SIRI SYARAHAN PERDANA PROFESOR

Innovative Approaches for Physical Considerations / 1

SIRI SYARAHAN PERDANA PROFESOR

INNOVATIVE APPROACHESFOR PHYSICAL CONSIDERATIONS IN

RESEARCH AND DEVELOPMENT OF COASTALPROTECTION STRUCTURES

ByProfessor Dr. Nor Aieni Haji Mokhtar

INTRODUCTION

It is a generally known fact that, our planet Earth is covered with71 percent water. Continuous energy dissipation takes placewhere the land meets the sea. As a consequence, coasts aresubject to deformation, of which coastal erosion posesgreater problems. This must be combated to prevent loss ofhighly valuable land and properties, structures andrecreational areas. It has been well interpreted that possiblecauses for erosion include sea level rise and coastalsubsidence, natural weathering, reduced sediment dischargefrom rivers into the coastal areas, and human impacts, such ascaused by structures.

Shoreline naturally, seasonably, and variably, gain and losesediments over the years. Eroding shoreline is caused tidal changesaggravated by winds and wave forces during storms. Due tohuman interference, coastal erosion has also been intensifiedvia dredging and mining activities for the purpose of landreclamation as well as removal of vegetative cover for economic andinfra-structural development. With rapid increase in developmentand economic activities along the water body areas, the problem of

2 / Siri Syarahan Perdana Profesor

coastal erosion is more persistent and increasingly demands ourserious attention. Thus, there is a need to protect our land, thenation’s greatest asset, from being washed and eroded away.

Malaysia, being a maritime country with a total stretch of 4800km coastline is experiencing threat of shoreline erosion of about29 percent. Figure below shows the distribution of coastalerosion experienced in the various states of Malaysia.

In the last 20 years, the economic consequences have grownsteadily that results in an increase in the utilisation of Malaysia’snearshore areas for agriculture, industries and commerce by 64percent. Growing wealth and improved means of transportation havebrought the beaches within our reach as resort areas for almosteverybody in the industrialised countries. At the same time, the

States in MalaysiaLeng

th o

f er

od

ing

sh

ore

line

(km

)

350300250200

150100500

Per

lisK

edah

Pen

ang P

erak

Sel

ango

rN

.Sem

bila

nM

elak

aJo

hor

Pah

ang Te

reng

ganu

Kel

anta

nLa

buan

Sar

awak

Sab

ah

Figure 2 Threat of coastal erosion has led to destruction to publicproperties and loss sediments info the sea

Figure 1Distribution of

coastal erosion


recreational values of the same areas are threatened by pollution ofmany kinds and often erosion, too (Figure 2). The search for andproduction of oil and gas from the continental shelf has furtheremphasized that the sea is increasingly becoming an important partof our life in the planet. In addition, the expansion of world trade ingeneral and the trade of developing countries in particular, requireconstructions of large number of harbours and terminals, and thatover a rather short span of years. The lack of sheltered areas withsufficient water depth to accommodate large tankers and bulkcarriers has led to the construction of terminals for these shipsand much more exposed locations than were previouslyconsidered feasible.

The Malaysian government, particularly the Department ofIrrigation and Drainage, has recognized the threat of critical coastalerosion under Category 1 and acted to counter it and to limit itsconsequence. This is clearly spelled out in the National Coastal ZoneManagement Plan and Guidelines (Garis Panduan JPS 1/97, 1997).To balance the need for infra-structural development and tominimize the impacts of coastal erosion, it is a mandatoryrequirement by the approval authorities that certain investigativestudies need to be carried out to assess the viability and to providedetailed engineering drawings for optimum design support.

In the last decades, major contributions to the designpractice have been made, thanks to new research facilities like alarge scale wind wave flumes, turbulent flow measurementdevices, numerical models, etc. Progress has been made inthe scientific basis of our knowledge that is empirical, basedon experiments and experience. Theoretical approachof the phenomena, by understanding the process and thedesign of protections especially in the unusual cases, is a mixof science and experience. Computer models play an increasingrole in engineering. For a hydraulic engineer, however, asheet of white paper and a pencil are still essential, especially atpreliminary stage of a design. A hand-made sketch of acurrent or wave pattern is as valuable as the application of


calculation rules. For both, a good insight into the physics of theprocesses involved is indispensable.

The Need to Investigate and Counter Problems in Designingand Constructing Coastal Protection Structures

Coastal engineering is a field for which there is no code of practice.Some standard procedures exist e.g. Coastal Protection Manual, USArmy Corps (CERC, 1984), but any applications of standard practiceis limited because solutions are necessarily site-specific. Thus, everyproject becomes a unique challenge. A healthy proportion ofingenuity and common sense is necessary. It is not possible todevelop solutions on a prototype scale, as one might design for abreakwater, for example. We do not have design codes; we cannotdefine input conditions with sufficient accuracy, and we areuncertain of the performance. Trial and error solutions on aprototype scale are not acceptable, since the costs involved inerrors and necessary project changes are normally prohibitive.Thus, most of the coastal projects are carefully designed usingmodels. The two basic types of models are physical models andnumerical models. The problem is solved or the design is madeusing these models, guided by experience we have and based on alimited suite of measured prototype conditions. The prototypemeasurements enter the design as data and it is very importantto be able to distinguish the difference between the input dataand calibration data. The physical models are meant for the detaildesign of coastal structures whilst the numerical or hydrodynamicmodels are meant to confirm the layout design and the predictionof impact or performance of the structures.

The challenge is to use the available tools to provide the bestproduct. All tools have shortcomings and it is essential thateach of the tools used is in the most appropriate manner sothat it brings its own strengths to design and its weaknessesminimized. This paper will outline research carried out by the authorand her team members and highlights some ways to optimize theoutput and to increase confidence in our designs for the future.


In this era of new millennium, it is a good time to reflect uponthe research carried out on coastal engineering design methods andthe tools that have been used particularly at the Coastal & OffshoreEngineering Institute, Universiti Teknologi Malaysia, Kuala Lumpur.It has been observed that the tools, namely physical modeling,numerical modeling and collection of field data all have its ownserious shortcomings. This paper a discusses physical modelingstudies of some coastal protection structure types and presentsdetailed discussion on the development of a revetment systemSine-Slab.

MATERIALS AND METHODS

This section provides an insight to the theoretical background andcommon understanding reported by previous researchers. Areview of aspects of managing beach deformation controllingworks, the impacts of large waves at the shoreline, the impactsof wave breaking and wave transformation in the surf zoneand wave-structure interaction are presented. The designphilosophy and design methodology for coastal protectionstructures breakwaters, groynes, revetment and artificial reef,aspects of physical modeling and components for designconsiderations including data requirements from the site conditionswill be highlighted. A summary of projects undertaken andfacilities available at COEI are also given.

Beach Deformation Controlling Works

Topographic change to be controlled are related to problems suchas erosion of foreshore due to storms, local erosion due to current,sedimentation in harbour and channel, blockage of rivermouth, etc.Coastal protection structures have been used to trap longshoresediment movement at one location whilst erosionpersists at the downstream side.

The procedure is to determine which method should beadopted from various works. The basis for consideration in the studyis as follows:


(i) Past and present characteristics of beach deformation andsediment movement of the objective beach. There is a need toanalyze the cause of deformation and the predominantsediment movement (direction and mode) to be controlled onthe basis of sounding data, bed material characteristics, riverrun-off, and weather sea conditions. We need to fix variousinput conditions, such as characteristics of beach, bathymetry,incoming waves, that will be used in the assessment of theeffect of the structures in the surrounding coast.

(ii) Selection of various methods: Based on analysis in (i), thechoice depends on functions of structures to control fluidmotion and sediment movement.

(iii) Evaluation of the effects of the selection on the surroundingcoast: Evaluation and assessment can be made by numericalmodeling or by hydraulic model experiments (physical model).Although many studies have been conducted, by numericalmethod for example, prediction for fluid motion close tostructures with sufficient accuracy is limited. By physical modelor experiments, on the other hand, unsolved problems stillremain especially related to movable bed, similitude law andreproducibility of the phenomena in the field in the laboratory.Hybrid method sometimes adopted whereby topographicchange is predicted numerically by using waves and currentfields obtained in the hydraulic experiments might becomeeffective tool.

(iv) Other evaluation and determination of evaluation criteria.

The cost of construction, view, durable years, water qualityenvironment, and relation to fishing industry are raised in these items.Standard evaluation criteria are not established and for thesereasons, they are determined on case-by-case basis. Figure 3shows the general procedure for determining the work to controlbeach deformation prior to construction.


Depending on the scale of the project, the scope of investigationincludes:

1. Measurement and analysis of oceanographic parameters andbeach profile.

2. Prediction of extreme wave climate from wind record.3. Joint probabilities of waves and tides.4. Modeling of wave transformation in shallow water.5. Hydrodynamic simulation of sediment transport.6. Design of structures.7. Fixed or preferably mobile bed-physical modeling of beaches.8. Detailed design.9. Construction methods.

10. Coastline management and monitoring.

Figure 3 A flow diagram of procedures for selection of measures tocontrol beach deformation

Investigation of present stateand characteristics of past topographicchanges and sediment movement

Selection of countermeasures

Determination ofstandard criteria

Assessment of other issues

optimum

Construction

Assessment for the effect of shore protectionAnd effect on surrounding coast

(i)

(ii)

(iii)

(iv)


Types of methods or structures used for various mitigativemeasures include:• Seawall of various types.• Armoured slopes and embankments or revetments.• Groynes.• Detached breakwaters.• Beach nourishment.

Coastal erosion is a localised problem and methods tocombat the problem vary from one location to another. It dependson climatic condition, i.e. wind, wave and current, soil conditionsand other environmental factors.

The existing shore protection structures include rockrevetment, gabion, Bakau pile seawall, concrete seawall, stonemasonry groyne, timber groyne, scrap type seawall with timber piles,rubblemound breakwater and pre-cast concrete block revetment.Rubblemound or rock revetment has been a traditionally anacceptable method of coastal defense. But the local supply ofrocks is limited,and the method is less environment-friendly,which is due to inaccessibility to water body and lack of beach. Beachnourishment is a “soft” method and is environment-friendly but ithas maintenance problem of finding enough quantities of sand atdistinct time intervals like once in every three to five years.

Pre-cast concrete systems are getting more popular these daysas their geometric shapes can be engineered to suit the designcriteria. This approach enabled industries for construction,manufacturing and marine to flourish and develop indigenousproducts suitable for the environment. Table 1 Shows the variousmethods of coastal protection methods being used in Malaysia.

Large Waves Impact at the Shoreline

Long waves in channels have served to provide much of the impetusto the study of waves. The wave motion in a channel isgoverned by mild-slope equation. The propagation of waves inchannel of various configurations (rectangular, triangular, trapezoidal


Table 1 Some methods of coastal protection being used in Malaysia

Rock/Rubblemound Revetment Beach Nourishment

Flex-Slab revetment system Rubblemound breakwaters as Groynes- perpendicular to shore

Tripod Rubblemound Offshore/Detached breakwaters – parallel to shore

Sine-Slab revetment system(New Product – Made in UTM, Malaysia)

A pair of rubblemound breakwatersas groynes for harbour protection


and arbitrary prismatic channels) have been investigated by manyresearchers ((Darymple R.A, Kirby J.T,Li, Li, (1994), Matthew &Akylass (1990), Isaacson (1978), Berkhoff, 1972, Peregrine (1968),Lamb (1945), Russel S, (1844) and Kelland as early as 1839)).Wave propagation can be modeled using a numerical eigenfunction expansion. More recent work (Norazizi Mohamad andNoraieni Mokhtar, 2000) had examined the short waves, such thatthe depth/wavelength ratio can exceed 1/20 or straight channels withrectangular and trapezoidal cross-sections. The water surfacedisplacement created by uniform wave train normally incident onthe channel and this is the resultant of superposition of theeigenmodes, determined numerically and experimentally usingParticle Image Velocimetry technique (PIV) from the lateraleigenvalue problem. Short waves in a channel can presentnavigational problems and may excite harbour oscillations.Sloping sidewalls have been shown to produce edge wave motionsexcited by the incident wave field. These edge waves have adifferent wavelength than the incident wave field and they arethe largest at the shoreline, hence providing potential for greaterwave damage and erosion there. Thus channel sidewalls mayreduce much of this wave energy, if they are sufficiently porousor if they are sloped. Though wave breaking has been ignored inthis linear analysis, it is of importance in the field and will bediscussed next.

