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Abstract
The construction of an artificial island in the shape of a
palm tree w ith a diam eter of approxim ately 5 km in
front of the coast of Dubai is nearing com pletion.
To protect the island against w ave attack, an offshore
crescent breakw ater surrounding the island w ith a total
length of 11 km w as constructed at the sam e tim e.
After com pletion, the island w ill be developed into
virtually self-contained com m unities including m arinas,
shopping centre, them e parks, restaurants and so forth.
The Client is D ubai Palm D evelopers, a subsidiary
com pany of the D ubai Ports, Custom s & Free Zone
Corporation. The m ain contractor for the reclam ationw orks, totalling som e 70 m illion m 3 of sand, is Van
O ord A CZ. The breakw ater construction w as carried
out under a separate contract aw arded to Achirodon
O verseas. The contract w as aw arded to Van O ord A CZ
at the end of 2001 and w orks have to be com pleted
end 2003.
O ne of the m ain challenges w as constructing the sand
fill for the island, w hich had to be carried out partly in
unprotected sea conditions, since the breakw ater w as
under construction sim ultaneously because of the tight
tim e schedule. Therefore an execution m ethodology
w as developed aim ing at an optim al schedule in term s
of speed of construction and m inim al risks of dam age
and sand losses.
First an inventory w as m ade of the different sand
transport m echanism s i.e. long-shore, cross-shore and
w ash-over transport and how this w ould effect the
w ork under construction taking into account a num ber
of possible execution strategies. From this study, the
optim al execution m ethodology w as derived.Also optim al logistics in term s of cycle tim es and
com bination of placem ent/rainbow ing has been
achieved, by im plem enting day-to-day survey results
into the D G PS tracking system . In this w ay underw ater
filling is m ade possible, leaving open sufficient space to
m anoeuvre the ships.
Terra et A qua N um ber 92 Septem ber 2003
R ob E . de Jong , M ark H . Lind o, S aee d A S aeed and Jan V rijho f
Execution Methodologyfor Reclamation WorksPalm Island 1
Figure 1. Artist im pression of Palm Island 1.
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Introduction
Jebel Ali Properties is developing a prestigious housing
and recreation project on new land to be reclaim ed in
the G ulf betw een D ubai City and M ina Jebel Ali.
The project, aptly nam ed Palm Island Project, com prisesan artificial palm -shaped island protected at the sea-
w ard side by an arm oured sem i-closed oval crescent
(Figure 1). The area under consideration has w ater
depths ranging betw een 8-10 m below Jebel Ali CD
(tidal range is approxim ately CD +0.5 m to C D +1.5 m )
and an alm ost horizontal to very m ild foreshore.
The island itself is built from locally dredged sand.
The dim ensions of Palm Island are im pressive: the
perim eter of the crescent is approxim ately 11 km long,
the surface to be reclaim ed is about 650 ha and the net
sand volum e is about 70 m illion m 3. The total tim e
allow ed to construct the island is tw o years.
The required sand is acquired by hopper and cutter
dredgers and is deposited in the lee of the oval
crescent surrounding it. The contractor Archirodon
O verseas is m ain contractor for the construction of the
rock arm our protected crescent, w here Van O ord A CZ
is the m ain contractor for the construction of the actual
island (Figure 2).
Since the crescent breakw ater and sand-filled island
w ere built sim ultaneously due to tim e restrictions, the
island w as partly unprotected during the first stages of
the construction. This m eans that during this construc-
tion period the integrity of the island w as endangeredby the incom ing w aves, m aking the progress and
success of its construction strongly dependent upon
the progress of the crescent construction providing a
sheltered area.
Therefore an optim al execution schedule in term s of
m axim um speed of construction and m inim al risks
(of dam age) w as developed by cleverly scheduling the
w orks taking into account and com bining the increasing
sheltering effect of the crescent under construction,
the relevant sedim ent transport processes and the
vessel characteristics and m ovem ents.
S H E L T E R I N G E F FE C T O F TH E C R E S C E N T
The w ave clim ate can be characterised as generally
m ild. The m ost frequent and m ost intense storm s
com e from a narrow range of directions in the W -N W
sector throughout the m onths N ovem ber to A pril.
These are locally referred to as Sham alevents.
Typically w ave events w ith significant w ave heights
(H s) of 1-2 m occur rather frequently in this season.
