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International Marine and Offshore Engineering Conference (IMOC 2013) Numerical study on the use of low crested detached breakwaters along the northern coast of Egypt S. Abohadima Assoc. Prof., Cairo University, Faculty of Engineering R. Marmoush Coastal and Marine Engineer, Dar El- Handasah K.A. Rakha Prof., Cairo University, Faculty of Engineering, Dept. of Irrigation and Hydraulics Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved. Abstract Many resorts were constructed along the northern coast of Egypt for recreational purposes. High waves often occur in the used-zone leading to uncomfortable conditions. Moreover, the resulting longshore current with high speeds due to wave breaking leads to undesirable current flow. Rip currents generated in the used-zone can also be a hazard to swimmers This study aims at testing the possibility of using detached low crested submerged breakwaters to provide suitable swimming conditions along the northern coast of Egypt. Detached low crested submerged breakwaters are considered as they do not obstruct the sea view and have lower negative impacts on the environment. This study attempts to provide a numerical examination for several configurations using different breakwater and the gap lengths. Three numerical models were used; refraction diffraction model for waves, hydrodynamic model for current circulation and one line model for shoreline movement. The best breakwater configuration to provide safe swimming area is recommended with an assessment of the negative impact on the shoreline stability. This study will be useful for the recreational resorts along the northern coast of Egypt. Keywords: Numerical modeling, rip currents, water waves, shoreline movement, detached breakwaters Nomenclature Tensor index (= 1 or 2 for x or y direction) Q is the total flux volume S β is the radiation stress U is the total velocity in the horizontal directions (α direction), w U is the horizontal shortwave induced particle velocity in the (α) direction, V is the total current velocity, V d is the depth varying current, t is the elevation of the wave trough, S β τ And B β τ are surface and bottom shear stress, is the horizontal turbulent stresses in the fluid, t is time, D B is berm height, D c is the closure depth, q is a source or sink in sediment Q s is the longshore sand transport rate (m3/sec) H is the significant wave height, C g is the wave group speed, bs is the angle of breaking with shoreline, the subscript “b” denotes breaker. A is the wave amplitude, k o denotes a constant wave number ɸ is the velocity potential; C is the wave celerity; Cg is the group velocity; k is the wave number K 1 and K 2 are empirical coefficients, s and are the densities of sand and water, respectively, p is the sand porosity, y is the shoreline position tan is the average bottom slope from shoreline to closure depth,

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  • International Marine and Offshore Engineering Conference (IMOC 2013)

    Numerical study on the use of low crested detachedbreakwaters along the northern coast of Egypt

    S. AbohadimaAssoc. Prof., Cairo University, Faculty of Engineering

    R. MarmoushCoastal and Marine Engineer, Dar El- Handasah

    K.A. RakhaProf., Cairo University, Faculty of Engineering, Dept. of Irrigation and Hydraulics

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Abstract – Many resorts were constructed along the northern coast of Egypt forrecreational purposes. High waves often occur in the used-zone leading to uncomfortableconditions. Moreover, the resulting longshore current with high speeds due to wavebreaking leads to undesirable current flow. Rip currents generated in the used-zone canalso be a hazard to swimmers This study aims at testing the possibility of using detachedlow crested submerged breakwaters to provide suitable swimming conditions along thenorthern coast of Egypt. Detached low crested submerged breakwaters are considered asthey do not obstruct the sea view and have lower negative impacts on the environment.This study attempts to provide a numerical examination for several configurations usingdifferent breakwater and the gap lengths. Three numerical models were used; refractiondiffraction model for waves, hydrodynamic model for current circulation and one linemodel for shoreline movement. The best breakwater configuration to provide safeswimming area is recommended with an assessment of the negative impact on theshoreline stability. This study will be useful for the recreational resorts along thenorthern coast of Egypt.

    Keywords: Numerical modeling, rip currents, water waves, shoreline movement, detachedbreakwaters

    Nomenclature Tensor index (= 1 or 2 for x or y direction)Q is the total flux volumeSβ is the radiation stress

    U is the total velocity in the horizontal directions (αdirection),

    wU is the horizontal shortwave induced particlevelocity in the (α) direction,V is the total current velocity,Vd is the depth varying current,

    t is the elevation of the wave trough,Sβτ And

    Bβτ are surface and bottom shear stress,

    is the horizontal turbulent stresses in the fluid,t is time,DB is berm height,

    Dc is the closure depth,q is a source or sink in sedimentQs is the longshore sand transport rate (m3/sec)H is the significant wave height,Cg is the wave group speed,bs is the angle of breaking with shoreline, the subscript“b” denotes breaker.A is the wave amplitude,ko denotes a constant wave numberɸ is the velocity potential;C is the wave celerity;Cg is the group velocity;k is the wave numberK1 and K2 are empirical coefficients,

    s and are the densities of sand and water, respectively,p is the sand porosity,y is the shoreline positiontan is the average bottom slope from shoreline toclosure depth,

  • Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    1. IntroductionDuring the summer season in Egypt, many residents

    spend their vacation along the northern coast (Figs. 1 &2). The regular summer beach activities are swimming,waddling and paddling besides enjoying the sea view.Swimming is considered the most important activitywithin sea water. Swimming takes place in the surf zoneextending offshore about 75 meters from the shoreline.This reach of sea will be denoted as the “used-zone”.

