Shore protection by oblique seabed bars

2017 ◽  
Vol 815 ◽  
pp. 481-510 ◽  
Author(s):  
Louis-Alexandre Couston ◽  
Mir Abbas Jalali ◽  
Mohammad-Reza Alam
Keyword(s):  
Multiple Scale ◽  
Coastal Protection ◽  
Bragg Resonance ◽  
Shore Protection ◽  
Resonance Mechanism ◽  
Small Frequency ◽  
Protection Efficiency ◽  
Parallel Direction ◽  
Incident Waves ◽  
Incident Wave Energy

Shore protection by small seabed bars was once considered possible because seafloor undulations strongly reflect surface waves of twice the wavelength by the so-called Bragg resonance mechanism. The idea, however, proved ‘unreliable’ when it was realized that a patch of longshore seabed bars adjacent to a reflective shore could result in larger waves at the shoreline than for the case of a flat seabed. Here we propose to revamp the Bragg resonance mechanism as a means of coastal protection by considering oblique seabed bars that divert, rather than reflect, shore-normal incident waves to the shore-parallel direction. We show, via multiple-scale analysis supported by direct numerical simulations, that the creation of a large protected wake near the shoreline requires a bi-chromatic patch to deflect the incident waves to the shore-parallel direction. With two superposed sets of oblique seabed bars, the incident wave energy becomes efficiently deflected far to the sides, leaving a wake of decreased wave activity downstream of the patch. We demonstrate that the shore protection efficiency provided by this novel arrangement is not affected by reflection of leaked waves at the shoreline, and that it is relatively robust against small frequency detuning.

Sheltering the Shore via Nearshore Oblique Seabed Bars

2016 ◽  
Author(s):  
Louis-Alexandre Couston ◽  
Mir Abbas Jalali ◽  
Mohammad-Reza Alam
Keyword(s):  
Field Measurements ◽  
Buffer Zone ◽  
Coastal Protection ◽  
High Momentum ◽  
Frequency Detuning ◽  
Resonance Mechanism ◽  
Broadband Spectrum ◽  
Parallel Direction ◽  
Wave Energy Flux ◽  
Incident Waves

Periodic seabed undulations, such as nearshore sandbars, are known to reflect incoming surface waves of twice the wavelength by the so-called Bragg resonance mechanism. In view of this property, longshore seabed-mounted bars were proposed long ago as a means of coastal protection against the high momentum of incident oceanic waves. Many theoretical, computational, experimental and field measurements were conducted to understand their effectiveness in shielding the shore. The idea, nevertheless, proved impractical when Yu and Mei (JFM 2000, [1]) showed that due to an inevitable finite reflection from the shoreline, energy can get trapped in the area between the shoreline and the patch of bars eventually resulting in a much higher wave energy flux impinging the shoreline. Here we propose an arrangement of oblique bars that shelters the shore by diverting, rather than reflecting, shore-normal incident waves to the shore-parallel direction. A protected buffer zone is thus created at the shoreline. We show that this novel arrangement can very efficiently shelter the shore, is almost insensitive to the distance between the bottom corrugations and the shoreline, is relatively robust against frequency detuning, and will discuss that it can be designed to protect the shore against almost the entire broadband spectrum of incident waves.

scholarly journals The Focusing Waves Induced by Bragg Resonance with V-Shaped Undulating Bottom

2021 ◽  
Vol 9 (7) ◽  
pp. 708
Author(s):  
Haiming Zhang ◽  
Aifeng Tao ◽  
Junhao Tu ◽  
Junwei Su ◽  
Shuya Xie
Keyword(s):  
Specific Area ◽  
Resonance Phenomenon ◽  
Coastal Protection ◽  
Bragg Resonance ◽  
Random Waves ◽  
Regular Waves ◽  
Optimal Angle ◽  
Focusing Effect ◽  
Center Axis ◽  
Incident Waves