Storm s w ith return periods of 5-10 year w ill produce
w aves in the order of 3.25 m w hilst the 1:100 years
design conditions have been set at H s=4 m . Storm
surges are lim ited to approxim ately 0.5 m above tidal
level (M H H W = CD +1.6 m ).
Execution M ethodology for R eclam ation W orks Palm Island 1
15
Rob de Jong obtained his Master
D egree in Civil Engineering from
the Technical U niversity D elft in
The Netherla nds (2001). Thereafter ,
he joined the Van Oord ACZ
Engineering D epartment whereestimating sand loss during the
construction of Palm Island was his
first major project.
Rob E. de Jong
After graduating in Civil Engineering,
Mark Lindo joined FC de Weger
International C onsultants, where he
was involved in the design and review
of several la rge-scale hydraulic and
civil engineering projects such as
storm-surge barriers and brea kwater
rehabilita tion projects. From 1986-1990
he was Head of the R&D Department
of AC Z Ma rine Contra ctors and also
part-time Scientific Of ficer at
Technical U niversity D elft. Since 1990
he is Head of the Engineering
Department VOACZ.
M ark H . Lindo
Saeed A Sa eed is D irector of P rojects
at P alm Island Developers, D ubai.
Jan Vrijhof is head of the Estimating &
Engineering D epartment at VOA CZ
since 1999. After obtaining his degree
in Civil Engineering (Coastal
Construction) at the Technical
U niversity D elft (1979), he joined thedredging industry. O ver the last 24
years he has worked in many positions
and locations. As project manager he
was responsible for a number of ma jor
dredging projects including one of the
Airport Core P rojects in H ong Kong,
the West K owloon R eclamation
Project. In 2001/2002 he was appointed
interim Project Manager during the
start-up of the Palm Island Project.
Jan Vrijhof
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To determ ine the sheltering effect of the crescent
under construction num erical w ave com putations have
been carried out w ith the 2-dim ensional num erical
w ave m odel SW AN . Since diffraction equations are not
yet m odelled in SW AN , an increased directional w ave
spreading has been applied in the SW AN w ave
com putations. The solution w as tuned using the
diffraction exam ples provided in the Shore Protection
M anual [1] and gave satisfying results for this situation.
The w ave com putations w ere carried out for a
com bination of 6 different w ave directions, 6 differentw ave heights and 18 different lengths of the crescent
under construction. Thus a total of 36 (6 x 6) w ave
com putations have been perform ed for 18 crescent
lengths, hence a total of 648 com putations.The
com pletion dates for the various crescent chainages and
thus crescent lengths w ere derived from the planning
of the breakw ater construction (Figure 3).
The ratio betw een the com puted w ave height and the
boundary w ave height give so-called transform ation
ratios. These transform ation ratios w ere com bined w ith
the nearshore m onthly w ave clim ates to determ ine the
m onthly w ave clim ates for the various stages of thecrescent construction. For each phase of the crescent
construction it w as thus possible to estim ate the
sheltering effect on the average w ave conditions by
com paring the w ave clim ate as com puted w ith and
w ithout the crescent (for each specific location,
relevant m onth and accom panying crescent length).
S E D I M E N T TR A N S P O R T P R O C E S S E S
W hen w aves attack the partially com pleted sand island,
they w ill m ove sand out of the predefined boundaries
of the fronds and trunk (Figure 1). Especially the ends
of the fronds w ill experience losses, since they w ill lose
sand by a com bination of littoral (long-shore) and
perpendicular (cross-shore) sand transport, w hilst they
are the least protected by the crescent during the
construction phase and are m ore vulnerable to adverse
3-dim ensional effects. Furtherm ore, there is no natural
sand supply. The rem oved sand is thus perm anently
lost. This m eans that either the lost sand m ust be
brought back into the profile or m ore sand m ust be
borrow ed. It is therefore very im portant to estim ate
how m uch sand w ill be transported outside the final
profiles by these w aves.
To be able to give a rough assessm ent of the anticipatedsand losses, the sand transport generated by w aves
w as quantified using sim ple but transparent m orpho-
logical m odels. It is em phasised that these m odels
(cross-shore and long-shore) w ere m ade for uniform
straight beaches and sandbars are not valid for areas
such as the end-section of the fronds. These m orpho-
logical m odels are discussed below m aking a distinc-
tion betw een tw o fundam entally different situations:
1. Crest level low er than the w ave run-up level
(w ash-over transport).
