Cost of beach maintenance in the Gulf of Cadiz (SW Spain)

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  • .Coastal Engineering 42 2001 143153www.elsevier.comrlocatercoastaleng

    /Cost of beach maintenance in the Gulf of Cadiz SW SpainJuan J. Munoz-Perez a,), Belen Lopez de San Roman-Blanco b,

    Jose M. Gutierrez-Mas c, Luis Moreno d, Gabriel J. Cuena ea Demarcacion de Costas en Andalucia-Atlantico, Ministerio de Medio Ambiente, cr Marianista Cubillo, 7, 11071 Cadiz, Spain

    b Coastal Department, HR Wallingford, Howbery Park, Wallingford OX10 8BA, UKc Facultad de Ciencias del Mar, Uni. de Cadiz. CASEM, 11540, Puerto Real, Spain

    d Ministry of Enironmental Protection, Pza. San Juan de la Cruz, srno.-28071 Madrid Spaine Sericio de Costas de Huela, Cr Rico, 15 21071, Huela, Spain

    Received 3 February 2000; received in revised form 16 August 2000; accepted 7 September 2000

    Abstract

    Beach erosion problems have been solved by adding sand to the beaches along the Gulf of Cadiz. The Gulf is located inSW Spain between the Portuguese border and the Strait of Gibraltar. During the last decade, more than 12=106 m3 of sandhave been nourished in 38 restoration operations carried out on 28 beaches. The main characteristics of the nourishment

    .campaigns year, volume, budget, transport method, sand data, etc. are presented. Location of sand borrow sites anddistance to the beaches are also shown. Monitoring programs have been performed in order to calculate sediment loss rates.These results have been related to the beach length, the berm width and the budget in order to obtain a variety ofrelationships for maintenance cost as, for example, the total annual cost for each beach. This information is very useful whendeveloping a strategy in coastal zone management. Furthermore, at least in reef-protected beaches, small yearly renourish-ments similar to the yearly losses, instead of greater nourishments performed with a periodicity of many years, lead to aneconomical saving, as well as to a better use of the natural resources. q 2001 Elsevier Science B.V. All rights reserved.

    Keywords: Beach nourishment; Coastal zone management; Beach erosion; Gulf of Cadiz

    1. Introduction

    The coastline of the Gulf of Cadiz has been inrecession for at least the last century. Subsidencephenomena, sea level rise or manmade barriers, asgroin constructions like the breakwater built in thePortuguese bank of the Guadiana River mouth, arethe causes.

    ) Corresponding author. Fax: q34-56-276-449. .E-mail address: juanjose.munoz@uca.es J.J. Munoz-Perez .

    Analysis of field data and aerial photographs overthe last half century show that the coastline hassuffered a recession rate of approximately 1 mryearin some points of the Spanish Southwest Atlantic

    .coast Munoz-Perez and Enriquez, 1998 .Because ofthe erosion, the Spanish Coastal Authority, in thepast dependent upon the Ministry of Public Worksand presently belonging to the Ministry of the Envi-ronmental Protection, decided to begin a coastalprotection program.

    Erosion is caused by a negative sediment budgetand, at the present, adding sand to the physiographic

    0378-3839r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. .PII: S0378-3839 00 00054-5

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153144

    unit appears to be the most natural way to solve theerosion problem. Some beach nourishment projectshave sometimes been complemented with the con-struction of some permeable and short groins ad-justed to the beach profile. This was only carried outwhen an important reduction of the annual nourish-

    ment requirement justified it Munoz-Perez and.Gutierrez-Mas, 1999 .

    Monitoring the behaviour of several beaches sincethe first nourishment allowed for a comparison withprevious works, as well as to establish real meanrates of erosion for each job and predict renourish-ment requirements in the future. Other countrieshave been monitoring for a much greater length of

    time see amongst others, Wijnberg, 1995; Lin and.Sasso, 1996; Shak and Ryan, 1996 , and compila-

    tions of information on this topic have also beenperformed. For instance, a database that documentsbeach nourishment episodes, which have occurred on

    .the US Eastern shoreline from New York to Florida .was presented recently by Valverde et al. 1999 .

