Coastal stabilization pilarczyk-2005
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Coastal stabilization pilarczyk-2005 Coastal stabilization pilarczyk-2005 Document Transcript

  • COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS IN INTERNATIONAL PERSPECTIVE KRYSTIAN W. PILARCZYK Rykswaterstaat, Hydraulic Engineering Institute: P.O. Box 5044, 2600 GA Delft, The Netherlands, HYDROpil Consultancy : krystian.pilarczyk@gmail.comABSTRACT. A brief overview of some available alternative systems for shore stabilization andbeach erosion control is presented. Special attention is paid to artificial reefs and geosystems.Geosystems (geobags, geotubes, geocontainers, geocurtains, etc.) have gained popularity in recentyears because of their simplicity in placement, cost effectiveness and environmental aspects.However, all these systems have some advantages and disadvantages, which have to be recognizedbefore application. For design and installation criteria the reader is guided to relevant documents.KEYWORDS: coastal stabilization, alternative systems, low-crested structures, geosystems. INTRODUCTIONCoastal users and managers all over the world are frequently faced with serious erosion of theirsandy coasts. Possible causes of erosion include natural processes (i.e. action of waves, tides,currents, sea level rise, etc.) and sediment deficit due to human impact (i.e. sand mining andcoastal engineering works). Countermeasures for beach erosion control function depend on localconditions of shore and beach, coastal climate and sediment transport. Continuous maintenanceand improvement of the coastlines, together with monitoring and studies of coastal processeshave yielded considerable experience on various coastal protection measures all over the world.In general, a coastal structure is planned as a practical measure to solve an identified problem.Starting with identification of the problem (e.g. shoreline erosion), a number of stages can bedistinguished in the design process for a structure: definition of functions, determination ofboundary conditions, creating alternatives, geometrical design and the final choice of functionalsolution. After the choice of functional solution has been made the structural design startsincluding creating structural alternatives (ie. using different materials and various executionmethods). The final choice will be made after verification of various structural solutions inrespect to the functional, environmental and economic criteria.This contribution presents an overview of the various available methods for shore stabilization andbeach erosion control, with special emphasis on the alternative solutions and novel materials andsystems in various design implementations. Within alternative systems special attention is paid toartificial reefs and geosystems. Additional information on alternative systems can be found inreferences and on the related websites. ALTERNATIVE SYSTEMS FOR COASTAL PROTECTIONVarious coastal structures can be applied to solve, or at least, to reduce erosion problems. Theycan provide direct protection (seawalls, dikes, revetments) or indirect protection (groins andoffshore breakwaters of various designs), thus reducing the hydraulic load on the coast. Rock andconcrete are usually the construction materials. Groins of various designs (including pocket andperched beaches) are often called ‘shore connected’ structures (Figure 1). 1
  • However, there is a growing interest both in developed and in developing countries in low cost or novel methods of shoreline protection particularly as the capital cost of defence works and their maintenance continues to rise. The shortage of natural rock in certain geographical regions can also be a reason for looking to other materials and systems. Despite this interest there is little published and documented information about the performance of low cost or patented structures especially at more exposed wave climate. Novel systems as geosystems (geotubes, geocontainers, geocurtains) and some other (often patented) systems (Reef Balls, Aquareef, prefabricated units, beach drainage, etc.) have gained popularity in recent years because of (often but not always) their simplicity in placement and constructability, cost effectiveness and their minimum impact on the environment. These new systems were applied successfully in number of countries and they deserve to be applied on a larger scale. Because of the lower price and easier execution these systems can be a good alternative for traditional coastal protection/ structures. The main obstacle in their application is however the lack of proper design criteria. An overview is given on application and performance of some existing novel systems and reference is made to the actual design criteria. Additional information on these systems can be found in Pilarczyk and Zeidler (1996), Pilarczyk (2000), and in references and on websites. d. Geotube as an offshore breakwaterFigure 1. Examples of shore-control and low-crested structures StructuresLow crested and submerged structures (LCS) as detached breakwaters and artificial reefs arebecoming very common coastal protection measures (used alone or in combination with artificialsand nourishment) (Pilarczyk, 2003). As an example, a number of systems and typicalapplications of shore-control structures is shown in Figures 1 to 4.The purpose of LCS structures or reefs is to reduce the hydraulic loading to a required levelallowing for a dynamic equilibrium of the shoreline. To obtain this goal, they are designed to allow 2
  • the transmission of a certain amount of wave energy over the structure in terms of overtopping andtransmission through the porous structure (emerged breakwaters) or wave breaking and energydissipation on shallow crest (submerged structures). Due to aesthetical requirements low freeboardsare usually preferred (freeboard around SWL or below). However, in tidal environment andfrequent storm surges they become less effective when design as a narrow-crested structures. That isalso the reason that broad-crested submerged breakwaters (called also, artificial reefs) becamepopular, especially in Japan (Figures 2 and 3). However, broad-crested structures are much moreexpensive and their use should be supported by a proper cost-benefit studies. On the other hand thedevelopment in alternative materials and systems, for example, the use of sand-filled geotubes as acore of such structures, can reduce effectively the cost (Pilarczyk, 2000, 2003, Fowler et al., 2003,Lawson, 2003). The upgrading of (integrated/muldidisciplinary) design criteria for LCS structurestook recently place in the scope of European project DELOS (Delos, 2005); see 2. Objectives of low-crested/reef structures (onshore) (offshore) foot protection block rubble stone AquareefFigure 3. Example of Aquareef (Hirose et al., 2002).The relatively new innovative coastal solution is to use artificial reef structures called “ReefBalls” as submerged breakwaters, providing both wave attenuation for shoreline erosionabatement, and artificial reef structures for habitat enhancement. An example of this technologyusing patented Reef BallTM is shown in Figure 4. Reef Balls are mound-shaped concrete artificial 3
