Showing papers on "Breakwater published in 2005"

Tidal and longshore sediment transport associated to a coastal structure

Abstract: In order to understand the subtidal marine dynamics relative to the coastal engineering works in the Bahia Blanca Estuary (Argentina), the balance of sediment transport caused by tidal currents was estimated in the Puerto Rosales area and compared with the predicted potential littoral transport. The breaking wave height used in the littoral drift calculation was estimated after applying different wave transforming procedures over the deepwater wave which was predicted by the occurrence of predominant wind, blowing long enough in an essentially constant direction over a fetch. The effect of a breakwater on currents and circulation was studied by bathymetric and side-scan sonar records, sedimentology, and tidal current measurements. Different modes of transport occur on either sides of the breakwater. On the east side, longshore transport is the principal mode, and on the west side, tidal transport is predominant.

Morphodynamic Characteristics and Short-Term Evolution of a Coastal Sector in SW Spain: Implications for Coastal Erosion Management

Abstract: In SW Spain, numerous tourist beaches have been nourished over recent years to counteract coastal retreat. Nourishment projects have not produced great endurance, mainly because of the lack of basic information on coastal dynamics and longshore sediment transport paths. In order to cover these aspects in a sandy coastal sector south of the Guadalquivir River mouth, a beach monitoring program was carried out between 1996 and 1998, with a secondary program between 2000 and 2002. Four main beach types were identified, each one with different volumetric trends during the monitoring periods. Most beaches recorded accretion because of the prevalence of fair weather conditions, which emphasized differences among beaches. In a broad sense, beaches located on intertidal rock platforms recorded erosion or no change. Those located updrift of rock platforms or human-made constructions (groins) recorded accretion. These structures divide the coast into several littoral cells, which control longshore sediment ...

Oblique irregular waves load on semicircular breakwater

Abstract: Based on oblique irregular wave physical model tests, the hydraulic characteristics of the semicircular breakwater are studied in this paper. The variations of wave forces on unit length of semicir...

Design considerations for barrier island nourishments and coastal structures for coastal restoration in Louisiana

Abstract: This article discusses background theory, template dimensions, and general guidelines for beach nourishment and coastal structures of Louisiana's barrier islands and chenier plain. Specific topics covered include major parameters governing nourishment performance, template morphometrics, inlet and breach closure, marsh restoration, and analysis of suitability and applicability of coastal structures and structure-nourishment combinations. Application of coastal sediment budgets to the design of coastal restoration projects in Louisiana's coast is discussed and illustrated with two case studies: (1) Holly Beach and (2) East Grand Terre.

Stability of Tetrapod Breakwaters for Different Placing Methods

Abstract: The application of artificial armor units in the construction of rubble mound breakwaters is quite common. Various armor units such as the cube, the tetrapod, the dolos, and the quadripod are commonly used. Recent additions are the accropode and the core-loc, which can be used in a single layer of armoring. The stability of such breakwaters has been the subject of many studies to date. One area of interest has been the effect of the armoring unit placement method on the stability of breakwaters. The present study aims to compare two known methods of tetrapod placement in relation to breakwater stability. The results of the study are also reviewed in the light of earlier studies on breakwater stability.

Numerical simulation on joint motion process of various modes of caisson breakwater under wave excitation

Abstract: A caisson breakwater may experience various modes of motions under wave action. The elementary motion modes are classified into two categories, i.e. the horizontal and rotational vibration coupled motion and the horizontal slide and rotational vibration coupled motion. The motion modes of caisson will transform from one to another depending on the wave forces and the motion behaviours of a caisson. The numerical models of the two motion modes of caisson are developed, the numerical simulation procedure for joint motion process of the two modes of caisson breakwater under wave excitation is presented and tested by a physical model experiment. It is concluded that the simulation procedure is reliable and can be applied to the dynamic stability analysis of caisson breakwaters. Copyright © 2005 John Wiley & Sons, Ltd.

ICEM: Integrated Coastal Engineering Model

Abstract: A morphodynamical model for coastal areas has been developed by simultaneously simulating the dynamics of waves, coastal currents, and sediment transport rates. The sediment transport rates are calculated on a staggered two-dimensional grid, and then the sediment budget is used to predict the coastal morphology changes. The model can simulate short-term and long-term morphological changes around coastal structures. A case study along the Nile Delta coast in Egypt is used to demonstrate the effectiveness of the present model by calibrating and verifying the model results with field measurements. The model can be applied to coastal domains with similar characteristics with appropriate parameter calibration.