    Also, the economic importance of beaches and their .tourism has been examined by Houston 1995, 1996 .

    The federal spendings for shoreline preservation andthe revenues for the government and benefits for the

    .national economy have been compared King, 1999 .Nevertheless, the yearly cost of the different beachnourishment programs is a little published parameteryet. The range of this value could prove to be veryinteresting in providing a better design tool for futurenourishment projects and to decide whether theyshould be carried out or not.

    The main aim of this paper is to describe amorphological and economical evaluation of thebeach nourishment maintenance strategy carried outin the Gulf of Cadiz during the 1990s.

    2. Data compilation

    The coastline which is to be studied is locatedalong the Gulf of Cadiz, facing the Atlantic Oceanon the southwest coast of Spain, between the Guadi-ana River mouth and the Strait of Gibraltar. Ageneral view of the area and the location of the 28beaches, where the 38 nourishments were carriedout, are presented in Fig. 1. The region has a mesoti-dal range with a medium neap to spring variation

    .1.203.30 m . Most of the beaches are composed of .fine-medium sand D s250 mm consisting of50

    8595% quartz and 515% calcium carbonate. Inmany beaches, the typical profiles intersect a sub-merged reef and, consequently, are not sand rich.Wave decay due to the wave breaking over thesubmerged reef, the changes on the resulting beachprofile shape and the stability of the beach were

    .discussed by Munoz-Perez et al. 1999a .Wave climate data have been collected by two

    waverider buoys included in the Spanish Wave .Recording Network known as REMRO . The first

    of these buoys, named ASevilleB, was installed infront of the Guadalquivir river mouth anchored at adepth of y12 m. The second one, named ACadizB,was anchored at a depth of y22 m, 3 miles seawardfrom a rocky shoal in front of the city of Cadiz.Statistically elaborated data are available in the Mar-itime Works Recommendations ROM 0.391 .MOPT, 1991 .

    Geophysical campaigns have been performed overthe entire width of the coast in order to identify

    submerged borrow sand areas Esgemar, 1991; Ge-.omytsa, 1991a,b, 1994 . Soundings of the sea bottom

    were carried out to check the thickness of sedimentdeposits. Location of borrow sites and dredged vol-umes are shown in Fig. 2. A large number of surfacegrab sediment samples were also collected to iden-tify the borrow sand characteristics.

    A conventional topographic surveying techniquewas employed in the aerial part of the beach. Adifferential leveling with reference to a benchmarklocated in the seaside promenade was performed atthe hour of the spring low tide. It was possible tosurvey up to elevation y1.00 m. Due to the fact thatbathymetric contours were made with an echosounderon boat and differential global position system .DGPS at the spring high tide, an area of overlapwith the aerial topography relates both surveys to thesame datum or Azero levelB. For a comprehensivedescription about the accuracy of the method, see

    .Munoz-Perez 1995 . The total cost of the monitor-ing works was US$450,000 during the last decade,only 1.2% of the beach restoration investments.

    Currents were also measured. The final aim ofthese measurements being the calibration of themathematical models developed to study differentaspects of the coastline evolution.

  • ()

    J.J.Munoz-Perez

    etal.r

    CoastalEngineering42

    2001143

    153

    145

    Fig. 1. Location of the 28 beaches renourished in the decade 19891998.

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153146

    Fig.

    2.Lo

    catio

    noft

    hesa

    nd

    borro

    wsit

    esin

    the

    Gul

    fofC

    adiz

    .

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153 147

    Once the beach restoration was finished, newbathymetric surveys were carried out in the majorityof cases. These were performed once per year for, atleast, a period of 2 years. Hence, profile comparisonscould be made and erosion rates estimated.