    Often high waves reach the used-zone leading touncomfortable and in many cases dangerous conditionsduring swimming. Moreover, the resulting longshorecurrent with high speeds due to wave breaking leads toundesirable swimming conditions. Cross currents such asrip currents generated in the surf zone can also be ahazard to swimmers.

    According to coastal guard manuals and openswimming racing regulations, a value of 0.5 m waveheight and 0.3 m/sec. current velocity (i.e., longshoreand/or crossshore) are the maximum acceptable valuesfor safe swimming conditions.

    In Egypt, several resorts such as Nakheel, Kerir,Marabella and Marina constructed protection systems tocontrol the used-zone hydrodynamics as shown in Figs. 1& 2. These systems led to negative impacts on theshoreline stability with erosion to the east of thestructures constructed [1].

    Because of the tourism value of the northern coastbeaches, the proposed protection system should notobstruct sea view or reduce the water quality.

    Numerous previous studies covered the mechanism ofprotection systems to control hydrodynamics withassociated environmental impacts (specially submergeddetached breakwaters).

    Six selected project sites were studied by [2] withdifferent geometric characteristics and in wide-rangingclimate conditions that were monitored and analyzedduring the DELOS. They investigated characteristics ofthe European structure protections by Low CrestedStructures (LCSs). In addition, their study described thesites and prototype observation of the impact of LCSs; a)description of the site, environmental conditions andresponse to its construction , b) description of theecological impacts and socioeconomic effects whereavailable.

    The study by [3] confirmed the inability to clearlydifferentiate between erosive and accretive shorelineresponse since submerged structures can result in bothshoreline erosion and accretion. The published prototypeobservations do not even indicate a clear relationshipbetween the mode of shoreline response and measurableenvironmental and structural variables (i.e., erosionresulted for: long structures as well as short structures,structures with higher crest levels as well as lower crestlevels, both broad-crested and narrow-crested structuresand both steep and mild bed slopes)

    It was confirmed however, in general that underoblique wave incidence the superposition of theunidirectional longshore current (which is weakened in

    the lee of a submerged structure) on the nearshorecirculation pattern resulting from the flow over thestructure appears to result in a gradient in the longshorecurrent. At the up-drift side, the structure inducednearshore circulation would oppose the ambientlongshore current, resulting in a lower net longshorecurrent in this region. At the down-drift side, the twocurrents converge, and the net longshore current isenhanced. The net result is deposition of sediment on theup-drift section of the shoreline behind the structure, andsome erosion on the down-drift section. Along coastlineswith substantial longshore sediment transport (e.g. theGold Coast, Australia) this mechanism can account forthe development of a salient in the lee of the structure.

    A simple relationship between the breaking parameter(Ɣ2) and the relative submergence (dc/Hm0) was proposedby [4]. This relation can be used in wave models formodeling wave transmission and wave energy decay oversubmerged breakwaters. The calculated transmissioncoefficients using the provided approach were comparedwith values calculated using the empirical equations by[5] and [6]. For this purpose, six hypothetical test caseswere considered with varying submergence depth.

    The study by [7] concluded that Incident andtransmitted wave angles are not always similar: forrubble mound structures, the transmitted wave angle isabout 80% of the incident one, whereas for smoothstructures the transmitted wave angle is equal to theincident one for incident wave angles less than 45degreesand is equal to 45degrees for incident wave angles largerthan 45 degrees.

    In this study the usage of a series of Submerged LowCrested Detached Breakwaters (SLCDBWs) is tested toalleviate the above mentioned problems. The presentstudy aims to investigate the efficiency of usingSLCDBWs in order to provide safe swimming for theNorthwestern Coast of Egypt. For this purpose numericalmodels were used to study several alternative layouts forSLCDBWs.

    The acceptable conditions used in this study are 0.5 mfor wave height and 0.3 m/s for currents.

  • Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Figure 1: Sample of Projects along Northern Coast of Egypt West ofAlexandria (a,b and c are Nakheel, Kerir and Marabella respectively).

    Figure 2: Sheltered swimming areas about 90 km west of Alexandria(Marina zone).

    2. Numerical ModelsThree numerical models were used to simulate thewaves, hydrodynamics and shoreline changes. TheREF/DIF numerical model was used to model thenearshore wave field and the radiation stresses. TheSHORECIRC numerical model was used to predict thewave-induced currents. Finally the GENESIS shorelinechange model was used to predict the shoreline changesdue to the different alternatives. The validation of thesemodels using published data for other areas was providedin [8].