  • reef modules that mimic natural coral heads. The modules have holes of many different sizes inthem to provide habitat for many types of marine life. They are engineered to be simple to makeand deploy and are unique in that they can be floated to their drop site behind any boat byutilizing an internal, inflatable bladder. Worldwide a large number of projects have already beenexecuted by using this system. The first applications were based purely on experience from previous smaller projects. Since recently, more well documented design criteria are available. Stability criteria for these units were determined based on analytical and experimental studies. For high energetic wave sites the units can be hydraulically anchored with cables to the sea bed). Wave transmission was studied in Canada (Armono and Hall, 2003).Technical design aspects are treated by Lee Harris on the websites mentioned below.Figure 4. Example of Reef Balls units (Barber, 1999).More information can be obtained from:,,and, on wave transmission and design:; Armono%20and%20Hall.pdf ,Prefabricated systemsThere exist a number of other novel and/or low cost materials and methods for shore protection(gabions and stone mattresses, open stone asphalt, used tire pile breakwaters, sheet pile structures,standing concrete pipes filled with granular materials, concrete Z-wall (zigzag) as breakwater,geotextiles curtains (screens), natural and mechanical drainage of beaches, and various floatingbreakwaters, etc. Most of them are extensively evaluated and documented. However, more recently,a new family of prefabricated concrete elements as SURGEBREAKER offshore reef system,BEACHSAVER reef, WAVEblock, T-sill elements and others have been developed and applied.The details on these systems can be found in references and on the websites. However, because ofvery narrow crest these prefabricated breakwaters are only efficient during mild wave conditionsand their effect usually disappear during storm conditions, and because of scour and/or settlement,even loosing their stability. The recent evaluation of performance of prefabricated, narrow-crestedbreakwaters can be found in (Stauble, D.K., and Tabar, J.R., 2003) and on the US Army websites: (;352).Some of these breakwaters are applied for comparison with other systems in recent US NationalShoreline Erosion Control Development and Demonstration Program (Section 227):andbetter/more reliable information on the effectiveness of these systems can be expected within afew years. The website;3provides details on sites and systems applied, and also provide some documentation ifavailable. 4
  • Some other systemsDistorted ripple mat. A new concept for creating shore accretion is actually developed andapplied in Japan. A distorted (precast concrete blocks) ripple mat (DRIM) laid in the surf zoneinduces a landward bottom current providing accretion of a shore; see Figure 5 (Irie et al., 1994,1998, Nobuyuki Ono et al., 2004).Figure 5 Principle of distorted ripple mat and applicationThe strong asymmetry of (artificial) ripple profile generates current near the bottom to onedirection and thus sediment movement, whose concentration is high near the bottom, can becontrolled with only very little environmental impact. The hydraulic condition on which thedistorted ripple mat can control the sediment transport most effectively is studied experimentallyand numerically and its capability to retain beach sand is tested through laboratory experiments(Figure 5) and field installation. The definite onshore sediment movement by the control ofDRIM is expected if the relative wave height H/h is less than 0.5, where H is the wave height andh is the water depth. The optimum condition for the efficient performance of DRIM is that do/λ>1.7, where do is the orbital diameter of water particle and λ is the pitch length of DRIM, and thiscondition coincides with the condition in which natural sand ripples grow steadily. DRIM is ableto control bottom currents so long as wave direction is within 50 degrees from the directionnormal to the crest line of ripples.Beach drainage (dewatering)systems. Beach watertable drainage is thought to enhance sanddeposition on wave uprush while diminishing erosion on wave backwash (Figure 6). The netresult is an increase in subaerial beach volume in the area of the drain. The larger prototypedrainage by pumping istallations used in Denmark and Florida suggest that beach aggradationmay be artificially induced by beach watertable drainage. The state of the art of this technique ispresented in (Vesterby, 1996). Most recent evaluation of drainage systems can be found on thewebsite:;191. It is 5
  • concluded that the drainage system has, in general, a positive effect on diminishing thebeach erosion, however, its effectiveness is still difficult to control.Figure 6. Principles of beach drainageThe idea to achieve lowering of the watertable without pumps by enhancing the beachs owndrainage capacity or hydraulic conductivity through the use of strip drains has been applied inAustralia (Davis et al, 1992) and in Japan (Katoh et al, 1994). However, these new techniques arestill in rudimentary stage and much more research and practical experience is still needed beforeapplication of these systems on larger scale. WAVE TRANSMISSION AND COASTAL RESPONSEFor shoreline control the final morphological response will result from the time-averaged (i.e.annual average) transmissivity of the applied systems. However, to simulate this in the designingprocess, for example, in numerical simulation, it is necessary to know the variation in thetransmission coefficient for various submergence conditions. Usually when there is need forreduction in wave attack on structures and properties the wave reduction during extremeconditions (storm surges) is of interest (reduction of wave pressure, run up and/or overtopping).In both cases the effectiveness of the measures taken will depend on their capability to reduce thewaves. While considerable research has been done on shoreline response to exposed offshorebreakwaters, very little qualitative work has been done on the effect of submerged offshore reefs.Therefore, the main purpose of this paper is to provide information on wave transmission for low-crested structures and to refer the reader to recent literature. The transmission coefficient, Kt, defined as the ratio of the wave height directly shoreward of the breakwater to the height directly seaward of the breakwater, has the range 0<K<1, for which a value of 0 implies no transmission (high, impermeable), and a value of 1 implies complete transmission (no breakwater). Factors that control wave transmission include crest height and width, structure slope, core and armour material (permeability and roughness), tidal and design level, wave height and period.Figure 7. Distribution of waves along the center of reef (Ohnaka&Yoshizwa, 1994, Aono&Cruz,1996) 6