2. Crest level above the w ave run-up level
(cross- and long-shore transport)
For the calculations use has been m ade of the
expertise and/or m odels of W L | D elft H ydraulics,
Alkyon, Professor Bijker and VO ACZs in-house
expertise and m odels.
WA S H -O V E R TR A N S P O R T
W hen the crest level is low er than the w ave run-up
level, w aves w ill w ash over the created berm , that can
than be seen as a sand bar. This sand bank w ill reshape
in tim e due to sand transport by w aves and currents.
Three sub-m echanism s for this w ash-over transport
can be distinguished. For each of those system s the
sand grains are m ainly stirred up by the w ave-induced
16
Figure 2. Trailing suction hopper dredger Volvox Atalanta feeding the Palm w ith the Burj-Arab H otel in the background.
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the partially constructed fronds. These increased flow
velocities, in com bination w ith the expected local
w ave clim ate w ere then used to estim ate sedim ent
transport rates at various locations in the project area.
These sedim ent transport rates w ere determ ined using
form ulations of Van Rijn [2], w hich have beenim plem ented in the profile m odel U N IBEST-TC by
W L | D elft H ydraulics.
The calculations show ed that the sand losses during
the w inter are dom inated by the m ost severe storm s.
Especially w hen breaking of the w ave starts the trans-
port rates increase considerably. The actual duration
and severity of these storm s m ay differ considerably
orbital flow s. The origin of the current that is required to
transport the stirred-up sand grains, how ever differs.
These currents are:
1. Tidal current parallel to the shore
2. D ow n-slope directed density currents
3. (Breaking) w ave-induced current
For the assessm ent of the w ash-over transport the
local bathym etry and the com plete subm erged
Palm Island w as taken into account. Tw o levels of
the subm erged island w ere considered: CD 4 m and
CD 6 m . The breakw ater under construction w as not
taken into account. A 3D flow m odel w as used to get
an indication of the increased tidal flow velocities over
Execution M ethodology for R eclam ation W orks Palm Island 1
17
Figure 3. Typical results SW AN w ave transm ission calculations for 6 execution stages of the crescent (offshore significant w ave
height 2.25 m , m ean w ave direction as indicated by the arrow ).
FE B 2002 MA Y 2002
AU G 2002 NO V 2002
FE B 2003 MAY 2003
= non-constructed part breakwater
= constructed part breakwaterH s [m]
15
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from one w inter to the other. Changing the incom ing
w ave height +/10% resulted in a + /300% change in
the calculated transport rates. This m eans that the
associated sand loss m ay differ dram atically from one
w inter to the next.
The berm level also influences the num ber of w aves
that are forced to break. Accordingly, the calculated
transport rates for the berm level of CD 6 m w ere
considerably low er (order 10 tim es) than for the berm
level of CD 4 m .
The calculation also show ed that the sand losses are
dom inated by cross-shore transport. N ot the tidal
current parallel to the shoreline, but the w ave driven
currents (perpendicular to the coastline) over the
partially constructed fronds are dom inant for the
expected sand losses. U nfortunately these transport
rates are very sensitive for the calculated near-bottom
flow velocities, w hich in their turn depend on the
m odelled (sand) bed roughness. The bed roughness
w as not exactly know n. W hen the bed roughness w as
varied betw een 1 cm and 10 cm , the calculated cross-
shore current velocity varied betw een 1 m /s-1.5 m /s.
For this range in current velocity the calculated
sedim ent transport rates differed a factor 10.
The m agnitude of the sedim ent transport is how ever
principally not equal to the losses, since part of the
transported sedim ent w ill resettle in the eventually
required profile.
D uring the construction, the reshaping of the
subm erged sand bars w ere m onitored. The m easure-
m ents indicated that reshaping in case of a crest level
of about CD -4 m only occurs during extrem e conditions
conform theory. The reshaping for this crest level is far
less than in case of a crest level above the w ater level.
The calculated transport rates are very dependent on
the w ave height. The real w ave clim ate outside the
breakw ater during the first w inter period (2001-2002)
w as m ilder than average. This m ild w inter w ave
clim ate w ould result in considerably low er calculatedsand transport since the losses are dom inated by
the highest w aves w ith only a sm all probability of
occurrence. These low transport rates w ere indeed
recorded.
L O N G -S H O R E TR A N S P O R T
For the berm w ith a crest level higher than the run-
up level of the w aves, the w aves are blocked.
Tw o transport directions are distinguished for this
situation: transport parallel to the berm (long-shore)
and transport perpendicular to the berm (cross-shore).