Intensive wave reflection occurs when the wavelengths of the incident waves and bottom undulations are in a 2:1 ratio. Existing studies have included the Bragg resonance phenomenon of waves passing over a continuous undulating bottom parallel to and oblique to the shoreline. More generally, the Bragg resonance mechanism is used as a means of coastal protection, rather than wave power generation. To focus the wave energy in a specific area, here, we propose sinusoidal sandbars of a horizontal V-shaped pattern, which is formed by two continuous undulating bottoms inclined at an angle to each other and the center axis of the angle is perpendicular to the shoreline. Based on the high-order spectral (HOS) numerical model, both the characteristics of Bragg resonance induced by the regular waves and random waves are investigated. In the scenario of regular waves, it shows that the wave-focusing effect is related to the angle of the V-shaped undulating bottom, and the optimal angle of inclination for the V-shaped undulating bottom is 162.24°. On that basis, considering the interactions between the random waves and the V-shaped undulating bottom of 162.24°, the Bragg resonance characteristics of random waves are studied. The BFI factor combining wave steepness and spectrum width can evaluate the focusing intensity of the Bragg resonance of the random waves. For BFI, in the range of 0.15–1.0, the values of Hsmax/Hs0 linearly increase with the increase of BFI.

scholarly journals Resilience from coastal protection

2015 ◽  
Vol 373 (2053) ◽  
pp. 20140383 ◽  
Author(s):  
Lesley C. Ewing
Keyword(s):  
Cultural Values ◽  
San Francisco ◽  
Coastal Communities ◽  
Coastal Hazards ◽  
Community Safety ◽  
Coastal Protection ◽  
Shore Protection ◽  
Coastal Community ◽  
Effective Community ◽  
Key Aspects

Coastal areas are important residential, commercial and industrial areas; but coastal hazards can pose significant threats to these areas. Shoreline/coastal protection elements, both built structures such as breakwaters, seawalls and revetments, as well as natural features such as beaches, reefs and wetlands, are regular features of a coastal community and are important for community safety and development. These protection structures provide a range of resilience to coastal communities. During and after disasters, they help to minimize damages and support recovery; during non-disaster times, the values from shoreline elements shift from the narrow focus on protection. Most coastal communities have limited land and resources and few can dedicate scarce resources solely for protection. Values from shore protection can and should expand to include environmental, economic and social/cultural values. This paper discusses the key aspects of shoreline protection that influence effective community resilience and protection from disasters. This paper also presents ways that the economic, environmental and social/cultural values of shore protection can be evaluated and quantified. It presents the Coastal Community Hazard Protection Resilience (CCHPR) Index for evaluating the resilience capacity to coastal communities from various protection schemes and demonstrates the use of this Index for an urban beach in San Francisco, CA, USA.

Subharmonic resonance of proposed storm gates for Venice Lagoon

1994 ◽  
Vol 444 (1920) ◽  
pp. 257-265 ◽  
Keyword(s):  
Experimental Evidence ◽  
Incident Wave ◽  
Laboratory Tests ◽  
Venice Lagoon ◽  
Subharmonic Resonance ◽  
Horizontal Axis ◽  
Trapped Modes ◽  
Resonance Mechanism ◽  
Trapped Mode ◽  
Incident Waves

A recent design of storm barriers at the inlets of Venice Lagoon consists of a number of articulated inclined gates hinged on a horizontal axis on the seabed. In laboratory tests with normally incident waves the gates have been found to oscillate at half of the incident wave frequency and out of phase with their immediate neighbours. In this paper we identify the resonance mechanism by first showing the existence of trapped modes as a consequence of the articulated construction. Experimental evidence is shown for the trapped mode and its subharmonic resonance by normally incident waves.

Information Technologies and Mathematical Modeling in Solving Environmental Problems in the Design of Shore Protection Structures

2019 ◽  
Vol 23 (9) ◽  
pp. 13-17 ◽  
Author(s):  
T.Yu. Khashirova ◽  
Z.G. Lamerdonov ◽  
S.A. Zhaboev ◽  
M.A. Enaldieva ◽  
M.M. Thabisimova ◽  
...  
Keyword(s):  
Information Technologies ◽  
Optimal Solution ◽  
Environmental Indicators ◽  
Design Solution ◽  
Coastal Protection ◽  
Shore Protection ◽  
Innovative Solutions ◽  
The Russian Federation ◽  
Selection Of ◽  
Integral Indicator

The proposed methodology for the selection of the optimal design solution of the coastal protection structure, adapted to the specific hydrological, hydraulic and morphological conditions of the river according to an integral indicator, including the reliability of the structure; economic and environmental indicators. Innovative solutions to protect the banks of rivers from erosion, patented in the Russian Federation, decision-making modeling algorithms are presented. The developed theory and methodology for choosing the optimal solution can be implemented on other subsystems.