    3. Results and discussion

    Data collected for the 38 beach nourishmentsperformed during the last decade are presented inTable 1. From left to right, the data specified are thefollowing.

    v .Date year and name of the beach whererestoration works were carried out. Successiverestorations performed on the same beach are shownby different ordinal numbers. So, Fuentebravia,Fuentebravia II and Fuentebravia III would note thefirst, second and third nourishment projects. Therewere 38 sand-pouring operations accomplished on 28beaches from 1989 to 1998.

    v Volume of sand poured in the nourishment,which was generally surveyed in the hopper and isexpressed in cubic meters. Total volume was 12.0=

    6 3 10 m with a maximum in Victoria Beach 2.0=6 3.10 m .v Final budget, in US$, where Spanish taxes as

    .16% value added tax VAT are not included andcost of hard structures such as groins, when neces-sary, are not considered. All costs were adjusted forSpanish inflation factors and converted to 1999 dol-lars. Global investment was US$37.5=106, that isUS$3.7=106ryear.

    v Transport method ground transport by trucks or.maritime dredging by trail suction is specified.

    Ground transport by trucks, from adjacent beaches ordunes, was performed to nourish 13 beaches. Thevolume transported was 6.5% of the total volume,while the cost was only the 5.5% with an averagevalue of US$2.7rm3. Distances vary from 0.4 to11.2 km with 4.2 km as the average value. On theother hand, volume dredged had an average cost ofUS$3.1rm3 and an averaged distance of 10.9 kmwithin a range from 0.5 to 35 km.

    v The main characteristics of the sediment arealso presented. It refers to the mean diameter, inmicrons, of the borrow sand which is very similar to

    the native one. Three different areas can be distin-guished along the coastline according to the grainsize. The western one, between Guadiana andGuadalquivir rivers, has a median grain size diameterwhich varies from 350 to 670 mm with an averagevalue of 450 mm. Sand size is finer betweenGuadalquivir river and the Strait of Gibraltar: D s50280 mm. A coarser grain size of 1000 mm is presentin Guadalquiton beach, in the Mediterranean Sea.Weight of the siltclay fraction is negligible, about1.6%. The percentage of the bioclastic fraction, i.e.the part composed of flat shell fragments which are,

    usually, very quickly transported seawards Munoz-.Perez et al., 1999b , is also indicated. This value

    varies extensively, from 3% to 32% with an averageof 12.9%.

    v The type of profile is specified: reef supportedor sand rich.

    v Location of the borrow site submerged or. .emerged and distance kilometer from the borrow

    area to the beach nourishment.Working with the previously described character-

    istics and along with the beach dimension, a new setof parameters related to the maintenance manage-ment are developed. These values presented in Table2 are as follows.

    v The erosion rate is computed by averaging thelosses after nourishments and based on total beachprofile measurements, throughout a monitoring pe-riod of at least two years. It is expressed in cubicmeters per year. These data are not specified in 14nourishment operations because no monitoring workswere performed.

    v Length of the beach where restoration workswere carried out and berm width achieved with thenourishment. Both of these values are expressed inmeters. The block diagram shown in Fig. 3 clarifiesthe meaning of beach length and berm width.

    v Sediment loss per year per longitudinal meter,obtained by dividing the yearly erosion rate by thebeach length. Average value is 37.5 m3rmryear.Greatest values correspond to Aculadero, Fuente-

    bravia and La Pena beaches 58, 90 and 1083 .m rmryear, respectively .

    v3 .Unit cost of sand US$rm , id est, the relation-

    ship between the real total budget and the fill volumeof the nourishment. The average value is aboutUS$3rm3 with a maximum of US$6.7rm3.

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153148

    Tabl

    e1

    Bea

    chnouris

    hmen

    tin

    the

    Gulf

    of

    Cadi

    zin

    the

    last

    deca

    de

    .Y

    ear

    Beach

    nam

    eV

    olu

    me

    Tota

    lbud

    get

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    spor

    tSa

    nd

    Kin

    do

    fpro

    file

    Bo

    rro

    ware

    aD

    ista

    nce

    km3

    .