  • As wave transmission increases, diffraction effects decrease, thus decreasing the size of sandaccumulation by the transmitted waves and weakening the diffraction-current moving sedimentinto the shadow zone (Hanson and Kraus, 1991). It is obvious that the design rules for submergedstructures should include a transmission coefficient as an essential governing parameter. Exampleof the transmission over the submerged structures (Aquareef) is shown in Figure 8. More detaileddescriptions of the functional and technical design of these reefs can be found in (Hirose et al.,2002). 1.0 0.8 R / H1/3 = 0.6 1.0 Ht/H1/3 0.8 0.6 0.4 0.4 0.2 0.0 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 B/L1/3Figure 8 .General transmission characteristic for AquaReef (Ht is the transmitted wave heightrecorded on the landward side, H1/3 and L1/3 are the significant wave height and wavelength at thetoe of the rubble mound, B is the crown width, and R is the submergence of the crown)Examples of prototype measurements in Japan can be found in (Hamaguchi et al., 1991,(Funakoshi et al., 1994, (Ohnaka and Yoshizwa, 1994). The Japanese design procedure can befound in Uda (1988) and Yoshioka (1993).Layout and Morphological ResponseMost commonly an offshore obstruction, such as a reef or island, will cause the shoreline in itslee to protrude in a smooth fashion, forming a salient or a tombolo. This occurs because the reefreduces the wave height in its lee and thereby reduces the capacity of the waves to transport sand.Consequently, sediment moved by longshore currents and waves builds up in the lee of the reef(Black, 2001). The level of protection is governed by the size and offshore position of the reef, sothe size of the salient or tombolo varies in accordance with reef dimensions. Of course, one canexpect this kind morphological change only if the sediment is available (from natural sources oras sand nourishment).The examples of simple geometrical empirical criteria for the lay-out and shoreline response of thedetached, exposed (emerged) breakwaters can be found in (i.e., Harris & Herbich, 1986, Dally &Pope, 1986, etc.). To include the effect of submergence (transmission) Pilarczyk proposes, at leastas a first approximation, adding the factor (1-Kt) to the existing rules. Then the rules for low-crestedbreakwaters can be modified to (for example):Tombolo: Ls/X > (1.0 to 1.5)/(1-Kt) or X/Ls< (2/3 to 1) (1-Kt), or X/(1-Kt) < (2/3 to 1) Ls)Salient: Ls/X < 1/(1-Kt) or X/Ls> (1-Kt), or X/(1-Kt) > Ls 7
  • For salients where there are multiple breakwaters: G X/Ls2> 0.5(1-Kt)Where Ls is the length of a breakwater and X is the distance to the shore, G is the gap width, andthe transmission coefficient Kt is defined for annual wave conditions.The gap width is usually L ≤ G ≤ 0.8 Ls, where L is the wavelength at the structure defined as: L = T (g h)0.5; T = wave period, h = local depth at the breakwater.As first approximation, Kt = 0 for emerged breakwaters and Kt = 0.5 for submerged breakwaterscan be assumed for average annual effects.These criteria can only be used as preliminary design criteria for distinguishing shorelineresponse to a single, transmissive detached breakwater. However, the range of verification data istoo small to permit the validity of this approach to be assessed for submerged breakwaters.In general, one may conclude that these simple geometrical design rules, both for emerged assubmerged breakwaters, are of limited value for design calculations because they do not includethe effect of the rate of sediment transport, which can be very different for a specific coast. It issupported by the studies on effect of offshore breakwaters along UK coast (Axe et al. 1996, andThomalla and Vincent, 2004). On the other side, it can be stated that numerical models (i.e., Genesis, Delft 2D-3D, Mike 21,etc.) can already be treated as useful design tools for the simulation of morphological shoreresponse to the presence of offshore structures. Examples can be found in (Hanson& Krause,1989, 1991, Groenewoud et al. 1996, Bos et al., 1996, Larson et al., 1997, Zyserman et al., 1999).As mentioned above, while considerable research has been done on shoreline response to exposedoffshore breakwaters, very little qualitative work has been done on the effect of submergedoffshore reefs, particularly outside the laboratory. Thus, within the Artificial Reefs Program(Black&Mead, 1999) (, Andrews (1997) examined aerial photographs seekingcases of shoreline adjustment to offshore reefs and islands. All relevant shoreline features in NewZealand and eastern Australia were scanned and digitized, providing123 different cases. A rangeof other statistics, particularly reef and island geometry, was also obtained. Some of these resultsare repeated below.To examine the effects of wave transmission on limiting parameters, data for reefs and islandswere considered separately. The data indicated that tombolo formation behind islands occurs withLs/X ratios of 0.65 and higher and salients form when Ls/X is less than 1.0. Therefore, for islandsthe Ls/X ratios determining the division between salients and tombolos are similar to those frompreviously presented breakwater research. Similarly, data resulting from offshore reefs indicatethat tombolo formation occurs at Ls/X ratios of 0.6 and higher, and salients most commonly formwhen Ls/X is less than 2. The data suggests that variation in wave transmission (from zero foroffshore islands through to variable transmission for offshore reefs) allows a broader range oftombolo and salient limiting parameters. Thus, a reef that allows a large proportion of waveenergy to pass over the obstacle can be (or must be) positioned closer to the shoreline than anemergent feature. Thus, from natural reefs and islands the following general limiting parameterswere identified: Ls LsIslands: Tombolos form when > 0.65 Salients form when < 1.0 X X L LReefs: Tombolos form when s > 0.60 Salients form when s < 2.0 X XNon-depositional conditions for both shoreline formations occur when Ls/X < ≈0.1. 8
  • The choice of the layout of submerged breakwaters can also be affected by the current patternsaround the breakwaters. The Japanese Manual (1988) provides information on various currentpatterns for submerged reefs (Yoshioka et al., 1993). However, for real applications it isrecommended to simulate the specific situation by numerical or hydraulic modelling. GEOSYSTEMS IN COASTAL APPLICATIONSGeotextile systems utilize a high-strengt synthetic fabric as a form for casting large units by fillingwith sand or mortar. Within these geotextile systems a distinction can be made between: bags,mattresses, tubes, containers and inclined curtains. All of which can be filled with sand or mortar.Some examples are shown in Figure 9.Mattresses are mainly applied as slope and bed protection.Bags are also suitable for slope protection and retaining walls or toe protection but the mainapplication is the construction of groynes, perched beaches and offshore breakwaters. The tubes andcontainers are mainly applicable for construction of groynes, perched beaches and (offshore)breakwaters, and as bunds for reclamation works (Figure 10). They can form an individual structurein accordance with some functional requirements for the project but also they can be usedcomplementary to the artificial beach nourishment to increase its lifetime. Especially for creatingthe perched beaches the sand tubes can be an ideal, low-cost solution for constructing thesubmerged sill .a) Geotube as a breakwater b) BEROSIN system (inclined curtain) as bed protectionFigure 9. Examples of application of geosystems Offshore breakwater at design water level CD+3.5 m 50 mFigure10. Example of reef structure composed with geotubes (Fowler et al., 2002); 9