Submerged Floating Breakwaters

1991 ◽  
Vol 113 (3) ◽  
pp. 205-210 ◽  
Author(s):  
D. V. Evans ◽  
C. M. Linton
Keyword(s):  
Circular Cylinder ◽  
General Theory ◽  
Incident Wave ◽  
Vertical Plate ◽  
Appreciable Amount ◽  
Submerged Body ◽  
Floating Breakwaters ◽  
Incident Waves ◽  
Incident Wave Energy ◽  
Horizontal Circular Cylinder

In this paper we show how a submerged body can, if properly tuned to the incoming waves, reflect an appreciable amount of the incident wave energy by creating waves through its own motion which effectively cancel the incident waves passing over it. A general theory for this phenomenon is described which is applied to the cases of a hinged vertical plate and a submerged tethered horizontal circular cylinder.

scholarly journals GEOLOGICAL CONTROLS ON PROCESS-RESPONSE, S.E. AUSTRALIA

1980 ◽  
Vol 1 (17) ◽  
pp. 56
Author(s):  
P.S. Roy ◽  
A.W. Stephens
Keyword(s):  
Sediment Characteristics ◽  
Coastal Evolution ◽  
Sediment Budgets ◽  
The Past ◽  
Nearshore Sediments ◽  
Induced Currents ◽  
Wave Induced ◽  
Incident Waves ◽  
Inner Continental Shelf ◽  
Incident Wave Energy

Results of regional geological studies on the southeastern Australian coast and inner continental shelf suggest that broad relationships between nearshore sediments and morphologies are often the result of factors other than incident waves and wave-induced currents. Five main factors (including wave action) have been identified: 1. degree of compartmentization and sand bypassing, 2. incident wave energy, 3. offshore sand loss to deep water sinks, 4. inherited sediment characteristics, and 5. substrate control. It is thought that these factors have controlled coastal evolution in the past and also influence present-day coastal changes. Identification of the role played by individual factors in specific areas provides valuable information on coastal sediment budgets.

scholarly journals METHOD FOR ESTABLISHING SHORE PROTECTION STRUCTURES FROM GABION

2020 ◽  
pp. 84-92
Author(s):  
S.I. Rogachko ◽  
◽  
H.V. Slobodianyk ◽  
N.B. Dolinskaya ◽  
◽  
...  
Keyword(s):  
Agricultural Land ◽  
Residential Buildings ◽  
Wind Waves ◽  
Coastal Protection ◽  
Main Task ◽  
Shore Protection ◽  
Progressive Method ◽  
Industrial Enterprises ◽  
Geological Conditions ◽  
Protection Structures

Abstract. The shores of seas, lakes, bays and reservoirs under the action of wind waves, drifting level ice, rainwater, wind erosion and other factors are subject to intensive destruction. As a result of this, the areas of valuable agricultural land and other lands are reduced. The destruction of the coasts is accompanied by landslides, which reduce the area of settlements where residential buildings, urban buildings, industrial enterprises, park areas, roads and other communications are located. In such cases there is a need for the construction of special protection structures, which will protect coasts from destruction. There are two methods of coastal protection ‒ active and passive. Experience in coastal protection shows, that in many cases, these methods can be successful when applied jointly. The types of structures of shore protection structures are diverse. Therefore, the main task of designers is to choose the most optimal of them, taking into account the climatic, hydrological and engineering-geological conditions of the region construction. The aim of this work is to create a progressive method of construction of shore protection structures on shallow shores of the seas and in shallow reservoirs. This paper considers the existing and innovative designs of shore protection structures made of various materials, the conditions of their use and technical and economic characteristics are analyzed. Based on the analysis, a progressive method of construction of shore protection structures from gabions is proposed. The using of the proposed method for the construction of shore protection structures from a box type gabion will speed up the construction process of such structures, as well as reduce the volume of material at the base, which will lead to a significant reduction in the cost of construction. The mass of gabions in each project should be determined on the parameters of the waves of the design storm in accordance to the recommendations of standards.