Reef Breakwaters for Coastal Protection Safety Aspects and Tolerances

Abstract: Submerged artificial reef breakwaters in the nearshore coastal zone can create the potential for a range of recreational activities as well as beach protection. As such, safety is an important issue when considering the design and construction of these types of structures. Investigations have been carried out for the proposed Palm Beach reefs and this paper provides an overview of the potential safety hazards and litigation threats presented by an artificial submerged structure to all potential users. Investigations into the safety aspects of these structures has incorporated: - extensive monitoring of the Narrowneck artificial reef [Gold Coast, Australia] - observations of natural reefs and beach breaks - physical model testing of a 1:10 sale submerged reef constructed of sand-filled geotextile containers at the Deagon Hydraulics Laboratory. The studies assessed the effect of a number of design parameters, including water depth above crest, roughness of the slope and truncation of the toe, on these safety aspects. The paper also covers the impact of achievable tolerances on the design, performance and safety of these structures and provides a number of guidelines for the design, management and maintenance of these structures in order to provide an acceptable level of risk.

A numerical wave flume to study the functionality and stability of coastal structures

Abstract: Adaptation of COBRAS VOF model for typical breakwater applications and worked out examples of water movement in and around breakwater cross sections.

Application of double skin breakwater with perforation for reducing green water loading on high speed container vessels

Abstract: This paper briefly reviews the phenomenon of green water faced by container ships and a time-domain method based on strip theory for predicting the occurrence of green water Verification of this method with experimental data in regular waves is also carried out showing good agreement A simple CFD hydrodynamic model is developed to represent the green water flow on deck and the parameters of this model are based on experimental data In order to test the appropriateness of this model, comparison in terms of horizontal green water load (acting on a vertical structure) and vertical deck pressure is carried out with test data Having achieved good agreement from this comparison, the research looks into the application of breakwaters in reducing the loading effects of green water Double-skin breakwaters with and without perforation are simulated facing similar green water condition Since protected structures can withstand a certain level of load without suffering detrimental effects, perforation is introduced to lessen the green water load that breakwater is to bear Three systematically varied sizes of perforated holes are simulated and effects are evaluated The research finally concludes on the performance of double-skin breakwater with/without perforation in reducing green water load and the overall effects of the perforation in balancing this load onto the structure and also the breakwater itself

Performance of Submerged Breakwaters as Environmental Friendly Coastal Structures

Abstract: An experimental study on the improvement for the problem of wave transmission in slightly submerged breakwaters is carried out in the present paper. The breakwater shape, effect of the porosity, water depth regarding the breakwater crest height and, dynamic stable deformed breakwater were examined as parameters. During the experiments, porosity was varied between 0.57–0.34, breakwater crest height to water depth ratio changed from 1 to 0.83. The similarity between a longshore bar and a dynamic stable submerged breakwater was also studied in one set of the experiments. Results indicated that a dynamic stable breakwater similar to a longshore bar resulted in better energy dissipation and the best transmission coefficient values determined between 0.3–0.1 in the mentioned condition.

Laboratory Study of Hydrodynamics Near Absorbing and Fully Reflecting Jetties

Abstract: : This physical model study of absorbing and reflecting jetties at coastal inlets was conducted to provide data sets that would aid in the calibration and verification of numerical wave models. The study was performed in the Coastal Inlet Research Program's (CIRP) idealized inlet experimental basin at the U.S. Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL), Vicksburg, MS. Safe navigation, sediment transport into navigation channels, and shoreline erosion are all concerns at coastal inlets and are related to the transformation of waves as they change direction and height due to complex bathymetry and coastal inlet structures. The idealized inlet physical model, created for inlet studies, provided a facility in which to make wave measurements of height and direction and the associated wave-generated currents in enough detail to document the wave height and current variation in a region with complex interactions. Measurements of wave information included use of wave rods for wave height and acoustic Doppler velocity sensors for wave direction and current. Qualitative dye photographs and videos were also obtained.

Wave Defending Effects of V-Type Bottom-Mounted Breakwaters

Abstract: An analytical method is developed for the study of the wave defending effects of the V-type bottom-mounted breakwater The breakwater is assumed to be rigid, thin, impermeable and vertically located in water of constant depth The fluid domain is divided into three sub-regions by an imaginary interface The velocity potential in each region is expanded by eigenfunctions By satisfying the corresponding boundary conditions and natching conditions in and between sub-regions, a set of linear algebraic equations can be obtained to determine the unknown coefficients for the eigenfunction ex pansions for each sub-region The accuracy of the present model is verified by a comparison with existing results for the case of an isolated breakwater Numerical results, in the form of contour maps of the relative wave amplitude around the breakwater, are presented for a range of wave and breakwater parameters The results show that the V-type bottommounted breakwater is generally effective in defending against waves In general, the wave height in the protected area is about 20 ～ 50 percent of the incident wave height

