scholarly journals Laboratory data on wave propagation through vegetation with following and opposing currents

2021 ◽  
Vol 13 (10) ◽  
pp. 4987-4999
Author(s):  
Zhan Hu ◽  
Simei Lian ◽  
Huaiyu Wei ◽  
Yulong Li ◽  
Marcel Stive ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wind Waves ◽  
Model Development ◽  
Laboratory Data ◽  
Coastal Vegetation ◽  
Vegetation Density ◽  
Wave Dissipation ◽  
Flume Experiments ◽  
Key Factor

Abstract. Coastal vegetation has been increasingly recognized as an effective buffer against wind waves. Recent laboratory studies have considered realistic vegetation traits and hydrodynamic conditions, which advanced our understanding of the wave dissipation process in vegetation (WDV) in field conditions. In intertidal environments, waves commonly propagate into vegetation fields with underlying tidal currents, which may alter the WDV process. A number of experiments addressed WDV with following currents, but relatively few experiments have been conducted to assess WDV with opposing currents. Additionally, while the vegetation drag coefficient is a key factor influencing WDV, it is rarely reported for combined wave–current flows. Relevant WDV and drag coefficient data are not openly available for theory or model development. This paper reports a unique dataset of two flume experiments. Both experiments use stiff rods to mimic mangrove canopies. The first experiment assessed WDV and drag coefficients with and without following currents, whereas the second experiment included complementary tests with opposing currents. These two experiments included 668 tests covering various settings of water depth, wave height, wave period, current velocity and vegetation density. A variety of data, including wave height, drag coefficient, in-canopy velocity and acting force on mimic vegetation stem, are recorded. This dataset is expected to assist future theoretical advancement on WDV, which may ultimately lead to a more accurate prediction of wave dissipation capacity of natural coastal wetlands. The dataset is available from figshare with clear instructions for reuse (https://doi.org/10.6084/m9.figshare.13026530.v2, Hu et al., 2020). The current dataset will expand with additional WDV data from ongoing and planned observation in natural mangrove wetlands.

scholarly journals Laboratory data on wave propagation through vegetation with following and opposing currents

2021 ◽  
Author(s):  
Zhan Hu ◽  
Simei Lian ◽  
Huayu Wei ◽  
Yulong Li ◽  
Marcel Stive ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Wind Waves ◽  
Laboratory Data ◽  
Coastal Vegetation ◽  
Wave Dissipation ◽  
Flume Experiments ◽  
Dissipation Process ◽  
Mangrove Wetlands ◽  
Key Factor ◽  
Current Flows

Abstract. Coastal vegetation has been increasingly recognized as effective buffer against wind waves. Recent studies have advanced our understanding of wave dissipation process in vegetation (WDV). In intertidal environments, waves commonly propagate into vegetation fields with underlying tidal currents, which may alter WDV, but such influence is often overlooked. The key mechanism of WDV with co-existing currents are understudied, as previous studies have drawn contradictory conclusions on the effect of following currents on WDV. Subsequent laboratory experiments have partly explained the inconsistent conclusions, but relevant data are rarely available for theoretical or modelling development. Additionally, while the vegetation drag coefficient is a key factor influencing WDV, it is rarely reported for combined wave-current flows. This paper reports a unique dataset from two flume experiments, including 668 wave-only and wave with following/opposing current tests. A variety of data including wave height, drag coefficient, in-canopy velocity and acting force on mimic vegetation stem are recorded. This dataset is expected to assist future theoretical advancement on WDV, which may ultimately lead to more accurate prediction of wave dissipation capacity of real coastal wetlands. The dataset is available from figshare (https://doi.org/10.6084/m9.figshare.13026530.v2; Hu et al., 2020) with clear instructions for reuse. The current dataset will expand with additional WDV data from ongoing as well as planned future observation in real mangrove wetlands.

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

scholarly journals Wave energy dissipation in the mangrove vegetation off Mumbai, India

2017 ◽  
Author(s):  
Samiksha S. Volvaiker ◽  
Ponnumony Vethamony ◽  
Prasad K. Bhaskaran ◽  
Premanand Pednekar ◽  
MHamsa Jishad ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Coastal Region ◽  
Measured Data ◽  
Vegetation Density ◽  
Mangrove Vegetation ◽  
Wave Height Attenuation ◽  
Set Up