    .

    mU

    S$m

    eth

    odD

    Perc

    en

    tPe

    rcen

    tsh

    ell

    50

    .m

    msi

    ltfr

    actio

    n

    1989

    Cast

    illa

    Beach

    1,69

    0,00

    03,

    813,

    333

    Trail

    suctio

    n60

    01.

    5Sa

    nd

    rich

    Pon

    ien

    tejet

    ty6.

    319

    90La

    An

    tilla

    1,30

    0,00

    05,

    333,

    000

    Trail

    suctio

    n50

    01.

    3Sa

    ndric

    hR

    om

    pidi

    llosp

    it6.

    119

    90La

    Cachu

    cha

    82,0

    3050

    5,40

    6Tr

    ucks

    300

    2.6

    8Sa

    nd

    rich

    San

    Pedr

    om

    ou

    th3.

    819

    91La

    Cale

    ta41

    ,440

    81,0

    32Tr

    ucks

    310

    3.6

    3R

    eefs

    upp

    orte

    dC

    ort

    adu

    rabe

    ach

    1.4

    1991

    Vic

    toria

    2,00

    0,05

    05,

    527,

    742

    Trail

    suctio

    n25

    02.

    411

    Sand

    rich

    an

    dC

    adi

    zC

    han

    nel

    5.2

    reefs

    upp

    orte

    d19

    91St

    a.

    Maria

    delM

    ar

    306,

    360

    557,

    419

    Trail

    suctio

    n35

    01.

    516

    Reefs

    upp

    orte

    dC

    adi

    zH

    arb

    ou

    ren

    tran

    ce

    6.0

    1991

    LaPe

    na67

    ,035

    216,

    774

    Tru

    cks

    230

    1.2

    29R

    eefs

    upp

    orte

    dV

    ald

    evaq

    uero

    sdu

    ne11

    .2

    1991

    Can

    osde

    Meca

    16,1

    0339

    ,914

    Truc

    ks23

    01.

    710

    Ree

    fsupp

    orte

    dTr

    afal

    gard

    une

    2.4

    1991

    Ro

    San

    Pedr

    o23

    ,159

    59,6

    49Tr

    ails

    uctio

    n22

    01

    15R

    eefs

    upp

    orte

    dSa

    nPe

    dro

    mouth

    0.5

    1992

    Reg

    la50

    2,00

    02,

    650,

    000

    Trai

    lsuctio

    n25

    02.

    58

    Reefs

    upp

    orte

    dPl

    acer

    San

    Jaci

    nto

    4.2

    1992

    Can

    osde

    Meca

    II12

    4,23

    426

    3,61

    9Tr

    ucks

    230

    1.5

    12R

    eefs

    upp

    orte

    dTr

    afal

    garD

    une

    2.4

    1992

    Fuen

    tebr

    avia

    75,0

    0021

    2,74

    8Tr

    ucks

    390

    0.3

    9R

    eefs

    upp

    orte

    dR

    ota

    Har

    bour

    0.9

    1993

    Car

    men

    23,1

    5043

    ,413

    Truc

    ks22

    00.

    515

    Sand

    rich

    Bar

    bate

    Har

    bour

    0.6

    1993

    Poni

    ente

    131,

    819

    187,

    062

    Truc

    ks39

    00.

    38

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    rich

    Atu

    nara

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    ,794

    33,7

    27Tr

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    250

    1.2

    12Sa

    ndric

    hC

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    tem

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    2.0

    1993

    LaPe

    naII

    170,

    000

    413,

    641

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    ks24

    01

    31R

    eefs

    upp

    orte

    dV

    alde

    vaqu

    eros

    dune

    11.2

    1993

    19

    94La

    Barr

    osa

    463,

    607

    1,24

    2,56

    4Tr

    ails

    uctio

    n29

    03.

    415

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    rich

    Plac

    erde

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    a25

    .119

    94Fu

    ente

    brav

    aII

    275,

    133

    540,

    733

    Trai

    lsuctio

    n28

    02.

