Tidal flats and saltmarshes have been a long-standing research focus because of their high socio-economic and ecological values.The evolution of tidal flat-marsh systems is highly complex due to the intertwined proces...Tidal flats and saltmarshes have been a long-standing research focus because of their high socio-economic and ecological values.The evolution of tidal flat-marsh systems is highly complex due to the intertwined processes operating over a variety of spatial and temporal scales.As a traditional research highlight,the role of regular hydrodynamic processes such as tides,waves,and river flows have been explored comprehensively with fruitful outcomes.Over past decades,the changing environment(e.g.,sea level rise,increasing anthropogenic activities,and extreme weather conditions)has attracted more attention with many reported insightful results.More recent advances indicate that biological activities play a critical role in tidal flat-marsh morphodynamics but are still poorly understood.The field of research that connects the bio-logical and physical processes is commonly described as"biogeomorphology"and requires the joint efforts by scientists from multiple dis-ciplines ranging from hydraulics,ecology,and geography to sociology.This review aims to provide a synthesis of the current research status of tidal flat-marsh morphodynamics,with a particular emphasis on the understanding of various processes and feedbacks underlying the devel-opment of morphodynamic models.Some future research needs and challenges are identified to facilitate a more sustainable management strategy for tidal flats and saltmarshes under climate change.展开更多
Understanding the sensitivity of tidal flats to environmental changes is challenging.Currently,most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats.In this stu...Understanding the sensitivity of tidal flats to environmental changes is challenging.Currently,most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats.In this study,we proposed an alternative empirical approach to explore tidal flat dynamics using statistical indices based on long-term time series of daily surface elevation development.Surface elevation dynamic(SED)indices focus on the magnitude and period of surface elevation changes,while morphodynamic signature(MDS)indices relate sediment dynamics to environmental drivers.The statistical analyses were applied to an intervention site in the Netherlands to determine the effect of recently constructed groynes on the tidal flat.Using these analyses,we were able to(1)detect a reduction in the daily SED and(2)determine that the changes in the daily SED were predominantly caused by the reduction in wave impact between the groynes rather than the reduction in tidal currents.Overall,the presented results showed that the combination of novel statistical indices provides new insights into the trajectories of tidal flats,ecosystem functioning,and sensitivity to physical drivers(wind and tides).Finally,we suggested how the SED and MDS indices may help to explore the future trajectories and climate resilience of intertidal habitats.展开更多
Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Chan...Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Changjiang River, the channel immediately downstream of the Three Gorges Dam(TGD), are assessed based on remote sensing images between 2000 and 2016. It can be found that the entire area of sandbars reduces drastically by 19.23% from 149.04 km~2 in 2003 to 120.38 km~2 in 2016, accompanied with an increase in water surface width. Owing to differences in sediment grain size and anti-erosion capacity, sandbar area in the upstream sandy gravel reach(Yichang-Dabujie) and downstream sandy reach(Dabujie-Chenglingji) respectively decreases by 45.94%(from 20.79 km~2 to 11.24 km~2) and 14.93%(from 128.30 km~2 to 109.14 km~2). Furtherly, morphological evolutions of sandbars are affected by channel type: in straight-microbend channel, mid-channel sandbars exhibit downstream moving while maintaining the basic profile; in meandering channel, point sandbars show erosion and deposition in convex and concave bank respectively, with mid-channel sandbars distributing sporadically; in bending-branching channel, point sandbars experience erosion and move downstream while mid-channel sandbars show erosion in the head part along with retreating outline. We document that the primary mechanism of sandbars shrinkages along the Yichang-Chenglingji Reach can be attributed to TGD induced suspended sediment concentration decreasing and increasing in unsaturation of sediment carrying capacity. Additionally, channel type can affect the morphological evolution of sandbars. Along the Yichang-Chenglingji Reach, sandbars in straight-microbend channel are more affected by water flow than that in bending-branching channel.展开更多
Geomorphic dynamics of alluvial rivers in response to upstream damming have substantial impacts on navigation, habitat protection, and channel stability. The purpose of this study was to determine how flow and sedimen...Geomorphic dynamics of alluvial rivers in response to upstream damming have substantial impacts on navigation, habitat protection, and channel stability. The purpose of this study was to determine how flow and sediment regimes, and meander characteristics affect the morphological adjustment of bends in the Lower Jingjiang Reach(LJR) before and after the Three Gorges Project(TGP). Based on detailed field measurements and hydrological and topographic datasets from 1991 to 2016, banks and point bars morphodynamics of 12continuous bends in the LJR were comprehensively analyzed. Point bars in the LJR mainly experienced a net deposition before the TGP operation, but substantially deteriorated with a net erosion rate of 4.6 million m^(3) yr^(-1) in the post-TGP periods(2003–2016), and erosion on heads and upstream margins of point bars was a general adjustment pattern in the 12 bends.The most significant morphological changes of point bars and banks occurred in 2006–2011,indicating a delayed response of the channel evolution of the LJR to damming. Detailed observations suggested that the medium discharges(16,000–18,000 m^(3) s^(-1)) were the most contributive discharges in shaping the morphology of point bars and banks in the LJR after damming. In addition, we revealed the importance of sediment supply on meander deformation of the LJR, driven by sediment exchange over point bars, and more upstream planform deformation tended to occur in bends with high sinuosity(>2.0) in the LJR after damming.The relationship between meander deformation and sinuosity was manifested through the geometric adjustment range of point bars. The morphological adjustments of point bars in the highly curved or compound bends of the LJR were more conducive to cause flow deflections,leading to form concave-bank bars after the TGP operation.展开更多