Abstract. Coastal regions of India are prone to sea level rise, cyclones, storm surges and human induced activities, resulting in flood, erosion, and inundation. The primary aim of the study is to estimate wave attenuation by mangrove vegetation using SWAN model in standalone mode, as well as SWAN nested with WW3 model for the Mumbai coastal region. To substantiate the model results, wave measurements were carried out during 5–8 August 2015 at 3 locations in a transect normal to the coast using surface mounted pressure level sensors under spring tide conditions. The measured data presents wave height attenuation of the order of 52 %. The study shows a linear relationship between wave height attenuation and gradual changes in water level in the nearshore region, in phase with the tides. Model set-up and sensitivity analyses were conducted to understand the model performance to vegetation parameters. It was observed that wave attenuation increased with an increase in drag coefficient (Cd), vegetation density, and stem diameter. For a typical set-up for Mumbai coastal region having vegetation density of 0.175 per m2, stem diameter of 0.3 m and drag coefficient varying from 0.4 to 1.5, the model reproduced attenuation, ranging from 49 to 55 %, which matches well with the measured data. Spectral analysis performed for the cases with and without vegetation very clearly portrays energy dissipation in the vegetation area as well as spectral changes. This study has the potential of improving the quality of wave prediction in vegetation areas, especially during monsoon season and extreme weather events.

scholarly journals Drag Force Modeling of Surface Wave Dissipation by a Vegetation Field

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2513
Author(s):  
Tze-Yi Yang ◽  
I-Chi Chan
Keyword(s):  
Numerical Experiments ◽  
Open Space ◽  
Wind Waves ◽  
Laboratory Data ◽  
Storm Surges ◽  
Coastal Vegetation ◽  
Force Modeling ◽  
Wave Height Attenuation ◽  
Large Wind ◽  
Natural Barrier

In this paper, we explore the use of coastal vegetation as a natural barrier to defend our shoreline from hazards caused by large wind waves, storm surges, and tsunamis. A numerical model based on XBeach is employed to evaluate the wave damping by vegetation. An explicit formula for the required drag coefficient used to help describe the additional force imposed by the vegetation is developed through a series of numerical experiments. Overall, our predictions agree reasonably with available laboratory data in the literature for various incident wave conditions and vegetation configurations. Our analysis suggests that a small unvegetated open space in the middle of a vegetation strip does not have a significant impact on the amount of wave height attenuation at the exit of the vegetated bed.

scholarly journals Wave energy dissipation in the mangrove vegetation off Mumbai, India

2018 ◽  
Author(s):  
Samiksha S. Volvaiker ◽  
Ponnumony Vethamony ◽  
Prasad K. Bhaskaran ◽  
Premanand Pednekar ◽  
Mhamsa Jishad ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Drag Coefficient ◽  
Wave Height ◽  
Wave Energy ◽  
Coastal Region ◽  
Measured Data ◽  
Vegetation Density ◽  
Mangrove Vegetation ◽  
Wave Height Attenuation ◽  
Set Up

Abstract. Coastal regions of India are prone to sea level rise, cyclones, storm surges and human induced activities, resulting in flood, erosion and inundation. The primary aim of the study is to estimate wave energy attenuation by mangrove vegetation using SWAN model, and validate the model results with measurements for the Mumbai coastal region. Wave measurements were carried out during 5–8 August 2015 at 3 locations in a transect normal to the coast using surface mounted pressure level sensors in spring tide conditions. The measured data presents wave height attenuation of the order of 52 %. The study shows a linear relationship between wave height attenuation and gradual changes in water level in the nearshore region, in phase with the tides. Model set-up and sensitivity analyses were conducted to understand the model performance to vegetation parameters. It was observed that wave attenuation increases with an increase in drag coefficient, vegetation density and stem diameter. For a typical set-up for Mumbai coastal region having vegetation density of 0.175 per m2, stem diameter of 0.3 m and drag coefficient varying from 0.4 to 1.5, the model reproduced attenuation, ranging from 49 to 55 %, which matches well with the measured data. Spectral analysis performed for the cases with and without vegetation very clearly portrays energy dissipation in the vegetation area. This study has the potential of improving the quality of wave prediction in vegetation areas, especially during monsoon season and extreme weather events.

scholarly journals Lidar Observations of the Swash Zone of a Low-Tide Terraced Tropical Beach under Variable Wave Conditions: The Nha Trang (Vietnam) COASTVAR Experiment

2020 ◽  
Vol 8 (5) ◽  
pp. 302 ◽  
Author(s):  
Luís Pedro Almeida ◽  
Rafael Almar ◽  
Chris Blenkinsopp ◽  
Nadia Senechal ◽  
Erwin Bergsma ◽  
...  
Keyword(s):  
Field Experiment ◽  
Wave Height ◽  
Sandy Beach ◽  
Wind Waves ◽  
Swash Zone ◽  
Key Factor ◽  
Wave Conditions ◽  
Run Up ◽  
Topographic Surveys ◽  
Lidar Observations

