Longshore current instability is important to nearshore hydrodynamic and sediment transport. This paper investigates the longshore current instability growth model based experimental data with different velocity profi...Longshore current instability is important to nearshore hydrodynamic and sediment transport. This paper investigates the longshore current instability growth model based experimental data with different velocity profiles of slopes1:100 and 1:40 by adopting a linear shear instability model with the bottom friction effects. The results show that:(1)Only backshear mode exists in the instability of longshore current for slope 1:40 and frontshear and backshear modes may exist slope 1:100.(2) The peaks of linear instability growth mode for slope 1:100 correspond to three cases: the dominant peak is formed by the joint action of both frontshear and backshear, or by backshear alone without the existence of the smaller peak or formed by either the frontshear or backshear.(3) Bottom friction can decrease the corresponding unstable growth rate but it cannot change the unstable fluctuation period. The results of fluctuation period, wavelength and spatial variation obtained by the analysis of linear shear instability are in good agreement with experimental results.展开更多
Water waves, wave-induced long-shore currents and movement of pollutants in waves and currents have been numerically studied based on the hyperbolic mild-slope equation, the shallow water equation , as well as the pol...Water waves, wave-induced long-shore currents and movement of pollutants in waves and currents have been numerically studied based on the hyperbolic mild-slope equation, the shallow water equation , as well as the pollutant movement equation, and the numerical results have also been validated by experimental data. It is shown that the long-shore current velocity and wave set-up increase with the increasing incident wave amplitude and slope steepness of the shore plane ; the wave set-up increases with the in- creasing incident wave period;and the pollutant morement proceeds more quiekly with the increasing incident wave amplitude and slope steepness of the shore palane. In surf zones, the long-shore currents induced by the inclined incident waves have effectively affected the pollutant movement.展开更多
A three-dimensional suspended sediment model (SED) developed by the present authors is coupled with the combinatorial model of COHERENS (Luyten et al., 1999) (the three-dimensional coupled hydrodynamical-ecologic...A three-dimensional suspended sediment model (SED) developed by the present authors is coupled with the combinatorial model of COHERENS (Luyten et al., 1999) (the three-dimensional coupled hydrodynamical-ecological model for Regional and Shelf Seas) and SWAN (Holthuijsen et al., 2004) (the third generation wave model). SWAN is regarded as a subroutine of COHERENS and gets time- and space-varying current velocity and surface elevation from COHERENS. COHERENS gets time- and space- varying wave relevant parameters provided by SWAN. Effects of wave on current are applied in bottom shear stress, wave-induced depth-dependent radiation stress and surface drag coefficient calculation. At the same time, the damping function of suspended sediment on turbulence is introduced into COHERENS. So the sediment model SED has feedback on circulation model COHERENS. The SED obtains current associated parameters from COHERENS. Then a coupled hydrodynamic-sediment model COHERENS-SED being able to account for interaction between wave and current is obtained. COHERENS-SED is adopted to simulate three-dimensional suspended sediment transport in the Huanghe River delta. In terms of simulation results, there is obvious difference between top and bottom layer of wave-induced longshore current. The values of time series of sediment concentration gotten by COHERENS-SED have, generally, an accepted agreement extent with measurement. Significant wave heights and wave periods obtained by COHERENS-SED show that wave simulation case with currentts effect can give better agreement extent with measurement than case without current's effect. In the meantime, suspended sediment concentration distributing rule obtained by COHERENS-SED is similar to former researches and measurement.展开更多
Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytic...Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper.展开更多
Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induc...Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole (2001) and Reniers and Battjes (1997) were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious.展开更多
A depth-integrated model for simulating wave-induced longshore current was developed with unstructured grids. Effects of surface roller and horizontal mixing under combined waves and currents were incorporated in the ...A depth-integrated model for simulating wave-induced longshore current was developed with unstructured grids. Effects of surface roller and horizontal mixing under combined waves and currents were incorporated in the numerical model. Recommended values of model coefficients were also proposed based on sensitivity analysis. Field observations and three series of laboratory measurements including two cases conducted on the plane beach and one implemented on the ideal inlet were employed to examine the predictive capability of this model. For the field case and laboratory cases conducted on the plane beach, numerical results were compared favorably with the measured data. For the case with an ideal inlet, simulated circulation pattern is supposed to be reasonable although some deviations between numerical results and measured data still can be detected.展开更多