Impact of Wave Transformation and Wave Breaking inthe Surf Zone

The waves generated by winds propagate for a distance from theocean and approach a beach. This random sea is a dominant forceto the beach profile evolution and many other coastalengineering subjects. As the water depth become shallow,the orbital motion of water particle commences to have aninfluence on the sea bottom material. Then, waves tend to dissipateenergy by friction, release most of the energy by breakingand cause a change in the beach profile (refer to Figure 4).


Through these physical processes, a wave height distributionacross the shore may change to a non-Raleigh distribution. In thelast few decades, numerous studies have been done on wavetransformation and breaking waves. Therefore, wave heightdistribution for regular and random waves can be numericallypredicted to some degree. As shown in Figure 5 below, interestingphenomena such as hydraulic jump and bore formationrelates to the wave and energy transformation analogous towave run-up and roller or undertow effect due to wave breaking andwave run-down respectively.

In contrast to a number of wave models, practical engineeringmethods for beach profile evolution due to random waves are stillfew, for instance Stive and Battjes (1984), Brian and Kamphuis

Figure 5 The predominant phenomena that relates to the wave andenergy transformation distribution

Figure 4

Uniform flow Tidal current Orbital motion Breaking wave

Hydraulic jump Bore

Wave celerity


(1990) and Sato and Mitsunobu (1991). In fact, for convenience andengineering usefulness, regular wave conditions are widely acceptedfor physical modeling as well as numerical experiment forcross-shore sediment transport. However, the mild transformationof random waves may result in the mild bar profile comparedwith the distinct bar-trough feature due to regular waves.

With the advent of technological innovation, the availability ofpowerful and fast PCs and data acquisition systems, simulationof beach profile evolution due to random waves is no longerunrealistic approach and has become practical even if a littlebit complicated (Kajima et al., Dette and Uliczka, 1986, and Krausset al., 1992). The Goda random wave model predicts information onseveral kinds of representative wave height distributions, for instance,maximum wave, significant wave, and mean wave heightdistributions. A cross-shore sediment transport model that is relatedto the wave energy flux is coupled with a mass conservationequation to obtain a new beach profile (Nishi, Sato and Wang, 1994).Based on Goda’s wave breaking criterion, later modified by Satoand Kobe (1983), the slope term in the breaking limit to the absolutevalue of the local beach slope is found as follows:

where Χ is the normalized wave height, HO is the significantwave height, κ = 15, LO= gT2/2 π, and the coefficient Α takes thevalue of 0.17 for regular waves. In the random wave breaking, Α isset to 0.18 for the upper breaking limit of random waves at Χ =Χ1

and 0.12 for the lower breaking limit Χ = Χ2.Proper development or protection of coastal zones generally

requires us to evaluate beach processes as accurately as possible.Prediction of beach processes under sheet flow condition is extremelyimportant, because significant short term beach deformation iscaused by large waves, under which the sheet-flow sedimenttransport is usually predominant. In addition, under such conditions,we cannot discard the symmetry of near-bottom orbital

Χb=Hb/HO=Α/[HO/LO]{1 – exp(–1.5 (πh/HO)(HO/LO)(1+κ|tan θ|4/3]}...(1)


velocity due to wave non-linearity and the presence of undertowparticularly in the surf zone (Watanabe, 1994). Non-linear wavetransformation on a sloping bed can be computed by a set ofBoussinesq-type equations including a breaker-induced energydissipation term in the surf zone, the undertow (return flow near thebed) usually develops to compensate the shoreward masstransport accompanying the breakers. Since the concentration ofsuspended sediment is very high near the bottom, the effect of theundertow on the sediment transport should be inevitably taken intoconsideration. A Ph.D Thesis (Mir Hammadul Azam, 1998) hasconfirmed this effect of suspended particles in dissipating the waveenergy on flat and mild sloped beds beach. The soft mudbed shows resistance against shear force applied on its surface upto certain point. Above this critical point, bed starts to erode.

The study experimentally examined several hydrodynamicproperties and the suspended sediment concentration underbreaking wave condition. Numerical investigation was also made toascertain its effectiveness and to understand the role of hydraulicparameters on surf zone dynamics. Wave deformation, meanflow generation and suspended sediment concentration wereobserved. The results showed that the ratio of the incipient breakerheight to the mean water depth (H/D)b was an important parameterthat described the intensity of wave breaking. Wave energydissipation rate was higher when the value of (H/D)b washigher than 0.78. The estimated roller size over a flat bed was smallerthan that of the typical surf zone. The magnitude of mean horizontalflow and degree of turbulence below the trough level wasdependent on (H/D)b. The mathematical model study includedthe solution of the equation of motion and turbulence transportequation in a coupled form. The model was developed for aquasi-steady situation over a 2-D vertical plane. The results of thestudy provided guidance for the calibration of model. Modelpredicted results were compared with experimental measurements.The comparisons were satisfactory. Application of the model showed


that the turbulence under breaking wave was damped by the increaseof sediment concentration in the water. The turbulent field wasremarkably sensitive to vortex size under broken waves. Findings ofthe study help to understand the hydrodynamics in a distinct case ofbreaking that occurs over mud flat. The model study can assist inunderstanding the role of important parameters, which havesignificant effect on bed erosion and sediment transport.

Wave - Structure Interaction

Shallow coastal areas are extremely dynamic regions where fluidmotions associated with both surface waves and currentsinteract with the bottom sediments. An extended form of theBoussinesq equations have been developed to mobile boundaryflow model for the computation of wave deformation due to

Figure 6 Definition of wave run-up and wave reflection, waveovertopping and wave transmission

reflected waveHr

run-down hs

Hiincident wave

Wave overtopping

Wave transmission

HtHi

run-up

z

Q


combined effects of refraction, diffraction, reflection, breakingwaves, and wave current interactions from very shallowconditions to intermediate depth over slowly varying slopes ofbed (Antunnes do Carmo and Seabra-Santos 1994).

There is a strong interaction between a wave and a wavedamping structure like a breakwater. This interaction is visible in frontof the structure (reflection), on the slope of structure (run-up) andbehind the structure (overtopping and transmission) [http://www.vssd.nl/hlf/PDFs/f011h10.pdf]. Even if a breakwater structureis stable under the action of waves, there is an interaction betweenthe structure and the wave field near structure. The discerningphenomena that lead to different wave patterns in the vicinity of thestructure include wave reflection, wave run-up, overtopping and wavetransmission as illustrated in Figure 6.

Wave reflection plays a role in front of the structure, waverun-up takes place on the slope of structure, overtopping andtransmission are important for the area behind the structure. It isthen useful to analyze which phenomenon influences the designproblem in question. Too often, formulae for run-up or overtoppingare used when the designer wishes to address wave transmission.The wave motion in front of a reflecting structure is determinedby the reflection coefficient Kr that is related to the ratio ofreflected wave height over incident wave height Hr/Hi. For a 100percent incoming wave energy is reflected, Hr/H i = 1, thisis valid for vertical wall with infinite height. The reflectioncoefficient for sloping structures, rough or permeable structuresand structures with limited crest level is smaller.

The extensive breaking of waves will result in a spectrum thathardly shows a clear peak. A lot of energy has been shiftedto the lower frequencies. Definition of wave peak becomesdifficult, but remains important because of the influenceon run-up. Wave run-up is the phenomenon in which an incomingwave crest runs up along the slope up to a level that may behigher than the original wave crest. The vertical distancebetween Still Water Level (SWL) and the highest point reached


by the wave tongue is called the run-up “z”. We can only speakof the run-up when the crest level of the structure is higherthan the highest level of the run-up. Run-up figures are mainlyused to determine the probability that certain elementsof the structure will be reached by the waves. Run-up can beindirectly used to estimate the risk of damage to the innerslope of the structure. It is not acceptable for a largepercentage of incoming waves to reach the crest andsubsequently caused damage to the inner slope. In mostcases, the 2 percent run-up is given: the run-up level that isexceeded by 2 percent of the incoming waves. InNetherlands, research on run-up has attracted a lot ofattention, particularly for assessing the required crestlevel for dikes and seawalls. (Battjes, 1994, Anonymous,1998). The run-up on a smooth impermeable slopeis expressed as

Z2% = 1.6 ξop HS ...(2)

With a maximum of 3.2, in which Z2% = run-up level exceededby 2 percent of the waves, HS = significant wave height andξop = breaker parameter for deep water and peak period. Therun-up level can effectively be reduced by designing a berm atstill water level, by increasing the roughness of the surface,or by increasing the permeability of the structure. Wavesapproaching the structure at an angle will also lead toreduced run-up levels. This reduction is expressed in terms ofreduction factor γ . The effective run-up is then calculated bymultiplying the value for smooth impermeable slopes by thecorrection factors. Run-up levels on rough, impermeable/non-porous slopes can easily be calculated by applying thecorrection factors as indicated in Table 2. The factors are validfor ξ op < 3 to 4, above the value of 4,the reductionis no longer applicable.

For rough slopes with limited permeability/porosity, it ispossible to apply the general run-up formula and to makecorrections as long as ξop < 3 to 4 as shown in Table 3.


Table 2 Correction factors for roughness

Table 3 Correction factors for roughness and permeability/porosity

Calculation of wave transformation through a submergedbreakwater is based on energy (E) conservation. The equationin a steady state is expressed as

/ Χ E (cg cos θ+U)+ / y E (cg sin θ+V)+Sxx U/ Χ+Sxy ( V/ Χ

+U/ y) + Syy V/ y = – D ...(3)

Where Sxx, Sxy and Syy are the radiation stresses, cg group velocity(U,V) depth averaged mean current velocities in the x and ydirections and θ is the angle of wave incidence.

The energy loss is thus dependent on the vertical andhorizontal velocities as well as the angle of wave incidence θ. Whenthe incident waves break on the submerged breakwater, energy lossby wave breaking Db must be added to D. Thus requiresunderstanding of the following:(a) Critical depth on the submerged breakwater for wave breaking.(b) Two-dimensional wave transformation on a permeable layer

and submerged breakwater.

Smooth, impermeable(asphalt/closely pitched concrete blocksOpen stone asphalt etc.GrassConcrete blocksQuarry stone blocks (granite, basalt)Rough concrete

Source: Wave-structure interaction; Breakwaters & closure dams

Structure γ1.0

0.950.9-1.0

0.90.85-0.9

0.85

One layer of stone on an impermeable baseGravel, Gabion mattressRip-rap rock, layer thickness n>2

Structure γ0.55-0.6

0.70.5-0.55


In terms of stability, there are two types of breakwaters:statically stable low crested breakwaters (exposed) and Staticallystable submerged breakwaters. Stability depends on

H/d = (2.1 + 0.1 Sd) exp (–0.14 NS) ...(4)

H = Crest height of structure, d = water level, Sd = accepteddamage level.

For static stability, NS = 1 to 4 (designed for no damage/displacement of units). For dynamic stability, NS = 6 to 20(developed profile). The stability criteria, designs are based on theguidelines provided by Shore Protection Manual, US Army Corps ofEngineers, 1987 and Manual on use of Rock in HydraulicEngineering, Centre for Civil Engineering Research Codes, 1995.

Overtopping is defined as the quantity of water passingover the crest of a structure per unit time Q (m3/s). The quantityof water is often a linear function of the length of structure, it isexpressed as a specific discharge per unit length (m3/s/m). Thestudy of overtopping quantities is related to the stability ofthe inner slopes of structures such as dikes. When designingbreakwaters, thequantity of overtopping may be importantto determine the capacity of the drainage facilities required forport areas directly protected by breakwater, or to assess the riskto people or installations on the crest of the breakwater.Although the assessment of these sometimes-subjectiverisks on the basis of model experiments is difficult, it ispossible to derive a trend. The quantity of wave overtoppingis largely influenced by the nature of the outer slope of thestructure. An added effect is the influence of the shape andnature of the crest (presence of the crown wall). Unfortunately,various model investigations (Bradbury et al., 1988; Owen,1980; Van der Meer and Stam, 1992; De Waaland der Meer, 1992, and Aminti and Franco, 1994) includingthose performed at COEI were carried out with varying


structures. Therefore, it is not possible to derive a generallyapplicable formula for overtopping. As a first approximationby using the formula of Bradbury et al., (1988) which isvalid for a structure without a crown wall,

Q* = a (R *)–b ...(5)

with Q* √[gHs 3]√Q Som

2π ...(6)

and

R* = (RC/HS)2 √Som

2π ...(7)

in which R* = dimensionless crest freeboard, RC = crest freeboardrelative to SWL in m, HS = significant wave height, Som = deepwater wave steepness, based on mean period, Q = specificdischarge in m3/s/m and Q* = dimensionless specific charge.Relevant values of the coefficients a and b depend onstructural details.

