scholarly journals Improved Coastal Erosion Prevention Using a Hybrid Method with an Artificial Coral Reef: Large-Scale 3D Hydraulic Experiment

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2801
Author(s):  
Taeyoon Kim ◽  
Seungil Baek ◽  
Yongju Kwon ◽  
Jooyong Lee ◽  
Sung Min Cha ◽  
...  
Keyword(s):  
Coral Reef ◽  
Hybrid Method ◽  
Coastal Erosion ◽  
Large Scale ◽  
Local Scour ◽  
Return Flow ◽  
Structural Failure ◽  
Submerged Breakwater ◽  
Sediment Transportation ◽  
Erosion Mitigation

Coastal erosion, a worldwide social issue, has garnered substantial attention. Numerous methods have been implemented to control coastal erosion problems; however, the presence of rigid structures limits erosion mitigation, thereby causing various challenges. For instance, in the case of submerged breakwaters, local scour in front of the structure and scour caused by the flow occurring in open inlets affect the subsidence and stability of the structure and can also cause structural failure. To solve these problems, this paper proposes a hybrid method of using a submerged breakwater with an artificial coral reef installation; further, this study evaluates the attenuation of waves and mitigation of sediment transportation through large-scale 3D hydraulic experiments. We found that the hybrid method with an artificial coral reef installed in the open inlet shows excellent wave control and plays a clearly beneficial role in the advancement of the shoreline. The artificial coral reef method reduced the return flow generated by the drag force at the breakwater shoulder and open inlet. In addition, scour at the breakwater shoulder was inhibited by collecting the sand escaping offshore. Simultaneously, scour at the open inlet was also mitigated. The application of the hybrid method compensated for the problems caused by local scour and erosion in the submerged breakwater, thereby leading to the improvement of its function. Therefore, the hybrid method proposed in this paper was determined to be applicable not only for submerged breakwaters, but also for various structures for controlling coastal erosion.

Erosion Mitigation Using Submerged Breakwater Composed of Artificial Reefs

2015 ◽  
Vol 744-746 ◽  
pp. 1171-1174
Author(s):  
Kyu Han Kim ◽  
Bum Shick Shin
Keyword(s):  
Wave Attenuation ◽  
Three Dimensional ◽  
Artificial Reef ◽  
Beach Erosion ◽  
Artificial Reefs ◽  
Return Flow ◽  
Two Dimensional ◽  
Submerged Breakwater ◽  
Erosion Mitigation ◽  
Study Offer

In this study, erosion mitigation by submerged breakwater with artificial reefs is investigated among other means of countermeasures. Beach erosion mechanism near the submerged breakwater and the performance of artificial reef blocks are analyzed in the laboratory. Two-dimensional and three-dimensional laboratory experiments are applied to the analysis. The results of two-dimensional experiments prove that new artifi-cial blocks showed a better performance than the existing blocks in terms of wave attenuation due to wave breaking turbulence near the crest of the structure. Three-dimensional experiments show reduced return flow velocity by half by installing another type of new artificial block in between submerged breakwaters. Return flow has been creating vulnerability in countermeasures by submerged breakwater. Therefore, artifi-cial reef blocks suggested by this study offer solutions to the existing mitigation problems with submerged breakwater.

scholarly journals Planar Installation Characteristics of Crown Depth-Variable Artificial Coral Reef on Improving Coastal Resilience: A 3D Large-Scale Experiment

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1526
Author(s):  
Sunghoon Hong ◽  
Seungil Baek ◽  
Yeonjoong Kim ◽  
Jooyong Lee ◽  
Adi Prasetyo ◽  
...  
Keyword(s):  
Coral Reef ◽  
Large Scale ◽  
Profile Analysis ◽  
Three Dimensional ◽  
Tracer Experiment ◽  
Beach Erosion ◽  
Beach Profile ◽  
Submerged Breakwater ◽  
Coastal Resilience ◽  
Scale Experiment