Aggregation is used to represent the real world in a model at an appropriate level of abstraction.We used the convection-diffusion equation to examine the implications of aggregation progressing from a three-dimension...Aggregation is used to represent the real world in a model at an appropriate level of abstraction.We used the convection-diffusion equation to examine the implications of aggregation progressing from a three-dimensional(3D)spatial description to a model representing a system as a single box that exchanges sediment with the adjacent environment.We highlight how all models depend on some forms of parametric closure,which need to be chosen to suit the scale of aggregation adopted in the model.All such models are therefore aggregated and make use of some empirical relationships to deal with sub-scale processes.One such appropriately aggregated model,the model for the aggregated scale morphological interaction between tidal basin and adjacent coast(ASMITA),is examined in more detail and used to illustrate the insight that this level of aggregation can bring to a problem by considering how tidal inlets and estuaries are impacted by sea level rise.展开更多
This paper reviews and discusses the current research status, trends, and future needs in the field of beach morphodynamics under the influence of storm sequences.The paper reviews how the three main research methods,...This paper reviews and discusses the current research status, trends, and future needs in the field of beach morphodynamics under the influence of storm sequences.The paper reviews how the three main research methods, field investigations, numerical modelling, and physical modelling, have been used to study beach morphodynamics during storm sequences.Available quantitative definitions of storm sequences at different sites are presented and discussed.It is shown that the definition of storm sequences is site-specific and requires knowledge of the storm climate, beach characteristics, and the temporal scale of beach recovery.Subsequently, the paper brings together currently available approaches aimed at describing the effect of storm sequences on beach erosion in a general way.The importance of storm chronology and the effects of an extreme storm within a sequence of storms are highlighted.Following that, the more poorly studied aspect of beach recovery in between storms within a sequence is discussed.Three indicators for defining beach recovery, namely the shoreline location, sediment volumes, and the beach state, are identified and compared.Finally, important research needs, including the need for detailed physical modelling, are identified.展开更多
Beach erosion has occurred globally in recent decades due to frequent and severe storms.Dongsha beach,located in Zhujiajian Island,Zhejiang Province,China,is a typical embayed sandy beach.This study focused on the mor...Beach erosion has occurred globally in recent decades due to frequent and severe storms.Dongsha beach,located in Zhujiajian Island,Zhejiang Province,China,is a typical embayed sandy beach.This study focused on the morphodynamic response of Dongsha beach to typhoon events,based on beach topographies and surficial sediment characteristics acquired before and after four typhoon events with varying intensities.The four typhoons had different effects on the topography and sediment characteristics of Dongsha beach.Typhoons Ampil and Danas caused the largest(-51.72 m3/m)and the smallest erosion(-8.01 m3/m),respectively.Remarkable alongshore patterns of beach profile volumetric changes were found after the four typhoon events,with more erosion in the southern and central parts of the beach and few changes in the northern part.Grain size coarsening and poor sorting were the main sediment patterns on the beach influenced by different typhoons.Typhoons that occurred in the same year after another typhoon enhanced the effect of the previous typhoon on sediment coarsening and sorting variability,but this cumulative effect was not found between typhoons that occurred during different years.A comparison of the collected data revealed that the topographic state of the beach before the typhoon,typhoon characteristics,and tidal conditions were possible reasons for the difference in the responses of Dongsha beach to typhoon events.More severe beach erosion was caused by typhoons with higher intensity levels and longer durations,and high tide levels during typhoons can determine the upper limit of the beach profile erosion site.Taken together,these results can be used to improve beach management for storm prevention.展开更多
Beach morphodynamic classifications have achieved extensive acceptance in foreign coastal geomorphological studies. Three beaches located in different zones of a headland-bay coast are classified according to a dimens...Beach morphodynamic classifications have achieved extensive acceptance in foreign coastal geomorphological studies. Three beaches located in different zones of a headland-bay coast are classified according to a dimensionless fall parameter, a relative tide range parameter and a dimensionless embayment scaling parameter. Synchronous data, including wave, tide, sediment and beach morphology, are respectively collected from the tangential beach, the transitional beach and the shadow beach of the Shuidong Bay during each spring tide for 16 successive months. The research results indicate that （1） the beach in the tangential zone falls between two major categories which are low tide terrace beaches with rips and barred beaches; the beach in the transitional zone exhibits two main types which are low tide bar/rip beaches and barred dissipative beaches; and the beach in the shadow zone mainly mirrors dissipative states with presence or absence of bars; and （2） the sequential changes and differences of beach states in different coastal zones reflect spatial and temporal variabilities of the headland- bay coast, totally meeting the actual measured beach morphology changes, showing that studies on wave- dominated, meso-macrotidal beaches need to consider the influences of the tides. Meanwhile, the research mainly provides a framework about beach state studies, due to different beach states with different erosion patterns, which requires the need to strengthen the researches in this respect, in order to further enrich theoretical basis for a beach topography evolution, beach morphodynamic processes and beach erosion orevention in China.展开更多
The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade,concerning that the sea level rise(SLR)and more frequent and int...The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade,concerning that the sea level rise(SLR)and more frequent and intense storms in the context of global climate change are expected to destabilize those islands.Here,we conduct a set of wave-flume laboratory experiments focusing on the morphodynamic change of reef islands to varying ocean forcing conditions(wave height and SLR).Subsequently,a phase-resolving XBeach numerical model is adopted to simulate the monochromatic wave process and its associated sediment dynamics.The adopted model is also firstly validated by laboratory experimental results as reported in this study.It is then used to examine the impacts of island morphological factors(island width,island height,island location and island side slope)on the island migration.The combined laboratory/physical and numerical experiment outputs suggest that reef islands can accrete vertically in response to the sea level rise and the increased storminess.展开更多