    512

    Ree

    fsupp

    orte

    dC

    adiz

    Cha

    nnel

    8.1

    1993

    19

    94El

    Acula

    dero

    172,

    448

    267,

    613

    Trai

    lsuctio

    n39

    00.

    517

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    fsupp

    orte

    dC

    adiz

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    nnel

    4.5

    and

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    16,2

    1640

    ,516

    Truc

    ks22

    00.

    812

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    rich

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    bate

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    bour

    0.4

    1994

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    III

    496,

    000

    1,02

    1,93

    6Tr

    ails

    uctio

    n30

    03.

    514

    Ree

    fsupp

    orte

    dPl

    acer

    deM

    eca

    4.0

    1994

    Fuen

    tede

    lGal

    lo39

    9,00

    01,

    037,

    419

    Trai

    lsuctio

    n23

    02

    18R

    eefs

    upp

    orte

    dPl

    acer

    deM

    eca

    13.0

    1994

    Isla

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    tina

    330,

    000

    887,

    000

    Trai

    lsuctio

    n35

    01.

    3Sa

    ndric

    hIs

    laC

    ristin

    aH

    arb

    our

    4.1

    1995

    LaB

    ota

    930,

    000

    3,18

    7,00

    0Tr

    ails

    uctio

    n67

    01.

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    20Sa

    ndric

    hPo

    nien

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    13Ju

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    sI

    1995

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    12,7

    7840

    ,516

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    230

    1.5

    32R

    eefs

    upp

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    evaq

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    .219

    95El

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    mpi

    dillo

    7,73

    511

    ,581

    Tru

    cks

    220

    111

    Reefs

    upp

    orte

    dR

    ota

    Harb

    our

    0.6

    1996

    LaC

    ost

    illa

    197,

    000

    948,

    746

    Trail

    suctio

    n38

    03

    9Sa

    nd

    rich

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    zC

    han

    nel

    11.0

    1996

    Acu

    lade

    roII

    75,6

    2524

    0,94

    6Tr

    ail

    suctio

    n25

    03.

    514

    Reefs

    upp

    orte

    dC

    adi

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    han

    nel

    4.5

    1996

    LaC

    ost

    illa

    II94

    ,566

    292,

    351

    Trail

    suctio

    n35

    01.

    28

    San

    dric

    hC

    adi

    zC

    han

    nel

    11.0

    1996

    Fuen

    tebr

    av

    aII

    I13

    4,80

    835

    1,67

    5Tr

    ail

    suctio

    n30

    03

    11R

    eefs

    upp

    orte

    dC

    adi

    zC

    han

    nel

    8.1

    1996

    Maz

    agon

    425,

    000

    1,40

    6,36

    4Tr

    ails

    uctio

    n35

    02

    Sand

    rich

    Hue

    lva

    Har

    bour

    7.2

    1996

    Mat

    alas

    cana

    s12

    5,00

    041

    3,63

    6Tr

    ails

    uctio

    n35

    02

    Sand

    rich

    Hue

    lva

    Har

    bour

    18.3

    1997

    LaA

    ntill

    aII

    300,

    000

    2,00

    0,00

    0Tr

    ails

    uctio

    n35

    00.

    3Sa

    ndric

    hH

    uelv

    aH

    arbo

    ur35

    .119

    97St

    a.M

    aria

    delM

    arII

    60,1

    8122

    8,38

    1Tr

    ails

    uctio

    n30

    00.

    310

    Ree

    fsupp

    orte

    dC

    adiz

    Cha

    nnel

    6.0

    1997

    LaB

    arro

    saII

    30,0

    0014

    2,57

    5Tr

    ails

    uctio

    n30

    00.

    210

    Sand

    rich

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    erde

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    a25

    .019

    98C

    ampo

    soto

    .73

    7,00

    02,

    578,

    453

    Trai

    lsuctio

    n30

    00.