An assessment of processes and strategies for management of the Penarth Coast

Abstract: In 1997, the effects of severe erosion along the Penarth foreshore became apparent when the beach surface fell to critical levels. From consideration of global influences, the physical and cultural environments and anthropogenic activities, including the construction of the Cardiff Bay Barrage, a five-year monitoring programme was devised to assess coastal processes, identify possible causes of the erosion and develop management strategies for protection of the Penarth coast. Approximately 1·5 km of the foreshore, comprising two orientations, NNE and NNW, were surveyed each September and April between 1997 and 2002, to assess summer and winter changes. Results showed in September 1997, sediment transport was southerly in direction whilst from April 2000, there was a consistent return to the traditionally accepted south to north longshore drift; verified by significant differences in longshore gradients. Foreshore analysis provided important regression models representing the variation of the shoreline indicator Mean High Water (MHW) with shoreline position (mean beach level) and gain/loss of beach material. Models represented the temporal variation of MHW and depth of closure with further significant correlation between the two-shoreline indicators (83·85%). A Management Response Indicator (MRI) equation provided a simple tool to rapidly assess the health of Penarth beach, MRI = 17·035 +tan·' (x14- x6)/240, whilst temporal variation of longshore gradients, demonstrated an important inter-relationship between beach evolution and orientation (97·37%). Significant temporal and spatial models identified changes in beach formation adjacent to the Barrage breakwater pre and post construction and showed its influence decreased with distance. A further management tool was developed to monitor beach evolution and morphological change in response to this structure. Analysis of ten-year water and wind data identified a projected mean sea level rise of 0-4mm/year and significant increases in easterly wind components between 1995 and 1997, coinciding with significantly higher extreme water levels. Following correlation of these forcing agents with shoreline indicators, supported by documented beach losses of 350 kg/m2 subsequent to an easterly storm, it was concluded that the unprecedented erosion of Penarth beach was caused by increased wave attack from the northeast and southeast quadrants. Function Analysis justified foreshore management from a development perspective whilst risk analysis supported management strategies. Initial recommendations of on-going monitoring to assess beach health were supported by developed models and underpinned by management responses detailed for each of three defined beach sections. These included beach nourishment, wave wall construction in conjunction with the proposed Penarth Headland Link and groyne removal adjacent to the Barrage.

Oblique Impact of Water Waves on Thin Porous Walls

Abstract: There is a paradoxical phenomenon in earlier studies when the incoming water wave is parallel to a porous breakwater, the water wave permeates completely without regard to the largeness of the the porosity of the porous breakwater. For solving the problem of the water waves obliquely impacting upon the thin porous wall, a new boundary condition on the thin porous wall—which can remedy the above mentioned paradoxical phenomenon—is proposed based on the concept that the incident angle remains unchanged when the water wave permeates into the wall. According to this new boundary condition, an analytic solution of an oblique water wave impacting on a thin porous wall of any permeability is obtained. It is found that the above paradoxical phenomenon, as the water wave is parallel to a thin porous wall, disappears. And, as the incident angle approaches 90°, the reflection coefficient and the transmission coefficient reasonably converge to 1 and 0, respectively, while on the contrary, those in the earlier investigations converge to 0 and 1.

Performance of Moored Floating Breakwaters

Abstract: In this paper the performance of moored floating breakwaters under the action of normal incident waves is investigated in frequency domain. A 3-dimensional hydrodynamic model is coupled with a static and dynamic model of the mooring lines, using an iterative procedure. The models are validated through comparison with numerical and experimental results. An extensive parametric study is performed. The initial draft of a base case floating breakwater is modified through the appropriate modification of the mooring lines’ length, directly affecting the mooring lines’ stiffness and damping. The existence of an “optimum” configuration (length of mooring lines and draft) for the frequencies examined, in terms of wave elevation coefficients and mooring lines’ forces, is clearly demonstrated.

Infilitration of overtopping water in a breakwater crest

Abstract: A number of equations has been developed for calculation overtopping quantities over breakwaters, as well as equations to describe the stability of the inner slope. However, not all the water which overtops the outer boundary of the breakwater will reach the inner slope; part of the water is infiltrated in the crest. In this paper data are presented on the percentage of water infiltrating in the crest of the breakwater. The results are compared with the equation presented in the UK overtopping manual.

Optimal shape design of coastal structures minimizing coastal erosion

Abstract: Coastal erosion is and will be an increasing major environmental issue. We apply shape optimization techniques to the design of coastal structures such as breakwaters, groins and other innovative shapes. Actually, we compute the solution of a boundary value problem describing the water waves scattered by the structure and modify accordingly its shape, in order to minimize a pre-defined cost function taking into account the strength (energy) of the waterwaves. The optimization procedure relies on a new global semi-deterministic algorithm, able to pursue beyond local minima.