A three-dimensional nearshore circulation model was developed by coupling CH3D, a three-dimensional hydrodynamic model and REF/DIF, a nearshore wave transformation model. The model solves the three-dimensional wave-av...A three-dimensional nearshore circulation model was developed by coupling CH3D, a three-dimensional hydrodynamic model and REF/DIF, a nearshore wave transformation model. The model solves the three-dimensional wave-averaged equations of motion. Wave-induced effects on circulation were introduced in the form of radiation stresses, wave-induced mass transport, wave-induced enhancement of bottom friction and wave-induced turbulent mixing. Effects of breaking waves were considered following Svendsen (1984a and 1984b) and Stive and Wind (1986). The model was successfully tested against the analytical solution of longshore currents by Longuet and Higgins (1970). The model successfully simulated the undertow as observed in a laboratory experiment by Stive and Wind (1982). In addition, the model was applied to a physical model by Mory and Hamm (1997) and successfully reproduced the eddy behind a detached breakwater as well as the longshore current on the open beach and the contiguous eddy in the open area of the wave tank. While the qualitative agreement between model results and experimental observations was very good, the quantitative agreement needs to be further improved. Albeit difficult to explain every discrepancy between the model results and observations, in general, sources of errors are attributed to the lack of understanding and comprehensive description of following processes: (1)the horizontal and vertical distribution of radiation stress, especially for breaking waves;(2)the detailed structure of turbulence;(3)Wave-current interaction (not included at this moment); and (4)the wave-current boundary layer and the resulting bottom shear stress.展开更多
The comparison results of three beach profile data repeatedly measured before and after the typhoon in Shuidong Bay,west Guangdong province which show that there are significant differences in beach profile erosion an...The comparison results of three beach profile data repeatedly measured before and after the typhoon in Shuidong Bay,west Guangdong province which show that there are significant differences in beach profile erosion and response process.And the changes of beach profile can be divided into:strong downward overall low shoreline regressive type and overall slight erosion shoreline regressive type.Application of the modified mildslope equation along three beach profile are simulated wave high reflection to the sea side,to the section vertical shore pressure gradient and including water roll force and radiation stress,the vertical shore forces one dimensional profile along the momentum conservation equation(radiation stress and water roll force)bottom friction and lateral mixing reaction between numerical solution,the momentum conservation equations of the wave increases the water flow velocity and section along the profile distribution of wave height and related forces.The analysis shows that the extent and difference of coastal erosion depend on the shoreline erosion mode stimulated by the maximum surge water of the coastal current and the maximum velocity of the coastal current and the dynamic state of the profile topography under the action of the profile location,morphology and incident wave elements.展开更多
The paper presents results of a study on the sediment supply and movement of highly turbid sediment plume within Malindi Bay in the Northern region of the Kenya coast. The current velocities, tidal elevation, salinity...The paper presents results of a study on the sediment supply and movement of highly turbid sediment plume within Malindi Bay in the Northern region of the Kenya coast. The current velocities, tidal elevation, salinity and suspended sediment concentrations (TSSC) were measured in stations located within the bay using Aanderaa Recording Current Meter (RCM-9), Turbidity Sensor mounted on RCM-9, Divers Gauges and Aanderaa Tempera- ture-Salinity Meter. The study established that Malindi Bay receives a high terrigenous sedi- ment load amounting to 5.7 x 106 ton.yr-1. The river freshwater supply into the bay is highly variable ranging from 7 to 680 m3.s-1. The high flows that are 〉 150 m3.s^-1 occurred in May during the South East Monsoon (SEM). Relatively low peak flows occurred in November during the North East Monsoon (NEM) but these were usually 〈70 m3.s^-1. The discharge of highly turbidity river water into the bay in April and May occurs in a period of high intensity SEM winds that generate strong north flowing current that transports the river sediment plume northward. However, during the NEM, the river supply of turbid water is relatively low occur- ring in a period of relatively low intensity NEM winds that result in relatively weaker south flowing current that transports the sediment plume southward. The mechanism of advection of the sediment plume north or south of the estuary is mainly thought to be due to the Ekman transport generated by the onshore monsoon winds. Limited movement of the river sediment plume southward towards Ras Vasco Da Gama during NEM has ensured that the coral reef ecosystem in the northern parts of Malindi Marine National Park has not been completely destroyed by the influx of terrigenous sediments. However, to the north there is no coral reef ecosystem. The high sediment discharge into Malindi Bay can be attributed to land use change in the Athi-Sabaki River Basin in addition to rapid population increase which has led to clearance of forests to open land for agriculture, livestock grazing and settlement. The problems of heavy siltation in the bay can be addressed by implementing effective soil con- servation programmes in the Athi-Sabaki Basin. However, the soil conservation programmes in the basin are yet to succeed due to widespread poverty among the inhabitants and the complications brought about by climate change.展开更多