Wulan Delta in Central Java has been experiencd coastal morphodynamics due to interface between Wulan River’s sedimentation and Java sea’s oceanographic process. This paper aims to analyze Wulan Delta’s morphodynam...Wulan Delta in Central Java has been experiencd coastal morphodynamics due to interface between Wulan River’s sedimentation and Java sea’s oceanographic process. This paper aims to analyze Wulan Delta’s morphodynamics as well as its impacts on the socio-economic condition of the community. The morphodynamics is interpreted visually and digitally using a maximum livelihood analysis of multiscale and multi-temporal images. The socio-economic impact is defined by field observations and in-depth interviews to the community and stakeholders. Analysis during the period of 1931-2010 showed that Wulan Delta had been changed morphologically from straight with small arc-like (arcuate) to bird-foot (digitate) with a plausible change into rounded (lobate) in the future, which represented dominant sedimentation by oceanographic rather than fluvial processes. Land expansion in Wulan Delta led to landuse change in Wedung, i.e. expansion of settlement area to 167 ha and fish pond area to 1014 ha in 2000-2010. Most settlements in the area, which are built linearly to river levees, own a high vulnerability to both river flood and tidal inundation. Therefore, dissemination about knowledge of the disaster and coastal zone management, as a means of increasing awareness, becomes necessary in integrating the coastal management in Wulan Delta together with improvement in infrastructure and proper regional development. The proper development strategy for the coastal village is aggressive maintenance strategy, including public infrastructure revitalization, quality improvement for human resources, and silvofishery system. Law enforcement on coastal zoning regulations is necessary to achieve an integrated and sustainable coastal zone management.展开更多
Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies.This paper carried out beach morphodynamic classifications for 12 straight beaches o...Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies.This paper carried out beach morphodynamic classifications for 12 straight beaches on headland-bay coasts based on field survey and evaluated the applicability of the most widely used dimensional fall velocity parameter(Ω)and relative tidal range parameter(RTR).One reflective,five intermediate and six non-barred dissipative beaches were visually classified and sand size seemed to be a key factor to differentiate these beaches.The studied beaches were in relatively low wave energy environments(Hs<1 m)and the absolute deep-water wave energy level of P0=3 KWm-1 was supposed to a critical threshold to characterize the applicability of theΩand RTR parameters.These two morphodynamic parameters were applicable for the beaches with P0>3 KWm-1 and MSR<2 m.It was found that the model of the traditional winter-and-summer profiles was not applicable in the study area in despite of distinct wave seasonality.The studied beaches were more possible to hover around a limited range due to relatively low background wave environments and variability without considering typhoon impacts,which needs further research on actual breaker wave conditions and beach morphodynamic type responses to typhoon events.展开更多
A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological p...A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events.Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves,where the undertow and longshore currents exist simultaneously,forming a spirallike circulation system in the surfzone.Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction,subsequently suppress the formation of sandbars,showing that a typical recovery profile under calm waves does not necessarily develop,but with a competing process of onshore drift,undertow and longshore currents.Sediment transport rate during storms reaches several hundreds of times as those under calm waves,and two storm events contribute approximately 60%to the beach erosion.Sediment transport pattern under calm waves is mainly bed load,but as the fine sands underneath begin to expose,the contribution of suspended load becomes significant.展开更多
Barito Delta morphodynamic had contradictive role with its potency and problem. Potency in Barito Delta may support the development of Banjarmasin City, but development of Barito Delta may decrease the capacity of tra...Barito Delta morphodynamic had contradictive role with its potency and problem. Potency in Barito Delta may support the development of Banjarmasin City, but development of Barito Delta may decrease the capacity of transportation in Barito River. Multitemporal topographic map and Landsat satellite image during the period 1862-2008 were used to analyze the long-term delta morphodynamic. The analysis consisted of delta growth, yearly growth, growth orientation, delta shape, and shoreline changes. The research showed that the Barito Delta had developed during the period 1862-2008. Barito Delta had developed to south orientation. The growth of Barito Delta during the period 1862-1946 was 27.82 km^2 or 0.33 km^2/year. However, during the period 1946-1997, Barito Delta growth was 175.82 km^2 or 3.45 km^2/year. Area of Barito Delta decreased during the period 1997-2004. The reduction of Barito Delta area was 4.73 km^2 or 0.67 km^2/year. Area of Barito Delta in years 2004-2008 increased about 3.38 km^2 or 0.84 km^2/year Shoreline during the period 1862-2008 had changed. Accretion occurred in Kuala Lupak River during the period 1862-1997, but erosion occurred during the period 1997-2004. The delta morphodynamics were influenced by human activities in watershed and delta such as landuse change and land degradation.展开更多
This work presents a new finite volume Godunov-type model for predicting morphological changes under the rapidly varying flood conditions with wetting and drying. The model solves the coupled shallow water and Exner e...This work presents a new finite volume Godunov-type model for predicting morphological changes under the rapidly varying flood conditions with wetting and drying. The model solves the coupled shallow water and Exner equations, with the interface fluxes evaluated by an Harten-Lax-van Leer-Contact （HLLC） approximate Riemann solver. Well-balanced solution is achieved using the surface gradient method and wetting and drying are handled by a non-negative reconstruction approach. The new model is validated against several theoretical benchmark tests and promising results are obtained.展开更多