Three m ethods to calculate the long-shore transport
rates w ere com pared.
CERC
The CERC form ula is com m only used to estim ate the
long-shore sedim ent transport. It is an em pirical relation
betw een the w aves and the long-shore transport for
relatively long and straight beaches, w here the along-
shore differences in the breaking w aves are sm all.The CERC form ula can be given as:
(1)
S long-shore sand transport [m 3/s]
A dim ensionless coefficient [-]
Hsig
significant w ave height [m ]
c w ave celerity [m /s]
cg
w ave group velocity [m /s]
n ratio cgto c [-]
angle betw een the w ave
crests w ith the shoreline []
Subscript 1indicates that the dim ensions at a w ater
depth of 10 m are used. Subscript brindicates that
the dim ensions at the breaker line are used.
In the Shore Protection M anual, a value of A = 0.050 is
derived based on m easurem ents on beaches w hich can
be characterised by a D50of about 200 m . At the Palm
Island project location sand of about 400 m is present.
Larger grain result in low er transport rates, the value of
A w as therefore adapted for the project location.
The effect of tidal current on the transport rates cannotbe incorporated in the CERC form ula. The tidal current
velocities at the project location are how ever lim ited to
extrem es of 0.25 m /s to 0.30 m /s, so the error of
neglecting them m ay be lim ited here.
The beach slope strongly effects the distribution of the
long-shore transport across the breaker zone. The effect
on the total long-shore transport is how ever lim ited,
since a steeper slope m eans a narrow er breaker zone,
but on the other hand a m ore (energy dissipating)
intensive breaker zone. The net effect is a slight
increase in the long-shore transport in case of a steeper
slope (Bijker [3]). The effect of neglecting the slope at all
is therefore expected to be lim ited as w ell.
BIJKER (1971) AND VAN RIJN (1993)
Alkyon calculated the long-shore transport for several
incident w ave directions w ith respect to the norm al on
the coastline using the transport m odel U N IBEST-LT.
The follow ing input data w as used:
Slope of 1:4
Constant tidal current of 0.1 m /s
A constant w ater level of CD +1 m
D50= 400 m
Bed roughness = 0.05 m
For the com putations the B ijker [3] and V an Rijn [2]
transport form ula for sand w ere applied.
Terra et A qua N um ber 92 Septem ber 2003
18
( ) (1112
1, sincos = brsig cnHAS
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C R O S S -S H O R E TR A N S P O R T
In case the crest level is above w ave run-up level not
only long-shore transport occurs, but also cross-shore
For several significant w ave heights (H s) w ith a w ave
approach angle of 45the long-shore sand transport
as calculated using the CERC, Bijker and Van Rijn
form ulation are show n in Figure 4.
The long-shore transport rates calculated w ith CERCand B IJKER are of the sam e order of m agnitude
(w ithin the m orphological accuracy factor of 2 to 3).
The VAN RIJN transports are approxim ately 100 tim es
higher than the transports calculated w ith the other
tw o form ulas. For m ore gentle slopes low er transport
rates are found w ith V AN RIJN , w hich is in contradic-
tion w ith the m easurem ents by B ijker [3] that indicate
that the slope has very little im pact on the total long-
shore transport.
As the long-shore sedim ent transport rates as calculated
w ith C ERC and B IJKER are in good agreem ent and the
CERC form ula is sim pler and faster, the CERC form ula
has been used for the determ ination of the resulting
m onthly long-shore sedim ent transports.
Execution M ethodology for R eclam ation W orks Palm Island 1
19
0
1
2
3
4
5
0 1 2 3 4 5
Hs [m]
Long-shoresandtra
nsport
[m3/s]
C E R C
BIJK E R
VAN RIJ N
Figure 4. Calculated long-shore transport rates for a 45 w ave
approach angle.
SWL
Crest line
SWL
Transition zone Active zone B ackshore
ho
hm
Figure 5A . Typical cross-profile before exposure to w aves.
Figure 5B . Typical cross-profile after exposure to w aves.
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transport. In case of cross-shore transport (perpendicular
to the coastline) sand w ill be m oved from the slope
dow nw ard (and to a lesser degree upw ard) and thus a
gentler slope w ill develop in tim e. The crest line w ill
shift in shorew ard direction and sand w ill deposit
outside the required profile.