Poorly-sorted conglomerate patches rich in granules or sturdy fossils or both, and reddish mud matrix within the interstices stand out amidst fine-grained siliciclastic shelf sediments of the trangressive systems trac...Poorly-sorted conglomerate patches rich in granules or sturdy fossils or both, and reddish mud matrix within the interstices stand out amidst fine-grained siliciclastic shelf sediments of the trangressive systems tract(TST) of the Lower Cretaceous Ukra Member, Kutch Basin, India. The siliciclastic shelf sediments contrast the conglomerates with their remarkable lateral extension. The fossils belong to a low-diversity group of sedentary bivalves that can be traced into the shoreface facies assemblage. The shelf sandstones are almost always sculpted by wave structures,especially hummocky cross-stratification while textures in the conglomerates suggest that the sediment settling was generally from suspensions. Textural variations in conglomerates reflect an immediate variation in flow viscosity prior to the downloading. The current structures obtained from the conglomerates record offshoreward palaeocurrent, in contrast to the shore-parallel palaeocurrent in the TST. The hummocky cross-stratified(HCS) beds are interpreted as seasonal storm deposits, while the conglomerate patches are taken as rip current deposits induced by waves of much longer periods. The glauconite-rich shale that alternates with conglomerates is probable fair-weather products. The conglomerates could not be recognized either in the coarse-grained shoreface deposits occupying the lower part of the overall fining-upward TST or in the coarsening-upward and glauconite-depleted highstand systems tract(HST). In contrast to the TST, the HST is dominantly tide-imprinted, having shore-normal palaeocurrent direction. It appears that intensification of waves and weakening of tides during transgression favored strong rip currents generation, which had presumably caused severe damage to the sea coast and to the shell banks growing preferably at the necks of the rip current channels. Rapid lateral facies transitions in the shoreface deposits at the basal part of the TST suggest enhanced irregularity in the coastline, possibly because of the mega cusps indented upon it. Frequency and intensity of storms enhanced during periods of global warming caused the transgression of the Early Cretaceous Ukra Sea.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51879237 and 11602222)the Research Fund of Zhejiang Ocean University(Grant No.11185010817)+2 种基金Zhejiang Provincial Natural Science Foundation of China(Grant No.LR16E090002)the Fundamental Research Funds for the Central Universities(Grant No.2018QNA4041)the Project of Research on structure properties of framed seawall along the Oujiang River in Lucheng District of Wenzhou City
文摘Longshore current instability is important to nearshore hydrodynamic and sediment transport. This paper investigates the longshore current instability growth model based experimental data with different velocity profiles of slopes1:100 and 1:40 by adopting a linear shear instability model with the bottom friction effects. The results show that:(1)Only backshear mode exists in the instability of longshore current for slope 1:40 and frontshear and backshear modes may exist slope 1:100.(2) The peaks of linear instability growth mode for slope 1:100 correspond to three cases: the dominant peak is formed by the joint action of both frontshear and backshear, or by backshear alone without the existence of the smaller peak or formed by either the frontshear or backshear.(3) Bottom friction can decrease the corresponding unstable growth rate but it cannot change the unstable fluctuation period. The results of fluctuation period, wavelength and spatial variation obtained by the analysis of linear shear instability are in good agreement with experimental results.
基金The National Basic Research ("973") Program of China under contract No.2005CB724202the National Natural Science Foundation of China under contract Nos.50709004 and 50779006.
文摘Water waves, wave-induced long-shore currents and movement of pollutants in waves and currents have been numerically studied based on the hyperbolic mild-slope equation, the shallow water equation , as well as the pollutant movement equation, and the numerical results have also been validated by experimental data. It is shown that the long-shore current velocity and wave set-up increase with the increasing incident wave amplitude and slope steepness of the shore plane ; the wave set-up increases with the in- creasing incident wave period;and the pollutant morement proceeds more quiekly with the increasing incident wave amplitude and slope steepness of the shore palane. In surf zones, the long-shore currents induced by the inclined incident waves have effectively affected the pollutant movement.