    2.1. Refraction Diffraction ModelThe REF/DIF Model is a steady-state model that cansimulate wave shoaling, refraction, diffraction andenergy dissipation. The REF/DIF model was developedby [9]. The model solves an approximation of the mildslope equations (MSE). The parabolic mild slopeequations (PMSE) [10] is solved that accounts for waveshoaling, refraction, diffraction, and breaking formonochromatic waves. Wave reflection is not included inthe model.The MSE are valid for bed slopes up to 1:3 [11] and canbe written as

    02 gg CCkCC (1)Assuming that the velocity potential can be divided into aforward and a backward component and neglecting thebackward component (neglecting the reflected waves),results in the parabolic form of the MSE would be

    0)()(22

    AkCC

    xiCCkkk

    yACC

    yxAkCCi ggogg

    (2)

    Furthermore a dissipation term may be added to includewave energy dissipation due to breaking as provided by[9].The PMSE considers wave diffraction in the directionperpendicular to the direction of propagation only (y-direction) and neglects wave diffraction in the directionof propagation (x-direction). This is a reasonableapproximation only when the solution marches in thedirection of wave propagation. It is found by [12] that theangle between the wave direction and the direction ofpropagation (x-axis) should not exceed 30o.The main input to the model is the bathymetric data andthe offshore wave rose. For the bathymetry, straight andparallel contours were assumed with the orientation ofthe shore that same as that for the first and secondprojects shown in Fig. 1. A beach slope of 50:1 was usedbased on data from several locations in the study area.Offshore wave data from the Western EuropeanArmaments Organization Research Cell (WEAORC2004) was used [13]. This Atlas includes large records ofpredicted (hindcast) wave data at certain points over theMediterranean. The present study used the wave data atpoint with (32 N and 29 E) which was selected as it is the

    7 emerged detachedbreakwaters

    4 emerged detachedbreakwaters

    Fig. 2

    a)

    b)

    c)

  • Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    closest location for the present study area. Figure 3provides a plot of the wave rose at this location where itcan be seen that the predominant waves are from theNW.

    Figure 3: Offshore wave rose

    The summer wave data was extracted from the total yearrecords to provide records for the probability ofoccurrence for different wave heights and the associateddirections. Also it provides records for the probability ofoccurrence for different wave heights and the associatedpeak periods. The summer season covers months of June,July and August.These data were analyzed to determine the predominantwave conditions for the summer season. The highestprobability of occurrence was found to be between 0.875m to 1.125 m and propagates from the direction making315 degrees with North. Based on this analysis, thepredominant wave characteristics for numerical modelingwere: 1.0 m as an average value of the wave heights withassociated wave period 6.5 seconds from the NWdirection which is equivalent to 315 degrees with northand makes 15 degrees with shoreline.The computational domain dimensions are 900 (parallelto shore) m x 700 (cross the shore) m with grid spacing2.5 m x 2.5 m with no sub-grids or subdivisions. Thus,the numbers of computing points are 361 and 281respectively.One unit of SLCDBW is installed in the middle of thedomain associated with two half units at the right and leftboundaries to avoid the cross boundaries effect. In allproposed alternatives, the SLCDBW are located 100 mfrom the shore or at 2 m depth and parallel to theshoreline.

    2.2. Water Circulation ModelThe SHORECIRC model is a quasi-3D finite differencemodel that combines the effects of vertical structure ofthe currents with the simplicity of a 2D-horizontal modelfor the nearshore circulation. This is done by using ananalytical solution for the 3D current profiles combinedwith the numerical solution for the 2D depth-averagedhorizontal equations. The model was originallydeveloped by [14] and several improvements wereincluded by different researchers [e.g. 15].The SHORECIRC model is based on the depth-integrated, time-averaged equations of continuity andmomentum, which in complete form and in tensornotation takes the following form:

    0Qt

    X(3)

    For continuity and,

    1 0

    d d

    d d o

    S B

    V V

    V V

    dt x h x

    d g hx x

    dx

    U U+

    0

    0

    0

    h

    h

    h

    z

    z

    z

    Q QQ

    S(4)

    For momentum where,

    d

    Q

    0hzU

    (5)

    2

    S d

    g

    U U0h

    z

    h2 h

    QQ (6)

    The third and fourth (integral) terms in the momentumrepresent the effect of the depth variation of the currenton the horizontal distribution of volume flux Q. Notingthat Sβ and Qw are outputs from the REF/DIF Model.The same grid size and domain used for the REF/DIFmodel was used in this model. The radiation stressescalculated from the wave data using linear wave theory isused as the input driving forces to the model.

    2.3. Shoreline Change ModelThe GENEralized model for SImulating Shorelinechange (GENESIS) is a finite difference one line modelthat assumes the beach profile shape remains constantand performs time dependent sediment budget analysis tocalculate the shoreline change over an arbitrary beach.Details on the model may be found in [16, 17, 18]. Themodel includes a wave transformation model to calculateshoaling, refraction, and diffraction. Wave transmissionat detached breakwaters and a variety of terminal and

    NORTH

    SOUTH

    WEST EAST

    5%

    10%

    15%

    20%

    25%

    WIND SPEED(m/s)

    >= 3.4

    3.0 - 3.4

    2.6 - 3.0

    2.2 - 2.6

    1.8 - 2.2

    1.4 - 1.8

    1.0 - 1.4

    0.6 - 1.0

    0.2 - 0.6

    Calms: 6.34%

    Hs (m)

  • Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    internal boundary conditions and constraints can beincluded.The governing equation for the rate of change ofshoreline position can be expressed as,

    0)(

    1

    qx

    QDDtt

    y scB

    (7)

    The empirical predictive formula for Qs is,

    bbsbsbgs x

    HaaCHQ

    cos2sin)( 21

    2(8)

    The first term in Eq. (8) corresponds to the “CERCformula” described in the [19] and accounts forlongshore sand transport produced by obliquely incidentbreaking waves.The second term in Eq. (8) is not a part of the “CERCformula” but describes the effect of the longshoregradient in breaking wave height which is usually muchsmaller than that from oblique wave incidence effectunless diffracted waves exist due to vicinity structures.The non-dimensional parameters a1 and a2 are given by,

    aK

    ps1

    15 216 1 1 1416

    ( / )( )( . ) /

    (9)

    22 7 / 28( / 1)(1 ) tan (1.416)s

    Kap

    (10)

    These coefficients were calibrated by [20] for theGENESIS model by simulating the shoreline change forthe beach at Marabella and Suez canal resorts along theEgyptian Northwestern coast using the data covering aperiod from 1990 to 1994. The calibration resulted in thefollowing values; K1 = 0.05 and K2 = 0.04. These valueswere used in this study.The computational domain dimensions are 3300 (parallelto shore) m. the extra 1000 m from left and right sides(compared to wave model) were included to avoid theboundary effects.

    3. Alternatives StudiedOne of the studied sites in [2] is Lido di Ostia. It’stouristic beaches in Italy lying along Mediterranean Seawere suffering from erosion. Selection of LCS was basedon aesthetics -not to obstruct sea view- andenvironmental -water refreshment- reasons. Function ofLCS is to hold the artificial beach at a shallower slope,reducing both offshore sand losses and long-shoretransport and enhancing the development of marine faunawithout endangering bathing and leisure navigation.LCS system geometry consists of:

    - 2800 m continuous -no gaps- LCS parallel toshoreline with associated submerged groins.

    - 100 distance between shoreline and LCS.-Water depth at LCS location is 4 m.- Water depth above LCS crest is 2 m.- LCS crest width is 15 m.

    - Beach slope 1:250.On the other hand, the environmental conditions at theLido di Ostia beach are:

    - Typical wave height is 1.0 m- Wave direction is SW- Spring tidal range 0.4 m.

    Historical observation of beach evolution shows anobvious tendency to equilibrium after using LCS andnourishment processes.Because of the high similarity in environmentalconditions between the present study area and Lido diOstia, most of the proposed LCS configurations weresimilar to those at Lido di Ostia.A number of alternatives for protection systems withvarious configurations of a SLCSDBW were proposedand examined from all related aspects to determine theoptimum geometry to be used along the NorthwesternCoasts of Egypt.[2] concluded that the main parameters governing theLCS efficiency are: a) LCS distance from shoreline andb) water depth above crest (negative freeboard).Moreover, [21] stated that the most important parameterscontrolling the detached breakwaters efficiency are: a)breakwater length, b) breakwater distance from shore andc) Surf zone width. Therefore, some parameters remainconstant in all alternatives such as breakwaters sideslope, orientation and crest width as they will not have asignificant effect on the resulting hydrodynamics.The present study focuses on only two main factors thatcan majorly affect the hydrodynamics changes which arethe breakwaters lengths and gaps widths while all othervariables remained constant. The study examines fivecases of protection systems with different breakwaterlengths and gap widths for the same numerical domain.For simplicity, each case was defined based on theblocking percentage which refers to the ratio ofbreakwater lengths to the total beach length. Thefollowing are the examined cases (Fig. 4):

    Case 0: 0 % blocking (Do nothing) whichrepresents the natural condition

    Case 1: 33 % blocking with 150 m SLCDBWlengths and 300 m gap length

    Case 2: 56 % blocking with 250 m SLCDBWlengths and 200 m gap length

    Case 3: 78 % blocking with 350 m SLCDBWlengths and 100 m gap length

    Case 4: 100 % blocking with 900 m SLCDBWlength with no gaps

    Another classification of the proposed protectionalternatives can be provided according to the ratiobetween the SLCDBWs length (B) to gap betweenSLCDBWs width (G):

    Case 0: (B/G=0) where SLCDBWs are not used Case 1: (B/G=0.5) where B=150 m and G= 300 m

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    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Case 2: (B/G=1.25) where B=250 m and G= 200 m Case 3: (B/G=3.5) where B=350 m and G= 100 m Case 4: (B/G=infinity) where continuous SLCDBW

    with no gaps.Seven transversal profiles were chosen at the mostcritical locations for the waves and current fieldsto display the behavior/values in all cases (Fig. 5).

    4. Model Results

    4.1. Wave Model In Case 0, the offshore limit of used-zone has waves

    with 1.1 m height which exceeds the 0.5 m(maximum safe wave height).High dissipation of energy at a water depth of 1.5 m-75 m offshore.

