2024 Vol. 46, No. 2
Display Method:
2024, 46(2): 1-13.
doi: 10.12284/hyxb2024025
Abstract:
Wastewater is usually discharged into the sea in the form of jet, and its dilution process is the result of the interaction of jet, wave and tidal current. In this study, based on the reasonable assumptions, the governing equations are integrated to the form of ordinary differential equations. According to the hydrodynamic characteristics of the jet in the wavy current environment, the entrainment and drag force functions of the jet are introduced to close the governing equations, thus the integral model for the turbulent jet under the combined action of waves and currents is established. Through comparison and verification, it is confirmed that the integral model can accurately simulate the time average movement and dilution process of the near-field jet under the wavy current environment. It is found that compared with a pure current environment, the influence range of jet on the surrounding water is larger than that in a wavy current environment, and the dilution capacity of jet can be remarkably enhanced by the wave effect. Based on the momentum integral simulation results, the empirical fitting formulas for the position of the jet cross-sectional trajectory line and the minimum dilution in the wavy current environment are established. The developed model could be served as an efficient and accurate tool to assess the environmental impacts of submarine outfalls on the surrounding waters.
Wastewater is usually discharged into the sea in the form of jet, and its dilution process is the result of the interaction of jet, wave and tidal current. In this study, based on the reasonable assumptions, the governing equations are integrated to the form of ordinary differential equations. According to the hydrodynamic characteristics of the jet in the wavy current environment, the entrainment and drag force functions of the jet are introduced to close the governing equations, thus the integral model for the turbulent jet under the combined action of waves and currents is established. Through comparison and verification, it is confirmed that the integral model can accurately simulate the time average movement and dilution process of the near-field jet under the wavy current environment. It is found that compared with a pure current environment, the influence range of jet on the surrounding water is larger than that in a wavy current environment, and the dilution capacity of jet can be remarkably enhanced by the wave effect. Based on the momentum integral simulation results, the empirical fitting formulas for the position of the jet cross-sectional trajectory line and the minimum dilution in the wavy current environment are established. The developed model could be served as an efficient and accurate tool to assess the environmental impacts of submarine outfalls on the surrounding waters.
2024, 46(2): 14-27.
doi: 10.12284/hyxb2024001
Abstract:
Based on the satellite altimeter observation data from 1993 to 2022, this paper analyzes the temporal and spatial characteristics of the multi frequency seasonal variation signal of sea surface height in the Sulawesi sea, and gives the dynamic interpretation by using Rossby standard mode theory. The spectral analysis shows that there is a strong intra-seasonal signal of 30–90 days in the sea surface height variation of Sulawesi sea, and its average power spectral density is 13 times of the average power spectral density of the signal in half a year. These seasonal signals have discrete and discontinuous spectral peak periods, and the peaks of 54.0 d and 64.4 d are the largest, which are 28 times and 23 times of the signal of 30–90 days, respectively. The theoretical analysis shows that the existence of Rossby standard modes in the nearly closed Sulawesi deep-sea basin. The seasonal variation observed by satellite altimeter is consistent with the two-dimensional spatial structure evolution, period and westward propagation velocity of Rossby standard mode results, the superposition of Rossby standard mode solutions presents a variance distribution similar to the sea surface height variation field. This shows that the inherent oscillation of Sulawesi Sea basin is one of the important mechanisms that contribute to its intra-seasonal variation.
Based on the satellite altimeter observation data from 1993 to 2022, this paper analyzes the temporal and spatial characteristics of the multi frequency seasonal variation signal of sea surface height in the Sulawesi sea, and gives the dynamic interpretation by using Rossby standard mode theory. The spectral analysis shows that there is a strong intra-seasonal signal of 30–90 days in the sea surface height variation of Sulawesi sea, and its average power spectral density is 13 times of the average power spectral density of the signal in half a year. These seasonal signals have discrete and discontinuous spectral peak periods, and the peaks of 54.0 d and 64.4 d are the largest, which are 28 times and 23 times of the signal of 30–90 days, respectively. The theoretical analysis shows that the existence of Rossby standard modes in the nearly closed Sulawesi deep-sea basin. The seasonal variation observed by satellite altimeter is consistent with the two-dimensional spatial structure evolution, period and westward propagation velocity of Rossby standard mode results, the superposition of Rossby standard mode solutions presents a variance distribution similar to the sea surface height variation field. This shows that the inherent oscillation of Sulawesi Sea basin is one of the important mechanisms that contribute to its intra-seasonal variation.