基金supported by 973 Project "Land-Sea interaction and its effect on the environment in the typical estuaries and offishore areas of China" under contract No. 2002CB412408Natural Science Foundation of Shandong Provinceunder contract No. Q2007E05
文摘A three-dimensional suspended sediment model (SED) developed by the present authors is coupled with the combinatorial model of COHERENS (Luyten et al., 1999) (the three-dimensional coupled hydrodynamical-ecological model for Regional and Shelf Seas) and SWAN (Holthuijsen et al., 2004) (the third generation wave model). SWAN is regarded as a subroutine of COHERENS and gets time- and space-varying current velocity and surface elevation from COHERENS. COHERENS gets time- and space- varying wave relevant parameters provided by SWAN. Effects of wave on current are applied in bottom shear stress, wave-induced depth-dependent radiation stress and surface drag coefficient calculation. At the same time, the damping function of suspended sediment on turbulence is introduced into COHERENS. So the sediment model SED has feedback on circulation model COHERENS. The SED obtains current associated parameters from COHERENS. Then a coupled hydrodynamic-sediment model COHERENS-SED being able to account for interaction between wave and current is obtained. COHERENS-SED is adopted to simulate three-dimensional suspended sediment transport in the Huanghe River delta. In terms of simulation results, there is obvious difference between top and bottom layer of wave-induced longshore current. The values of time series of sediment concentration gotten by COHERENS-SED have, generally, an accepted agreement extent with measurement. Significant wave heights and wave periods obtained by COHERENS-SED show that wave simulation case with currentts effect can give better agreement extent with measurement than case without current's effect. In the meantime, suspended sediment concentration distributing rule obtained by COHERENS-SED is similar to former researches and measurement.
文摘Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper.
基金The National Natural Science Foundation of China under contract Nos 50839001,51179025 and 50709004the Specialized Research Fund for the Doctoral Program of Higher Education of China under contract No.20070141032
文摘Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole (2001) and Reniers and Battjes (1997) were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious.
文摘A depth-integrated model for simulating wave-induced longshore current was developed with unstructured grids. Effects of surface roller and horizontal mixing under combined waves and currents were incorporated in the numerical model. Recommended values of model coefficients were also proposed based on sensitivity analysis. Field observations and three series of laboratory measurements including two cases conducted on the plane beach and one implemented on the ideal inlet were employed to examine the predictive capability of this model. For the field case and laboratory cases conducted on the plane beach, numerical results were compared favorably with the measured data. For the case with an ideal inlet, simulated circulation pattern is supposed to be reasonable although some deviations between numerical results and measured data still can be detected.
文摘A three-dimensional nearshore circulation model was developed by coupling CH3D, a three-dimensional hydrodynamic model and REF/DIF, a nearshore wave transformation model. The model solves the three-dimensional wave-averaged equations of motion. Wave-induced effects on circulation were introduced in the form of radiation stresses, wave-induced mass transport, wave-induced enhancement of bottom friction and wave-induced turbulent mixing. Effects of breaking waves were considered following Svendsen (1984a and 1984b) and Stive and Wind (1986). The model was successfully tested against the analytical solution of longshore currents by Longuet and Higgins (1970). The model successfully simulated the undertow as observed in a laboratory experiment by Stive and Wind (1982). In addition, the model was applied to a physical model by Mory and Hamm (1997) and successfully reproduced the eddy behind a detached breakwater as well as the longshore current on the open beach and the contiguous eddy in the open area of the wave tank. While the qualitative agreement between model results and experimental observations was very good, the quantitative agreement needs to be further improved. Albeit difficult to explain every discrepancy between the model results and observations, in general, sources of errors are attributed to the lack of understanding and comprehensive description of following processes: (1)the horizontal and vertical distribution of radiation stress, especially for breaking waves;(2)the detailed structure of turbulence;(3)Wave-current interaction (not included at this moment); and (4)the wave-current boundary layer and the resulting bottom shear stress.
基金Project funded by the National Nature Fund(41371498,42071007)。
文摘The comparison results of three beach profile data repeatedly measured before and after the typhoon in Shuidong Bay,west Guangdong province which show that there are significant differences in beach profile erosion and response process.And the changes of beach profile can be divided into:strong downward overall low shoreline regressive type and overall slight erosion shoreline regressive type.Application of the modified mildslope equation along three beach profile are simulated wave high reflection to the sea side,to the section vertical shore pressure gradient and including water roll force and radiation stress,the vertical shore forces one dimensional profile along the momentum conservation equation(radiation stress and water roll force)bottom friction and lateral mixing reaction between numerical solution,the momentum conservation equations of the wave increases the water flow velocity and section along the profile distribution of wave height and related forces.The analysis shows that the extent and difference of coastal erosion depend on the shoreline erosion mode stimulated by the maximum surge water of the coastal current and the maximum velocity of the coastal current and the dynamic state of the profile topography under the action of the profile location,morphology and incident wave elements.