It must be kept in mind that a vertical face breakwatercauses a lot of spray when hit by a wave. The spray may also beblown over the breakwater. This effect is normally difficult to bequantified.

Wave transmission is the phenomenon in which wave energypassing over through breakwater creates a reduced wave action inthe lee side of the structure. This will happen when considerableamount of water are overtopping the structure. Wave transmission isalso possible when the core of the structure is very permeable andthe wave period is relatively long. It is specifically the influence ofthese two factors that for a long time has prevented the derivation ofan acceptable formula for wave transmission by rubblemoundbreakwaters. In practice, limits of transmission coefficient kt areabout 0.1 and 0.9. It is remarkable that for Rc = 0, which representsa structure with the crest at SWL, the transmission coefficient isin the order of 0.5. This means that a relatively low structureis already rather effective in protecting the harbour area behind the


breakwater. In combination with the requirements for tranquilityin the harbour, the designer can decide on the minimumrequired crest level.

For traditional low crested breakwaters, the formuladeduced by Daemen (1991) relates transmission coefficient to anumber of structural parameters of the breakwater. To accountfor permeability, the freeboard Rc of the breakwater was madedimensionless by dividing it with the armour stone diameter and itreads as follows:

Kt = a [Rc/Dn50] + b ...(8)

In which Kt = Hst/Hsi = transmission coefficient,His = incoming significant wave height, Hst = transmittedsignificant wave height, Rc = crest freeboard relative to SWL,Dn50 = nominal diameter armour stone, B = crest width, Sop = wavesteepness. The values of a and b then varies for permeable andpermeable structures.

The high pressure from the wave breaking, run-up action andthe responding high pressure created below the revetment(filter layer) has to be neutralized and the associated energyto be dissipated. This effort is to prevent the structural slopeand the protective layer from damage and perhaps total failure orcollapse (Refer to Figure 7).

Wave attack on revetments will lead to a complex flow overand through the revetment structure (filter and cover layer). Duringwave run-up the resulting forces by the waves will be directedopposite to the gravity forces. Therefore the run-up is actually lesshazardous than the wave run-down.

Wave run-down will lead to the following two importantmechanisms:

(1) The downward flowing water will exert a drag force on the coverlayer and the decreasing freatic level will coincide with a down-ward flow gradient in the filter. Thus it may result in sliding.

(2) During maximum wave run-down, there will be an incomingwave that a moment later will cause an impact. Just before


the impact, there is a “wall” of water giving a high pressure underthe point of maximum run-down. Above the run-down point thesurface of the revetment is almost dry and therefore there is a lowpressure on the structure. The high pressure front will lead to anupward flow in the filter. This flow will meet the downward flow in therun-down region. The result is an outward flow and uplift pressurenear the point of maximum wave run-down.

Figure 7 The action of waves upon interacting witha sloped structure of a breakwater or revetment

Pressure development in a revetment structure

low pressure

at run-down

cover layerphreatic level

high pressurebelow revetment

filtera

breaking wave pressure head on the slope

SWL

slopemaximum difference inpressure on the cover layer

Schematization of pressure head on slope

slipcircle

Schematised development of S-profile and possiblelocal sliding in the base

Qf

Fbds


The schematized situation can be quantified on the basis of theLaplace equation form linear flow:

∂2Φ ∂2Φ∂y2 ∂z2

+ = 0

Φ = Φb = potential head in the filtery = coordinate along the slope (m)z = coordinate perpendicular to the slope (m)

The uplift pressure is dependent on the steepness and heightof pressure front on the cover layer (which is dependent on the waveheight, period and slope angle), the thickness of the cover layer andthe level of the freatic line in the filter or a slab structure. Theequilibrium of uplift forces and gravity forces leads to the following(approximate) design formula (Pilarczyk et al., 1998):

Hscr∆D = f D k’

b k0.33 ξ op

0.67 Hscr∆D

= For ξ op 0.67

or

Hscr∆D

= f D∆ξ op

with Λ ( )bDkk’

1/20.67

where Hscr = significant wave height at which blocks will be lifted out ξ op = tan α / (Hs/(1.56Tp

2 ))= breaker parameter [–]Tp = wave period at the peak of the spectrum [s]∆ = leakage length [m]∆ = (ρ

S – ρ)/ρ = relative volumetric mass of cover layer [–]

b = thickness of a sub-layer [m]D = thickness of a top layer [m]k = permeability of a sub-layer [m/s]k’ = permeability of a top layer [m/s]f = stability coefficient = KD mainly dependent on

structure type, tan α and friction [–]F = total (black box) stability factor [–]

... (10)

... (11)

...(9)


To evaluate the structural response y using wave loadapproach, there are two practical design methods available:the black box model and the analytical model. In both cases,the final form of the design method can be presented as criticalrelation of the load compared to strength, depending on thetype of wave attack:

cr

= function ξ opHs∆D

For revetments, the basic form of relation is:

cr

= ξ op2/3

Hs∆D

F with maximumcr

Hs∆D

= 8.0

in which F = revetment (stability) constant [–], Hs = (local)significant wave height [m], ∆ = relative density [–] , D = thicknessof the top layer [m], and ξop= breaker parameter [–].

The advantage of black box design formula is its simplicity.The disadvantage, however, is the value of F is known only veryroughly for many types of structures.

The analytical model is based on theory for placed stonerevetments on a granular filter (pitched blocks). In this calculationmodel, a large number of physical aspects are taken into account.In short, in the analytical model nearly all physical parameters thatare relevant to the stability have been incorporated in the leakagelength Λ = ( bDk /k’). The final result then F = f(Λ). To apply thedesign method for placed stone revetments under wave load toother systems (CUR/TAW, 1995), the following may be adapted:

• The revetment parameter F• The representative strength parameters ∆ and D• The design wave height Hs• The representative leakage strength Λ• The increased factor on the strength

...(12)

...(13)


Design Philosophy and Methodology: Towards InnovativeApproaches

The rigorous approach of innovation towards commer cializationof Research & Development (R & D) for coastal protection structuresinvolves basic research and understanding of the coastal processesand related phenomena for the wave, current-structure interaction,structural designing aptitude and common sense. It is based onprevious experience of others for the application of thetechnologies, model tests and technological development forindustrial application, prototype development and field tests,production of prototypes, and eventually competitive marketentry, sales and technical services.

Design Philosophy

A bank, eroding due to wave action, can be protected by making arevetment (Case A) or by constructing a wave attenuator(breakwater) perpendicular or parallel to the shore (Case B) or infront to the bank (Case C). The later was normally chosen when the“natural” look of the bank has to be preserved. Revetments andBreakwaters are constructed to protect land area (populationand economical values) against erosion or inundation dueto storm spells. There is still much misunderstanding on theuse of these structures and their possible disadvantagesrelated to the disturbance of the natural coastal processesand even acceleration of beach erosion.

However, in many cases, when the coastal area is under threatof further erosion or endangered by inundation such as in Nether-lands, leading to high economical and ecological losses, the struc-tures can be a “must” for survival. Absolute safety fromstorm surges or monsoons is nearly impossible to realize. Thus,it is more enlightening to examine the probability of failure ofcertain defense systems and to come up with value-addedsystems that have been optimized in terms of performance,workability, practicality, and cost.

Generally, the principle in the design is based on the


perception that the structure is to withstand the hydraulic forces dueto wave attack (Stability Criterion), capable of accommodatingfoundation deformation (Flexibility Criterion) and does not sufferloss of function due to ageing during its design life (DurabilityCriterion). It is also recognized that a common failure mode ofmodular concrete blocks is due to uplifting of the individual blocksand slope failure due to slip circle. Thus the design also focuson the interlocking system that would give better hold so as to allowfor no damage or displacement of individual units and systemstability and flexibility via sediment trapping and automatic drainagefeatures to accommodate impacts of nature’s forces and pressures.

Design Methodology

In designing coastal protection structures, the followingaspects have to be considered:

(i) The function of the structure.(ii) The physical environment.

Figure 8 ThedesignmethodologyNATURAL ENVIRONMENT

WATER LEVELS, TIDES, WAVES, CURRENT, SEABED

MODELLEVEL 3

MODELLEVEL 2

MODELLEVEL 1

SIMULATIONDESIGN

CONSEPTUALDESIGN

PRELIMINARYDESIGN

DETAILENGINEERING

GO TONEXT PHASE

REDESIGN

NO

YES

OK

CRITERIA

EVALUATION

FUNCTIONAL REQUIREMENTS

OBJECTIVESShoreline stabilizationBackshore protectionInlet stabilizationHarbour protection

CRITERIAPerformanceTechnical feasibilityEconomic feasibilitySosial/Political stability


(iii) The construction method.(iv) Operation and maintenance.

The main stages of design, simulation and evaluation canbe identified in the design process as shown in Figure 8.

Design Criteria

The innovative approaches for the physical considerations ofstructures involve basic research, comparative studies of existingdesigns, model development, trial simulation tests, prototypedevelopment and field testing. Consequent requirement is theresulting structural design should be effective and efficient.Effective means that the structure should be functional both forthe user and the environment. Efficient means that the cost of theeffective structure should be as low as possible and that theconstruction period should not be longer than necessary.Combination of this criteria of effective and efficient is “value formoney”. An integrated design process can be presented as inFigure 9 below

Geometrical Design

Selection of the structural concept depends on the function, thelocal environmental conditions and the construction constraints. Thegoverning criteria are the technical and economic feasibility for the

Figure 9 An integrated design process for optimizing effectivenessand efficiency

CostEnvironmentFunctionality

Technology Construction

Time

InitiativeFeasibility StudyProvisional designFinal DesignDetailed design


project under consideration. The function of the structure is mainlyto protect the hinterland against the adverse effect of high water andwaves. If the high-water protection is required, the structure shouldhave a height well above the maximum level of wave uprushduring the storms. This normally calls for high crest elevation. If,however, some overtopping is allowed in view of the character ofthe hinterland, the design requirement is formulated in terms ofthe allowable amount of overtopping. Obviously, crest elevationcan be reduced considerably in this case.

The shape of the cross-sectional profile of the structure is aninfluence on the distribution of wave forces, and thus, also influencesthe choice of material (type of protective units and their dimensions)suitable for slope protection (revetment) and the height of thestructure. The gradient of the slope must not be so steep that thewhole slope of the revetment can lose stability (throughsliding). This criterion gives, therefore the maximum slope angle. Moregentle (flatter) slopes lead to a reduced wave-force on the revetmentand less wave run-up; wave energy is dissipated overa greater length. A similar effect can be obtained by applying aberm (trapezoidal profile). Another point of economic optimizationcan be the available space for structural construction ofimprovement. All these factors should be taken into accountin optimizing structural slope. A common Dutch practice is to applya slope of 1 : 3 on the inner slope and between 1 : 3 and 1 : 5 onthe outer (seaward) slope. The mild slopes also minimize the scourat the toe of the structure (lower reflection). The minimum crestwidth is 2 m.

By studying the weaknesses of the existing systems,innovalue ideas for the elaboration of the design process dependson specific local circumstances, type of area, its development(economic value), availability of equipment, manpower andmaterials, etc. The cost of construction and maintenance generallyis a controlling factor in determining the type of structure to beused. The starting point is the cooperation with the client orfuture manager of the project.


The Field/Site Condition Studies

The detail requirements for reliable data in detailing the design ofcoastal protection structures comprised of:• Hydrographic surveys - Bathymetric Charts, shoreline,

seabed contour or seabed topography.• Hydraulic studies - water levels, tides, waves currents,

sediment transport.• Geo-technical studies - sediment sampling, slope stability.• Natural environment and socio-economic impacts.

It is very pertinent to obtain possibly, as certain the extremevalues of certain return period (e.g.,10, 20, 50 and 100 years) ofHighest Astronomical Tides (HAT), Lowest Astronomical Tides (LAT),significant wave height and wave period, Mean Sea Level (MSL) inorder to optimize the design by simulating the extreme conditionsexperimentally. Thus, values of run-up and run-downs, overtopping,stability coefficient and so forth can be gathered.