2024, 46(2): 28-39.
doi: 10.12284/hyxb2024019
Abstract:
Using multiple observational subsurface temperature and salinity datasets based on Argo, we analyze the trend of 0–1 500 m ocean heat content in the Pacific between 2004 and 2020. It was found that the long-term trend of the Pacific ocean heat content showed a shift in 2013. The ocean heat content in 2013–2020 increased rapidly compared with that in 2004–2012. The linear trend of the former reaches about 0.50 × 1022 J/a, which is significantly higher than that of the latter. The Pacific has recently experienced rapid warming. During 2013–2020, the largest linear trend of the ocean heat content in the Pacific appeared in the western North Pacific, followed by the Tropical Pacific and eastern North Pacific. While the ocean heat content in the entire South Pacific showed a slightly decreasing trend. In the western North Pacific, the rapid increase of ocean heat content was concentrated in the Kuroshio Extension areas, and this warming trend is likely to be caused by the northward shift of the Kuroshio Extension main axis. It is worth mentioning that there was a local decreasing trend of ocean heat content in the sea south of Japan, and this cooling trend is associated with the strengthening of the Kuroshio large meander. In the Tropical Pacific where the warming trend is the second largest, the rapid increase of ocean heat content is likely to be induced by the thermocline deepening. In addition, we point out that the rapid warming in the Pacific is reflected by the rapid rise of sea level. The linear trend of sea level per 1 cm/a corresponds to the linear trend of ocean heat content of 0.11 × 109 J/(m2·a). This study elucidates the rapid warming of the Pacific since the end of the global warming hiatus, deepening our understanding of recent thermal conditions in the Pacific.
Using multiple observational subsurface temperature and salinity datasets based on Argo, we analyze the trend of 0–1 500 m ocean heat content in the Pacific between 2004 and 2020. It was found that the long-term trend of the Pacific ocean heat content showed a shift in 2013. The ocean heat content in 2013–2020 increased rapidly compared with that in 2004–2012. The linear trend of the former reaches about 0.50 × 1022 J/a, which is significantly higher than that of the latter. The Pacific has recently experienced rapid warming. During 2013–2020, the largest linear trend of the ocean heat content in the Pacific appeared in the western North Pacific, followed by the Tropical Pacific and eastern North Pacific. While the ocean heat content in the entire South Pacific showed a slightly decreasing trend. In the western North Pacific, the rapid increase of ocean heat content was concentrated in the Kuroshio Extension areas, and this warming trend is likely to be caused by the northward shift of the Kuroshio Extension main axis. It is worth mentioning that there was a local decreasing trend of ocean heat content in the sea south of Japan, and this cooling trend is associated with the strengthening of the Kuroshio large meander. In the Tropical Pacific where the warming trend is the second largest, the rapid increase of ocean heat content is likely to be induced by the thermocline deepening. In addition, we point out that the rapid warming in the Pacific is reflected by the rapid rise of sea level. The linear trend of sea level per 1 cm/a corresponds to the linear trend of ocean heat content of 0.11 × 109 J/(m2·a). This study elucidates the rapid warming of the Pacific since the end of the global warming hiatus, deepening our understanding of recent thermal conditions in the Pacific.
2024, 46(2): 40-51.
doi: 10.12284/hyxb2024007
Abstract:
As potential mineral resources, rare earth elements (REY) and yttrium enriched sediments in the deep sea have attracted a lot of attention in recent years. It has been shown by studies that the enrichment process of REY is most likely to occur at the sediment-water interface (SWI), however studies on the early diagenetic processes in REY-enriched sediments are in general lacking. In this paper, we collected two short sediment cores in REY-enriched sediments in the Southeast Pacific Ocean, then we had conducted an in-depth analysis on the early diagenesis process of REY at SWI and its influence on the enrichment mechanism of REY in deep-sea sediment. The low Fe, Mn concentration and high Mo, U and V concentration in pore-water indicated that the sediment cores were in oxic environment. Compared to the REY in overlying water column, the dissolved REY in pore-water characterized by a middle rare earth elements (MREE). In sediment, phosphate phase is the main phase of REY, while the distribution pattern of REY in pore-water may be controlled by the phosphate content in sediments. Our results show that during the early diagenetic processes, the REY initially combined with Fe/Mn phase and other phases re-released into the pore-water, which is subsequently adsorbed by and eventually buried with the phosphate phase. Therefore, the early diagenetic process is an important mechanism of REY enrichment in deep sea sediments.