    53

    Reefs

    upp

    orte

    dPl

    acer

    deM

    eca

    31.5

    1998

    Punt

    aC

    ando

    r19

    ,211

    100,

    373

    Trai

    lsuctio

    n32

    00.

    58

    Reefs

    upp

    orte

    dC

    adiz

    Cha

    nnel

    14.2

    1998

    Gua

    dalq

    uito

    n17

    5,00

    053

    8,40

    0Tr

    ails

    uctio

    n10

    000.

    910

    Sand

    rich

    Gua

    diar

    om

    outh

    0.8

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153 149

    Tabl

    e2

    Mai

    nten

    ance

    cost

    of

    beac

    hes

    inth

    eG

    ulf

    of

    Cadi

    z

    Yea

    rB

    each

    nam

    eSe

    dim

    ent

    Beach

    Ber

    mSe

    dim

    entl

    ossr

    Co

    stM

    ateria

    lM

    ain

    ten

    an

    ce

    loss

    len

    gth

    wid

    thbe

    ach

    len

    gth

    ofs

    an

    dsu

    pply

    co

    st3

    33

    .

    .

    .

    .

    .

    mr

    year

    mm

    mr

    year

    rm

    US$

    rm

    Vol

    um

    er

    beac

    hV

    olu

    mer

    dry

    Per

    un

    ito

    fPe

    ru

    nit

    of

    Tota

    l3

    32

    .

    .

    .

    len

    gth

    mr

    msu

    rface

    mr

    mbe

    ach

    len

    gth

    dry

    surf

    ace

    US$

    rye

    ar2

    .

    .

    US$

    rye

    arr

    mU

    S$r

    m

    1989

    Cast

    illa

    Beach

    100,

    000

    2000

    110

    502.

    2684

    57.

    711

    317

    .422

    6,00

    019

    90La

    An

    tilla

    50,0

    0035

    0050

    144.

    1037

    17.

    459

    30.2

    205,

    000

    1990

    LaC

    achu

    cha

    560

    356.

    1614

    64.

    219

    91La

    Cale

    ta36

    020

    1.96

    115

    5.8

    1991

    Vic

    toria

    70,0

    0035

    0070

    202.

    7657

    18.

    255

    23.0

    193,

    200

    1991

    Sta.

    Maria

    delM

    ar

    30,0

    0060

    045

    501.

    8251

    111

    .391

    20.7

    54,6

    0019

    91La

    Pena

    65,0

    0060

    018

    108

    3.23

    112

    6.2

    350

    20.0

    209,

    950

    1991

    Can

    osde

    Meca

    750

    32.

    4821

    7.2

    1991

    Ro

    San

    Pedr

    o37

    08

    2.58

    637.

    8

    1992

    Reg

    la35

    ,000

    1500

    3823

    5.28

    335

    8.8

    123

    46.7

    184,

    800

    1992

    Can

    osde

    Meca

    II75

    024

    2.12

    166

    6.9

    1992

    Fuen

    tebr

    avia

    725

    142.

    8410

    37.

    419

    93C

    arm

    en50

    0012

    003

    41.

    8819

    6.4

    812

    .594

    0019

    93Po

    nien

    te70

    023

    1.42

    188

    8.2

    1993

    ElPa

    lmar

    800

    41.

    7923

    5.9

    1993

    LaPe

    naII

    85,0

    0080

    030

    106

    2.43

    213

    7.1

    259

    17.2

    206,

    550

    1993

    19

    94La

    Barr

    osa

    45,0

    0012

    0040

    382.

    6838

    69.

    710

    126

    .112

    0,60

    019

    94Fu

    ente

    brav

    aII

    65,0

    0072

    560

    901.

    9737

    96.

    317

    612

    .512

    8,05

    0

    1993

    19

    94El

    Acula

    dero

    35,0

    0060

    040

    581.

    5528

    77.

    291

    11.1

    54,2

    5019

    94La

    Hie

    rbab

    uena

    4000

    730

    35

    2.50

    227.

    414

    17.9

    10,0

    0019

    94C

    anos

    deM

    eca

    III

    26,5

    0075

    070

    352.