    In Case 1 and within blocked zones, the transmittedwave in lee side is 0.5 m high directly behind theSLCDBWs (Fig. 6b).Diffracted waves around SLCDBWs rounded headstowards the sheltered area results in 0.7 m heightbehind SLCDBWs directly and approach the surfzone at 0.6 m height (Fig. 6c).In gaps zones, waves propagate exactly as if there isno protection (similar to Case 0) (Fig. 6e).

    In Case 2 and Case 3, the previous description ofCase 1 can be applied however the length ofsheltered areas behind protection system is directlyproportional to SLCDBW length (Fig. 6a and 6d).

    For Case 4, the resulting wave field is very similarin behavior to the blocked reaches in the previousexamined Cases (1, 2 and 3) without any diffractionphenomena (Fig. 8).[21] used a modified relationship for a case ofrelative submergence equal to 1.06 that givesbreaking parameter equal to 1.15 and a transmissioncoefficient of 0.76. Other empirical equations by [5]and [6] give 0.59 and 0.68 respectively.Results of model show good agreement withprevious values (Transmission coefficient is 0.5 fora relative submergence of 1).Fig. 6a, shows slight diversion of incident wavesover SLCDBWs. Value of diversion complies withthe 80% reduction in wave angle for rough rubblemounds concluded in [7]

    4.2. Wave Induced Currents In Case 0, offshore the wave breaker line the

    currents are very weak.

    Within the surf zone, the longshore currents takereaches a maximum value of 0.22 m/s.

    In Case 1, at the east side of SLCDBWs, thegenerated longshore currents s are diverted to moveto the east direction along the gap and parallel to theshoreline with a speed around 0.32 m/s just behindthe breakwater head and within the used-zone. Suchcurrent speed is slightly higher than the safeswimming currents range (less than 0.3 m/s.) (Fig.7a and 7b).The second behavior was at the west side ofSLCDBWs, where longshore currents are divertedto the west direction to interact with the longshorecurrent from the east side of the previousSLCDBW. This interaction results in a clockwisecurrent cell (eddy) turning around the western headcenter with an average speed of 0.32 m/sec. Part ofcurrent’s eddy exists in the SLCDBW gap andused-zone. Finally, the generated currents areexceeding the safe swimming limit (to be 0.3 m/s.)(Fig. 7a and 7c).Behind the SLCDBWs, the water conditions aresafe for swimming (within acceptable values of safeswimming).Moderate crossshore current with 0.2 m/s speednear the shoreline along the domain. (Fig. 7d and7e).

    For Case 2, the results are similar to Case 1 withhigher speed of the generated longshore current atthe eastern side of SLCDBWs reaching 0.45 m/s.The size and extend of the current cell generated atthe western head is larger and stronger with a speedreaching 0.45 m/s.For the protected area directly behind theSLCDBWs, the water conditions are calm (samecurrents speeds as in Case 1).

    For Case 3, current speeds are the worst. Thegenerated current at the eastern head exceeds 0.5m/sec. and interacts immediately with the currentcell at the western head for the next SLCDBWs.The lee side of SLCDBWs are as Case 2.

    In Case 4 as the used-zone is totally protected, thedissipated wave energy is the highest. Thus thegenerated longshore is located exactly as in Case 0,but with lower speeds around 0.1 m/sec. Swimmingin used-zone is totally safe (Fig. 8).Model results are in a good agreement with currentspattern mentioned in [3].

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    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Figure 4: Proposed cases of protection systems with SLCDBWs.

    Figure 5: Locations of transversal profiles performed in wave andcurrent fields.

    a) Wave vectors distribution of Case 3 (78% blocking)

    b) Wave height values for all cases with sea bed level at C.L

    c) Wave height values for all cases with sea bed level at C.R 1

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    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    d) Wave height values for all cases with sea bed level at C.L 2

    e) Wave height values for all cases with sea bed level at C.L 3

    Figure 6: REF/DIF result and cross-shore profiles on wave field forCase 2 (56% blocking).

    a) Velocity vectors distribution of Case 1 (33 % blocking).

    b) Longshore current velocity for all cases at C.R 1

    c) Longshore current velocity for all cases at C.L 1

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    d) Wave height values for all cases with sea bed level at C.L 2

    e) Wave height values for all cases with sea bed level at C.L 3

    Figure 6: REF/DIF result and cross-shore profiles on wave field forCase 2 (56% blocking).

    a) Velocity vectors distribution of Case 1 (33 % blocking).

    b) Longshore current velocity for all cases at C.R 1

    c) Longshore current velocity for all cases at C.L 1

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    d) Wave height values for all cases with sea bed level at C.L 2

    e) Wave height values for all cases with sea bed level at C.L 3

    Figure 6: REF/DIF result and cross-shore profiles on wave field forCase 2 (56% blocking).

    a) Velocity vectors distribution of Case 1 (33 % blocking).

    b) Longshore current velocity for all cases at C.R 1

    c) Longshore current velocity for all cases at C.L 1

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    d) On/Offshore current velocity for all cases at C.R 1

    e) On/Offshore current velocity for all cases at C.L 1

    Figure 7: SHORECIRC result and cross-shore profiles on currents’fields for Case 1 (33% blocking).