  • They can also be used to store and isolate contaminated materials from harbour dredging,and/or to use these units as bunds for reclamation works.An interesting application for shore erosion control is the geocurtain known under the nameBEROSIN (Figure 9b). The BEROSIN curtain is a flexible structure made of various wovengeotextiles, which after placing by divers near the shore and anchoring to the bed catches the sandtransported by currents and waves providing accretion on a shore and preventing the erosion. Thehorizontal curtain (sheet) can be easily spread (at proper sea conditions) by a small workboat andtwo divers. The upper (shore-side) edge, equipped with some depth-compensated floaters, should beproperly anchored at the projected line. The sea-side edge is kept in position by the workboat. Byballasting some of the outside pockets at the lower edge with sand or other materials and with helpof divers, the lower edge is sinking to the required position. The proper choice of permeability ofgeotextile creates the proper conditions for sedimentation of suspended sediment in front/or underthe curtain and at the same time allowing the water to flow out without creating too high forceson the curtain and thus, on the anchors. In case of Pilot project at the coast of Vlieland (NL),some of the horizontal curtains placed in the intertidal zone have provided a growth of abeach/foreshore of 0.5 to 1.0 m within a week while others within a few weeks (Pilarczyk, 2000).These geocurtains can also be applied for construction of submerged sills and reefs.In the past, the design of geotextile systems for various coastal applications was basedmostly on rather vague experience than on the general valid calculation methods.However, the increased demand in recent years for reliable design methods for protectivestructures have led to the application of new materials and systems (including geotextilesystems) and to research concerning the design of these systems. Contrary to research onrock and concrete units, there has been no systematic research on the design and stabilityof geotextile systems. However, past and recent research in The Netherlands, USA,Germany and in some other countries on a number of selected geotextile products hasprovided some useful results which can be of use in preparing a set of preliminary designguidelines for the geotextile systems under current and wave attack (Pilarczyk, 2000). Theresults from the recent, large scale tests, with large geobags, can be found on the website: main (large) fill-containing geosystems (geobags, geotubes and geocontainers filled withsand or mortar) and their design aspects are briefly discussed below. For more detailedinformation on these and other coastal protection systems and measures applied nowadaysthroughout the world, together with recommendations and guidelines, the reader will be guided tothe relevant manuals and publications (see references and websites).GeobagsGeobags can be filled with sand or gravel (or cement, perhaps). The bags may have differentshapes and sizes, varying from the well-known sandbags for emergency dikes to large flat shapesor elongated "sausages" (see Figure 11). The most common use for sandbags in hydraulicengineering is for temporary structures. Uses for sand- or cement-filled bags are, among otherthings: · repair works (see Figure 11); · revetments of relatively gentle slopes and toe constructions; · temporary or permanent groynes and offshore breakwaters; · temporary dikes surrounding dredged material containment areas. 10
  • Because this material is easy to use andcheap, it is extremely suitable fortemporary structures. A training groyneis a good example. The working of agroyne is difficult to predict in advance.That is why it is a good procedure tomake such a construction using arelatively cheap product first, to see howone thing and another works out, andsubsequently either make improvementsor, after some time, a permanentstructure. Above a flow velocity of 1.5m/s, the geosystems filled with sandcannot be used because the sand in thesystems is no longer internally stable. Figure 11 Application of geobagsSandbags can be placed as follows:1. As a blanket: One or two layers of bags placed directly on the slope. An "interlocking" problem arises if the bags are filled completely. The bags are then too round. A solution is not to fill the bags completely, so that the sides flatten out somewhat, as a result of which the contact area becomes larger.2. As a stack: Bags stacked up in the shape of a pyramid. The bags lie half-overlapping with the long side parallel to the shoreline.When installing geosystems, one should see to it that this does not take place on a roughfoundation. Sharp elements may easily damage the casing of the element. Geosystems must notbe filled completely. With a fill ratio of approximately 75% an optimum stability of the elementsis reached. A sound soil protection is necessary if gravel (sand) sausages are used incircumstances where they are under attack of flow or waves. Stability criteria arediscussed inPilarczyk (2000). The first indication on stability, based on small-scale tests, is given below:- Stability on slopes  Hs  2.5   =  ∆ D cr ξ op (1)For sand-filled bags the relative density is including water in pores (∆=1).- Stability of crest elements of breakwaters around SWL (for units lying parallel to the axis of astructure) H/∆ b = 0.5 to 1 (2)In which ‘b’ is the width of the unit.More recent, large scale tests, with large geobags, can be found on the website: (Oumeraci et al., 2003). 11
  • Figure 12. Large-scale tests Wave Flume HannoverStability criteria Hannover (Restall et al., 2004):- on the slope (3)where D=L.sinα, with L= the length of geobag placed perpendicularly to the structure face.-stability of the crest elements of slope structure (4)where Rc is the distance between the crest and the Still Water Line.Tube systemGeotube is a sand/dredged material filled geotextile tube made of permeable but soil-tightgeotextile. The desired diameter and length are project specific and only limited by installationpossibilities and site conditions. The tube is delivered to the site rolled up on a steel pipe. Inletsand outlets are regularly spaced along the length of the tube. The tube is filled with dredgedmaterial pumped as a water-soil mixture (commonly a slurry of 1 on 4) using a suction dredgedelivery line (Figure 13). The choice of geotextile depends on characteristics of fill material. Thetube will achieve its desired shape when filled up to about 80%; a higher filling grade is possiblebut it diminish the friction resistance between the tubes.Figure 13. Filling procedure of Geotube 12
  • Tube can be filled on land (e.g. as dikes for land reclamation, bunds, toe protection or groyns) orin water (e.g. offshore breakwaters, sills of perched beaches, dikes for artificial islands orinterruption of gullies caused by (tidal)currents). The tube is rolled out along the intendedalignment with inlets/outlets centered on top. When a tube is to be placed in water, the effects ofbuoyancy on the tube geotextile prior to filling as well as on the dredged materials settlingcharacteristics must be considered. In order to maximize inlet/outlet spacing, an outlet distantfrom the inlet may be used to enhance the discharge of dredged slurry and thereby encourage andregulate the flow of fill material through the tube so that sufficient fill will flow to distant points.The tube will achieve its desired shape when it is filled up to about 70 to 80% of the theoreticalcircular diameter or a height equal to about a half of the flat width of the tube; a higher fillinggrade is possible but it diminishes the frictional resistance between the tubes.Commonly, the filter geotextile (against scour) and flat tube are fully deployed by floating andholding them in position prior to beginning the filling operation. The filter geotextile is oftenfurnished with small tubes at the edges when filled with sand holds the filter apron at place. Thisapron must also extend in front and behind the unit, commonly 2 times the height of the entirestructure or 2 to 3 times the local wave height.Container systemGeocontainer is a mechanically-filled geotextile and "box" or" pillow" shaped unit made of a soiltight geotextile. The containers are partially prefabricated by sawing mill widths of theappropriate length toegether and at at the ends to form an elongated "box". The "box" is thenclosed in the field, after filling, using a sewing machine and specially designed seams (Figure 14).Barge placement of the site-fabricated containers is accomplish using a specially configuredbarge-mounted crane or by bottom dump hoppers scows, or split barges. The containers are filledand fabricated on the barge and placed when securely moored in the desired position. Positioningof barge for consistent placement - a critical element of constructing "stacked" underwaterstructures - is accomplished with the assistance of modern surveying technology. The volume ofapplied geocontainers was up to 1000 m3. 13