Option for Rock/Rubblemound or Pre-cast Concrete Blocks forArmoured Slopes

Traditionally, in developing countries, rubble-mound or rockrevetment has been an accepted method of coastal defense. Thoughin terms of economic of use it is acceptable, but the supply of rocksis limited and the method is less environmental friendly as this meansblasting off the rocks from the quarries. Alternatively, various typesof articulated blocks have been designed and prefabricated in theform of pre-cast concrete blocks. These blocks provide a higherstability coefficient value KD, compared to rocks, thus, allowing theuse of a lighter weight of the blocks as well as provision foradditional esthetical design features that can provide the strengthagainst the impacts of the waves, current and tidal changes. Theproduction of pre-cast concrete and composite systems alsoprovide a new avenue for manufacturers in their product line ofbusiness. Eventually, a design engineer has to decide on theproduct performance over the costs or vice versa. The ultimateaim is to retard erosion and to break the impact of waves as well as


entrap sediments. Thus, an approachable solution is soughttowards the design and development of innovative systemsthat are aesthetic multifunction shoreline structures.

Case A - Analytical Design Method of Block Revetments

With or without protection, coastal banks are proned to damageas they are continuously exposed to various attacks from the waves.The slope instability, collision or aggression by vessels,subsidence, the instability of the protection structure, waveovertopping and toe erosion as shown in Figure 10.

The approachable method is to prevent the collapse ordamage or armoured protection by avoiding the structural failuredue to slip circle as shown by ABC in the Figure 11 below.

Figure 10 Various forms of shoreline instability

instability of protection wave overtopping toe erosion

subsidencecollision/agressioninstability of slope

A

B

C

flexible

sandtightDESIGN

strong

permeable

Figure 11 Analytical approach of designing revetments


The design should encompass the compromise for structuralstrength, permeability, filter layer compactness and flexibilityof the system. The various factors that may lead to structuralfailure are generalized as shown in the Figure 12.

To create a stable beach, wave damping mechanism in theform of slope protection at the bank or wave reductor nearshore(artificial reef) can be designed where a balance of structuralstrength and load to neutralize the forces is created as illustrated inthe Figure 13 below. The dimensionless stability parameterH/∆d is evaluated.

Figure 12 Factors contributing to structural failure

Figure 13

Macro instability

Structural failure

Erosion of slope

Micro instability Instability of protection

Toe erosion

Wave overtopping

Subsidence

Aggressioncollision

Soil parameters - wave and current conditions - geometry

erosion

revetment

wave reductorunstable

stable

A

B

load

stre

ngth

A

B

damage

H/∆d as mobility parameter

H/∆d

H/∆d as stability parameter

α


Case B - Control of Beach Deformation Using Groyne.

A groyne is a structure constructed along a coast usuallysticking out from the normal direction of the shoreline by controllinglongshore sediment transport. This type of structure has beenutilised to prevent coastal regions including river mouths fromboth erosion and accretion of sand. The fundamental methodologyto arrest related erosion problems involve as follows.

A retreat of the shoreline is caused by the longshore gradientof the total longshore sediment transport. The movement ofthe longshore sediment transport can be controlled by constructinga group of groynes such that the longshore sediment transport maybe reduced. Enclosure of part of the beach from the surroundingareas by constructing a pair of groynes to make a pocket beachwhere the sediment transport rate is closed. A T-type and L-typegroyne are normally constructed for controlling sediment movementin the cross-shore direction. A pair or group of groynes areconstructed to control longshore movement of replenishedsand through a sand-by passing system.

The trap rate of the longshore sediment transport rate of agroyne is a function of the dimensions and plane arrangement ofgroynes (length of groynes, spacing, etc.) and the characteristic ofthe incident wave and the beach (bottom slope, bed material, etc.).It is needless to say that the trap rate increases with the increasinglength of the groyne. The function of the groyne where the longshoresediment transport develop is to tap part of the sediment transportedin the longshore direction to settle it in the upstream of the groynes.The rest of the sand is transported through the groynes downward.When the length of the groyne is long enough to trap the wholelongshore sediment transport, severe erosion takes place in thedownstream side of the groyne. The groyne tends to reduce itsfunction to trap sediment after the amount deposited sand in theupstream side of it exceeds its capacity.


Case C - Artificial Reefs

Measures to preserve sandy beaches using other coastalstructures such as groynes, revetments and offshore breakwatersoften conflict with the criteria needed for tourism which is to sustainand preserve the natural beauty of the beach. The development oflow crested wide submerged breakwater known as artificial reef isan alternative that provide protection for the coastline and at thesame time induce marine life. Low crested structures can be dividedinto 3 categories; dynamically stable reef breakwaters, staticallystable low-crested breakwaters (exposed) and statically stablesubmerged breakwaters.

Recently, the number of coasts where artificial reefs areconstructed is increasing. The object of the construction is thereduction of coastal disasters and the effective utilization of the coastalarea by reproducing the function of the natural reef in the seanaturally. In this system, the width of the breaker zone becomeswider than that of the native beach and the potential for preventingdisaster increases. The submerged breakwater in the perchedbeach-type artificial reef is required to be able to reduce theenergy of high incident waves that may become dangerousto the beach behind it and to keep replenished sand. Reductionof wave overtopping by the use of artificial reef (Goda,1985; CERC, 1984, Sawaragi et al., 1988).

The artificial reefs are, however, of various shapes, sizes andmaterials. They are designed tailored for specific functionsdepending on the needs and requirements of the respectivecountries. Some are made of an assemblage of used rubber tyres(Malaysia), branches of plants such as mangrove, bambooand coconuts (Philippines), rubblemounds (Indonesia) pre-castconcrete and PVC (Japan and USA).

The pre-cast concrete is proposed due to a more systematicapproach in the design of the structure whereby optimum height ofthe breakwater can be prepared in accordance to the most efficientstructure to retard the waves or to dissipate the wave energy. “HexReef” and “Restar”, the referred artificial reefs are among those whichhave been invented and designed in mind with advantages, and as


a possible alternative for inducing marine life that resembles thefunctions of natural reef.

Siltation Studies

Apposing to erosion, there is the sedimentation or siltation phenom-ena. Siltation is one of the most difficult coastal problems and so toois the counter measure against sedimentation due to siltation. Sub-merged breakwaters have been used as protection works againstshoaling in navigation channel at Kumamoto Port (Tsuruya et al.,1990). COEI has also experienced conducting the physical modelingstudies of siltation by using submerged berms.

Physical Modeling of Coastal Protection Structures

The criterion for a model to replicate the prototype involves severaltypes of similarity. These include:

Geometric similarity:

For undistorted model, the vertical scale η1 = 1m /1p where 1m and 1p

are the length for model and prototype respectively, and the ratiosfor each parts should be the same throughout.

Dynamic similarity:

The forces in the model has to be in the same relative magnitude asthe prototype. For wave models, this normally expressed in thedimensionless quantity namely Froude Number Fr, i.e

Fr = [v2 /gd]1/2 ...(14)

(Where v is the velocity, g the gravity and d is the water depth). ThisFr must be the same in model and prototype. The physical modelingof waves follows the assumption that the wavelength is scaled as thelength scale.


Physical models are used because they can simulateproblems we do not fully understand. They actually help us tounderstand problems better and point to possible solutions, but theresults are essentially qualitative. The main challenge inphysical modeling is to translate the qualitative results intouseful quantities.

Other scaling rate of prototype (p) versus model (m) whichare of great concern apart from the length η1 = 1p/1m includes timeηt = (η1)1/2 e.g., for wave period T, velocity ηv = (η1)1/2 and sedimentsize ηd50 = (η1)1/4.

Scale and laboratory effects will need to be substantiallyreduced in the future to make such interpreted physical modelingresults believable. One example of interest to coastal engineers, forwhich not all of the coefficients are known and there isconsiderable uncertainty about applicable relationships, issediment transport by waves and currents, computation of ensuingmorphological changes. Both numerical and physical models ofcoastal morphology have major problems. Physical models,however, even though they are plagued by scale and laboratoryeffects, the results will give reasonable qualitativeapproximations.

Key Tasks of Physical Modeling Study

Stage 1: Inception Data assembly and familiarization, data review, Scoping field investigation and laboratory experiment, Site study, confirmation of work and methodology, Construction of physical model.

Stage 2: Laboratory testing & simulation testsVariable parameters include wave height, current, waterdepth, wave period, model configurationsMeasurement and observations: Reflection, run-up,overtopping, settlement, displacement, sedimentdeposition, etc.

Stage 3: Data analysis, evaluation and reporting


Laboratory Facilities at the Coastal and Offshore EngineeringInstitute (COEI)

The experiments for the hydraulic model investigations werepossible to be carried out at COEI due to the availability of the stateof the art instrumentation and facilities. These include:• A wave basin (5 m ∞ 20 ∞ 1 m). Equipped with a computer-

controlled piston type of wave generator capable ofgenerating regular and random waves.

• 4 Fixed bed Test channels/flumes (separate channel forsand and mud) fabricated with wave making facilities,circulating current, reservoir with agitation tank for mud supply,variable slopes and wave absorbers.

• Particle Image Velocimetry (PIV) system using Argon Ion Laserand complete image interrogation system.

• Laser-Doppler Velocimetry (LDV): fiber-optic linked system.• Acoustic Doppler Velocimetry (ADV)system (3-D velocity

measurement).• Miniature currentmeters.• Data acquisition systems and computing facilities.• Wave sensors, wave probes and wave gauges.• Suspended sediment monitor (OBS).• Workshop facilities.

Velocity measurements and mapping of the flow couldobtained using the Particle Image Velocimetry system (PIV) model6200 manufactured by TSI Inc., USA. In this experimental set-up, thelaser beam was shot above and parallel to the test flume and thenreflected down from the top by a mirror. It was spread into a lightsheet by the appropriate combinations of cylindrical and sphericallenses, illuminating a plane parallel to the flow in the flume. Acamera, which was placed alongside the flume, focused the movingparticles through a rotating polygon mirror. The image captured isanalysed by using the interrogation system and PIV software.Current flow and circulations around structures could be understoodin detail. Studies related to the 3-D flow profiles around structurescould be obtained using the Acoutic Doppler Velocimeter.


Wave measurements using wave sensors and theacquisition system enables regular and random wavemeasurements could be captured instantaneously, N wavesfrequently simulated up to 5000 waves.

The water supply system mainly provides non-salinewater. The availability of workshop facilities, enables COEI tofabricate its own design structural models for the physicalmodeling studies. Technical support staff at COEI and withthe technical support services of counterparts from UK,Netherlands, India and Singapore as well as local consultantshas enabled comparative research breakthroughs to becarried out at the Institute. Most of the research conductedderived support from the government IRPA/RMC 61030, 72096,72106, 71658 and UTM/COEI for facilities & instrumentations,whilst others are contract research sponsored by clientsfrom government agencies and engineering consulting firms.

Physical Modeling Studies: Model Versus Prototype

A brief report on the related research on coastal protectionstructures (revetments and breakwaters) carried out at the Coastaland Offshore Engineering Institute (COEI), Universiti TeknologiMalaysia (UTM) is presented in this section. Table 4 gives asummary of the projects.

Table 4

Sine-Slab system as coastalprotection measureScale: 1 : 3, 1 : 5

Exhibit size: 1 : 10, 1 : 5, 1 : 3, 1 : 1

MOSTE,RMC/UTMDID MelakaZen ConcreteIndustries SdnBhd, Shah’sBeach Resort

Start1995

1999

Model,prototype testscompletedPatented andcommercialisedOn-going R &D&C,InnovativeR & D

1.

Physical modeling study ofsubmerged berm for theproposed harbour at KualaBaram, Mir i , SarawakScale: 1 : 20

2. JuruteraPerundingWahba

1994 HydraulicModel testscompleted

No. Title of Project Sponsor/Client Year Status


* Recent work carried out while at Bureau of innovation& Consultancy, UTM.

3.

Hydraulicmodel tests,numericalmodeling, flowmapping

Siltation Study and submergedberm for Kuala Perlis Jetty

Public WorksDepartment

1994 Hydraulicmodel testscompleted

Hydraulicmodel testscompleted

Physical modeling study ofsubmerged berm for theproposed fishing harbour atBatu Maung, PenangScale: 1 : 15

FisheriesDevelopmentAuthority ofMalaysia

19984.

Physical modeling study ofartificial reef (Hex reef) forcoastal protection and beachformation at Pulau Layang-LayangScale: 1 : 20

Physical modeling study of HexReef for the proposed coastalprotect ion at TerengganuRivermouthScale: 1 : 20

Resuspension of suspendedsediments under breaking wave(Kuala Perlis)

Siltation problem andsubmerged berm ascountermeasure, Scale: 1 : 20

PetronasResearch &ScientificServices(PRSS)

Field/underwatersobservationscompleted

Proposed,awaitingbudget

5. NationalHydraulicResearchInstitute(NAHRIM)

1995 Hydraulicmodel andprototype testscompleted

NationalHydraulicResearchInstitute(NAHRIM)

1998 Hydraulicmodel testscompleted

6.