    0666

    19.

    473

    19.5

    54,5

    90

    1994

    Fuen

    tede

    lGal

    lo52

    ,000

    1200

    3043

    2.60

    333

    11.1

    113

    28.7

    135,

    200

    1994

    Isla

    Cris

    tina

    40,0

    0018

    0040

    222.

    6918

    34.

    660

    12.3

    107,

    600

    1995

    LaB

    ota

    50,0

    0042

    0040

    123.

    4322

    15.

    541

    18.7

    171,

    500

    1995

    Chi

    ca12

    025

    3.17

    106

    4.3

    1995

    ElR

    ompi

    dillo

    4000

    800

    25

    1.50

    104.

    87

    7.5

    6000

    1996

    LaC

    ostil

    la15

    ,000

    1200

    2013

    4.82

    164

    8.2

    6039

    .272

    ,300

    1996

    Acu

    lade

    roII

    11,0

    0060

    020

    183.

    1912

    66.

    358

    19.8

    35,0

    9019

    96La

    Cos

    tilla

    II12

    0010

    3.09

    797.

    919

    96Fu

    ente

    brav

    aII

    I62

    ,000

    725

    3186

    2.61

    186

    6.0

    223

    15.7

    161,

    820

    1996

    Maz

    agon

    30,0

    0015

    0028

    203.

    3128

    310

    .166

    33.1

    99,3

    00

    1996

    Mat

    alas

    cana

    s30

    ,000

    700

    1843

    3.31

    179

    9.9

    142

    33.1

    99,3

    00

    1997

    LaA

    ntill

    aII

    2000

    406.

    6715

    03.

    819

    97St

    a.M

    aria

    delM

    arII

    10,0

    0060

    012

    173.

    7910

    08.

    463

    32.2

    37,9

    0019

    97La

    Bar

    rosa

    II12

    003

    4.75

    258.

    319

    98C

    ampo

    soto

    .45

    ,000

    3000

    2815

    3.50

    246

    8.8

    5230

    .915

    7,50

    019

    98Pu

    nta

    Can

    dor

    200

    145.

    2296

    6.9

    1998

    Gua

    dalq

    uito

    n50

    030

    3.08

    350

    11.7

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153150

    Fig. 3. Block diagram clarifying some concepts of a beach nourishment.

    v Restoration volume divided by the beach length 3 .m rm .

    v2Volume requirements to get 1 m of berm or

    dry beach.v Maintenance cost in different units: price per

    year for every meter length beach, price for everysquare meter of berm and finally, the annual mainte-nance cost of each beach.

    Despite the importance of the annual total costparameter, the most adequate parameter to comparecosts between different beaches is the annual mainte-

    .nance cost per unit of beach length US$ryearrm .If one of the main goals of a nourishment scheme isto maintain the dry surface of the beach for touristexploitation, this parameter is very useful in decidingwhere to best invest public funds. In our particularcase, these values normally range from US$7 toUS$142ryearrm with an average of US$100r

    yearrm and only La Pena and Fuentebravia restora-tions exceed US$150ryearrm reaching a maximumof US$350ryearrm.

    It is noteworthy that the biggest erosion rate wasobserved directly after a big nourishment in reef-sup-

    .ported beaches. As Munoz-Perez et al. 1999ashowed, no equilibrium beach profile is possiblewithin a distance less than 30100 m from the edgeof the reef. So, as you feed more sediment, moresand is transported quickly seawards. Perched orreef-protected beaches, whose profiles are not sandrich, loose sand rapidly when the volume dumpedsurpasses the geometric limits set down by the mor-

    phological characteristics Munoz-Perez et al.,.1999a . It is also worth noting the fact that a reduc-

    tion in the volume of the successive restorations ofthe beaches of Santa Maria del Mar Beach and of

    Aculadero Beach from 306,000 to 60,181 and from

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153 151

    3 .172,448 to 75,625 m , respectively was related to asubstantial reduction in the annual rates of erosionfrom 30,000 to 10,000 and from 35,000 to 11,000

    3 .m ryear , while no significant changes in waveclimate were observed during the monitoring period.The former figures were obtained by profile compar-isons carried out with the yearly bathymetric surveysperformed during the 2 years ensuing the nourish-ments.