    Figure 8: Wave and currents fields for Case 4 (100% blocking)respectively.

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    d) On/Offshore current velocity for all cases at C.R 1

    e) On/Offshore current velocity for all cases at C.L 1

    Figure 7: SHORECIRC result and cross-shore profiles on currents’fields for Case 1 (33% blocking).

    Figure 8: Wave and currents fields for Case 4 (100% blocking)respectively.

    Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    d) On/Offshore current velocity for all cases at C.R 1

    e) On/Offshore current velocity for all cases at C.L 1

    Figure 7: SHORECIRC result and cross-shore profiles on currents’fields for Case 1 (33% blocking).

    Figure 8: Wave and currents fields for Case 4 (100% blocking)respectively.

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    Figure 9: Length of safe swimming zone percentage from theSLCDBW total length of Cases 1, 2 and 3 and chart showing such

    values.

    Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Figure 9: Length of safe swimming zone percentage from theSLCDBW total length of Cases 1, 2 and 3 and chart showing such

    values.

    Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Figure 9: Length of safe swimming zone percentage from theSLCDBW total length of Cases 1, 2 and 3 and chart showing such

    values.

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    4.3. Safe Swimming AreasFigure 9 shows the limits of generated safe swimmingarea within used-zone as follows: Case 1 with B/G=0.5 generates protected length for

    swimming behind SLCDBW of about 28% from thetotal breakwater length.

    Case 2 with B/G=1.25 generates protected lengthfor swimming behind SLCDBW of about 60% fromthe total breakwater length.

    Case 3 with B/G=3.5 generates protected length forswimming behind SLCDBW of about 67% from thetotal breakwater length.

    N.B: Centerline of swimming area is the samecenterline of breakwaters.

    Figure 10: Shoreline changes and sediment transport rates after 1 yearfor all proposed cases of protections respectively.

    4.4. Shoreline Changes ModelThe results show that using SLCDBWs for protectionwill result in formation of salient’s behind the breakwaterand erosion down drift the SLCDBW. As the blockingpercentage increases the formed salient dimensionsincrease and extend of erosion increases. Such impactwill harm the neighboring beaches in the downdrift inaddition to the loss of part of the swimming area due tothe salient. Salient’s and erosion dimensions (length andwidth) can be expressed as factors of breakwater distancefrom shoreline (Fig. 10).

    Model results show fair agreement with shoreline linechanges described in [3].

    5. ConclusionsThis paper provided a study on the use of SLCDBWs

    to produce suitable swimming areas along the Northcoast of Egypt. Three numerical models were used in thisstudy, the refraction diffraction model for wavetransformation, the water body circulation model forhydrodynamics and the GENESIS one line shore changesmodel for shoreline changes.

    Usage of SLCDBWs provides water exchange with nosea view obstruction. At the same time, SLCDBWscontrols nearshore hydrodynamic fields.

    The model results showed that in order to produce asufficient area suitable for swimming, the SLCDBWshould extend over the full length of the resort. Thenegative impact however on the downdrift beaches willrequire a detailed study to mitigate such effects.

    6. References(1) Frihy, O. M. (2001). The necessity of environmental impactassessment (EIA) in implementing coastal projects: lessons learnedfrom the Egyptian Mediterranean Coast. Ocean & CoastalManagement, Volume 44, Issues 7–8, 2001, pp. 489–516

    (2) Lamberti A., Archetti R., Kramer M., Paphitis D., Mosso C., andRisio M. (2005). European experience of low crested structures forcoastal management. Coastal Engineering international journal forcoastal, harbor and offshore engineers 52 (2005) 841–866.

    (3) Ranasinghe R. and Turner I. (2006). Shoreline response tosubmerged structures: A review. Coastal Engineering internationaljournal for coastal, harbor and offshore engineers 53 (2006) 65 – 79.

    (4) Johnson, H. (2006). Wave modelling in the vicinity of submergedbreakwaters. Coastal Engineering international journal for coastal,harbor and offshore engineers 53 (2006) 39 – 48.

    (5) Seabrook, S., and Hall, K. (1998). Wave transmission at submergedrubble mound breakwaters. Proceedings of 26th InternationalConference on Coastal Engineering, ASCE, Copenhagen, DK, pp.2000–2013.

    (6) D'Angremond, K., van der Meer, J.W., and De Jong, R.J. (1996).Wave transmission at low crested structures. Proceedings of 25thInternational Conference on Coastal Engineering. ASCE, pp. 3305–3318.

    (7) Van der Meer J., Briganti R., Zanuttigh B.and Wang B. (2005).Wave transmission and reflection at low-crested structures: Designformulae, oblique wave attack and spectral change. Coastal

    Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    4.3. Safe Swimming AreasFigure 9 shows the limits of generated safe swimmingarea within used-zone as follows: Case 1 with B/G=0.5 generates protected length for

    swimming behind SLCDBW of about 28% from thetotal breakwater length.

    Case 2 with B/G=1.25 generates protected lengthfor swimming behind SLCDBW of about 60% fromthe total breakwater length.