7. MOSTE,COEI,UTMPhD Thesis

1997-1998

Hydraulicmodel tests,numericalmodeling, fieldobservations

8. MOSTEUTM/RMCMSC Thesis

1997 Hydraulicmodel tests forvariousconfigurationscompleted

Wave propagation over adepressed bottom topographyLaser-based, Particle ImageVelocimetry Technique

9. UTM/COEIPhD Thesis

1999

Monitoring of south breakwaterat PAB export terminal, Tg.Sulong, Kemaman, Terengganuwith Hydrographic SurveyGroup, FKSG, UTM

10*. 2002 Fieldobservationshydrographicsurvey

Monitoring restar at Pulau Rhu,Besut, Terengganu

11*. Yayasan EhsanBerhad

2002

Coastal monitoring andprotection works for PetronasFacilities, Terengganu

12*. PRSS 2002

No. Title of Project Sponsor/Client Year Status


RESULTS AND DISCUSSION

Limitation of the Studies

The reliability of the model simulation tests also rely on the modelingscale, the limitation on the size of the wave basin or wave flumes willreduce the accuracy as the size gets smaller. At times it is possibleto perform distorted modeling with varying vertical andhorizontal length scale due to limitation on the size of facilities.Limited number of models due to cost and constraint on time alsopose a hindrance to obtain a comprehensive data for designguidelines. The modeling of non-cohesive beach material is not atrivial process. Many model laws have been derived (Dalrymple,1985). Problems arise in the scaling of sediments especially as inthe mud case. As sediment becomes significantly smaller, itsproperties change (for example, becoming cohesive and this maynot migrate under the action of waves as desired). Due to thislimitation, the sediment samples for the laboratory tests will be largerthan the modeling scale of which d50 should be the fourth power ofthe length scale η1. Sediment samples of size below than 0.1 mm isalso difficult to be simulated. In our studies, in order to preserve mostof the properties of sediment, the actual sediment samples collectedfrom the site as seeding samples was used. This will result ina mud sample with larger sediment size than that obtained bysimple scaling of d50 by η1 . Reports of other previous studies,however, have shown that this is the mostfeasible approach.

The following section briefly describes results of some of theearlier projects undertaken.

Physical Modeling Study of Submerged Berm for the ProposedFishing Harbour at Batu Maung, Penang

The Fisheries Development Authority of Malaysia (LKIM) wasconcerned about the sedimentation problem in relation to theproposed infra-structural development at the fishing harbour atBatu Maung, Penang. The objective of the study was to perform a


physical modeling study for the performance of the proposeddesigns of berms in controlling sedimentation. Previous modelingstudy by Hydec Engineering Sdn Bhd had suggested to adoptalternative 2 scheme after modeling using MIKE21 and LITPACK.This comprised of a northern breakwater (555 m length) constructedto Mean Sea Level and the Southern breakwater (668 m length)constructed above the Highest Astronomical Tide. Thetypical cross-section of the proposed berm is 2 m and 4 m crestwidths with a slope of 1 : 3, 2 m allowance for side base lengths and1 m base thickness to allow for settlement. The height of the bermwas then a variable parameter.

The experimental study was conducted on a 18 meter longwave flume of cross section 60 cm ∞ 55 cm as shown in Figure 14.It had flow re-circulating facility through a water tank. A false bedwas constructed with a slope of 1 : 2 in front. A depression wasprovided at the end of the bed. A perforated wave damper wasplaced at the end of the flume. 1 : 15 scaled model of the proposedberm was constructed and placed before the depression.A mechanical stirrer was set into the water tank. The purpose ofplacing the stirrer was to stir the water so that sediments are notsettled in the tank.

Figure 14 Typical experimental set-up and facilities for berm study

PumpReservoir

Out

In

WavegeneratorWave

gauge

Berm

Not to scale

ADV083


Flow was generated using a pump that had a control valve toregulate the flow. A PC-controlled DC motor oscillated the flaptype wave paddle. The amplitude of the paddle could be adjustedby changing the shaft position on the motor wheel.

Based on the requirements of the engineering designs for thefacilities at Batu Maung fishing harbour and the COEI laboratoryfacilities, the physical modeling study was conducted in thelaboratory in order to study the effectiveness of the proposedsubmerged berm by establishing the current and sediment flowpattern for variable height to depth (h/d) ratio i.e varying the height hof the berm at (or the water depth) under corresponding current andwave condition (including extreme conditions) (Refer to figure 15).

The factors considered in the design of the mitigativemeasures against sedimentation (dredged basin and submergedberm) in the study area include the Design Water level (DWL), thedesign wave characteristics, design water depth, design waveperiod and design berm height, sediment transport characteristics,sediment samples and current range.

Figure 15 The test flume showing the set-up of thephysical modeling study for the submerged berm inpreventing siltation in a depression channel

AbsorberOBS/ADVDepression channel

Location of berm

Mud fluid flow

Wavegenerating

facility

Dataacquisition

system

Stirrer


Four types of berm configurations were tested andsimulated in the laboratory at a model scale of 1 : 15, one is shown inFigure 16. The results have shown a tendency for berms with greaterheights to be more efficient. In addition, if the crest width is longer,more sediments will be settled down and trapped upstream asthe velocity slows down upon reaching the crest and less sedimentsdeposited downstream due to longer travel time. Variation ofberms efficiency in reducing sediment deposition with relativeberm height were presented. The reduction in sediment depositionincrease linearly with berm height. For lower sedimentconcentration, the reduction of deposition increased with h/dat slower rate initially, but a steep increase in reduction of depositionoccurred when h/d increased above 0.8. With h/d, when sedimentconcentration was higher, both of the results show that theefficiency of the berm was very low when the relative berm heightwas low. The efficiency of the berm was reduced when thesediment concentration was increased. This was because,over the depression, where the mean velocity was less thanthat before the berm, the deposition rate increased with thesediment concentration. Under relatively less wave-currentaction, the increase of sediment concentration enhanced theflocculation process of the fine cohesive sediment particles.Flocculated sediments deposited at higher rate with theincrease of the settling velocity.

Figure 16 Berm model made of fiber-glass used in the experiment


Among the issues arising as limitation of the study include:

(i) The scaling of sediment properties were simplified interms of its size, salinity and non-saline fluid with noflocculating properties.

(ii) The test was a one-dimensional representation of a purelytwo dimensional scenario and uni-directional wave-currentwas gross simplification of the actual phenomena.

(iii) Part of the total channel width was taken under considerationdue to limitation of the space.

(iv) Seaward open end of the berm was not represented in thestudy and structure was limited laterally by flume walls.

(v) Waves were considered monochromatic.(vi) Bed load transport was not incorporated for the study,

therefore, interaction of suspended load and bed load wasnot represented.

By comparison in the efficiency for the reduction of sedimentbased on simulated conditions of physical parameters at Batu Maung,the configuration for berm 4, which have a length of 146.54 cm, heightof 20.00 cm and crest width of 26.6 cm or prototype length of 21.98m, height of 3 m and crest width of 4 m was recommended. For amodel free board of 7 cm equivalent to prototype free board of 1.05m, the study has shown that berm 4 will provide about 80 percentefficiency. On the other hand, if berm 3 was chosen, it may not be asefficient (η = 65 percent) but it is not economical due to morematerial is required to construct for greater height of the berm.Configuration for model 4 was recommended for a cost effectivesolution in this project.

Physical Modeling Study of Artificial Reefs

(a) (Hex reef) for coastal protection, beach formation andenhancement of marine life at Pulau Layang-Layang.

(b) Other studies on artificial reefs-Restar.

Sandy beaches of small islands or atolls located on coralreefs are constantly exposed to wave attacks as well as the


detrimental effects as a result of coastal development boom.Unwise development of beach resorts and coastal structures oftencause coastal erosion in some areas and sedimentation inothers. Pulau Layang-Layang, the island being named after oneof the species of the sea birds at one time would have becomean irony due to reduction in colony and possible disappearanceof the birds. This was due to the unavailability of beach sandfor nesting, not to mention destruction of hard and soft corals.Hard structures have been installed around the island toprevent coastal erosion due to wave attack especially duringseasonal storms. Sedimentation and reduction in water qualityhas caused severe effects on the marine habitat.

Studies related to applications and impacts of introducingartificial reef i.e., pre-cast concrete structures towards providingsolutions to coastal protection against erosion and as tools formarine habitat enhancement have been conducted by Malaysianresearchers (Malaysian Dept. of Fisheries, UPMT, NAHRIM,COEI-UTM). New development in the technology of the constructionof artificial reefs in Malaysia has also introduced the applicationof PVC pipes which was launched in 1991 in Kedah (S. Wagimanet al., 1994 and Kushairi, 1998).

Terumbu Layang-Layang “Swallow Reef” on Admiraltycharts, is an isolated submerged coral atoll in the SouthChina Sea, 200 km northeast of Kota Kinabalu, Sabah. PulauLayang-Layang and Pulau Tioman renowned forspectacular diving destinations, each has a test beddesignated for pioneer studies and assessment for coralrehabilitation and enhancement of marine life using speciallydesigned pre-cast concrete structures.

The geometrical design is largely determined by the factthat marine equipment is normally required for construction.Sometimes, the construction is done with land-based equipment viaa (temporary) causeway, but this approach is not forward as itrequires substantially more material handling. In most cases, the


armour of the front face is protected near the bottom by a toe. Theintroduction of artificial reef the Hex Reef for the breakwateris aimed to satisfy design considerations. It has the features ofsatisfying the stability criteria (broad base), segmented andinterlocking and made of semi-permeable pre-cast concretematerial (with some spaces in between) that provides an increasein absorption of wave energy. The specially designed Hex Reefwas aimed at introducing a breakwater that also functions as abreeding ground for the marine life, (NAHRIM Report, January 1996).Artificial reef has been found effective in dissipating incomingwave energy (due to its width) and reduction in wave height in(NIZAM, 1996). In this study, energy dissipation due to reductionof wave heights H and variation in velocities U had beeninvestigated around the model structure, the effects and theperformance evaluated.

Physical modeling study at model scale of 1 : 20 wereconducted prior to installation of the Hex Reef at Pulau Layang-Layang (N. Mokhtar et al.). The research described here basically toprovide information on site study and preliminary monitoring resultsor baseline study. COEI had constructed a physical model andperformed hydrodynamic tests on the three types ofcombinations: combination 1, combination 2 and combination 3.The study was based on the proposal (NAHRIM, 1996) andinformation from Jurutera Perunding Wahba (Semenanjung) andJurukur Teguh Sdn. Bhd.

The following information were obtained at early stage fordesign considerations, for example in the case of Pulau Layang-Layang, the Design Water Level (D.W.L), HAT = 2.2 m on C.D,MSL = 0.8 m on C.D, LAT = 0 m on C.D. Consequently, a rangeof water levels are established in determining wave forces orimpacts on a structure. From hydrographic survey chart, thereappears a large variation in bed topography. Waves alsoappear to be non uni-directional but possible impacts ofoblique waves are not considered in this modeling study.


Theoretically, it has been reported that in such situations therewould be an increase in littoral sediment transport. The designconcept and implementation is based on the diagrams as shown inFigure 17.

In early February 1997, after the physical modeling/laboratorystudy was completed, the prototypes were then produced bySin Matu Sdn. Bhd. at a casting yard in Limbang, Sarawak. Weightof each module of Type A = 2000 kg, height: 1200 mm, base 1200mm, top side: 900 mm with one side slope 4 : 1. The design conceptof a combination of a groyne (80 m) and a detached breakwater(140 m) was adopted. Artificial reefs, a single side of combination1 (type A) of Hex Reefs were assembled in the form of a groyne anda detached breakwater were built at latitude 07 22' 15 N andlongitude 113 50 02' E (Figure 18) to protect the coast andfacilitate beach formation in April 1997. The static stabilityparameter NS of Hex Reef for the type A is ~ 2, Characteristicdiameter D =1.2 m, Significant wave height 2 m and relative massdensity ∆1.1. Prototype settings adopted for bed elevation: –5 m,an equivalent slope: 1.8 m and wave period: 8 seconds. Additionalbaseline data collection and biotic monitoring study was conducted

Figure 17 The concept of artificial Reef namely Reef Hex as coastalprotection structure with suitable combination types

Combination 1 Combination 2 Combination 3

(A) The Hex Reef Concept

HEX REEF – A Product of NAHRIM


for the detached breakwater to assess the damage,colonization and re-growth of the marine life 2–3 months later.