A field experiment was conducted at a tropical microtidal intermediate sandy beach with a low tide terrace (Nha Trang, Vietnam) to investigate the short-term swash-zone hydrodynamics and morphodynamics under variable wave conditions. Continuous 2D Lidar scanner observations of wave height at the lower foreshore, subsequent run-up and swash-induced topographic changes were obtained. These data were complemented by detailed real-time kinematic GPS topographic surveys. Variable wave and tide conditions were experienced during the field experiment with relatively large swell waves (offshore significant wave height, Hs = 0.9 m to 1.3 m; peak wave period, Tp = 8 to 12 s) concomitant with spring tides at the beginning of the period, followed by mild wind waves (offshore Hs under 0.5 m and Tp 5 s) and neap tides. This resulted in the following morphological sequence: berm erosion followed by rapid neap berm reformation and beach recovery within a few days. New insights into the link between intra-tidal swash dynamics and daily beach profile evolution were found using the Lidar dataset. While waves directly cause morphology changes on a wave-by-wave basis, tidal levels were found to be a key factor in determining the morphological wave-effect (accretive or erosive) due to modulated interaction between surf and swash hydro-morphodynamics.

scholarly journals Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 90
Author(s):  
Md Abedur Rahman ◽  
Norio Tanaka ◽  
A. H. M. Rashedunnabi
Keyword(s):  
Laboratory Experiments ◽  
Flow Analysis ◽  
Maximum Energy ◽  
Energy Reduction ◽  
Coastal Vegetation ◽  
Vegetation Density ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Tsunami Inundation ◽  
Tsunami Mitigation

As a countermeasure against tsunami inundation, the present study conducted a series of laboratory experiments using a compound mitigation system in which a seaward embankment (E) followed by landward coastal vegetation (V) over a mound (M) (EMV) was investigated in supercritical flow conditions. The changes of flow around the mitigation system and energy reduction were clarified under varying conditions of mound height and vegetation density. Cases of an embankment followed by only a mound (EMNV) were also considered for comparison. Experimental results showed that three basic types of flow structures were observed within the mitigation system in EMV cases. A water cushion was created within the mitigation system mainly due to the combined effects of the mound and vegetation. It significantly reduced the maximum total energy in EMV cases by approximately 41–66%, whereas in EMNV cases, the maximum energy reduction was found to be 23–65%. Increments in both mound height and vegetation density increased the intensity of the water cushion within the mitigation system by offering more drag and reflecting the flow, and hence, significantly reduced the energy of the flow.

scholarly journals Attenuation of Wave Energy Due to Mangrove Vegetation off Mumbai, India

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4286 ◽  
Author(s):  
Samiksha S. V. ◽  
P. Vethamony ◽  
Prasad K. Bhaskaran ◽  
P. Pednekar ◽  
M. Jishad ◽  
...  
Keyword(s):  
Climate Change ◽  
Drag Coefficient ◽  
Wave Energy ◽  
Measured Data ◽  
Stem Diameter ◽  
Coastal Hazards ◽  
Sensitivity Analyses ◽  
Vegetation Density ◽  
Mangrove Vegetation ◽  
Set Up

Coastal regions of India are prone to sea level rise, cyclones, storm surges, and human-induced activities, resulting in flood, erosion, and inundation, and some of these impacts could be attributed to climate change. Mangroves play a very protective role against some of these coastal hazards. The primary aim of the study was to estimate wave energy attenuation by mangrove vegetation using modeling, and to validate the model results with measurements conducted off Mumbai coast, where a mangrove forest is present. Wave measurements were carried out from 5–8 August 2015 at three locations in a transect normal to the coast using surface-mounted pressure-level sensors in spring tide conditions. The measured data presented wave height attenuation of the order of 52%. Model set-up and sensitivity analyses were conducted to understand the model performance with respect to vegetation parameters. It was observed that wave attenuation increases with an increase in drag coefficient, vegetation density, and stem diameter. For a typical set-up in the Mumbai coastal region having a vegetation density of 0.175 per m2, stem diameter of 0.3 m, and drag coefficient varying from 0.4 to 1.5, the model reproduced attenuation ranging from 49% to 55%, which matches reasonably well with the measured data. Spectral analysis performed for the cases with and without vegetation very clearly portrays energy dissipation in the vegetation area. This study also highlights the importance of climate change and mangrove vegetation.

scholarly journals THE ONE-DIMENSIONAL WAVE SPECTRA AT LIMITED FETCH

1972 ◽  
Vol 1 (13) ◽  
pp. 13
Author(s):  
Hisashi Mitsuyasu
Keyword(s):  
Similarity Theory ◽  
Wind Waves ◽  
Laboratory Data ◽  
Peak Frequency ◽  
Wave Spectra ◽  
One Dimensional ◽  
Wide Range ◽  
Laboratory Tank ◽  
The One ◽  
Dimensional Wave

The data for the spectra of wind-generated waves measured in a laboratory tank and in a bay are analyzed using the similarity theory of Kitaigorodski, and the one-dimensional spectra of fetch-limited wind waves are determined from the data. The combined field and laboratory data cover such a wide range of dimensionless fetch F (= gF/u2 ) as F : 102 ~ 10 . The fetch relations for the growthes of spectral peak frequency u)m and of total energy E of the spectrum are derived from the proposed spectra, which are consistent with those derived directly from the measured spectra.

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