As potential mineral resources, rare earth elements (REY) and yttrium enriched sediments in the deep sea have attracted a lot of attention in recent years. It has been shown by studies that the enrichment process of REY is most likely to occur at the sediment-water interface (SWI), however studies on the early diagenetic processes in REY-enriched sediments are in general lacking. In this paper, we collected two short sediment cores in REY-enriched sediments in the Southeast Pacific Ocean, then we had conducted an in-depth analysis on the early diagenesis process of REY at SWI and its influence on the enrichment mechanism of REY in deep-sea sediment. The low Fe, Mn concentration and high Mo, U and V concentration in pore-water indicated that the sediment cores were in oxic environment. Compared to the REY in overlying water column, the dissolved REY in pore-water characterized by a middle rare earth elements (MREE). In sediment, phosphate phase is the main phase of REY, while the distribution pattern of REY in pore-water may be controlled by the phosphate content in sediments. Our results show that during the early diagenetic processes, the REY initially combined with Fe/Mn phase and other phases re-released into the pore-water, which is subsequently adsorbed by and eventually buried with the phosphate phase. Therefore, the early diagenetic process is an important mechanism of REY enrichment in deep sea sediments.
2024, 46(2): 52-63.
doi: 10.12284/hyxb2024015
Abstract:
Quantitative studies on the spatial distribution of geometric parameters of complex submarine sand waves in the developmental area are rare, and the correlation between the complex geometric parameters of sand waves and environmental variables has not been clarified. Based on measured data of water depth, sediment grain size and flow velocity in the western area of Hainan Island, the environmental variables of the study area were quantified and extracted. The morphological parameters of complex submarine sand waves were calculated using an automated extraction and analysis method, and the correlation between sand wave geometric parameters and environmental variables was analyzed. The results show that the morphological characteristics of submarine sand waves in the study area are complex and variable, with an average wavelength ranging from 64 to 340 m and an average wave height ranging from 0.39 to 4.13 m. There is a strong positive correlation between wave height and steepness, as well as between wave height and the average angle of the lee side. There is also a strong positive correlation between wavelength and symmetry, and a strong positive correlation between median sediment grain size and the average angle of the lee side and wave height. The development of submarine sand waves in the study area is less influenced by water depth. Under the action of tidal currents, sediment transport is mainly by traction, and the erosion of submarine sand waves is relatively weak. The evolution of sand waves is mainly characterized by vertical growth and migration, with wave height growth prioritized over wavelength increase. Under stable tidal flow conditions, regional sediment supply and sediment grain size can both affect the scale of submarine sand waves.
Quantitative studies on the spatial distribution of geometric parameters of complex submarine sand waves in the developmental area are rare, and the correlation between the complex geometric parameters of sand waves and environmental variables has not been clarified. Based on measured data of water depth, sediment grain size and flow velocity in the western area of Hainan Island, the environmental variables of the study area were quantified and extracted. The morphological parameters of complex submarine sand waves were calculated using an automated extraction and analysis method, and the correlation between sand wave geometric parameters and environmental variables was analyzed. The results show that the morphological characteristics of submarine sand waves in the study area are complex and variable, with an average wavelength ranging from 64 to 340 m and an average wave height ranging from 0.39 to 4.13 m. There is a strong positive correlation between wave height and steepness, as well as between wave height and the average angle of the lee side. There is also a strong positive correlation between wavelength and symmetry, and a strong positive correlation between median sediment grain size and the average angle of the lee side and wave height. The development of submarine sand waves in the study area is less influenced by water depth. Under the action of tidal currents, sediment transport is mainly by traction, and the erosion of submarine sand waves is relatively weak. The evolution of sand waves is mainly characterized by vertical growth and migration, with wave height growth prioritized over wavelength increase. Under stable tidal flow conditions, regional sediment supply and sediment grain size can both affect the scale of submarine sand waves.