In the site study, apart from the wave climate, physicalproperties of the sea-water and current were also measured for 4stations (Figure 17). Among the instruments used include wave probeand recorder, self-recording current meter, Salinity and PH meters.Of the two breakwaters of prototype A constructed, the groynebeing shorter and well exposed, hence do not appear to have muchimpact on marine life. The offshore breakwater being longer with agreater proportion being submerged, thus some underwaterobservations and assessment of living organisms were conductedusing underwater cameras and transect-lines approach respectively.An increase in the colony of Layang-Layang birds has also beenobserved since the completion of the installation of the structuresdue to accumulated beach sediments formed for the nesting area.

The concept of combining the groyne with a detachedbreakwater had shown to be successful to trap sediments for theformation of artificial beach. A single modular row units of Hex Reeftype A was used to stabilize the coast thus prevent further erosion ofthe beach which was necessary as a nesting groundfor the seabirds. The study was, however, insufficient as the rate ofaccretion or accumulation of sediments need to be estimated and

Figure 18 Study location of Hex Reef at Pulau Layang-layang


measured by tracer methods, for example. Since the breakwater werenot submerged or exposed particularly during the low tide, theeffectiveness for marine enhancement tool is reduced. Structuresmay be subjected to radically different types of waveaction as the water level at the site varies. The Hex Reef Structuresystem provides segmented modules of a breakwater with zoningof the crest widths into several layers and crevices. The unstabilityalso have been shown to occur at the edge and bottom of thestructure where greater turbulence and unsteady flow are generated.This can be minimized by having toe protection as suchother rocks or other vertical structure of heights at least 10–20percent height of the individual Hex reef module being placed infront of the structure.

Field work involving hydraulic study including wavemeasurements and visual inspection for the monitoring theperformance of the completed system is required in order to providesubsequent detailed design of the system or other similar systemsat the particular location around the island or elsewhere. Continuousmonitoring of the performance of the artificial reef systems shouldbe conducted and with a greater frequency of the data collectionand analysis, a greater understanding for the eco-engineeringsolution to restore and conserve the marine environment could begathered. Further analysis on the impact of the reef will be carriedout via computer modeling, physical modeling and bioticmonitoring for this year as part of the study phase 2. From theencouraging laboratory and field results, the Hex Reef has thepotential to be commercialized and applied elsewhere in other partsof Malaysia and worldwide.

This pioneer experiment on coral rehabilitation using concretestructures, however, has showed that coral may grow and multiplyto some extent over a devastated area when given the chance to doso under oceanographically proper physical conditions created. Ar-tificial reef and artificial habitat technology, if utilized and implementedin an acceptable manner, would provide an alternative solution tocounter problems with threatening deterioration of habitat ordepletion in marine resources.


Other Artificial Reef Studies - Restar at Pulau Tioman and PulauRhu

A separate research is undergoing for the application of the Restar(Restoration of Artificial Reef Structure) and adjacentarea around Manggo Beach, Tekek, Pulau Tioman. Restar isactually an assemblage of Sine-Slab weighing 2000 kg designedfor loading of marine life of up to 700 kg. This study aims forcoastal protection and the possible affect of diadema on thesettlement of coral larvae. Until that further research is completed,no appropriate deduction could possibly be made with respectto this. From the preliminary field results, Restar also has thepotential for creating a habitat for marine life. Anotherencouraging observation site for Restar study is at Pulau Rhu,Besut, Terengganu (Yayasan Ehsan, 2002). Unfortunately,there was no opportunity for physical modeling study of thesystem conducted yet.

Physical Modeling Study of Hex Reef for the Proposed CoastalProtection at Terengganu Rivermouth

In the case of the problems of blockage encountered at theTerengganu river-mouth, proposed structures are in the form ofshore-connected pair of groynes using artificial reef structure i.e.,Hex Reef to control fluid motion (waves and current) resulting inreduction of wave height and sediment transport NAHRIM, 1998.The water depth needs to be maintained at certain width ofthe channel for traffic at the same time providing calm wateron the leeside of the breakwater. The Hex reef blocks were testedfor various model configurations. Unstability and damage tostructures around the curve of the breakwaters were observedespecially for combination type with high h/d. Accretion wereobserved upstream and erosion were detected downstreamof the structure.

Experimental results were sought for breakwaters installedat the northern part of the rivermouth, with varying heights ofthe structure (combination types) and alignment types. Typical model


cross-sections of breakwaters were fabricated in a two-dimensionalwave channel in the laboratory. The model scale was taken as 1/20.Model does not include the base material for rubble stones torepresent the rocks for prevention of scour or settlement of thestructure. Three different sea levels were assumed in the presentexperiment. H.H.W.L (Highest High Water Level) and L.L.W.L (Low-est Low Water Level) were considered. Five different wave heightswere employed for the regular tests and two extreme wave heightswere used as contract waves to assess the damage level. The twocontract waves had the significant wave heights as 4.4 m and 5.3 mrespectively. The experiments involve getting the wavetransformation, velocity profiles, sedimentation profiles(morphological changes) and stability experiments during normaland extreme conditions.

The experimentally maximum damage ratios for breakwaters(straight and cornered alignment) were reasonable, i.e., seasidedamage normally should be less than 5 percent and leeside-sidedamage less than 6 percent. Therefore researchers at COEI wereconfident that the groyne would be safe within the given hydraulictests conditions but special caution has to be prepared i.e., toprovide additional protection in the form of rocks or rubblemound atthe cornered section and edge of the breakwater to prevent scourand unstability due to overtopping and wave breaking.

The Design and Development of Sine-Slab for CoastalProtection System: Special Case Study of a RevetmentSystem

Sine-Slab® is a special product of a revetment systemdeveloped by the Coastal and Offshore Engineering Institute underthe IRPA program by funded by MOSTE (Vot. No. 72106, Project No.03-02-06-0185) and promoted for commercialization by UTMvia Bureau of Innovation and Consultancy and Uni-TechnologiesSdn. Bhd. Based on patent licensing arrangement, the product ismanufactured and marketed by Zen Concrete Industries Sdn. Bhd.for Malaysia only from February 1998-2003. The Sine-Slab® systemis uniquely designed to work with nature’s forces. It is effectively


stable and durable against hydraulic loading, at the same timebeing effective in trapping sediment, aesthetic and environment-friendly. Based on our investigations, the stability coefficientKD is found to be superior in comparison to the available pre-castconcrete revetment systems in the market (KD = 40 for Sine-Slab,compared with reported values of KD = 15.8 for Dolos, KD = 7–20 forparallel-piped quarry stones, KD = 12 for Tribar). Records of field useof the system have shown to be effective and enhance the stabilizationof the beach area.

Design Concept and Methods

There exist in the world wide market, as an integrated part of acoastal protection structure or revetment, pre-cast concrete namelyArmorflex, Flex-slab, Basalton, Channel Lock, Core-Loc, Hydroblock,Petraflex, Terrafix, A-Jacks, etc. The pre-cast concrete block systemshave received considerable attention in recent years due to theiraesthetic appearance and providing the solution of certainmedium-wave protection problems. The blocks could be laid eitherby block-by-block hand placement or by cabled systems that can beplaces as large mats. Then industry is becoming competitive andnew products have reached the market.

The researcher has taken the inventive and innovative stepsto fulfill the objectives to provide a more effective method for erosioncontrol using pre-cast concrete system—a more stable and durablebarrier to wave action and tidal changes but not a barrier for publicto access the water mark. Its shape is adaptable to the sinusoidalshape of the waves (hence the name “Sine-Slab” was obtained).The concrete system is designed to provide sufficient drainage andpressure relief as it is an environment-friendly method that allowsnatural vegetation growth.

Sine-Slab® (Design No. 2055381, Patent Application No. PI9504122, DU 2001/) is an articulated pre-cast concrete productdesigned to accommodate the forces of nature. It has several uniquefeatures that are not found in other erosion control methods. It can


assure continuous construction and maximum stability via the 4-sidedinterlocking units.

The effective keying means by hook locking system andslot locking system comprising grooves and flanges that resistdisplacement and prevent erosion of the sub-soil (Figure 19).The sinusoidal shape and perforation pattern of the Sine-Slabneutralize pressure from changing water levels and absorb energyfrom waves, current and turbulent water action. Sine-Slab® hashollow space structure (void ratio >10 percent) that acts ascanal system to drain away surface water. This provides a naturalbuffer to dissipate, disperse energy and impact of loading.

Figure 19 Sine-Slab design concept

Female Locking Device(Hook Locking System)

Male Locking Device(Hook Locking System)

Female Locking Device(Slot Locking System)

SIDE ELEVATION


The trapped sediment would allow vegetation growth andstrengthens the interlocking system further. The concave-curved or reentrant-faced structure is most effective for reducingovertopping or run-up thus reducing spray and protects thecrest. The stepped-face wall provides access to the beach areaand reduces scouring of the backwash. Weighing about 50 kg(600 ∞ 300 ∞ 120 mm) designed for maximum wave heightof 2 m, the high strength concrete (grade 40) is able to distributestress and resist elevation movement.

It is envisaged that other sizes will be produced later to caterfor different site conditions. The prototypes of first version wereproduced by a gang-mould of eight. Production rate is between100 –120 per day. Simple and fast method of laying would shortenthe installation time.

Research Methodology

In view of the economic and environmental factors associated withcoastal protection works, it is considered that the protectionstructure carries not only the requirement that the beach iseffectively lined to prevent the possibility of further ingress ofthe erosion, but also the system should be so well engineered,so substantial that it could be clearly expected that thepossibility of catastrophic situations do not exist. Negativeimpacts to the nearby areas should be minimised. It istherefore to be expected that upon completion of the project,it would be of the highest technical quality and best materialand method available. Thorough research and carefulconsideration for proper design is important.

Design Criteria and Governing Hydraulic Parameters

The basic variables of the hydraulic and geo-technical processesusually appear in various stability formulae, describinga limit state, e.g. no movement, no displacement or no deformation.Stochastic variables S, for loading and strength R areimportant parameters to determine expected damage of


the structure and consequence maintenance cost. In thedesign, appropriate distribution of strength R be must chosento obtain the desired reduction of the probability of failure(or safety) at a given distribution of loading S. the aspectsof the limit of the criteria includes run-up, overtopping andreflection of waves, armour stability, filter criteria, pressurerelief for geo-technical stability, wave transmission, allowancefor settlement and avoidance of flanking. In the design criteria,aspects of sliding, uplift and surface resistant are taken intoconsideration. The interlocking system in the combination oftongue and groove mechanism adds to the stability.

The theory for selection of the product size is based uponHudson’s and Meer’s Formula which is a stability formula for armourunits on rubble structures developed by the U.S. Army WaterwaysExperiment Station (WES), Mississippi, (CERC,1984). The Hudson’sformula states that

W50 = (WrHS3 )/KD(Sr–1)3 cot ϕ ...(15)

where Wr = unit weight (saturated surface dry) of armour unit,HS = Significant wave height,Sr = relative density of armour unit relative to water,Sr = Wr/Ww (Wχ is the unit weight of water),W50 = weight of individual armour unit,ϕ = angle of slope measured from the horizontal in

degrees, and KD = Stability coefficient

that varies primarily with the shape of armour units, roughness ofthe armour unit surface, sharpness of the edges and degree ofinterlocking obtained in placement, and the number of unitscomprising the thickness of the armour layer (revetment). In terms ofstability number NS, it is independent of wave period T and itsrelationship with wave height H, KD and slope cot ϕ, it is expressed as

NS = H/{(M/ρ)1/3}∆ = H/∆D50 = (KD cot gϕ)1/3 ...(16)


where H = wave height, M = mass of unit, ρ = density of material, ∆= submerged relative density = ρr/ρw–1, D50 = characteristicdiameter of the unit, KD = Stability coefficient, g = gravity and ϕ =slope angle.

Meer’s formula (Van der Meer, 1988) includes the effects ofregular waves and distinguishes between plunging and surgingwaves. Besides the wave period and slope angle, other influence onstability such as duration of storms and the permeability of structurewere also included. The formulae relates the incident waveconditions and the level of damage that may be allowed to thedimensionless stability number, H/∆D50. This leads to

H/∆D50 = 6.2 P0.18 (Sd šN) 0.2 ξ m–0.5 for plunging waves ...(17)

H/∆D50 = 1.0 P–0.13 (Sd š/N) 0.2 šcot α ξ mp for surging waves ...(18)

Where P = notional permeability factor, Sd = damage number = Ac/

D502, N = number of waves, ξ m = Irribaren number = tan α /Sm1/2

and Sm = 2π HS/gTm2, Tm is the mean wave period.In practice, these formulae can give arrange of armour sizes

depending on the choices made in the damage level, Sd. For mostcases, design damage is set at Sd = 2 as equivalent to “nodamage”. For slopes smaller than 1 : 2.5, damage may be permittedto rise, say Sd = 3 – 4 without increasing the overall failure.