Reticulate dunes are one of the commonest dune types, and yet the least understood. Reticulate dunes at southeastern Tengger Desert are constituted by NE-SW trending primary ridges and nearly vertical secondary ridges...Reticulate dunes are one of the commonest dune types, and yet the least understood. Reticulate dunes at southeastern Tengger Desert are constituted by NE-SW trending primary ridges and nearly vertical secondary ridges. The result of field work studying the morphodynamics and formation mechanism for reticulate dunes in this area shows that the primary ridges were formed by dominant northwest wind and the secondary ridges developed and maintained by alternating dominant wind and subdominant northeast wind on the basis of the primary ridges. Viewed from morphodynamics, reticulate dunes correspond to the complex transverse dune on which the longitudinal element superimposed.展开更多
A large tidal channel has developed along the northern shore of the Hangzhou Bay.Its length and width are about 50 and 10 km,respectively.It serves as an important navigation channel and provides port construction loc...A large tidal channel has developed along the northern shore of the Hangzhou Bay.Its length and width are about 50 and 10 km,respectively.It serves as an important navigation channel and provides port construction locations.This contribution investigates the morphological response of the tidal channel to the large-scale embankment in recent decades and the physical mechanisms,based on an idealized 2D morphodynamic model.The tidal channel was reproduced within a timescale of several years,with spatial scales comparable to the real situation.The results showed that the macroscopic sediment transport pattern in the bay,namely,entering in the north and leaving in the south,was not changed by the embankment.The tidal range and sediment flux increased to a certain extent,because of the decrease of the cross-sectional width.Meanwhile,the longitudinal gradient of the residual sediment transport enlarged slightly.As a result,the tidal channel was eroded significantly,because of the nonlinear interaction among hydrodynamics,sediment transport,and morphological change.Furthermore,there are inherent connections among the main morphological features in the bay.Complementary to other approaches,this model provides a useful tool to predict the morphodynamic behavior for the estuarine planning and regulations.展开更多
Bangladesh is a riparian country that is criss-crossed by the many tributaries and distributaries of the mighty Ganges,Brahmaputra,and Meghna river systems.Gorai-Madhumati,a distributary of the Ganges River is an exam...Bangladesh is a riparian country that is criss-crossed by the many tributaries and distributaries of the mighty Ganges,Brahmaputra,and Meghna river systems.Gorai-Madhumati,a distributary of the Ganges River is an example where morphological development of the river is associated with frequent channel shifting within the catchment area.The main objective of this research is to quantify the extent of channel migration,erosion-accretion,river width,sinuosity,and charland morpho-dynamics from 1972 to 2018 using geospatial techniques combined with satellite images and hydrological data.The study also addressed the impacts of Farakka Barrage construction in India on the shifting,flow behavior,and siltation of Gorai-Madhumati River.The study shows that bar surface areas have abnormally increased in both segments after 1975 due to the construction of Farakka Barrage.Water flow in the Gorai-Madhumati has dropped remarkably in the downstream and instigated huge sedimentation in this region.Analysis of the time series satellite images revealed that the morphology of the river channel experienced huge changes simultaneously with the changes in the seasonal flow and sedimentation all over the study period.Migration trend has frequently shifted and taken place in the NW and NE direction in the observed sections of the river.Throughout the study period,total amount of accretion was greater than the net percentage of erosion on both banks of the river.River discharge,bar accretion,and erosion history show that the Gorai-Madhumati River will no longer exist with the present flowing condition without attention and proper river management.展开更多
The accuracy and efficiency of a class of finite volume methods are investigated for numerical solution of morphodynamic problems in one space dimension.The governing equations consist of two components,namely a hydra...The accuracy and efficiency of a class of finite volume methods are investigated for numerical solution of morphodynamic problems in one space dimension.The governing equations consist of two components,namely a hydraulic part described by the shallow water equations and a sediment part described by the Exner equation.Based on different formulations of the morphodynamic equations,we propose a family of three finite volume methods.The numerical fluxes are reconstructed using a modified Roe’s scheme that incorporates,in its reconstruction,the sign of the Jacobian matrix in the morphodynamic system.A well-balanced discretization is used for the treatment of the source terms.The method is wellbalanced,non-oscillatory and suitable for both slow and rapid interactions between hydraulic flow and sediment transport.The obtained results for several morphodynamic problems are considered to be representative,and might be helpful for a fair rating of finite volume solution schemes,particularly in long time computations.展开更多
The morphodynamic responses of tidal networks to anthropogenic reclamation and de-reclamation projects are investigated through a three-stage numerical simulation.In the first stage,the natural development of tidal ne...The morphodynamic responses of tidal networks to anthropogenic reclamation and de-reclamation projects are investigated through a three-stage numerical simulation.In the first stage,the natural development of tidal networks is modelled in an open coast without any anthropogenic interventions.At the beginning of the second stage,parts of the computational domain are enclosed by sea dikes,which represents the implementation of the reclamation project.These sea dikes are removed or opened in the third stage to simulate the recovery of the tidal networks after de-reclamation.Each stage was set to last 100 years.The model results indicate that land reclamation can lead to three effects on tidal network morphology:(i)completely terminating the development of channels inside the projected area,(ii)hindering the development of the channel network in front of the dikes,and(iii)turning the channel direction near the corners of the dikes.When removing all the sea dikes,the previously reclaimed areas are quickly occupied by tidal networks.However,the morphology cannot be fully restored to its original natural state,although the entire reclaimed areas are returned.The effects of opening breaches are relatively slow,and tree-like network structures are formed inside the reclaimed areas.展开更多
Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dun...Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dune chronologies and the complexity of paleo-dune deposits as paleoenvironmental records. This paper addresses questions on the paleoenvi- ronmental implications of dune chronostratigraphies that have been raised by those reviews, in the specific case of crescentic dunes, using a case study from the Mu Us dune field, north-central China. The processes of turn-over and stabilization of relatively small crescentic dunes are first investigated by observational evidence. In combination with the analysis of a simplified sand preservation model and stratigraphic records, the effect of dune morphody- namics on sand preservation is demonstrated. It is especially evident that thick, nearly in- stantaneously deposited sand units record dune stabilization near the very end of a dune activity episode, while thin sand units may signal the preservation of sand deposited earlier in episodes of activity. Interpreting the distribution of luminescence ages that indicate sand deposition over time is not as simple as assumed in some previous work. Low frequency of sand ages could indicate an interval of either dune field stabilization or extensive dune activity but poor sand preservation. A peak of sand age frequency likely represents a shift in dune field activity towards stabilization, not a peak of active dune extent, especially if it partially overlaps with an independently identified interval of stabilization （e.g. one recorded by pa- leosols）. The nature and magnitude of these biases in the distribution of sand ages over time are strongly affected by the magnitude of net sand accumulation, which is in turn related to sand supply, transport capacity and sand availability, and ultimately climate change. Rela- tively short dune stabilization and turn-over time （101 to 102 yrs） indicate that dune geomor- phic processes can quickly respond to short-term disturbance, but the chronology of that response must be interpreted in light of how those processes influence age distributions.展开更多
基金supported by the National Natural Science Foundation of China(Grants No.41976156 and 51925905)the Natural Science Foundation of Jiangsu Province(Grant No.BK20200077)+2 种基金the Nantong Science and Technology Bureau(Grant No.MS 12021083)the Marine Science and Technology Innovation Project of Jiangsu Province(Grant No.JSZRHYKJ202105)the Fundamental Research Funds for the Central Universities(Grant No.B210204022).
文摘Tidal flats and saltmarshes have been a long-standing research focus because of their high socio-economic and ecological values.The evolution of tidal flat-marsh systems is highly complex due to the intertwined processes operating over a variety of spatial and temporal scales.As a traditional research highlight,the role of regular hydrodynamic processes such as tides,waves,and river flows have been explored comprehensively with fruitful outcomes.Over past decades,the changing environment(e.g.,sea level rise,increasing anthropogenic activities,and extreme weather conditions)has attracted more attention with many reported insightful results.More recent advances indicate that biological activities play a critical role in tidal flat-marsh morphodynamics but are still poorly understood.The field of research that connects the bio-logical and physical processes is commonly described as"biogeomorphology"and requires the joint efforts by scientists from multiple dis-ciplines ranging from hydraulics,ecology,and geography to sociology.This review aims to provide a synthesis of the current research status of tidal flat-marsh morphodynamics,with a particular emphasis on the understanding of various processes and feedbacks underlying the devel-opment of morphodynamic models.Some future research needs and challenges are identified to facilitate a more sustainable management strategy for tidal flats and saltmarshes under climate change.
基金supported by the Royal Netherlands Academy of Arts and Sciences(KNAW)(Grant No.PSA-SA-E-02)the Province of Zeeland,the Netherlands(Grant No.CoE-Buitendijks)。
文摘Understanding the sensitivity of tidal flats to environmental changes is challenging.Currently,most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats.In this study,we proposed an alternative empirical approach to explore tidal flat dynamics using statistical indices based on long-term time series of daily surface elevation development.Surface elevation dynamic(SED)indices focus on the magnitude and period of surface elevation changes,while morphodynamic signature(MDS)indices relate sediment dynamics to environmental drivers.The statistical analyses were applied to an intervention site in the Netherlands to determine the effect of recently constructed groynes on the tidal flat.Using these analyses,we were able to(1)detect a reduction in the daily SED and(2)determine that the changes in the daily SED were predominantly caused by the reduction in wave impact between the groynes rather than the reduction in tidal currents.Overall,the presented results showed that the combination of novel statistical indices provides new insights into the trajectories of tidal flats,ecosystem functioning,and sensitivity to physical drivers(wind and tides).Finally,we suggested how the SED and MDS indices may help to explore the future trajectories and climate resilience of intertidal habitats.
基金National Natural Science Foundation of China,No.41576087National Science Foundation for Young Scientists of China,No.41706093Fund of the Key Laboratory of Coastal Science and Engineering,Beibu Gulf,Guangxi,No.2016ZZD01
文摘Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Changjiang River, the channel immediately downstream of the Three Gorges Dam(TGD), are assessed based on remote sensing images between 2000 and 2016. It can be found that the entire area of sandbars reduces drastically by 19.23% from 149.04 km~2 in 2003 to 120.38 km~2 in 2016, accompanied with an increase in water surface width. Owing to differences in sediment grain size and anti-erosion capacity, sandbar area in the upstream sandy gravel reach(Yichang-Dabujie) and downstream sandy reach(Dabujie-Chenglingji) respectively decreases by 45.94%(from 20.79 km~2 to 11.24 km~2) and 14.93%(from 128.30 km~2 to 109.14 km~2). Furtherly, morphological evolutions of sandbars are affected by channel type: in straight-microbend channel, mid-channel sandbars exhibit downstream moving while maintaining the basic profile; in meandering channel, point sandbars show erosion and deposition in convex and concave bank respectively, with mid-channel sandbars distributing sporadically; in bending-branching channel, point sandbars experience erosion and move downstream while mid-channel sandbars show erosion in the head part along with retreating outline. We document that the primary mechanism of sandbars shrinkages along the Yichang-Chenglingji Reach can be attributed to TGD induced suspended sediment concentration decreasing and increasing in unsaturation of sediment carrying capacity. Additionally, channel type can affect the morphological evolution of sandbars. Along the Yichang-Chenglingji Reach, sandbars in straight-microbend channel are more affected by water flow than that in bending-branching channel.