A strategy towards estimating a sediment budget for the Baltic Sea coastline of Schleswig-Holstein, Germany

2020 ◽  
Author(s):  
Tanita Averes ◽  
Klaus Schwarzer ◽  
Jacobus Hofstede ◽  
Arfst Hinrichsen ◽  
Hans-Christian Reimers ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Sediment Budget ◽  
Coarse Grained ◽  
Coastal Protection ◽  
Shore Protection ◽  
The Baltic Sea ◽  
Coastal Morphology ◽  
Protection Measures ◽  
Variable Character ◽  
The Baltic

<p>Sea level rise along with the changing climate leads to severe enhancement of hydrodynamic impact to coastlines worldwide. Along the Baltic Sea coast of Schleswig-Holstein (Germany), this leads to the erosion of exposed glacial cliffs (up to 30 % of the coastline) and abrasion platforms (unknown extend). Irreversible land loss and seafloor deepening are the consequences, causing socio-economic and environmental concerns in affected areas. However, the adjacent coastal sections benefit from the development as the mobilized material constitutes the main sediment source to the nearshore bar and beach systems. Here, temporal built up of nearshore bars and the deposition at sandspits and beaches functions as natural shore protection.</p><p>The heterogenous and dynamic morphology, exposition and geology of the cliff sections and their offshore continuation complicates system understanding and management of the Schleswig-Holstein coastline. The availability of coarse-grained sediments (sand, gravel, stones) from the poorly sorted glacial till, forming the cliffs, is comparatively low. This lack of obtained material suitable to build up a coastal morphology attributes a central role to the source areas and the quantification of the sediment budget regarding coastal preservation.</p><p>On this account we attempt to develop a strategy towards a classified coastal sediment budget, which is based on a comprehensive field and literature data base, addressing the highly variable character of the observed coastline described in morphological, morphodynamic, geological, sedimentological, hydrodynamic and anthropogenic parameters.</p><p>The coastline of Schleswig-Holstein is structured into 58 active cliff sections for individual description via categorized cliff profiles. Furthermore, 22 abrasion platforms are defined in the offshore region and characterized by descriptive summaries. The data summary reveals well investigated zones (e.g. Schönhagen, Stohl, Heiligenhafen, Brodten), serving as potential pilot areas for complementary studies, but also identifies study areas which require further research.</p><p>The literature values for past cliff retreat and eroded sediment volumes bear high uncertainties. This is due to the fact that former studies are based on unequal spatial extend of cliff sections, variable time intervals and differing methods. Further, computation of eroded material volumes is lacking important input parameters, e.g. the degree of compaction and the grain size distribution. This is considered for budget calculations and their confidence for individual coastal units in template form.</p><p>The current study compiles and visualizes the heterogenous data for further scientific applications. The project aims to support future studies on the sediment availability and transport in the near-shore system using hydrodynamic modelling and thus creates a sound scientific base for system understanding and new governmental regulations concerning coastal protection measures at the Schleswig-Holstein Baltic Sea.</p>

scholarly journals DESIGN AND CONSTRUCTION OF THE BOSCOMBE MULTI-PURPOSE REEF

2011 ◽  
Vol 1 (32) ◽  
pp. 58
Author(s):  
Shaw Trevor Mead ◽  
Chris Blenkinsopp ◽  
Andrew Moores ◽  
Jose Borrero
Keyword(s):  
High Intensity ◽  
Late Summer ◽  
Wave Climate ◽  
Poor Quality ◽  
Coastal Protection ◽  
English Channel ◽  
Shore Protection ◽  
Morphological Response ◽  
Left Hand ◽  
Structure Monitoring

The Boscombe Reef is a multipurpose reef structure designed primarily for the enhancement of surfing amenity at Boscombe, Poole Bay, England. The reef was designed to maximise the small and generally poor-quality surfing wave climate of the eastern English Channel coast. The reef was constructed from 54 large, sand filled geotextile containers ranging in size from 1 to 5 m diameters and 15 to 70 m long with a total volume of approximately 13,000 m3. Construction of the reef began in the summer of 2008, was suspended during the following winter and was completed in the late summer of 2009. The reef is now in service and provides a high intensity right hand surfing ride of up to 70 m and a shorter left hand ride of up to 30 m. Although the reef was not designed as a coastal protection structure, monitoring of the morphological response supports that the reef promotes shore protection through the formation of an inshore salient.

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