For structural stability, the blocks must be heavy enough toprovide sufficient weight to resist the uplift pressure and waveforces. However, a heavier block could create a problem ofhandling and installation in such instances mechanisation isnecessary. Wave action on a sloping structure will cause thewater surface to oscillate over a vertical range that is generallygreater than theincident wave height. The design run-up levelwill be used to determine the level of the structure crest or the upperlimit of protection or as indicator of possible overtopping orwave transmission. The run-down level will determine the lowerextent of the main armour protection and toe protection. The ShoreProtection Manual (1984) gives values of KD for rough angular


stones as equal to 2.0 for breaking waves and 4.0 for non-breakingwaves. Influences in the stability namely wave height, slope angle,permeability need to be closely considered. Based on siteconditions of water levels, waves, currents and other environmentfactors, initial cross-section can be designed. The detailed design ofthe Sine-Slab system involves consideration for the stability ofthe cover layer, the security of foundation, the minimization ofsettlement and sliding as well as toe protection to preventundermining. These call for concern on the slope, crest elevation,cover layer thickness, filter layer, overtopping, and scour of the toe.Physical modeling tests for the hydraulic model investigationwere carried out for the Pilot Project (COEI, Pilot Project, May1998,Technical Seminar, September 1999).

Laboratory Tests

Hydraulic model investigation carried out at COEI (Figure 20) involvedphysical modeling study at appropriate scaling for selectedconditions at a site location. Variable conditions for water levels,wave periods, wave heights and model scale sizes were simulatedin order to obtain relationships of the relevant parameters, thatis wave height Hs, water levels (LAT, MLSW, MLWN, MSL, MHWSand HAT), wave period-wave steepness Sm, Irribean Number ζm

which is related to the surf similarity parameter (ζm = tan ϕ /HS/Sm)Coefficient for stability KD and Stability Number NS. Laboratorytests (Figure) at extreme conditions for highest water level, HAT,significant wave height HS, and critical wave period of the siteare conducted to check for run-up, stability, failure and settlement.Hydraulic model tests were carried out in the laboratory at modelscales of 1 : 5 and 1 : 3 and variable parameters, namely wave height,water level, wave period and slopes (1 : 1, 1 : 2, 1 : 3, and 1 : 5).

Production Tests

Tests at the factory involve the determination of product strength viacompression tests for the female and male interlocking parts. The


Figure 20 Hydraulic model investigation for model scaled at 1 : 5 underwave attack were carried out at various conditions to check on the run-up,stability and settlement

Figure 21 Simulation tests for stability and run-up were conducted at theCOEI laboratory for guidance in the detail design of prototypes

0.5

0.3

0.7

0.9

1.1

0 0.005 0.01 0.015 0.02 0.025

Valu

es o

f R

/H

Values of H/gT2

LATMSLHATLAT ConditionMSL ConditionHAT Condition


exercise determines the extent of the requirement ofreinforcement and handling care during transportation. Trialtests were also conducted for the installation methods bymechanization.

Field Study

The project setting or the pre-installation procedure includes studiespertaining to the site condition. The scope of work under the designand built comprise of land reclamation located at Melaka Tengah(102° 8' longitude, 2° 14' latitude) comprising 120 m shorelinefronting Shah’s Beach Resort, south of a heartland, Tanjung Keling.The area has been identified as a Critical Erosion Area under theNational Coastal Erosion Study (1985). Based on information anddata gathered, the area was undergoing severe erosion due tochanges in the shoreline due to infra-structural development inthe vicinity of the resort. It was retreating more than a meter per year.Based line data and information are gathered prior to theconstruction. These also include the rate of erosion, marine weather,shoreline geometry survey and hydrographic survey for the profilesand bathymetry, current, tidal and wave height measurement, grabsampling as well as the general conditions of the environment(aspects of social use, accessibility and infra-structure) of the site.

Construction for a Shoreline Protection System - Pilot StudyProject

The construction of marine works is a tricky business. Thecontractor does not only exercise his technical know-how, he mustalso be intuitive and adaptable to the rough sea conditions andintelligently working with the tides. It must be emphasized thatexecutive methods cannot be learned from textbooks butexperience and guidance of experienced senior personnel mustbe obtained on the work-site itself. For practical design work,


besides the environmental boundary conditions other additionalconditions considered in the design of revetment structures.These include the stability of the cover layer, the securityof the foundation, the minimization of settlement and sliding andtoe protection to prevent undermining especially duringconstruction at varying tide levels. The overall design location orlevel position of filter layer, toe protection (MLWS), mid-sectionof the revetment (MSL) and crest level (HAT) (Refer to Figure 22).

In the process of constructing the 120 m length of theSine-Slab revetment, prior to the installation, systematic planningare necessary, these include site preparation, toe protection,earthworks, laying of the geo-textile, filling of gravel layer,installation of Sine-Slab(r) revetment system, crest and run-up area,construction of the seawall, earthworks for the beach andmonitoring study.

Figure 23 shows the chronological events that lead to theconstruction of the Pilot Project.

5000

200

300

400

700

300

900

200 1000

300 3500

24.6

5.0

.53

.0.4

023

.61

17.0

00.

44

11.0

21.

77

9.93

1.72

-3.00

-2.00

-1.00

0.00

1.00

2.00

SAND FILL

100mm STONE

SEAWALLSANDFILL

EXISTINGCONCRETE WALL

HEIGHT

OFFSET

DATUM R.T. - 4.000

+ 2.0MLSD

+ 2.2m LSD

+ 2.0m LSDSINE - SLAB

GEOTEXTILE TS 750 OR EQUIVALENT

220

31

GRADE A

HAT = 1.60

MHWS = 0.90

MSL = 0.00

MLWN = -0.30

MLWS = -0.90

LAT = -1.05

-0.50100mm - 150mm

STONEØ

GEOTEXTILE TS 750OR EQUIVALENT

TYPICAL CROSS SECTION COASTAL PROTECTION WORKS USING SINE-SLAB®

AT SHAH MOTEL BEACH FRONT TANJUNG KELING, MELAKAScale 1 : 30Scale down at 55 : 1

Figure 22 A typical cross-section of the revetment system constructedfor the Pilot Project


Figure 23 Chronological of events for the Pilot Project

April 1999

February 1999

July 1997

September 1998


Field tests and monitoring work for Sine-Slab revetment

system have been carried out to check on the performance of the

system and to prepare for future design guides. A series of

monitoring program are conducted to check on the system as part

of the post-installation and maintenance procedure. Baseline data

was determined as the comparison reference for future system

performance interpretation and analysis. Initial profile of Sine-Slab

was taken to provide sufficient data for detail quantitative

assessment of the actual behaviour of the structures. To achieve this,

Sine-Slab® system was divided into grid lines at every 10 m interval

and closer grid intervals of 2 unit of Sine-Slab at critical areas to

seaward. The locations as well as the level of grid lines were

determined using the survey equipment and the water-pass.

Continuous monitoring and measurement of parameters are being

carried out for the first one one-year after the completion of the

construction of the revetment. The parameters include tide, wave

and current measurement, settlement, grab sampling, stress and

strain, porepressure and beach profile.

The system was stable to withstand the wave attacks and

hydraulic loading during the seasonal storms and the highest

astronomical tide experienced for a hundred year’s event (i.e.,

December 4, 1999) as given in Figure 24.

The walkover surveys from time to time are conducted to check

for overall condition, settlement and change of alignment. This would

enable the researchers to check on changes and performance of

the structural system in detail. Designed to work with nature’s forces,

the product has been found not only preventing further ingress of

the erosion but survey results of beach profiles (three sets of data

taken at four months intervals and 1 12 years later) have shown that

there was a substantial accumulation of sediments trapped by

structures over a period two years in the splash zone as shown in

Figure 25.


Figure 24 The revetment system is stable against the attack ofwaves during the extreme storm conditions

Figure 25 Accumulation of sediments as observed in the splashzone, showing the structural effectiveness in trapping sedimentsbrought by the waves and tides thus enhancing the stabilization of thebeach area


Settlement of the revetment on average in the range of 1–20 mm, themaximum being at the expected location where the sub-soil is soft(based on the detailed soil investigation) and at the corners wherethe structure units were not locked to each other.Accumulation of the sediments in the range of 0 mm to 600 mmthick, the maximum sites being at the toe section, up to about 40percent of the slope section. Very little settlement and accumulationwere found at the crest area. Marine algae were also observed onthe rocks at the toe where there would be mostly underwater, and atsome places on the rocks, snails, clams and barnacles were alsofound. Creepers or sea vegetation has covered some parts of therevetment system providing the green effect thus softening the lookof the hard concrete structure. Close observations are beingconducted further for signs of structural and physical deterioration(e.g., corrosion and cracks) as well as potential damage particularlyat the location of expected sub-soil instability and at the corneredstructures or turning angles.

Visitors to the once lost beach area can now walk on the slabsand at the same time still get to the water. This is a great advantageof Sine-Slab® compared to others available in the market. Specialemphasis of the research is given to the overall stability of therevetment system that comprise of the toe protection, Sine-Slab®

with the filter layer system and the run-up factors. Monitoringresults of the Pilot Project, as well as the first and secondcommercial projects are encouraging. Continuous R & D is beingcarried out for the design and product improvement to facilitateproduction, material composition and durability, economic factorsand environmental outlook. Applications of Sine-Slab® include forshore protection, land reclamation projects, flood control, ship berthsand docks in harbors, beaches and marinas.

Design and Product Durability Improvement

The research will continue for analyzing and solving othertechnicalities involving automatic production, installation andmaintenance (replacement method) as well as for added value


designs, which are practical and effective to be used for maintenanceof coastal protection structures. Apart from protecting the coastlinefrom further erosion, the product will in the future be in the market toprovide solution to erosion problem and significantly enhance thenatural or biological features of the coastal and riverside area. Newimproved design is needed to facilitate production to meet theincreasing demand, new material composition by introduction ofwaste material as partial cement replacement for cost effectivenessas well as other aspect include product strength and durabilityunder marine environment, value added options for installationmaintenance and eco-friendliness that will put the product at acompetitive edge.

The new design accommodates interlocking components,maintenance feature, drainage and sediment trap facility and mostof all enable mass production by compression method. Thisconsequently will reduce the production cost whilst the unit price

Table 4 Features comparison of existing and improved Sine-Slab

No Features Existing Sine-Slab Improved Sine-Slab

Dimensions (mm)i. Prototype Size 1ii. Prototype Size 2

465 x 325 x 135600 x 300 x 135

650 x 300 x 1351000 x 450 x 200

i. Verticalii. Horizontal

Full Interlocking(Groove & Flange)

Full Interlocking(Groove & Flange)

FlexibleEfficient Drainage 2 Holes Single HoleSediment TrapReinforcement

ii. Male

5.8 t/f9.3 t/f

To be determinedTo be determined

Concrete Grade Gred 40 Gred 40Production Method

i. Daily Rateii. Cost Of Production

Gang Mould100 pcs / dayRM 10

Press Machine720 – 1440 pcs / dayTo be determined

Installation Method Manual Manual / MachineryCorner Handling Method Rigid Slope,

No InterlockingAdjustable SlopeSemi Interlocking

Maintenance Moderate Easy

Environment friendly13.

12.

11.10.

9.8.

6.5.4.3.

1.

i. Female

Interlocking2.

7. Structural Strength(Compression Test)

√

√

√

√

√ √

√ √


can be lowered. Thus the product becomes more value-added,competitive and attractive to users. The previous 50 kg design(600 mm ∞ 300 mm ∞ 135 mm) will be replaced with the new designof 50 kg (650 mm ∞ 300 mm ∞ 135 mm) and 100 kg (1000 mm ∞450 mm ∞ 200 mm). The 100 kg design will be suitable for EastCoast of Peninsular Malaysia as well as Sabah and Sarawak asthe waves there are much bigger and stronger.