基金Key Program of National Natural Science Foundation of China,No.U2040219National Natural Science Foundation of China,No.51579015Program of National Key Research and Development Plan of China,No.2016YFC0402108, No.2016YFC0402103。
文摘Geomorphic dynamics of alluvial rivers in response to upstream damming have substantial impacts on navigation, habitat protection, and channel stability. The purpose of this study was to determine how flow and sediment regimes, and meander characteristics affect the morphological adjustment of bends in the Lower Jingjiang Reach(LJR) before and after the Three Gorges Project(TGP). Based on detailed field measurements and hydrological and topographic datasets from 1991 to 2016, banks and point bars morphodynamics of 12continuous bends in the LJR were comprehensively analyzed. Point bars in the LJR mainly experienced a net deposition before the TGP operation, but substantially deteriorated with a net erosion rate of 4.6 million m^(3) yr^(-1) in the post-TGP periods(2003–2016), and erosion on heads and upstream margins of point bars was a general adjustment pattern in the 12 bends.The most significant morphological changes of point bars and banks occurred in 2006–2011,indicating a delayed response of the channel evolution of the LJR to damming. Detailed observations suggested that the medium discharges(16,000–18,000 m^(3) s^(-1)) were the most contributive discharges in shaping the morphology of point bars and banks in the LJR after damming. In addition, we revealed the importance of sediment supply on meander deformation of the LJR, driven by sediment exchange over point bars, and more upstream planform deformation tended to occur in bends with high sinuosity(>2.0) in the LJR after damming.The relationship between meander deformation and sinuosity was manifested through the geometric adjustment range of point bars. The morphological adjustments of point bars in the highly curved or compound bends of the LJR were more conducive to cause flow deflections,leading to form concave-bank bars after the TGP operation.
文摘Aggregation is used to represent the real world in a model at an appropriate level of abstraction.We used the convection-diffusion equation to examine the implications of aggregation progressing from a three-dimensional(3D)spatial description to a model representing a system as a single box that exchanges sediment with the adjacent environment.We highlight how all models depend on some forms of parametric closure,which need to be chosen to suit the scale of aggregation adopted in the model.All such models are therefore aggregated and make use of some empirical relationships to deal with sub-scale processes.One such appropriately aggregated model,the model for the aggregated scale morphological interaction between tidal basin and adjacent coast(ASMITA),is examined in more detail and used to illustrate the insight that this level of aggregation can bring to a problem by considering how tidal inlets and estuaries are impacted by sea level rise.
基金supported by the EPSRC FloodMEMORY Project(Grant No.EP/K013513/1)the HYDRALAB~+ Integrated Infrastructure Initiative,RESIST(Contract No.654110)Horizon 2020,European Community
文摘This paper reviews and discusses the current research status, trends, and future needs in the field of beach morphodynamics under the influence of storm sequences.The paper reviews how the three main research methods, field investigations, numerical modelling, and physical modelling, have been used to study beach morphodynamics during storm sequences.Available quantitative definitions of storm sequences at different sites are presented and discussed.It is shown that the definition of storm sequences is site-specific and requires knowledge of the storm climate, beach characteristics, and the temporal scale of beach recovery.Subsequently, the paper brings together currently available approaches aimed at describing the effect of storm sequences on beach erosion in a general way.The importance of storm chronology and the effects of an extreme storm within a sequence of storms are highlighted.Following that, the more poorly studied aspect of beach recovery in between storms within a sequence is discussed.Three indicators for defining beach recovery, namely the shoreline location, sediment volumes, and the beach state, are identified and compared.Finally, important research needs, including the need for detailed physical modelling, are identified.
基金The Zhejiang Provincial Natural Science Foundation of China under contract No.LHZ22D060001the Scientific Research Funds of the Second Institute of Oceanography,Ministry of Natural Resources under contract Nos JG2315 and XRJH2309the National Key R&D Program of China under contract No.2022YFC3106200.
文摘Beach erosion has occurred globally in recent decades due to frequent and severe storms.Dongsha beach,located in Zhujiajian Island,Zhejiang Province,China,is a typical embayed sandy beach.This study focused on the morphodynamic response of Dongsha beach to typhoon events,based on beach topographies and surficial sediment characteristics acquired before and after four typhoon events with varying intensities.The four typhoons had different effects on the topography and sediment characteristics of Dongsha beach.Typhoons Ampil and Danas caused the largest(-51.72 m3/m)and the smallest erosion(-8.01 m3/m),respectively.Remarkable alongshore patterns of beach profile volumetric changes were found after the four typhoon events,with more erosion in the southern and central parts of the beach and few changes in the northern part.Grain size coarsening and poor sorting were the main sediment patterns on the beach influenced by different typhoons.Typhoons that occurred in the same year after another typhoon enhanced the effect of the previous typhoon on sediment coarsening and sorting variability,but this cumulative effect was not found between typhoons that occurred during different years.A comparison of the collected data revealed that the topographic state of the beach before the typhoon,typhoon characteristics,and tidal conditions were possible reasons for the difference in the responses of Dongsha beach to typhoon events.More severe beach erosion was caused by typhoons with higher intensity levels and longer durations,and high tide levels during typhoons can determine the upper limit of the beach profile erosion site.Taken together,these results can be used to improve beach management for storm prevention.
