the plovers.
The
project also bought time for the Ocean Course. With some beach sections
widened by over 500 ft, the project created a smoother transition
between the accretion zone and the erosion zone. It restored downcoast
sand transport (although the rate will not be known until further
surveys are completed by CSE). And it now allows the Ocean Course to
focus on the 2007 Senior PGA Championship, instead of the accelerating
erosion along the 18th hole. Instead of sand being trapped by the
shoal-bypass event east of the Ocean Coarse, beach sand now flows past
the sand traps of the 16th and 18th fairways. Instead of a wave of
erosion migrating along Kiawah Island, there is now the probability of
a new cycle of accretion.
Contrary
to popular wisdom, some East Coast beaches like Kiawah Island are
gaining sand by natural processes. Barrier islands, lagoons, and even
healthy stands of salt marsh can form in only a few years –
if you've never seen that happen, just visit Kiawah's eastern end. The
2006 project was an attempt to work with this healthy system. There
will be no development in the project area and – it is hoped
– no need for another project of this sort at Kiawah in the
coming years.
Arcadian
Shores