2024, 46(2): 64-78.
doi: 10.12284/hyxb2024021
Abstract:
In recent years, natural processes and human activities have significantly altered the Huanghe River channel and the coastal geomorphic pattern, while the impact of the dramatic geomorphic evolution on the coastal hydrodynamics has not been fully studied. Based on series images captured by the Landsat satellites and bathymetric measurements, this paper analyzed the shorelines and topography changes of the Huanghe River Delta from 1992 to 2020. Several sets of numerical models covering the entire Bohai Sea were established by TELEMAC-2D to investigate the response of tidal dynamics to geomorphic evolution and its depositional effects in the Huanghe River Delta. The results show that the erosion and deposition had significant spatial and temporal heterogeneity, and there were multiple siltation and erosion centers. The erosion center outside the old Qingshuigou Estuary moved 9.6 km to the south during 2000–2020, and the one outside the Diaokou Estuary moved 6.4 km to the east during 1992–2015. The tidal dynamics were dominated by the coastline and terrain changes on the medium and long time scales. The tidal range of the Diaokou estuary decreased, while the old and the new estuary increased. And the tidal range at 5 m depth had a maximum variation of 0.27 m. The K1 tidal amplitude increased significantly, while the M2 tidal amplitude was considerably reduced, and the amphidromic point near Dongying port eastward migration of 3.8 km. The high velocity outside the Diaokou Estuary and the old estuary continued to weaken, and another high velocity area gradually developed outside the current estuary. The continuous and stable high velocity area caused the erosion of the subaqueous delta and the coarsening of sediment.
In recent years, natural processes and human activities have significantly altered the Huanghe River channel and the coastal geomorphic pattern, while the impact of the dramatic geomorphic evolution on the coastal hydrodynamics has not been fully studied. Based on series images captured by the Landsat satellites and bathymetric measurements, this paper analyzed the shorelines and topography changes of the Huanghe River Delta from 1992 to 2020. Several sets of numerical models covering the entire Bohai Sea were established by TELEMAC-2D to investigate the response of tidal dynamics to geomorphic evolution and its depositional effects in the Huanghe River Delta. The results show that the erosion and deposition had significant spatial and temporal heterogeneity, and there were multiple siltation and erosion centers. The erosion center outside the old Qingshuigou Estuary moved 9.6 km to the south during 2000–2020, and the one outside the Diaokou Estuary moved 6.4 km to the east during 1992–2015. The tidal dynamics were dominated by the coastline and terrain changes on the medium and long time scales. The tidal range of the Diaokou estuary decreased, while the old and the new estuary increased. And the tidal range at 5 m depth had a maximum variation of 0.27 m. The K1 tidal amplitude increased significantly, while the M2 tidal amplitude was considerably reduced, and the amphidromic point near Dongying port eastward migration of 3.8 km. The high velocity outside the Diaokou Estuary and the old estuary continued to weaken, and another high velocity area gradually developed outside the current estuary. The continuous and stable high velocity area caused the erosion of the subaqueous delta and the coarsening of sediment.
2024, 46(2): 79-92.
doi: 10.12284/hyxb2024017
Abstract:
Beach nourishment, as a widely-adopted soft solution to coastal erosion, can effectively alleviate the beach erosion induced by the construction of artificial islands. This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example. Based on the bimonthly surveys of beach profiles and shorelines since nourishment, the characteristics of beach erosion and accretion and the associated driving factors were analyzed by using empirical orthogonal function (EOF) and digital shoreline analysis system methods. The EOF results showed that the first two eigenvalues accounted for more than 90% of the total variance, which could reflect the main spatio-temporal changes of the beaches. The area with conspicuous changes, corresponding to the first spatial mode, was located between the outer edge of the beach berm to the mean sea level, in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone. The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment, followed by mild profile changes. The second spatial mode demonstrated the impact of typhoons on the beaches, resulting in the accumulation and leveling of some low-lying sites on the beach berms in the wave shadow zone. This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages. The first stage was the adaptation period, during which the artificially designed beach profile adjusted to the equilibrium state for adapting to the local hydrodynamics. The equilibrium time of nourished profiles was approximately 4 months, during which beach changes were dominated by cross-shore sediment transport. The second stage was dominated by the longshore sediment transport induced by the artificial island, resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone. At that time, the nourished beach shoreline in Haikou Bay had not reached the equilibrium state. The beaches on both sides of the wave shadow zone would continue to retreat in the future, while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium. This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.