基金The National Natural Science Foundation of China under contract No.41301005the Postdoctoral Science Foundation of China under contract No.2014M552118
文摘Beach morphodynamic classifications have achieved extensive acceptance in foreign coastal geomorphological studies. Three beaches located in different zones of a headland-bay coast are classified according to a dimensionless fall parameter, a relative tide range parameter and a dimensionless embayment scaling parameter. Synchronous data, including wave, tide, sediment and beach morphology, are respectively collected from the tangential beach, the transitional beach and the shadow beach of the Shuidong Bay during each spring tide for 16 successive months. The research results indicate that （1） the beach in the tangential zone falls between two major categories which are low tide terrace beaches with rips and barred beaches; the beach in the transitional zone exhibits two main types which are low tide bar/rip beaches and barred dissipative beaches; and the beach in the shadow zone mainly mirrors dissipative states with presence or absence of bars; and （2） the sequential changes and differences of beach states in different coastal zones reflect spatial and temporal variabilities of the headland- bay coast, totally meeting the actual measured beach morphology changes, showing that studies on wave- dominated, meso-macrotidal beaches need to consider the influences of the tides. Meanwhile, the research mainly provides a framework about beach state studies, due to different beach states with different erosion patterns, which requires the need to strengthen the researches in this respect, in order to further enrich theoretical basis for a beach topography evolution, beach morphodynamic processes and beach erosion orevention in China.
基金The National Natural Science Foundation of China under contract Nos 51979013 and 51909013the National Key Research and Development Program of China under contract Nos 2021YFC3100502 and 2021YFB2601105the Hainan Provincial Natural Science Foundation of China under contract No.421QN0978.
文摘The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade,concerning that the sea level rise(SLR)and more frequent and intense storms in the context of global climate change are expected to destabilize those islands.Here,we conduct a set of wave-flume laboratory experiments focusing on the morphodynamic change of reef islands to varying ocean forcing conditions(wave height and SLR).Subsequently,a phase-resolving XBeach numerical model is adopted to simulate the monochromatic wave process and its associated sediment dynamics.The adopted model is also firstly validated by laboratory experimental results as reported in this study.It is then used to examine the impacts of island morphological factors(island width,island height,island location and island side slope)on the island migration.The combined laboratory/physical and numerical experiment outputs suggest that reef islands can accrete vertically in response to the sea level rise and the increased storminess.
文摘Wulan Delta in Central Java has been experiencd coastal morphodynamics due to interface between Wulan River’s sedimentation and Java sea’s oceanographic process. This paper aims to analyze Wulan Delta’s morphodynamics as well as its impacts on the socio-economic condition of the community. The morphodynamics is interpreted visually and digitally using a maximum livelihood analysis of multiscale and multi-temporal images. The socio-economic impact is defined by field observations and in-depth interviews to the community and stakeholders. Analysis during the period of 1931-2010 showed that Wulan Delta had been changed morphologically from straight with small arc-like (arcuate) to bird-foot (digitate) with a plausible change into rounded (lobate) in the future, which represented dominant sedimentation by oceanographic rather than fluvial processes. Land expansion in Wulan Delta led to landuse change in Wedung, i.e. expansion of settlement area to 167 ha and fish pond area to 1014 ha in 2000-2010. Most settlements in the area, which are built linearly to river levees, own a high vulnerability to both river flood and tidal inundation. Therefore, dissemination about knowledge of the disaster and coastal zone management, as a means of increasing awareness, becomes necessary in integrating the coastal management in Wulan Delta together with improvement in infrastructure and proper regional development. The proper development strategy for the coastal village is aggressive maintenance strategy, including public infrastructure revitalization, quality improvement for human resources, and silvofishery system. Law enforcement on coastal zoning regulations is necessary to achieve an integrated and sustainable coastal zone management.
基金National Science Foundation of China,No.41301005,No.41701011Postdoctoral Science Foundation of China,No.2014M552118China Scholarship Council,No.201608410419。
文摘Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies.This paper carried out beach morphodynamic classifications for 12 straight beaches on headland-bay coasts based on field survey and evaluated the applicability of the most widely used dimensional fall velocity parameter(Ω)and relative tidal range parameter(RTR).One reflective,five intermediate and six non-barred dissipative beaches were visually classified and sand size seemed to be a key factor to differentiate these beaches.The studied beaches were in relatively low wave energy environments(Hs<1 m)and the absolute deep-water wave energy level of P0=3 KWm-1 was supposed to a critical threshold to characterize the applicability of theΩand RTR parameters.These two morphodynamic parameters were applicable for the beaches with P0>3 KWm-1 and MSR<2 m.It was found that the model of the traditional winter-and-summer profiles was not applicable in the study area in despite of distinct wave seasonality.The studied beaches were more possible to hover around a limited range due to relatively low background wave environments and variability without considering typhoon impacts,which needs further research on actual breaker wave conditions and beach morphodynamic type responses to typhoon events.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51779112 and 51879096)Research Innovation Fund of Tianjin Research Institute for Water Transport Engineering(Grant Nos.TKS20200401 and TKS180405).