Coastal resilience has received significant attention for managing beach erosion issues. We introduced flexible artificial coral reef (ACR) structures to diminish coastal erosion, but planar installation effects should be considered to evaluate the feasibility of coastline maintenance. In this study, we conducted a three-dimensional large-scale experiment to investigate the characteristics of planar installation of ACR, focusing on the wave mitigation performance, wave profile deformation with delay, nearshore current movement, deposition and erosion trends, and beach profile variation. We found that the ACR diminished the wave height by ~50% and the current intensity by ~60% compared with that of a conventional submerged breakwater made of dolos units. Using the dispersion velocity of the dye in a tracer experiment, the dispersion time of the ACR was approximately 1.67-times longer than that of the dolos and the current velocity was reduced, revealing that ACR significantly reduced structural erosion. With dolos, severe erosion of >10 cm occurred behind the structure, whereas there was only slight erosion with the ACR. Moreover, in a vertical beach-profile analysis, the ACR exhibited greater shoreline accretion than that of dolos. These results indicate the potential of ACR in improving coastal resilience.

scholarly journals Stokes drift through corals

2021 ◽  
Author(s):  
Joseph J. Webber ◽  
Herbert E. Huppert
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Porous Layer ◽  
Large Scale ◽  
Fluid Layer ◽  
Ocean Waves ◽  
Stokes Drift ◽  
Inviscid Fluid ◽  
Porous Bed ◽  
Vertical Drift

AbstractMotivated by shallow ocean waves propagating over coral reefs, we investigate the drift velocities due to surface wave motion in an effectively inviscid fluid that overlies a saturated porous bed of finite depth. Previous work in this area either neglects the large-scale flow between layers (Phillips in Flow and reactions in permeable rocks, Cambridge University Press, Cambridge, 1991) or only considers the drift above the porous layer (Monismith in Ann Rev Fluid Mech 39:37–55, 2007). Overcoming these limitations, we propose a model where flow is described by a velocity potential above the porous layer and by Darcy’s law in the porous bed, with derived matching conditions at the interface between the two layers. Both a horizontal and a novel vertical drift effect arise from the damping of the porous bed, which requires the use of a complex wavenumber k. This is in contrast to the purely horizontal second-order drift first derived by Stokes (Trans Camb Philos Soc 8:441–455, 1847) when working with solely a pure fluid layer. Our work provides a physical model for coral reefs in shallow seas, where fluid drift both above and within the reef is vitally important for maintaining a healthy reef ecosystem (Koehl et al. In: Proceedings of the 8th International Coral Reef Symposium, vol 2, pp 1087–1092, 1997; Monismith in Ann Rev Fluid Mech 39:37–55, 2007). We compare our model with field measurements by Koehl and Hadfield (J Mar Syst 49:75–88, 2004) and also explain the vertical drift effects as documented by Koehl et al. (Mar Ecol Prog Ser 335:1–18, 2007), who measured the exchange between a coral reef layer and the (relatively shallow) sea above.

scholarly journals Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai‘i: case study

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Yuko Stender ◽  
Michael Foley ◽  
Ku’ulei Rodgers ◽  
Paul Jokiel ◽  
Amarjit Singh
Keyword(s):  
Coral Reef ◽  
Coral Cover ◽  
Ecological Impact ◽  
Coastal Protection ◽  
Benthic Habitat ◽  
Engineering Structures ◽  
Camera System ◽  
Reef Environment ◽  
Submerged Breakwater ◽  
Coral Reef Environment

AbstractConstruction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

scholarly journals Sea level and coastal erosion require large-scale monitoring

Eos ◽  
2003 ◽  
Vol 84 (2) ◽  
pp. 13 ◽  
Author(s):  
Stephen P. Leatherman ◽  
Bruce C. Douglas ◽  
John L. LaBrecque
Keyword(s):  
Sea Level ◽  
Coastal Erosion ◽  
Large Scale

scholarly journals LARGE-SCALE LABORATORY EXPERIMENTS AND NUMERICAL MODELING OF WAVE FORCE AND PRESSURE ACTING ON THE URBAN STRUCTURES