  • Figure 14 Filling and placing of geocontainerThe advantage of these large barge-placed geocontainers include:* Containers can be filled with locally available soil, which may be available from simultaneous dredging activities;* Containers can be relatively accurately placed regardless of weather conditions, current velocities, tides, or water depths;* Contained material is not subject to erosion after placing;* Containers can provide a relatively quick system build-up;* Containers are very cost competitive (for larger works).General Design ConsiderationsWhen applying geobags, geotubes and geocontainers the major design considerations/problemsare related to the integrity of the units during filling, release and placement impact (impactresistance, seam strength, burst, abrasion, durability), the accuracy of placement on the bottom(especially at large depths), and the stability under current and wave attack.The geotextile fabric used to construct the tubes is designed to:* contain sufficient permeability to relieve excess water pressure,* retained the fill-material,* resist the pressures of filling and the active loads without seams or fabric rapture,* resist erosive forces during filling operations,* resist puncture, tearing, and ultraviolet light.The following design aspects are particularly of importance for the design of containers:a) Change of shape of units in function of perimeter of unit, fill-grade, and opening of split barge,b) Fall-velocity/equilibrium velocity, velocity at bottom impact, 14
  • c) Description of dumping process and impact forces,d) Stresses in geotextile during impact and reshaping,e) Resulting structural and executional requirements, andf) Hydraulic stability of structure.Some of these aspects are briefly discussed hereafter.Shape and mechanical strength of geotubes. For the selection of the strength of the geotextileand calculation of a required number of tubes for a given height of structure, knowledge of thereal shape of the tube after filling and placing is necessary. The change of the cross-section of thetube depends on the static head of the (sand)slurry. Depending on this static head, the layingmethod and the behaviour of the fill-material inside the tube, it is possible that the cross-sectionalshape of the filled tube (with a theoretical cross-section with a certain diameter, D) will vary froma very flat hump to a nearly fully circular cross-section. More recently, Silvester (1985, 1990)and Leshchinsky (1995, 1996) prepared some analytical or numerical solutions and graphsallowing the determination of the shape of sand- or mortar-filled tubes based on someexperiments with water. The Leshchinskys method (PC-program) combines all the previousdevelopments and can be treated as a design tool.The design of the shape of the geotube is an iterative process. To obtain a proper stability of thegeotube and to fulfill the functional requirements (i.e. required reduction of incomingwaves/proper transmission coefficient the width and the height of the tube (= a certain crest level)must be calculated. If the obtained shape of geotube does not fulfill these requirements a new(larger) size of a geotube must be taken into account or a double-line of tubes can be used.Dumping process of containers and practical uncertainties. A summary of various forcesduring the dumping and placement process is given in Figure 15 ( Pilarczyk, 2000).1. The required perimeter of geotextile sheet must be sufficient enough to release geocontainerthrough the given split width bo for a required cross-sectional area of material in the bin of bargeAf (or filling-ratio of fill-material in respect to the max. theoretical cross-section). The derivationof the required minimum length of perimeter of geotextile sheet is given in (Pilarczyk, 2000).After opening of the split of a barge the geocontainer is pulled out by the weight of soil but at thesame time the friction forces along the bin side are retarding this process. Due to these forces thetension in geotextile is developing at lower part and both sides of the geocontainer. The upperpart is free of tension till the moment of complete releasing of geocontainer. The question is howfar we are able to model a friction and the release process of geocontainer.2. Geocontainer will always contain a certain amount of air in the pores of soil and between thesoil and the top of (surplus) geotextile providing an additional buoyancy during sinking. Theamount and location of air pockets depends on soil consistency (dry, saturated) and uniformity ofdumping. The air pockets will exert certain forces on geotextile and will influence the way ofsinking. The question is how to model in a proper way the influence of soil consistency and aircontent on shape and stresses in geotubes/geocontainers.3. The forces due to the impact with the bottom will be influenced by a number of factors: * consistency of soil inside the geocontainer (dry, semi-dry, saturated, cohesie, etc.) and its physical characteristics (i.e. internal friction); * amount of air; * permeability/airtightness of geotextile; * strength characteristics of geotextile (elasticity/elongation vs. stresses, etc.); * fall-velocity (influenced by consistency of soil; saturated soil diminish amount of air but increases fall speed); * shape and catching surface of geocontainer at impact incl. effect of not horizontal sinking (i.e. catching of bottom with one end); 15
  • * type of bottom (sand, clay, soft soil, rock, soil covered with rockfill mattress, etc.) and/or type of sublayer (i.e. layer of previous placed containers). Figure 15 Development of forces during dumping of geocontainersDuring the impact the cross-sectional shape of geocontainer will be undergoing a continousreshaping; from cone shape, first probably into a transitional cylindrical shape, and through acertain relaxation, into a semi-oval shape or flat triangular/rectangular shape dictated by soil type,perimeter and elongation characteristics of geotextile. The question is how far we are able tomodel this impact phenomena and resulting forces/stresses in geotextile. The impact forces withthe bottom are a function of the fall velocity (dump velocity) of a geocontainer.4. In final situation the geocontainers will perform as a core material of various protectivestructures or as independent structure exposed to loading by currents and waves, and otherloadings (ice, debris, ship collision, vandalism, etc.). In most cases the geocontainers will befilled by fine (loosely packed) soils. The question is how these structures will behave in