W ith several cross-shore transport m odels, the shape
of the foreshore (slope) for various w ave conditions and
sand characteristics can be estim ated. Also a prediction
of the tim e-dependent developm ent of the profile can
be m ade. Eventually a m ore or less equilibrium profile
w ill develop.
In case of exposure to w aves, the coastal zone can
be divided in 3 different zones as show n in Figure 5B .
The active zone is the zone that is directly influenced
by w ave action. The transition and backshore zones are
not directly influenced by the w aves.
The upper boundary for the active beach profile hm
theoretically equals the w ave run-up level above still
w ater level. As a result of the (tidal) variation of the still
w ater level, the active zone varies in tim e.
In the breaker zone a lot of sand is in suspension and
considerable changes in the profile m ay take place
w ithin hours or days. Seaw ards of the breaker zone
seasonal profiles can occur as a result of seasonal
changes in the w ave clim ate. Therefore, the actual
low er boundary (hm ) for the active zone is dependenton the tim e scale that is considered.
The cross-shore transport in the active zone is difficult to
quantify. Three m odels have been applied to estim ate
this cross-shore transport:
SWARTS MODEL
In the m odel of Sw art it is assum ed that for a certain
sand grading (characterised by its m edian grain diam eter
D50) and for certain w ave conditions (characterised by
the w ave height and w ave period) an equilibrium profile
w ill develop (as show n in Figure 5B). It takes som e
tim e to develop this equilibrium profile. The rate ofchange of the profile is proportional to the difference in
shape of the existing and the equilibrium profile.
The larger this difference in shape, the faster initial
profile changes takes place.
Sw arts m odel (see [4], [5] and [6]) gives em pirical
relations to determ ine the equilibrium beach profile
and cross-shore sand transport as a function of the
w ave height, the w ave period and the grain size.
These relations are m ainly based on a large num ber of
sm all-scale (m ainly regular w ave) m odel test studies
but are validated w ith prototype m easurem ents.
In [5] also an em pirical relation for the speed at w hich
the equilibrium profile is reached, is given.
For the Palm Island project a translation w as m ade from
the regular w ave relations as presented by Sw art to
irregular w ave conditions. M oreover, the im pacts of the
(tidal) still w ater variations w ere taken into account by
extending the range of the active zone (see Figure 5B ).
This m odified Sw arts m odel enabled the calculation ofthe tim e-dependent beach profile developm ent.
DUROSTA
The estim ated erosion of the cross-shore profile w as
also calculated by A lkyon using the D U RO STA m odel.
This m odel w as developed for com puting the offshore-
directed sedim ent transport of a (steep) dune profile
during storm conditions. The D U RO STA m odel is
therefore assum ed suitable for com puting the erosion
process along the steep initial slopes of the Palm Island.
UNIBEST-TC
U nibest-TC is the cross-shore sedim ent transport
m odule of the U nibest Coastal Softw are Package, a
softw are program developed by W L | D elft H ydraulics.
It is designed to com pute cross-shore sedim ent
transports and the resulting profile changes along any
coastal profile of arbitrary shape under the com bined
action of w aves, long-shore tidal currents and w ind.
The m odel allow s for constant, periodic and tim e series
of hydrodynam ic boundary conditions to be prescribed.
Indicative calculations w ere m ade using the m odified
SW ART, D U RO STA and U N IBE ST-TC m odel to
com pare the results. In this indicative calculations thefollow ing profile w as m odelled:
Crest level CD +3 m
Flat seabed level CD9 m
SW L at CD +1 m (no tidal variations w ere taken into
account)
Initial profile w as assum ed to have a 1:4 slope
D50= 400 m
In Figure 6 the calculated tim e-dependent regression of
the crest line (see Figure 5A) for all three m odels is
plotted.
From Figure 6A it can be seen that especially theestim ated regression speed during the first few days
differs considerably. The reason for this m ight be that
both the U N IBEST-TC and the SW ART m odels are not
derived for the steep initial slopes as are present at the
Palm Island project. Sw art [4] m entioned that the tim e
dependent calculation is inaccurate in the situation of
very steep slopes, but w ithout quantifying w hen an
initial slope is too steep. In the situation of steep slopes
in com bination w ith sm aller w aves, the horizontal
dim ension of the breaker zone becom es sm all w hich
also results in instabilities in the U N IBEST-TC
calculations. D U RO STA w as developed to m odel dune
regression in case of severe storm s. D uring this
regression steep slopes are present. The initial slope
for the m odelled conditions w ill how ever norm ally be
Terra et A qua N um ber 92 Septem ber 2003
20
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(a few hundred m etres) fronds, w hich are affected by
head effects (see next section). This seem s to be
confirm ed by the fact that the sand that w as w ashed
aw ay from the higher parts of the slopes w as not
deposited at the low er part of the slope, but w as totally
rem oved from the profile. The M O D IFIED SW ART
m odel assum es a long strait frond w ith constant long-shore transport. Therefore the sand balance is closed
for this m odel, resulting in m ore sand dow n slope.