Beach nourishment, as a widely-adopted soft solution to coastal erosion, can effectively alleviate the beach erosion induced by the construction of artificial islands. This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example. Based on the bimonthly surveys of beach profiles and shorelines since nourishment, the characteristics of beach erosion and accretion and the associated driving factors were analyzed by using empirical orthogonal function (EOF) and digital shoreline analysis system methods. The EOF results showed that the first two eigenvalues accounted for more than 90% of the total variance, which could reflect the main spatio-temporal changes of the beaches. The area with conspicuous changes, corresponding to the first spatial mode, was located between the outer edge of the beach berm to the mean sea level, in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone. The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment, followed by mild profile changes. The second spatial mode demonstrated the impact of typhoons on the beaches, resulting in the accumulation and leveling of some low-lying sites on the beach berms in the wave shadow zone. This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages. The first stage was the adaptation period, during which the artificially designed beach profile adjusted to the equilibrium state for adapting to the local hydrodynamics. The equilibrium time of nourished profiles was approximately 4 months, during which beach changes were dominated by cross-shore sediment transport. The second stage was dominated by the longshore sediment transport induced by the artificial island, resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone. At that time, the nourished beach shoreline in Haikou Bay had not reached the equilibrium state. The beaches on both sides of the wave shadow zone would continue to retreat in the future, while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium. This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.
2024, 46(2): 93-106.
doi: 10.12284/hyxb2024013
Abstract:
Tidal flats maintain a complex ecosystem, while its formation is driven by multi-factor interaction, including hydrodynamics, sediment transport, and biological processes. In particular, investigating tidal flat biological processes and elucidating their biological-physical effects are current research hotspots and challenges in the field of marine science. This study focused on intertidal biofilms, constructed a two-dimensional biomorphodynamic model which coupled biofilms with hydrodynamics, sediment transport, and bed level change, to explore the role of biofilms in sediment transport and geomorphological evolution. The biomorphodynamic model was validated using literature data, indicating that the constructed model can simulate the growth pattern and interannual variation of biofilms well. Model results show that tidal creeks with biofilm attachment are more fully extended towards the landward side, showing a branching distribution when hydrodynamics are weak, and biofilms were distributed on both sides of the intertidal zone. Through quantitative analysis of tidal creek morphology, it is found that the presence of biofilms promoted an increase in the number of tidal creek and their development in the vertical direction, while limiting the increase in their width. Compared to tidal flats without the influence of biofilms, the average depth of tidal creeks increases, the total area decreases, the total length increases, the average width decreases, and the overall volume increases. The research outcome of this study deepens the understanding of the role of biofilms on tidal flat evolution and provides a scientific basis for coastal zone protection and ecological restoration projects.
Tidal flats maintain a complex ecosystem, while its formation is driven by multi-factor interaction, including hydrodynamics, sediment transport, and biological processes. In particular, investigating tidal flat biological processes and elucidating their biological-physical effects are current research hotspots and challenges in the field of marine science. This study focused on intertidal biofilms, constructed a two-dimensional biomorphodynamic model which coupled biofilms with hydrodynamics, sediment transport, and bed level change, to explore the role of biofilms in sediment transport and geomorphological evolution. The biomorphodynamic model was validated using literature data, indicating that the constructed model can simulate the growth pattern and interannual variation of biofilms well. Model results show that tidal creeks with biofilm attachment are more fully extended towards the landward side, showing a branching distribution when hydrodynamics are weak, and biofilms were distributed on both sides of the intertidal zone. Through quantitative analysis of tidal creek morphology, it is found that the presence of biofilms promoted an increase in the number of tidal creek and their development in the vertical direction, while limiting the increase in their width. Compared to tidal flats without the influence of biofilms, the average depth of tidal creeks increases, the total area decreases, the total length increases, the average width decreases, and the overall volume increases. The research outcome of this study deepens the understanding of the role of biofilms on tidal flat evolution and provides a scientific basis for coastal zone protection and ecological restoration projects.
2024, 46(2): 107-116.
doi: 10.12284/hyxb2024003
Abstract:
As a national key construction sea area, the trend of offshore wind power construction in the Jiangsu sea area towards the open sea is the main trend of future development. The open sea areas have more surge components, and the wave spectrum often appears in the form of bimodal spectrum. Therefore, the wave characteristics of bimodal spectrum waves need further in-depth research to provide reference basis for offshore construction. Based on the observation data of the buoy station throughout 2018, 1223 bimodal spectral data were obtained through outlier testing and bimodal spectral identification. The bimodal spectral characteristics of waves in the Jiangsu sea area were studied, and different typical bimodal spectral types were compared. The fitting of the measured bimodal spectra was carried out, and the corrected spectral width parameters were proposed. The dependency relationship between the correction coefficient, peak rise factor, and spectral width parameters was explored, and the bimodal spectral fitting expression was obtained. The results indicate that the Ochi–Hubble spectrum proposed based on the North Atlantic sea area and the Torsethaugen spectrum proposed based on the Norwegian sea area are not applicable to the bimodal spectrum type in the Jiangsu sea area. The bimodal JONSWAP fitting spectrum proposed in this paper has adaptability and can scientifically and reasonably describe the bimodal spectrum in the Jiangsu sea area, and is widely applied to different wind and terrain conditions in the sea area.