基金funded by START and implemented as part of IGBP-LOICZ AfriCat Pilot project on the ‘Coastal Impacts of Damming and Water Abstraction in Africa’
文摘The paper presents results of a study on the sediment supply and movement of highly turbid sediment plume within Malindi Bay in the Northern region of the Kenya coast. The current velocities, tidal elevation, salinity and suspended sediment concentrations (TSSC) were measured in stations located within the bay using Aanderaa Recording Current Meter (RCM-9), Turbidity Sensor mounted on RCM-9, Divers Gauges and Aanderaa Tempera- ture-Salinity Meter. The study established that Malindi Bay receives a high terrigenous sedi- ment load amounting to 5.7 x 106 ton.yr-1. The river freshwater supply into the bay is highly variable ranging from 7 to 680 m3.s-1. The high flows that are 〉 150 m3.s^-1 occurred in May during the South East Monsoon (SEM). Relatively low peak flows occurred in November during the North East Monsoon (NEM) but these were usually 〈70 m3.s^-1. The discharge of highly turbidity river water into the bay in April and May occurs in a period of high intensity SEM winds that generate strong north flowing current that transports the river sediment plume northward. However, during the NEM, the river supply of turbid water is relatively low occur- ring in a period of relatively low intensity NEM winds that result in relatively weaker south flowing current that transports the sediment plume southward. The mechanism of advection of the sediment plume north or south of the estuary is mainly thought to be due to the Ekman transport generated by the onshore monsoon winds. Limited movement of the river sediment plume southward towards Ras Vasco Da Gama during NEM has ensured that the coral reef ecosystem in the northern parts of Malindi Marine National Park has not been completely destroyed by the influx of terrigenous sediments. However, to the north there is no coral reef ecosystem. The high sediment discharge into Malindi Bay can be attributed to land use change in the Athi-Sabaki River Basin in addition to rapid population increase which has led to clearance of forests to open land for agriculture, livestock grazing and settlement. The problems of heavy siltation in the bay can be addressed by implementing effective soil con- servation programmes in the Athi-Sabaki Basin. However, the soil conservation programmes in the basin are yet to succeed due to widespread poverty among the inhabitants and the complications brought about by climate change.
基金the Council of Scientific and Industrial Research (CSIR) Government of India sponsoring the Project No.24(0336)/14/EMR-Ⅱthe Department of Science and Technology (DST) Government of India sponsoring an Inspire Fellowship。
文摘Poorly-sorted conglomerate patches rich in granules or sturdy fossils or both, and reddish mud matrix within the interstices stand out amidst fine-grained siliciclastic shelf sediments of the trangressive systems tract(TST) of the Lower Cretaceous Ukra Member, Kutch Basin, India. The siliciclastic shelf sediments contrast the conglomerates with their remarkable lateral extension. The fossils belong to a low-diversity group of sedentary bivalves that can be traced into the shoreface facies assemblage. The shelf sandstones are almost always sculpted by wave structures,especially hummocky cross-stratification while textures in the conglomerates suggest that the sediment settling was generally from suspensions. Textural variations in conglomerates reflect an immediate variation in flow viscosity prior to the downloading. The current structures obtained from the conglomerates record offshoreward palaeocurrent, in contrast to the shore-parallel palaeocurrent in the TST. The hummocky cross-stratified(HCS) beds are interpreted as seasonal storm deposits, while the conglomerate patches are taken as rip current deposits induced by waves of much longer periods. The glauconite-rich shale that alternates with conglomerates is probable fair-weather products. The conglomerates could not be recognized either in the coarse-grained shoreface deposits occupying the lower part of the overall fining-upward TST or in the coarsening-upward and glauconite-depleted highstand systems tract(HST). In contrast to the TST, the HST is dominantly tide-imprinted, having shore-normal palaeocurrent direction. It appears that intensification of waves and weakening of tides during transgression favored strong rip currents generation, which had presumably caused severe damage to the sea coast and to the shell banks growing preferably at the necks of the rip current channels. Rapid lateral facies transitions in the shoreface deposits at the basal part of the TST suggest enhanced irregularity in the coastline, possibly because of the mega cusps indented upon it. Frequency and intensity of storms enhanced during periods of global warming caused the transgression of the Early Cretaceous Ukra Sea.