S E D I M E N T P R O C E S S E S A R O U N D E N D
S E C TI O NS O F F R O N D S
As m entioned before the sand transport m odels have
been applied for uniform , straight slopes; no boundary
effects have been incorporated. W ith som e engineering
judgem ent the m odels can be applied for the gently
curved fronds, taking into account the changing incident
w ave angle. H ow ever the erosion pattern for the
unprotected ends of the palm tree fronds is m ore
com plicated.
far sm oother (beach profile) than present here, so it
cannot be guaranteed that the m odel is suitable for this
situation.
From Figure 6B , it can be seen that the U N IBEST-TC
m odel results in a far sm aller regression speed than theD U RO STA and M O D IFIED SW AR T m odel. D uring the
erosion, parts of the steep fronds w ill slide into sea due
to the (too) steep slopes and w ave run-up. This process
is not m odelled in U N IBEST. Therefore the erosion rate
for high w aves (w here this sliding occurs frequently) can
be expected to be underestim ated by U N IBEST-TC .
The results for the D U RO STA and M O D IFIED SW ART
are w ithin a m argin of a factor 2-3 that is usually applied
for the accuracy for sedim ent transport calculations.
Both m ethods show considerable sand loss. For practi-
cal reasons the M O D IFIED SW ART m odel w as used to
calculate the profile changes as a result of the local
w ave clim ates as calculated using the SW AN w ave
m odel. These calculations show that the sm aller w aves
are not of im portance for the ultim ate beach profile
w hich develops after a m onth. This profile is prim arily
determ ined by the higher w aves (Hs> 0.5 m ).
As soon as the first frond em erged and a storm took
place, the profile deform ations w ere m easured to verify
the m odels used and update the dum p strategy if
required. The effects of the storm (about 6-8 B eaufort)
as occurred on April 4th 2002, w ith an estim ated dura-
tion of 12 hours and w ith a significant w ave height nearthe central top branch of about 1.25 m , w as used for
this. The disadvantage of this early m easurem ent w as
that the frond length above the w ater w as lim ited to a
few hundred m etres. This m eans that no long straight
uniform beach w as present, resulting in head effects
(see next section). M oreover, the frond of investigation
w as still under construction so that new ly deposited
sand also influenced som e of the cross-shore profiles.
N evertheless, the real cross-shore sections before and
after the storm could be schem atised as presented in
Figure 7. The profiles after the storm w ere also
calculated using the M O D IFIED SW ART m odel (w ith
tidal w ater level variation included) for the first tw osituations w ith no overtopping this m odel can be used
for (Figure 7A and 7B).
The m easured cross-sections after the storm show
that the am ount of sand transported from the profile for
a crest level at the still w ater level (Figure 7C) is far
larger than w hen this crest level is brought up higher
before the storm occurs (Figure 7A and 7B ). The
m easurem ents show that considerable regressions of
the crest line can indeed be expected in relative short
tim e spans. The real deform ations w ere in good
agreem ent w ith the predicted ones. The m easured
regression exceeded the calculated regression a little.
This w as probably caused by the fact that the
m easured profiles w ere taken from relative short
Execution M ethodology for R eclam ation W orks Palm Island 1
21
-50
-40
-30
-20
-10
0
0 500 1000 1500 2000
D uration of exposure to Hsig=1m waves [hours]
Crestlineregression[m]
MODIFIED SWART
U NIB ES T-TC
DUROSTA
Figure 6A. Calculated crest line regression for significant w ave
height of 1 m .
Figure 6B. Calculated crest line regression for significant w ave
height of 3 m .
-150
-125
-100
-75
-50
-25
0
0 20 40 60 80 100 120 140
D uration of exposure to Hsig= 3m wa ves [hours]
Crest
lineregression[m]
MODIFIED SWARTU NIB E ST-TC
DUROSTA
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Terra et A qua N um ber 92 Septem ber 2003
22
Crest level at C D + 2.5 m
-9
-7
-5
-3
-1
1
3
-40 -20 0 20 40 60 80 100
P re-sto rm (A pril 3rd) P ost-sto rm (A pril 5th) P ost-stro m ca lcula ted
Figure 7A. Typical m easured and calculated profile deform ations for crest level at CD +2.5 m .