2020 ◽  
pp. 28
Author(s):  
Dayeon Lee ◽  
Sungwon Shin ◽  
Hyoungsu Park ◽  
Dan Cox
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Wave Force ◽  
High Elevation ◽  
Coastal Communities ◽  
Submerged Breakwater ◽  
Sea Levels ◽  
Urban Structures ◽  
Overland Flows ◽  
Hard Structures

Low lying coastal communities are most vulnerable to the flooding which causes from sea-level rise (SLR), and extreme coastal flooding events such as hurricanes and tsunami. Notably, the high elevation of sea-levels due to SLR and local tidal conditions could accelerate the damages on the coastal communities. Hard coastal structures such as a submerged breakwater and seawall would consider minimizing the impacts of overland flows to the urban area from the extreme coastal events, but the effectiveness of those hard structures are significantly alter depending on the various waves and sea-level conditions.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/GCOOpB4C3tA

scholarly journals Incorporating feasibility and collaboration into large-scale planning for regional recovery of coral reef fisheries

2018 ◽  
Vol 604 ◽  
pp. 211-222 ◽  
Author(s):  
KR Jones ◽  
JM Maina ◽  
S Kark ◽  
TR McClanahan ◽  
CJ Klein ◽  
...  
Keyword(s):  
Coral Reef ◽  
Large Scale ◽  
Coral Reef Fisheries

Diurnal Mountain Winds

2000 ◽  
Author(s):  
C. David Whiteman
Keyword(s):  
Large Scale ◽  
Blow Up ◽  
Thermal Structure ◽  
Temperature Inversion ◽  
Return Flow ◽  
Wind System ◽  
Valley Wind ◽  
Deep Layers ◽  
Horizontal Pressure ◽  
Upper Level

Diurnal mountain winds develop over complex topography of all scales, from small hills to large mountain massifs and are characterized by a reversal of wind direction twice per day. As a rule, winds flow upslope, up-valley, and from the plain to the mountain massif during daytime. During nighttime, they flow downslope, down-valley, and from the mountain massif to the plain. Diurnal mountain winds are strongest when skies are clear and winds aloft are weak. Diurnal mountain winds are produced by horizontal temperature differences that develop daily in complex terrain. The resulting horizontal pressure differences cause winds near the surface of the earth to blow from areas with lower temperatures and higher pressures toward areas with higher temperatures and lower pressures. The circulations are closed by return, or compensatory, flows higher in the atmosphere. Four wind systems comprise the mountain wind system, which carries air into a mountain massif at low levels during daytime and out of a mountain massif during nighttime. The slope wind system (upslope winds and downslope winds) is driven by horizontal temperature contrasts between the air over the valley sidewalls and the air over the center of the valley. The along-valley wind system (up-valley winds and down-valley winds) is driven by horizontal temperature contrasts along a valley’s axis or between the air in a valley and the air over the adjacent plain. The cross-valley wind system results from horizontal temperature differences between the air over one valley sidewall and the air over the opposing sidewall, producing winds that blow perpendicular to the valley axis and toward the more strongly heated sidewall. The mountain-plain wind system results from horizontal temperature differences between the air over a mountain massif and the air over the surrounding plains, producing large-scale winds that blow up or down the outer slopes of a mountain massif. The mountain-plain circulation and its upper level return flow are not confined by the topography but are carried over deep layers of the atmosphere above the mountain slopes. Because diurnal mountain winds are driven by horizontal temperature differences, the regular evolution of the winds in a given valley is closely tied to the thermal structure of the atmospheric boundary layer within the valley, which is characterized by a diurnal cycle of buildup and breakdown of a temperature inversion.

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