practiceunder various types of external and internal loadings.Practical note: The prototype experience indicate that geocontainers with volume up to 200 m3and dumped in water depth exceeding 10 m have been frequently damaged (collapse of seams)using geotextile with tensile strength lower than 75 kN/m, while nearly no damage was observedwhen using the geotextile with tensile strength equal or more than 150 kN/m. This informationcan be of use for the first selection of geocontainers for a specific project. The placing accuracyfor depths larger than 10 m is still a problem (Bezuijen et al., 2004)Durability. Durability of geotextiles is frequently coming question especially concerning theapplications where a long life-span is required. Geotextile is a relatively new product. The firstapplications are from 60s. Recently, we have tested in the Netherlands some 30-years oldgeotextiles used as a filter in revetment structures. In general, these geotextiles were still in agood conditions (still fulfilling properly the prescribed filter and strength functions). Thetechnology of geotextiles is improved to a such extend that the durability tests under laboratory 16
  • condition indicate the life-time of geotextiles at least of 100 years (when not exposed to UVradiation).There is no problem with durability of the geosystems when they are submerged or covered byarmour layers. However, in case of exposed geosystems the UV radiation and vandalism are thefactors, which must be considered during the design. All synthetics are vulnerable to UV. Thespeed of UV degradation, resulting in the loss of strength, depends on the polymer used and typeof additives. Polyesters (PET) are by nature more light stable than, for example, polyamide (PA)and polypropylene (PP). As an example, the Dutch tests with geosynthetic ropes (stabilised andnot stabilised) exposed to various environment have provided the following results (see Table)concerning the strength of the surface yarns after 3 years (in %) in comparison with the originalstrength.To avoid the problem with light degradation the fabrics must be properly selected (i.e. polyester)and UV stabilized. As the period in which the fabric is exposed is short (in terms of months), noserious problems are to be expected. In case of more or less permanent applications underexposed conditions the fabric must be protected against direct sunlight. There is a number ofmethods of surface protection for geosystems. To provide additional UV and abrasion protectionto the exposed sections of tubes, a coating of elastomeric polyurethane is often used. This coating,however, has a tendency to peel after about a number of months and therefore, has to be re-applied.Table 1: Results durability tests on geosynthetic ropes fabric type land-climate sea-climate intertidal zone 50 m under ebb-flood the sea PET: stabilised 63% 62% 94% 93% PA : stabilised 33% 8% 85% 91% PA : no 14% 6% 80% 71% PP : stabilised 41% 46% 93% 95% PP : no 1% 16% 92% 95%Note: the geosynthetics under water and in the intertidal zone show very little degradation instrength in comparison with geosynthetics placed on land; in the inter-tidal zone the geosyntheticsare covered very soon by algae which provide very good UV protection. The permanent surface protection by riprap or blockmats is a rather expensive solution and itwill normally be applied only when it is dictated by necessity due to a high wave loading ordanger of vandalism or other mechanical damage ie. boating, anchoring, etc. In other cases it willbe probably a cheaper solution to apply a temporary protection of geotextile tubes by anadditional layer of a strong geotextile provided with special UV-protection layer. This extraprotection can be realized by adding the highly U.V.-stabilized nonwoven fleece needled onto themain fabric. The function of this felt layer is also to trap the sediment particles and algae, whichgive again extra U.V.-protection. REMARKS ON STABILITY ASPECTSStructural design aspects of low-crested structures are relatively well described in a number ofpublications (Ahrens, 1987, Uda, 1988, Van der Meer, 1987, 1988, CUR/CIRIA, 1991, USCorps, 1993, Pilarczyk&Zeidler, 1996, Vidal et al., 1992, 1998, etc). Some useful information onthe design of breakwaters on reefs in shallow water can be found in Jensen et al. (1998). 17
  • Usually for submerged structures, the stability at the water level close to the crest level will bemost critical. Assuming depth limited conditions (Hs=0.5h, where h=local depth), the (rule ofthumb) stability criterion becomes: Hs/∆Dn50=2 or, Dn50= Hs/3, or Dn50=h/6, where Dn50=(M50/ρs)1/3; Dn50 = nominal stone diameter and M50 and ρs= average mass and density of stone.The upgraded stability formulas for LCS structures, including head effect and scour, can be foundin (Delos, 2005; should be noted that some of useful calculation programs (including formula by Van der Meer)are incorporated in a simple expert system CRESS, which is accessible in the public domain( or Useful information on functional design and thepreliminary structural design of low crested-structures, including cost effectiveness, can be foundin CUR (1997). Alternative solutions, using geotubes (or geotubes as a core of breakwaters), aretreated in (Pilarczyk, 2000). An example of this application can be found in (Fowler et al., 2002). CONCLUSIONSThe author does not intend to provide the new design rules for alternative coastal structures.However, it is hoped that this information will be of some aid to designers looking for newsources, which are considering these kinds of structure and improving their designs.Offshore breakwaters and reefs can be permanently submerged, permanently exposed or inter-tidal. In each case, the depth of the structure, its size and its position relative to the shorelinedetermine the coastal protection level provided by the structure. To reduce the cost somealternative solutions using geosystems can be considered. The actual understanding of thefunctional design of these structures needs further improvement but may be just adequate forthese structures to be considered as serious alternatives for coastal protection.Continued research, especially on submerged breakwaters, should further explore improvedtechniques predict shore response and methods to optimise breakwater design. A good step(unfortunately, limited) in this direction was made in a collective research project in theNetherlands (CUR, 1997). Research and practical design in this field is also the focus of the“Artificial Reefs Program” in New Zealand (, the International Society for ReefStudies (ISRS) (, and the European Project DELOS (EnvironmentalDesign of Low Crested Coastal Defence Structures, 1998-2003) (, the past and recent research in The Netherlands, USA, Germany and in some othercountries on a number of selected geotextile products (geosystems) has provided some valuableresults, which can be of use in preparing a set of preliminary design guidelines for the geotextilesystems under current and wave attack (Pilarczyk, 2000).The following conclusions can be drawn on application of geosystems based on the actualdevelopments and experience.* Geosystems offer the advantages of simplicity in placement and constructability, costeffectiveness, and minimal impact on the environment.* When applying this technology the manufacturers specifications should be followed. Theinstallation needs an experienced contractor.* When applying geotubes and geocontainers the major design considerations/problems arerelated to the integrity of the units during release and impact (impact resistance, seam strength,burst, abrasion, durability etc.), the accuracy of placement on the bottom (especially at largedepths), and the stability.* Information presented on the stability criteria in (Pilarczyk, 2000) and some recent publicationswill be of help in preparing the preliminary alternative designs with geosystems. 18
