land Reclamation Procedures

7/26/2019 land Reclamation Procedures

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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

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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

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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


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.


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.


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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


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


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


9/12


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 .


-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 .


-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 .


10/12

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


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.


11/12

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


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


12/12

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


25

Documents

land Reclamation Procedures