Crest level at C D + 2.0 m
-9
-7
-5
-3
-1
1
3
-40 -20 0 20 40 60 80 100
P re-sto rm (A pril 3rd) P ost-sto rm (A pril 5th) P ost-stro m ca lcula ted
Figure 7B. Typical m easured and calculated profile deform ations for crest level at CD +2.0 m .
Crest level at C D + 1.0 m
-9
-7
-5
-3
-1
13
-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100
P re-st orm (A pr il 3r d) P ost -st or m (A pr il 5t h)
Figure 7C. Typical m easured and calculated profile deform ations for crest level at CD +1.0 m .
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and cross- and long-shore com putations it becam e
clear that w hen building up the sand body above the
w aterline in unprotected w ater, the cross- and long-
shore transport w ould result in unacceptable sand
losses. D uring a rough w inter, unprotected fronds
could even break through. The profile deform ations are
dom inated by the (short term ) extrem e conditions they
are exposed to.
Frond ends that w ere not sheltered by further offshore-
located fronds w ere subjected to all three erosion
phenom ena: cross-shore, long-shore and w ash-over
transport (see Figure 8). The w ash-over transport takes
sand from the far frond ends to the frond back slope
w here som e kind of sand spit w ill be form ed.The obliquely incom ing w aves w ill generate cross-
shore and long-shore transport although it is expected
that long-shore transport from the far frond tip w ill be
m inim al. First a certain beach length is required for
sand to be suspended over the w ater colum n before
transport takes place. Therefore, it w as expected that
the frond-tips w ould be m ainly subjected to w ash-over
and cross-shore transport. The result thus w ill be that
the frond tips w ill be low ered and stretched.
Further tow ards the spine w here long-shore transport
picks up, the w idth of the frond w ill be reduced as sand
is transported aw ay and deposited in m ore sheltered
w aters behind the previous frond.
It m ay be clear that those sections are very vulnerable
to losses, w hich in turn are hard to predict. Therefore
these ends w ere constructed only w hen protected
sufficiently.
E X E C U T I O N P H I L O S O P H Y
From the com bined results of w ave propagation studies
Execution M ethodology for R eclam ation W orks Palm Island 1
Figure 8. Erosion phenom ena frond ends.
Figure 9. O ptim um production and safety are obtained by keeping corridors and space open for m anoeuvring and constant
m onitoring of the progress.
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W hen keeping the crest level sufficiently deep below
the w ater level, the deform ations only occur during
extrem e storm conditions. W hen staying sufficiently
deep, the overall profile deform ations ow ing to w aveaction w ill be far m ore lim ited than in case of a crest
above w ater.
Since repair of dam aged sections w ould have been
disproportionately expensive, an execution m ethodology
w as developed w hich w as first of all based on
m inim ising the sand transport by w aves and currents.
In addition to this also the follow ing requirem ents w ere
taken into account:
The inevitable sand transport should resettle w ithin
the final profiles as m uch as possible.
O ptim al logistics should be achieved in term s of
cycle tim es and com bination of dum ping andrainbow ing taking into account ship restrictions
(draft, m axim um rainbow distance).
Production capacity and planning should m eet the
tim e of delivery.
Safety of the operations should be ensured.
E X E C U T I O N M E TH O D O L O G Y
Based on the com bined results of w ave propagation
studies and cross- and long-shore com putations,
the client could be convinced that the construction of
Palm Island itself should be closely related to the
progression of the breakw ater, since the protection
provided by it, w as essential. Therefore the follow ing
execution m ethodology w as developed based on the
requirem ents m entioned above, the com putation
results and the progression schedule of the breakw ater.
D uring first w inter
Especially at the beginning of the first w inter,
starting at the end of 2001, the sheltering of the
partly constructed breakw ater w as very lim ited
(see Figure 10). The profiles therefore rem ained
below the CD4 m during the first w inter, since this
results in low er transport rates then w hen com ing
above w ater.
The w idth of the fronds at this stage w as kept
slightly sm aller than required to allow som e
reshaping w ithout m aterial ending up outside the
eventual required profile.