  • * The geotextile systems can be a good and mostly cheaper alternative for more traditionalmaterials/systems. These new systems deserve to be applied on a larger scale. However, there arestill much uncertainties in the existing design methods. Therefore, further improvement of designmethods and more practical experience under various loading conditions is still needed.* The state-of-the-art of the actual knowledge on the geosystems in hydraulic and coastalengineering can be found in Pilarczyk (2000), Lawson (2003), Bezuijen et al. (2004), and Restallet al., (2004).These new efforts will bring future designers closer to more efficient application and design ofthese promising coastal solutions. The more intensive monitoring of the existing structures willalso help in the verification of new design rules. The intention of this literature search is to uncoverthe technical information on these systems and make them available for the potential users. It willhelp to make a proper choice for specific problems/projects and it will stimulate the furtherdevelopments in this field. International cooperation in this field should be further stimulated. REFERENCES AND SELECTED BIBLIOGRAPHYAhrens, J., 1987, Characteristics of Reef Breakwaters, USAE CERC TR 87-17, Vicksburg.Andrews, C.J., 1997, Sandy shoreline response to submerged and emerged breakwaters, reefs orislands. Unpublished Thesis, University of Waikato, New Zealand (see:, T. and E.C. Cruz, 1996, Fundamental Characteristics of Wave Transformation AroundArtificial Reefs, 25th Coastal Engineering, Orlando, USA.Armono, H.D. and Hall, K.R., 2003. Wave transmission on submerged breakwatersmade of hollow hemispherical shape artificial reefs, Canadian Coastal Conference.Asakawa, T. and Hamaguchi, N., 1991, Recent developments on shore protection inJapan; Coastal Structures and Breakwaters’91, London.Axe, P. Illic, S. and Chadwick, A. (1996). Evaluation of beach modelling techniquesbehind detached breakwaters, ASCE, Proc. 25th ICCE, Orlando, USA.Barber, T., 1999, What are Reef Balls, Southwest Florida Fishing News.Bezuijen, A. et al., 2004, Placing accuracy and stability of geocontainers, 3rd EuroGeo,Munich, Germany.Black, K. and S. Mead, 1999, Submerged structures for coastal protection, ASR, Marine andFreshwater Consultants, New Zealand: (, K. and C.J. Andrews, 2001, Sandy Shoreline Response to Offshore Obstacles, Part I:Salient and tombolo geometry and shape, Journal of Coastal Research, Special Issue on Surfing.Black, K., 2001, Artificial Surfing Reefs for Erosion Control and Amenity: Theory andapplication, Journal of Coastal Research, 1-7 (ICS 2000 Proceedings), New Zealand.Black, K. and S. Mead, 2001, Wave Rotation for Coastal Protection, Proceedings Coasts &Ports 2001, Gold coast, Australia.Bos, K.J., J.A. Roelvink and M.W. Dingemans, 1996, Modelling the impact of detachedbreakwaters on the coast, 25th ICCE, Orlando, USA.CUR, 1997, Beach nourishments & shore parallel structures, R97-2, PO.Box 420, Gouda, NL.CUR/CIRIA, 1991, Manual on use of rock in coastal engineering, CUR/CIRIA report 154, Centrefor Civil Engineering Research and Codes (CUR), Gouda, the Netherlands.d’Angremond, K., Van der Meer, J.W., and de Jong, R.J., 1996, Wave transmission at low-crested structures, 25th Int. Conf. on Coastal Eng., Orlando, Florida.Dally, W.R. and J. Pope, 1986, Detached breakwaters for shore protection, Technical reportCERC-86-1, U.S. Army Engineer WES, Vicksburg, MS. 19
  • Delft Hydraulics, 2002, AmWaj Island development, Bahrain; physical modelling of submergedbreakwaters, Report H4087.DELOS, 2005, Environmental Design of Low Crested Coastal Defence Structures; D 59DESIGN GUIDELINES, EU 5th Framework Programme 1998-2002, Pitagora Editrice Bologna;, Ch. and Hamer, B., 2000, Successful implementation of an offshore reef scheme; 27thCoastal Engineering 2000, Sydney.Fowler, J., Stephens, T., Santiago, M. and De Bruin, P., 2002, Amwaj Islands constructed withgeotubes, Bahrein, CEDA Conference, Denver, USA., H., Siozawa, T., Tadokoro, A. and Tsuda, S., 1994, Drifting Characteristics ofLittoral sand around Submerged Breakwater, Hydro-Port’94, Yokosuka, Japan.Goda, Y., 1995, Wave damping characteristics of longitudinal reef system; Advances in coastalstructures and breakwaters’95, London.Groenewoud, M.D., J. van de Graaff, E.W.M. Claessen and S.C. van der Biezen, 1996,Effect of submerged breakwater on profile development, 25th ICCE., Orlando, USA.Hamaguchi, T., T. Uda, Ch. Inoue and A. Igarashi, 1991, Field Experiment on wave-Dissipating Effect of Artificial Reefs on the Niigata Coast, Coastal Engineering in Japan, JSCE,V. 34, No. 1, June.Hanson, H. and Kraus, N.C., 1989. GENESIS: Generalised model for simulating shorelinechange. Report 1: Technical Reference, Tech. Rep. CERC-89-19, US Army Engr., WES.Hanson, H. and Kraus, N.C., 1990, Shoreline response to a single transmissive detachedbreakwater, Proc. 22nd Coastal Engrg. Conf., ASCE, The Hague.Hanson, H. and Kraus, N.C., 1991, Numerical simulation of shoreline change at Lorain, Ohio.J. of Waterways, Port, Coastal and Ocean Engrg., Vol. 117, No.1, January/February.Harris, Lee E.; ;- Submerged Reef Structures for Habitat Enhancement and Shoreline Erosion Abatement- FIT Wave Tank & Stability Analysis of Reef Balls;-, M.M. and J.B. Herbich, 1986, Effects of breakwater spacing on sand entrapment,Journal of Hydraulic Research, 24 (5).Hirose, N., A. Watanuki and M. Saito, 2002, New Type Units for Artificial Reef Developmentof Eco-friendly Artificial Reefs and the Effectiveness Thereof, PIANC Congress, Sydney, seealso 28th ICCE, Cardiff; 2002;HSU, J.R.C. and Silvester, R., 1990. Accretion behind single offshore breakwater. Journal ofWaterway, Port, Coastal and Ocean Engineering, 116, 362-381.Jimenez, J.A. and A. Sanchez-Arcilla, 2002, Preliminary analysis of shoreline evolution in theleeward of low-crested breakwaters using one-line models, EVK3-2000-0041, EU DELOSworkshop, Barcelona, 17-19 January.Itoh, K., Toue, T. and D Katsui, H., 2001, Numerical simulation of submerged breakwaterdeformation by DEM and VOF; Advanced Design of Maritime Structures in the 21st Century,Yokosuka, Japan.Jensen, Th., Sloth, P. and Jacobsen, V., 1998, Wave Dynamics and Revetment Design on aNatural Reef, 26th Coastal Engineering, Copenhagen.Katoh, K., Yanagishima, S., Nakamura, S. and Fukuta, M., 1994. Stabilization of Beach inIntegrated Shore Protection System, Hydro-Port’94, Yokosuka, Japan.Kono, T. and Tsukayama, S., 1980, Wave transformation on reef and some consideration on itsapplication to field, Coastal Engineering in Japan, Vol. 23.Kuriyama, Y.,Katoh, K. and Ozaki, Y., 1994. Stability of Beaches Protected with DetachedBreakwaters, Hydro-Port’94, Yokosuka, Japan. 20