    Case 3 with B/G=3.5 generates protected length forswimming behind SLCDBW of about 67% from thetotal breakwater length.

    N.B: Centerline of swimming area is the samecenterline of breakwaters.

    Figure 10: Shoreline changes and sediment transport rates after 1 yearfor all proposed cases of protections respectively.

    4.4. Shoreline Changes ModelThe results show that using SLCDBWs for protectionwill result in formation of salient’s behind the breakwaterand erosion down drift the SLCDBW. As the blockingpercentage increases the formed salient dimensionsincrease and extend of erosion increases. Such impactwill harm the neighboring beaches in the downdrift inaddition to the loss of part of the swimming area due tothe salient. Salient’s and erosion dimensions (length andwidth) can be expressed as factors of breakwater distancefrom shoreline (Fig. 10).

    Model results show fair agreement with shoreline linechanges described in [3].

    5. ConclusionsThis paper provided a study on the use of SLCDBWs

    to produce suitable swimming areas along the Northcoast of Egypt. Three numerical models were used in thisstudy, the refraction diffraction model for wavetransformation, the water body circulation model forhydrodynamics and the GENESIS one line shore changesmodel for shoreline changes.

    Usage of SLCDBWs provides water exchange with nosea view obstruction. At the same time, SLCDBWscontrols nearshore hydrodynamic fields.

    The model results showed that in order to produce asufficient area suitable for swimming, the SLCDBWshould extend over the full length of the resort. Thenegative impact however on the downdrift beaches willrequire a detailed study to mitigate such effects.

    6. References(1) Frihy, O. M. (2001). The necessity of environmental impactassessment (EIA) in implementing coastal projects: lessons learnedfrom the Egyptian Mediterranean Coast. Ocean & CoastalManagement, Volume 44, Issues 7–8, 2001, pp. 489–516

    (2) Lamberti A., Archetti R., Kramer M., Paphitis D., Mosso C., andRisio M. (2005). European experience of low crested structures forcoastal management. Coastal Engineering international journal forcoastal, harbor and offshore engineers 52 (2005) 841–866.

    (3) Ranasinghe R. and Turner I. (2006). Shoreline response tosubmerged structures: A review. Coastal Engineering internationaljournal for coastal, harbor and offshore engineers 53 (2006) 65 – 79.

    (4) Johnson, H. (2006). Wave modelling in the vicinity of submergedbreakwaters. Coastal Engineering international journal for coastal,harbor and offshore engineers 53 (2006) 39 – 48.

    (5) Seabrook, S., and Hall, K. (1998). Wave transmission at submergedrubble mound breakwaters. Proceedings of 26th InternationalConference on Coastal Engineering, ASCE, Copenhagen, DK, pp.2000–2013.

    (6) D'Angremond, K., van der Meer, J.W., and De Jong, R.J. (1996).Wave transmission at low crested structures. Proceedings of 25thInternational Conference on Coastal Engineering. ASCE, pp. 3305–3318.

    (7) Van der Meer J., Briganti R., Zanuttigh B.and Wang B. (2005).Wave transmission and reflection at low-crested structures: Designformulae, oblique wave attack and spectral change. Coastal

    Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    4.3. Safe Swimming AreasFigure 9 shows the limits of generated safe swimmingarea within used-zone as follows: Case 1 with B/G=0.5 generates protected length for

    swimming behind SLCDBW of about 28% from thetotal breakwater length.

    Case 2 with B/G=1.25 generates protected lengthfor swimming behind SLCDBW of about 60% fromthe total breakwater length.

    Case 3 with B/G=3.5 generates protected length forswimming behind SLCDBW of about 67% from thetotal breakwater length.

    N.B: Centerline of swimming area is the samecenterline of breakwaters.

    Figure 10: Shoreline changes and sediment transport rates after 1 yearfor all proposed cases of protections respectively.

    4.4. Shoreline Changes ModelThe results show that using SLCDBWs for protectionwill result in formation of salient’s behind the breakwaterand erosion down drift the SLCDBW. As the blockingpercentage increases the formed salient dimensionsincrease and extend of erosion increases. Such impactwill harm the neighboring beaches in the downdrift inaddition to the loss of part of the swimming area due tothe salient. Salient’s and erosion dimensions (length andwidth) can be expressed as factors of breakwater distancefrom shoreline (Fig. 10).

    Model results show fair agreement with shoreline linechanges described in [3].

    5. ConclusionsThis paper provided a study on the use of SLCDBWs

    to produce suitable swimming areas along the Northcoast of Egypt. Three numerical models were used in thisstudy, the refraction diffraction model for wavetransformation, the water body circulation model forhydrodynamics and the GENESIS one line shore changesmodel for shoreline changes.

    Usage of SLCDBWs provides water exchange with nosea view obstruction. At the same time, SLCDBWscontrols nearshore hydrodynamic fields.

    The model results showed that in order to produce asufficient area suitable for swimming, the SLCDBWshould extend over the full length of the resort. Thenegative impact however on the downdrift beaches willrequire a detailed study to mitigate such effects.