Material Composition

Design of concrete mixes was initially based entirely on compressivestrength. More recently the practice of designing for a definiteflexural strength, indirect tensile strength or for a definitedurability where exposure conditions are severe, has beendeveloped. In spite of these developments, compressive strengthremains the common criterion of concrete quality. Concrete isthe most widely used and versatile construction material. Therefore,the durability of this material is of great importance in lowmaintenance long-lasting structures. In order to reduce the cost ofproduction but not to compromise on structural strength, a lowercontent of cement i.e, lower grade from 40 to 25–30 is proposed.Another alternative is to replace cement partially with other materialsuch as Ground Granulated Blast Furnace Slag from steel waste(GGBS). Furthermore, concrete made from Portland cement alonecan be vulnerable to attack from sulphates, chloride, acids andalkali-silica reactions. This is a particular problem in marine, coastaland other harsh environments, or areas subject to wide temperatureextremes. Replacing a percentage of the cement with GGBSproduces a significantly less permeable concrete withimproved resistance to aggressive conditions. These compositecements offer workability and strength advantages through lowerwater content in the mix and a reduction in early age heatdevelopment. This helps to minimize the possibility of thermalcracking. Proportions of GGBS may be varied to achieve particularperformance qualities.

Other optional replacement material is Palm Oil Fuel Ash(POFA).The usage of (POFA) is also being studied for marine


application. From previous studies done, concrete mix using POFAis able to reduce bleeding, higher concrete strength at later stage,provides good workability as well as cost reduction of concrete. Thecompressive strength, flexural strength and modulus dynamic ofelasticity of concrete using POFA is yet to be determined.

For the effort towards prevention of corrosion of reinforcementwire and structural cracks, a proposal has been drawn to utilisewaterproof concrete using caltite or bio-based material forstructural coating. This will be tested at the Pilot project site.

The innovation process in the development of Sine-Slabsystem is presented as shown in Figure 26 below.

Figure 26 The Innovation process for the development of Sine-Slab system

Secure Funding/ Research Grant

Development of Idea

Design preparationPatent searchMarket study

Patent drafting

Model construction

Laboratory tests

Development of prototypes

Legal document

Patent Application

Literature survey, Desk studies Appointment ofRA/Post Grad student

Team members

Negotiations forpatent licensee

Signing MOAContractual Agreement

Financing

Identification offield site for PilotProject

Publications, Exhibitions

Mass production

Construction for Pilot Project

Product launching,Marketing

Monitoring and product improvementDesign Guidelines

Design confirmation, Prototype production

Hydraulic model simulation tests for various scales

RESEARCH1993

DEVELOPMENT1995

COMMERCIALISATION1998

INNOVATIVE R & DFor sustainability 1999


ACHIEVEMENTS AND CHALLENGES FOR FUTURE WORK

Figure 27 below shows the results of the installation of Sine-Slabsystem as Pilot and commercial projects.

Figure 27 Photos of the Sine-Slab project

Sine-Slab Revetment System Construction of prototypes

Shah’s Beach Resort, Tg. Keling Butterworth, Penang (540 m)

Tanjung Keling & Lereh (150 m) Lereh, Melaka (180 m)

Tanjung Keling, Melaka Tioman Island & Rhu Island


The invention and product development of Sine-Slab has wonseveral national and international awards including Gold medalsin the 27th International Exhibition of Inventions in Geneva,Switzerland (1999) for construction/Civil Engineering Category,a Special Award from the International Jury for the World IntellectualProperty Organization (WIPO) for best woman inventor and inthe Iranian 13th Khwarizmi International Award (2000). The projectalso earned the National Inventors Award (1999) and Gold Medalfor UTM’s University Discovery Award (1999) and InnovationAward (2000).

Current research project under IRPA RM 8 undertaken at theFaculty of Civil Engineering involves the study of economical,socio-economic impacts climate change due to ENSO events inMalaysia.

Recent proposed work involves the design and developmentof floating breakwater systems using composite material of HighDensity PolyEthylene (HDPE). Additives and natural waste fibersmade of rice husk and oil palm fiber are introduced into the polymerto enhance strength and durability against marine weatherconditions (proposed collaborative work with teams from Facultyof Chemical Engineering and Chemical Resources, COEI, MarineLaboratory, Center for Hydrographic Survey, UTM and PetronasResearch & Scientific Services (PRSS).

Other project in the pipeline is the marine innovation of thedevelopment of artificial reef using ashcrete for recreational andmarine habitat. From reports of 40 countries from six continents, theapplication of the habitat technology involving artificial reefs formultiple use in the fishing industry, management, restoration andenhancement of resources, releasing of fries, mariculture and catch.All reports have shown that increase in fish catch achievable in therange from 20 percent - 4000 percent. The habitats were created forthe effective management of other marine resources and means ofdisposing waste products such old boats and tyres.

Pre-cast concrete systems thus would enhance the supply ofthese artificial reefs and specially designed for various purposes tosuit functions, marine requirements and applications for localenvironment and conditions. New designs and materials which


imitates the tree-like and fan-shape feature of the corals would bemore familiar and pleasing to marine creatures as well as nature’slovers. Apart from enriching the marine life and fish resourceenhancement, income from tourism would also boost the nation’seconomy.

Several proposals for the application of Sine-Slab systems asrevetment have been proposed to PSC Naval Dockyard in Lumut,Kelantan SEDC for Sabak, Bukit Keluang/Pulau Rhu coastaldevelopment project, PETRONAS Kerteh coastline managementproject and Terengganu Rivermouth project.

The challenge ahead for University Technologi Malaysia is toprovide the mechanism for the commercial success of theinnovative product to be implemented primarily to combat the localerosion problem before actually going for global market.Continuous backing of R & D results and technical reports ofsuccess stories need to be strengthened. Solutions to meet thespecific requirements of a variety of problems need to be provided.Additional related design applications for reservoirs and lakes,hill-slope protection as well as application for artificial reef is underway.Product and design improvement is targeted at cost effectivenessand quality for production (automation), installation, maintenanceand product durability as well as product composition and variety.Competing with other products is one thing, but a sound financialbacking and a dynamic operation of business organisation isanother. Forming strategic alliances (synergising andstrengthening relationships with potential customers), effectivemarketing, strong leadership, management and technical experts inthe team are indeed necessary. The uses of K-Economy andE-Commerce through the internet in the US have revamped theold-line industry and had actually saved millions of dollars.The productivity revolution will spread to other parts of the worlddue to globalization and future companies will be using the webtechnology to boost productivity at every stage of the businessprocess. Malaysia’s Industrial Master Plan 2 (IMP2) will see the needto step up R & D (Design), Manufacturing and Marketing topenetrate global market. Greater emphasis will be given toR & D and global marketing that involve processes such as


Innovation, Collaboration, Design, Purchasing, Manufacturing,Logistics, Marketing and Services via the internet.

CONCLUSIONS

This paper has highlighted some of the aspects of designingcoastal protection structures and case studies undertaken at theCoastal & Offshore Engineering Institute (COEI) of UTM.By realizing the problem and issues related to erosion at the coastalareas, particularly the high cost of supply, installation andmaintenance of existing structures and failures of some mitigativemeasures, a suitably designed pre-cast concrete block is one ofthe many options which engineers may find acceptable to use forcoastal protection works. For the product to be acceptable andused, the R & D phases involve the innovation system that includesstudy, design, laboratory simulation, field tests and provision ofdesign guides from track records of performance as well ascommercialisation phase.

Physical models are very close to simulations of prototype asthe results of the investigation will give qualitative information.Physical models are plagued by scale, laboratory effects and highcosts. Physical modeling however, will play a pivotal role betweenfield observations, which are necessarily spot measurements ofcontrolled and uncontrolled physical events, and the more-or-lessfull understanding of the problem needed for a numerical model. Tomitigate measures to combat the shoreline deformations byconstructing coastal protection structures, the frequent cropped upquestions will be the importance of physical modeling vis a vis tocomputer modeling. Numerical models need to be properlybenchmarked, calibrated and verified.

The cost of modeling can be controlled by using a compositemodel approach consisting three distinct phases of physical modelingphase; The analysis of physical modeling results, and thecomputation phase—a complete numerical model, physicalprocess model results provide appropriate coefficients and transferfunctions. In the case of revetments, physical modeling is sufficientfor detail design of structure, bathymetric data, geo-technical


data and other physical data on tides, wave, etc. But for lay outdesign, hydrodynamic modeling needs to be performed to ascertainsediment transport wave refraction and current effects. Engineeringstudies need to provide useful answers within a limited time andbudget, for examples, in the case of Hex Reef breakwater projects atPulau Layang-layang, Terengganu Rivermouth, submerged berm forBatu Maung and for Kuala Baram. Research teams need to becomprised of a cohesive team effort to establish expertise in bothphysical and numerical modeling.

In summary, the general formulation on stability of Sine-Slab®

against wave attack has to be treated as practical formulation fordesign purposes. It has been generally acknowledged that blockweight, geometric shape and method of interlocking all playimportant roles in the overall system performance breakwaters. Thecoefficient of stability KD in the Hudson’s formula could be the choiceof parameter involved to differentiate performance of differentsystems. Coastal protection structures based on revetment methodsuch as Sine-Slab® may no longer in future be only “hard”engineering structure, but with added value design, structuraldurability, texture and colour of natural sand and vegetatedsystems, it will enhance the eco-friendliness and provideengineering solution that is compatible with nature. Pre-castconcrete and added value systems can be a good and mostlycheaper alternative for traditional material/systems. These newsystems deserve to be applied on a larger scale. The newly deriveddesign methods and stability criteria by taking intoconsideration of the stability of the filter layer will be of help inpreparing the preliminary alternative designs with these systems.However, there are many uncertainties in the design methods.Therefore, experimental verification and further improvement ofdesign methods as well as more practical experience at variousloading conditions are needed.

This paper has presented the innovation experience garneredthrough the Sine-Slab project. It is hoped that through practicalexperience and continuous R & D, however limited the knowledgemay be, it would be useful to systemise this knowledge and to make


it available to design engineers. The output of the research projectreported has not been confined to laboratory or publications of theresearch papers for academic reasons, but the information andIntellectual Property (IP) created has great potential forcommercialisation in the manufacturing, construction and maritimeindustry whilst providing solution to the pertinent problem of soilerosion. In other words, results of R & D are diffused and technologybeing utilized for protecting the environment and benefiting thesociety. The experience in undertaking the related research andmanagement of the technology is beneficial to be extended asconsultancy services for designing planning and management of thecoastal areas from erosion.

ACKNOWLEDGEMENT

The author wishes to thank all the sponsors and clients forthe research and consultancy projects undertaken. For the projecton the development of Sine-Slab, the author wishes to thank UniversitiTeknologi Malaysia (UTM); the Science & Technology Division ofMinistry of Science Technology and the Environment, (MOSTE); ZenConcrete Industries Sdn Bhd; especially to Zulkipli Hj. Husin andZulkifli Ghazali, Aziz Ahmad of Geo-textile (M) Sdn. Bhd.; Ir. KamalHj. Kassim of Jurutera Perunding MSA Sdn. Bhd,; Shah’s BeachResort, Dept. of Irrigation and Drainage, Melaka, especially MokhtarAbd. Rahim; Utama Permai Sdn. Bhd, and Bustaman & Co. Specialgratitudes and appreciation to participating members particularlyProf. Hadibah Ismail, Shamsuddin Abd Rahman, Zakaria Ayob,Md. Halim Mustari, Noor Hanisah Wok, Norazizah Abd. Kadir,Asrol Wahab, Amran Shukor and the rest of the team in COEI,Prof. Abd Aziz Ibrahim (former director of COEI); ResearchManagement Centre and the team especially Abd. RahmanShafie, and Assoc. Prof. Azlan Abd. Rahman; Bureau of Innovationand Consultancy especially to Prof. Dr. Abd. Karim Mirasa,Assoc. Prof. Hanizam, Norhisham Hamid, Assoc. Prof. Dr. KhaliliKhalil and Taha Othman and Uni-Technologies Sdn. Bhd.,especially Assoc. Prof. Aziz Md. Amin and Mohd Naim,Kamal Bani Hashim of Centre for Invention, Technovation


Park; Ahmad Shahlan Mardi of Centre for Hydrographic Studies;Prof. Azmi Abdullah of AutoCad Training Centre, Ismail Sallehand Siti Norulhana of Media and Graphic Unit UTM, andthe Faculty of Civil Engineering, especially the Dean,Assoc. Prof. Dr. Ahmad Mahir Maktar and Assoc. Prof. Dr.Fadhali Zakaria of Universiti Teknologi Malaysia fortheir support and contribution in this research project. Specialthanks to my assistants M. Santanam of IIT, Madras, RahimahMuhammad, Noor Azura Mohd Bunori, Nasrollah Muhamad,Zoolhilmi Muhamad, Tuan Aphzan Tuan Mad, and JasvinderSingh for their efforts and contributions.

SIRI SYARAHAN PERDANA PROFESOR

Documents

Transcript of SIRI SYARAHAN PERDANA PROFESOR