In betw een the sand bars, corridors and space form anoeuvring is kept in order to allow the dredgers
to operate in a safe and efficient m anner during the
construction of the fronds.
The TS H D had such dim ensions that this sand could
be dum ped and did not have to be rainbow ed.
After first w inter
Based on scheduled progress of the breakw ater and
offshore w ave clim ate, the w ave and cross- and
long-shore sand transport m odel w ere used to
determ ine w hich fronds w ere sheltered enough at
w hat stage. This w ay the fronds w ere given free to
construct above w ater one by one, starting at the
m ost protected top end of the Palm .
The sequence of the filling w as anti-clockw ise from
Terra et A qua N um ber 92 Septem ber 2003
24
Figure 10. Satellite pictures of Palm Island show ing the progress at approxim ately 3-m onth intervals.
8 D EC 2001 22 M AR 2002 26 jun 2002
22 SEP 2002 7 JAN 2003 25 M AR 2003
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Van O ord ACZ determ ined the right strategy of staying
underw ater the first w inter and only raised those
fronds above w ater w hich had sufficient protection
from the crescent breakw ater from then on.
References
[1]Coastal Engineering Research Center (1984).
Shore Pro tection M anual. U .S G overnment Printing Office,
Washington, DC, USA.
[2]Rijn, L.C. van (1993).
Pri nciples of Sediment T ransport in Rivers, Estuaries
and Coastal Seas. Aqua Publications, Amsterdam,
The Netherlands.
[3]Bijker, E.W., (1971).
Longshore transport computations , Journal of
Waterways, Harbour s and Coastal Engineering D ivision,
Vol. 97, No. WW4.
[4]Swart,J.H., (1974).
Off shore sediment transport and equilibrium beach pro-
files, report on model investigations . Report number M 918,
Part II .
[5]Swart, J .H., (1976).
Predictive equations regarding coastal transports,
ASCE Proceedings 15th Conference on Coastal Engineering.
H awaii. Vol. II . Cha pter 66.
[6]Graaff, J. van de, (1978).
Transport of sand perpendicular t o the coast.
Cour se Coastal Dynamics and Coastal Protection CT .KK5,
Foundation of Postgraduate Education for Civi l Engineering.
D elft, The Netherlands. (in Dutch).
W est to East as to allow the TSH D to reach the
reclam ation fronds via the anticipated corridor in the
Eastern part of the crescent breakw ater w ith m ini-
m um obstruction from already constructed sand fill
allow ing m axim um production of each dredger in a
safe m anner. O ptim al logistics in term s of cycle tim es and
com bination of placem ent/rainbow ing has also been
achieved, by im plem enting day-to-day survey results
into the D G PS tracking system . In this w ay safe
underw ater filling w as m ade possible, leaving open
sufficient space to m anoeuvre the ships.
From the satellite pictures in Figure 10, w hich w ere
taken w ith a tim e interval of about three m onths, it can
be seen that the planned m ethodology has indeed
been applied. O n the first tw o pictures even the under-
w ater berm s can be seen from space. It is also clear
that the fronds are constructed one by one starting at
the top of the Palm . O nly the top of the trunk w as
raised above the w ater before schedule. This w as done
at the request of the client.
Conclusions
A thorough study of the m echanism s responsible for
possible sand losses from the reclam ation area prior to
execution of the w orks gave a good insight in the risks
and provides tools for defining the best strategy for the
execution of the w orks.
Cross-shore transport resulted in considerable slope
deform ations, once the reclam ation area is above
w ater even w ith lim ited w ave action during a lim ited
tim e, w hich is in accordance w ith the calculations
carried out.
These deform ations are even m uch m ore severe, if the
crest level is raised to just below the w ave run up level.
Therefore, if going above w ater, the final crest level
should be reached as soon as possible.
The frond ends experienced sim ilar but m ore severedeform ations (com bination w ash-over/long-shore/cross-
shore transport) as anticipated.
Reshaping ow ing to w ash-over transport w ith a crest
level of about CD 4 m only occurred during extrem e
conditions conform theory. The reshaping w as
how ever far less than in case of a crest level above the
w ater level.
Especially at the beginning of the w inter the sheltering
of the partly constructed breakw ater w as very lim ited
and the exposure of the fronds w ould have been large.
Since the real reshaping in case of a crest at least
CD4 m w as indeed considerably less than in case of a
crest above the w ater level, it can be concluded that
Execution M ethodology for R eclam ation W orks Palm Island 1
25
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