    6. References(1) Frihy, O. M. (2001). The necessity of environmental impactassessment (EIA) in implementing coastal projects: lessons learnedfrom the Egyptian Mediterranean Coast. Ocean & CoastalManagement, Volume 44, Issues 7–8, 2001, pp. 489–516

    (2) Lamberti A., Archetti R., Kramer M., Paphitis D., Mosso C., andRisio M. (2005). European experience of low crested structures forcoastal management. Coastal Engineering international journal forcoastal, harbor and offshore engineers 52 (2005) 841–866.

    (3) Ranasinghe R. and Turner I. (2006). Shoreline response tosubmerged structures: A review. Coastal Engineering internationaljournal for coastal, harbor and offshore engineers 53 (2006) 65 – 79.

    (4) Johnson, H. (2006). Wave modelling in the vicinity of submergedbreakwaters. Coastal Engineering international journal for coastal,harbor and offshore engineers 53 (2006) 39 – 48.

    (5) Seabrook, S., and Hall, K. (1998). Wave transmission at submergedrubble mound breakwaters. Proceedings of 26th InternationalConference on Coastal Engineering, ASCE, Copenhagen, DK, pp.2000–2013.

    (6) D'Angremond, K., van der Meer, J.W., and De Jong, R.J. (1996).Wave transmission at low crested structures. Proceedings of 25thInternational Conference on Coastal Engineering. ASCE, pp. 3305–3318.

    (7) Van der Meer J., Briganti R., Zanuttigh B.and Wang B. (2005).Wave transmission and reflection at low-crested structures: Designformulae, oblique wave attack and spectral change. Coastal

  • Abohadima, Marmoush and Rakha

    Copyright © 2013 Arab Academy for Science, Technology and Maritime Transport – All Rights Reserved.

    Engineering international journal for coastal, harbor and offshoreengineers 52 (2005) 915–929.

    (8)Marmoush R. (2013). Study on the Use of Segmented Low CrestedDetached Breakwaters Along the Northern Coast of Egypt. M.Sc.thesis, Faculty of Engineering, Cairo University.(9) Kirby, J. T. and R. A. Dalrymple. 1991: User’s Manual – CombinedRefraction/Diffraction Model: REF/DIF 1 Version 2.3. Center forApplied Coastal Research. University of Delaware, Newark, Delaware.

    (10) Radder, A. C. 1979: On the parabolic equation method for water-wave propagation. Journal of Fluid Mechanics, 95:159-176.

    (11) Booij, N. 1983: A note on the accuracy of the mild-slope equation.Coastal Engineering, 17:191-203.

    (12) Dodd, N. 1988: Parabolic approximations in water waverefraction and diffraction. Ph.D. Thesis, University of Bristol, pp. 104.

    (13) Western European Armaments Organization Research Cell(WEAORC) (2004). Wind and Wave Atlas of the Mediterranean Sea. 33pages.

    (14) Svendsen, I. A., and Putrevu, U. 1990: Nearshore circulation with3-D profiles. Proceedings of the 22nd Coastal Engineering Conference,pp. 241-254.

    (15) Van Dongeren, A.R. and I.A. Svendsen 1997: An Absorbing-Generating Boundary Condition for Shallow Water Models. J. ofWaterways, Ports, Coastal and Ocean Engineering, vol. 123, no. 6, pp.303-313.(16) Gravens, M. B., Kraus, N. C., and Hanson, H. 1991: GENESIS:generalized model for simulating shoreline change. Report 2,Workbook and System User’s Manual. Technical Report CERC-89-19,Coastal Engineering Research Center, US Army Engineer WaterwaysExperiment Station, Vicksburg, MS.

    (17) Hanson, H., and Kraus, N. C. 1989: GENESIS: Generalizedmodel for simulating shoreline change. Report 1, Technical Reference.Technical Report CERC-89-19, Coastal Engineering Research Center,US Army Engineer Waterways Experiment Station, Vicksburg, MS.

    (18) Hanson, H. 1987: GENESIS, a generalized shoreline changemodel for engineering use. Report No. 1007, Department of WaterResources Engineering, University of Lund, Lund, Sweden.

    (19) Shore Protection Manual, SPM (1984), 4th ed., 2 Vols, US ArmyEngineer Waterways Experiment Station, Coastal EngineeringResearch Center, US Government Printing Office, Washington, DC.

    (20) Rakha, K.A., and Abul-Azm, A.G. 2001: Modelling of ShorelineChanges along the North Western Egyptian Coast. Proceedings of theMEDCOAST 01 conference, pp. 1467-1478.

    (21) Mangor, K. (2004). Shoreline Management Guidelines. DHIWater and Environment. 294 p.

    Authors’ information1 Department of Engineering Mathematics and physics, Faculty of Eng.,

    Cairo University. 2 Department of Coastal and Marine Engineer, DarEl-Handasah, 3 Dept. of Irrigation and Hydraulics, Faculty of

    Engineering, Cairo University.

    The group is interested in the fields of numerical modeling andcomputational fluid dynamics. The group is interested in calculatingwater circulation and environmental impacts due to different activitiesin coastal zones.