    For economical studies, it would be important toknow whether a relationship exists between size of

    .job total cubic meters of project and unit price. Inorder to accomplish this, Fig. 4 was prepared withthe purpose of displaying the actual cost in US$rm3versus the nourishment volume, making a clear dis-tinction between the contributions made by truck andtrail suction. In the first place, it is noteworthy to

    state that the volumes transported by truckloads donot surpass 200,000 m3. Their price, with only oneexception, fluctuates between 1 and 3 US$rm3 al-though bearing no defining trend. On the other hand,two separate groups can be defined amid the nour-ishments carried out by trail suction dredgers. Thefirst one reaches up to 600,000 m3 of sand. Thoughthe costs are very spread out, a simple linear fit bythe least squares method shows a decreasing ten-dency. The same tendency, the lessening of costs asvolumes increase, though subject to a slighter disper-sion rate, can be observed in the existing rangebetween 600,000 and 2,000,000 m3.

    Fig. 5 shows the volume of sand placed on thebeaches per year and, also, the annual cost of thenourishment in the last decade. The rather largenourishments and investments in the initial years are

    3.Fig. 4. Cost of sand US$rm in different beach restorations versus their nourishment volumes.

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153152

    3. . .Fig. 5. Sand nourishments m and investments US$ per year in the Gulf of Cadiz 19891998 .

    because of the need to replace the existing deficit. Inlater years, the need for sand has reduced and stabi-lized about 1=106 m3 of sand corresponding toUS$3=106ryear.

    4. Conclusions

    The data collected from the 38 beach nourishmentcampaigns that have been carried out on 28 beaches

    .in the Gulf of Cadiz SW Spain during the lastdecade are presented. Within the values of the differ-ent parameters demonstrated, it is important to pointout that the average annual volume nourished tomaintain more than 400 km of coastline was 1.2=

    106 m3. This imposed an averaged cost of US$3.75=106 a year, which has to be related to the enor-mous income that tourism yields in the area everyyear.

    The cost of transport by truck is slightly lowerthan the transport by dredger and dumping through

    3.tubes US$2.7 against US$3.1rm , although thevolume carried by the truck was only 6.5% of thetotal.

    The relationships between the costs and the geo-metric characteristics of the beach suggest manyparameters, all of them of great help when attempt-ing to make decisions on sustainable and economicalmaintenance of the beaches within the framework ofcoastal zone management. Nevertheless, the annual

  • ( )J.J. Munoz-Perez et al.rCoastal Engineering 42 2001 143153 153

    maintenance cost per unit of beach length appears tobe the most useful parameter when comparing thedifferent investments done. Its average value be-comes US$100ryearrm, but with a great range ofscatter: from US$7 to US$350ryearrm.

    Substantial decrease in the sand volumes nour-ished within successive restorations carried out oncertain beaches led to drastic reductions in the yearlyerosion rates. In addition, it may be concluded that,at least in reef-protected beaches, small yearly re-nourishment, similar to the yearly losses, instead ofgreater nourishment performed with a periodicity ofmany years, leads to economical savings, as well asto a better use of the natural resources.

    Finally, it is noteworthy to point out that a de-creasing tendency in the cost per unit of the sandpoured can be acknowledged as the nourishmentvolume increases, this being specially noticeable inthose volumes superior to 600,000 m3.

    Acknowledgements

    The authors wish to acknowledge the contributionof the Federal Coastal Authority of the Ministry ofEnvironmental Protection, for their support through-out the data collection campaigns. The valuableremarks of Professor William Allsop are greatlyappreciated. This work was partially funded by theNational Office of Science and Technology throughcontract Mar 98r0796.

    References

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