  • Larson, M., Kraus, N.C. and Hanson, H., 1997, Analytical Solutions of the One-Line Model ofShoreline Change Near Coastal Structures, J. Waterway, Port, Coastal and Ocean Engrg.,ASCE., Vol. 123, No.4, July/August.Leshchinsky, Dov, and Leshchinsky, Ora, 1995, Geosynthetic Confined Pressurized Slurry(GeoCops): Supplement Notes for Version 1.0, May 1995 (Nicolon/US Corps).Leshchinsky, Dov, Leschinsky, Ora, Hoe I. Ling, and Paul A. Gilbert, 1996, GeosyntheticTubes for Confining Pressurized Slurry: Some Design Aspects, Journal of GeotechnicalEngineering, ASCE, Vol. 122, No.8, August.Lawson, C.R. (2003) “Geotextile containment: international perspectives”, ProceedingsSeventeenth GRI Conference, Geosynthetic Institute, Philadelphia, USA, December, pp. 198-221.Ming D. and Chiew Y-M., 2000, Shoreline Changes behind Detached Breakwater, J.Waterway,Port, Coastal, and Ocean Engng., Vol. 126, No.2, March/April.Nakayama, A., N. Horikosi and H. Kobayashi, 1993, The planning and design of MultipurposeArtificial Barrier Reefs, Coastal Zone’93, Coastline of Japan II, New Orleans.Nakayama, A., Yamamoto, M., Yamamoto, J. and Moriguchi, A., 1994. Development ofWater-Intake Works with Submerged Mound (WWSM), Hydro_Port’94, Yokosuka, Japan.Ohnaka, S. and Yoshizwa, T., 1994, Field observation on wave dissipation and reflection by anartificial reef with varying crown width; Hydro-Port’94, Yokosuka, Japan.Okuyama, Y., Adachi, K., Miyazaki, S., and Teruya, M., 1994. Characteristics of WaveDeformation on the Reef, Hydro-Port’94, Yokosuka, Japan.Pilarczyk, K.W. (ed.), 1990, Coastal Protection, A.A. Balkema (publisher), Rotterdam.Pilarczyk, K.W. and Zeidler, R.B., 1996, Offshore breakwaters and shore evolution control,A.A. Balkema, Rotterdam (, K.W., 2000, Geosynthetics and Geosystems in Hydraulic and Coastal Engineering,A.A. Balkema, Rotterdam (;, K.W., 2003, Design of low-crested (submerged) structures: An overview, 6thCOPEDEC, Sri Lanka. ( ).RESTALL, S. et al, 2004, Australian&German experiences with geotextile containers for coastalprotection, 3rd EuroGeo, Munich, Germany.Sanchez-Arcilla, A., Rivero, F., Gironella, X., Verges, D. and Tome, M., 1998, Verticalcirculation induced by a submerged breakwater, 26th Coastal Engineering, Copenhagen.Sawaragi, T., I. Deguchi and S.K. Park, 1988, Reduction of wave overtopping rate by the useof artificial reef, Proc. 21st Int. Conf. on Coastal Eng., ASCE.Sawaragi, T., 1992, Detached breakwaters; Short Course on Design and Reliability of CoastalStructures, Venice, 1-3 October 1992.Sawaragi, T., 1995, Coastal Engineering-waves, beaches, wave-structure interactions, Elsevier.Seabrook, S.R. and Hall, K.R., 1998, Wave transmission at submerged rubble moundbreakwaters, 26th Int. Conf. On Coastal Eng., Copenhagen. Smit, D. et al.,, 1995. Submerged-crest breakwater design; Advances in coastal structures andbreakwaters’95, London.Thomalla F. and Vincent Ch. (2004). Designing Offshore Breakwaters using empiricalrelationships: a case study from Norfolk, UK, Journal of Coastal Research, Vol.20, No.4. Uda, T., 1998, Function and design methods of artificial reef (in Japanese); Ministry ofConstruction, Japan (see also, Coastal Zone’93). US Army Corps, 1993, Engineering Design Guidance for Detached Breakwaters as ShorelineStabilization Structures, WES, Technical Report CERC–93-19, December.Van der Biezen, S.C., Roelvink, J.A., Van de Graaff, J., Schaap, J. and Torrini, L., 1998.2DH morphological modelling of submerged breakwaters, 26th ICCE, Copenhagen.Van der HIDDE, 1995, BEROSIN, Bureau van der Hidde, Harlingen, P.O.B. 299, Netherlands.Van der Meer, J.W., 1987. Stability of breakwater armour layers. Coastal Eng., 11. 21
  • Van der Meer, J.W., 1988. Rock slopes and gravel beaches under wave attack. Doctoral thesis,Delft University of Technology. Also: Delft Hydraulics Communication No. 396Van der Meer, J.W., 1990a. Low-crested and reef breakwaters. Delft Hydraulics Rep. H 986.Van der Meer, J.W., 1990b. Data on wave transmission due to overtopping. Delft Hydraulics.Van der Meer, J.W. and d’Angremond, K., 1991. Wave transmission at low-crested structures,ICE, Thomas Telford. In: Coastal structures and breakwaters. London, UK, p.25-4.Vesterby, H., 1996, Beach Drainage -state of the art -, Seminar on Shoreline ManagementTechniques, 18 April, Wallingford.Vidal, c., Losada, M.A., Medina, R., Mansard, E.P.D. and Gomez-Pina, G., 1992, Anuniversal analysis for the stability of both low-crested and submerged breakwaters, 23rd CoastalEngineering, Venice.Vidal, C., Losada, I.J. and Martin, F.L., 1998, Stability of near-bed rubble-mound structures,26th Coastal Engineering, Copenhagen.Von Lieberman, N. and Mai, S., 2000, Analysis of an optimal foreland design; 27th CoastalEngineering 2000, SydneyWamsley, T. and J. Ahrens, 2003, Computation of wave transmission coefficients at detachedbreakwaters for shoreline response modelling, Coastal Structures’03, Portland, USA.Yoshioka, K., Kawakami, T., Tanaka, S., Koarai, M. and Uda, T., 1993. Design Manual forArtificial Reefs, in Coastlines of Japan II, Coastal Zone’93, ASCE. Related websitesCoastal Page & Links Transfer: (English, downloads) 22
  • Engineering Manual US;8 programme US Army Corps of Engineers; Section 227;3;139 tubes and containers, H., M. Hinz, M. Bleck and A. Kortenhaus, 2003, Sand-filled Geotextile Containers for Shore Protection, Proceedings ‘Coastal Structures 2003’, Portland, Oregon, USA;; Molina, Juan Antonio, 2007, Hydraulic Stability of Geotextile Sand Containers for Coastal Structures - Effect of Deformations and Stability Formulae -, PhD-thesis, Leichtweiß- Institut für Wasserbau, Technical University of Braunschweig, Germany; 23
  • Bezuijen, A., de Groot, M.B., Klein Breteler, M. and Berendsen, E., 2004, Placing accuracy and stability of geocontainers, 3rd EuroGeo, Munich, Germany, also Proc. 7th IGS, Nice; see also: (reports Delft Cluster 1, Coast and River).Van Steeg, P. and Klein Breteler, M., 2008, Large scale physical model tests on the stability of geocontainers, , Report H4595, Delft Hydraulics and Delft Geotechnics for Delft Cluster; Scour Control Technologies breakwaters;48[PDF] Long Term Remedial Measures of Sedimentological Impact due to ...Bestandsformaat: PDF/Adobe Acrobat - HTML versie... 321 Long Term Remedial Measures of Sedimentological Impact due to CoastalDevelopments on the South Eastern Mediterranean Coast Littoral2000/docs/vol2/Littoral2002_40.pdf -Beach drainage/dewatering;191Gravity drainage: Equalizer:[PDF] A Trial of the Pressure Equalisation Module Method of Beach ...Bestandsformaat: PDF/Adobe Acrobat - HTML versiePage 1. A Trial of the Pressure Equalisation Module Method of Beach Protection -Sand-bypassing overview Ripple Mat & ReefBalls 24
  • systems rows: etd-111897-164358/unrestricted/ch1and2.pdVetiver Grass: design online,%20Seawalls%20and%20Bulkheads%20-%20Sloped%20Revetments.pdf;23Headlands&T-groins: 25
  • developments: Fill: structures: [PDF] Soft Engineering Techniques for CoastsBestandsformaat: PDF/Adobe Acrobat - HTML versie... Sediment grain size, roundness, sphericity and specific gravity need to reflect ...2.1.3 Trickle charging - the slow recharging of beaches by the placing of[PDF] Stability of Tandem BreakwaterBestandsformaat: PDF/Adobe Acrobat - HTML versie... Submerged breakwaters have been widely used for coastal protection as wave ... waveheight,wave breaking over the submerged reef, wave transmission and waves -[PDF] Shoreline and Channel Erosion Protection: Overview of AlternativesBestandsformaat: PDF/Adobe Acrobat - HTML versiePage 1. WRP Technical Note HS-RS-4.1 January 1998 Shoreline and ChannelErosion Protection: Overview of Alternatives PURPOSE: This Breteler, M.; Pilarczyk, K.W.; Stoutjesdijk, T., 1998, Design of alternative revetments, 26th International Conference Coastal Engineering, Copenhagen, Denmark; (see also website: (insert Breteler for author). 26