As a national key construction sea area, the trend of offshore wind power construction in the Jiangsu sea area towards the open sea is the main trend of future development. The open sea areas have more surge components, and the wave spectrum often appears in the form of bimodal spectrum. Therefore, the wave characteristics of bimodal spectrum waves need further in-depth research to provide reference basis for offshore construction. Based on the observation data of the buoy station throughout 2018, 1223 bimodal spectral data were obtained through outlier testing and bimodal spectral identification. The bimodal spectral characteristics of waves in the Jiangsu sea area were studied, and different typical bimodal spectral types were compared. The fitting of the measured bimodal spectra was carried out, and the corrected spectral width parameters were proposed. The dependency relationship between the correction coefficient, peak rise factor, and spectral width parameters was explored, and the bimodal spectral fitting expression was obtained. The results indicate that the Ochi–Hubble spectrum proposed based on the North Atlantic sea area and the Torsethaugen spectrum proposed based on the Norwegian sea area are not applicable to the bimodal spectrum type in the Jiangsu sea area. The bimodal JONSWAP fitting spectrum proposed in this paper has adaptability and can scientifically and reasonably describe the bimodal spectrum in the Jiangsu sea area, and is widely applied to different wind and terrain conditions in the sea area.
2024, 46(2): 117-130.
doi: 10.12284/hyxb2024011
Abstract:
Based on the non-hydrostatic model SWASH, a numerical wave flume was established to systematically investigate the hydrodynamic characteristics of the interaction between waves, mangroves, and vertical sea dikes through a comparative experiment with and without mangroves. The study analyzed the influence of factors such as wave steepness, relative water depth, Ursell number, mangrove length, density, and characteristic diameter on the wave height in front of the sea dike and the maximum wave pressure on the windward side of the sea dike. The results indicate that in the absence of mangroves, the Goda formula cannot accurately estimate the impact load on the vertical sea dike. In a numerical experiment with a model scale of 1∶10, a 2 m-wide mangrove in front of the dike was observed to reduce wave height by 6% to 45% and wave pressure by 11% to 74%. However, in conditions with relatively large wave heights and smaller characteristic parameters of the mangrove, an increase in the wave height in front of the dike by approximately 4% to 26% was noted. In the hydraulic conditions considered in this study, the maximum wave pressure decreased by 58% to 93% with a decrease in wave steepness, by 42% to 72% with an increase in relative water depth, and by 87% to 96% with a decrease in the Ursell number. The attenuation rates of wave height and wave pressure in front of the dike non-linearly increased with the increase in the width, density, and characteristic diameter of the mangroves. These findings provide a scientific basis for a deeper understanding of the wave-damping effects of mangroves, as well as for the design and planning of coastal protection projects combining mangrove ecosystems with sea dikes.
Based on the non-hydrostatic model SWASH, a numerical wave flume was established to systematically investigate the hydrodynamic characteristics of the interaction between waves, mangroves, and vertical sea dikes through a comparative experiment with and without mangroves. The study analyzed the influence of factors such as wave steepness, relative water depth, Ursell number, mangrove length, density, and characteristic diameter on the wave height in front of the sea dike and the maximum wave pressure on the windward side of the sea dike. The results indicate that in the absence of mangroves, the Goda formula cannot accurately estimate the impact load on the vertical sea dike. In a numerical experiment with a model scale of 1∶10, a 2 m-wide mangrove in front of the dike was observed to reduce wave height by 6% to 45% and wave pressure by 11% to 74%. However, in conditions with relatively large wave heights and smaller characteristic parameters of the mangrove, an increase in the wave height in front of the dike by approximately 4% to 26% was noted. In the hydraulic conditions considered in this study, the maximum wave pressure decreased by 58% to 93% with a decrease in wave steepness, by 42% to 72% with an increase in relative water depth, and by 87% to 96% with a decrease in the Ursell number. The attenuation rates of wave height and wave pressure in front of the dike non-linearly increased with the increase in the width, density, and characteristic diameter of the mangroves. These findings provide a scientific basis for a deeper understanding of the wave-damping effects of mangroves, as well as for the design and planning of coastal protection projects combining mangrove ecosystems with sea dikes.
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