文摘A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events.Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves,where the undertow and longshore currents exist simultaneously,forming a spirallike circulation system in the surfzone.Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction,subsequently suppress the formation of sandbars,showing that a typical recovery profile under calm waves does not necessarily develop,but with a competing process of onshore drift,undertow and longshore currents.Sediment transport rate during storms reaches several hundreds of times as those under calm waves,and two storm events contribute approximately 60%to the beach erosion.Sediment transport pattern under calm waves is mainly bed load,but as the fine sands underneath begin to expose,the contribution of suspended load becomes significant.
文摘Barito Delta morphodynamic had contradictive role with its potency and problem. Potency in Barito Delta may support the development of Banjarmasin City, but development of Barito Delta may decrease the capacity of transportation in Barito River. Multitemporal topographic map and Landsat satellite image during the period 1862-2008 were used to analyze the long-term delta morphodynamic. The analysis consisted of delta growth, yearly growth, growth orientation, delta shape, and shoreline changes. The research showed that the Barito Delta had developed during the period 1862-2008. Barito Delta had developed to south orientation. The growth of Barito Delta during the period 1862-1946 was 27.82 km^2 or 0.33 km^2/year. However, during the period 1946-1997, Barito Delta growth was 175.82 km^2 or 3.45 km^2/year. Area of Barito Delta decreased during the period 1997-2004. The reduction of Barito Delta area was 4.73 km^2 or 0.67 km^2/year. Area of Barito Delta in years 2004-2008 increased about 3.38 km^2 or 0.84 km^2/year Shoreline during the period 1862-2008 had changed. Accretion occurred in Kuala Lupak River during the period 1862-1997, but erosion occurred during the period 1997-2004. The delta morphodynamics were influenced by human activities in watershed and delta such as landuse change and land degradation.
基金supported by the UK Engineering and Physical Sciences Research Council(Grant No.EP/F030177/1)
文摘This work presents a new finite volume Godunov-type model for predicting morphological changes under the rapidly varying flood conditions with wetting and drying. The model solves the coupled shallow water and Exner equations, with the interface fluxes evaluated by an Harten-Lax-van Leer-Contact （HLLC） approximate Riemann solver. Well-balanced solution is achieved using the surface gradient method and wetting and drying are handled by a non-negative reconstruction approach. The new model is validated against several theoretical benchmark tests and promising results are obtained.
基金Project supported by the National Natural Science Foundation of China (Grant No. NSFC-49501001).
文摘Reticulate dunes are one of the commonest dune types, and yet the least understood. Reticulate dunes at southeastern Tengger Desert are constituted by NE-SW trending primary ridges and nearly vertical secondary ridges. The result of field work studying the morphodynamics and formation mechanism for reticulate dunes in this area shows that the primary ridges were formed by dominant northwest wind and the secondary ridges developed and maintained by alternating dominant wind and subdominant northeast wind on the basis of the primary ridges. Viewed from morphodynamics, reticulate dunes correspond to the complex transverse dune on which the longitudinal element superimposed.
基金supported by the National Natural Science Foundation of China(41676085)Zhejiang Provincial Natural Science Foundation of China(LY16D060004).
文摘A large tidal channel has developed along the northern shore of the Hangzhou Bay.Its length and width are about 50 and 10 km,respectively.It serves as an important navigation channel and provides port construction locations.This contribution investigates the morphological response of the tidal channel to the large-scale embankment in recent decades and the physical mechanisms,based on an idealized 2D morphodynamic model.The tidal channel was reproduced within a timescale of several years,with spatial scales comparable to the real situation.The results showed that the macroscopic sediment transport pattern in the bay,namely,entering in the north and leaving in the south,was not changed by the embankment.The tidal range and sediment flux increased to a certain extent,because of the decrease of the cross-sectional width.Meanwhile,the longitudinal gradient of the residual sediment transport enlarged slightly.As a result,the tidal channel was eroded significantly,because of the nonlinear interaction among hydrodynamics,sediment transport,and morphological change.Furthermore,there are inherent connections among the main morphological features in the bay.Complementary to other approaches,this model provides a useful tool to predict the morphodynamic behavior for the estuarine planning and regulations.
文摘Bangladesh is a riparian country that is criss-crossed by the many tributaries and distributaries of the mighty Ganges,Brahmaputra,and Meghna river systems.Gorai-Madhumati,a distributary of the Ganges River is an example where morphological development of the river is associated with frequent channel shifting within the catchment area.The main objective of this research is to quantify the extent of channel migration,erosion-accretion,river width,sinuosity,and charland morpho-dynamics from 1972 to 2018 using geospatial techniques combined with satellite images and hydrological data.The study also addressed the impacts of Farakka Barrage construction in India on the shifting,flow behavior,and siltation of Gorai-Madhumati River.The study shows that bar surface areas have abnormally increased in both segments after 1975 due to the construction of Farakka Barrage.Water flow in the Gorai-Madhumati has dropped remarkably in the downstream and instigated huge sedimentation in this region.Analysis of the time series satellite images revealed that the morphology of the river channel experienced huge changes simultaneously with the changes in the seasonal flow and sedimentation all over the study period.Migration trend has frequently shifted and taken place in the NW and NE direction in the observed sections of the river.Throughout the study period,total amount of accretion was greater than the net percentage of erosion on both banks of the river.River discharge,bar accretion,and erosion history show that the Gorai-Madhumati River will no longer exist with the present flowing condition without attention and proper river management.
基金This work was partly performed while the third author was a visiting professor at CMLA,Ecole normale superieure de Cachan.Financial support provided by CLMA,ENS Cachan is gratefully acknowledged。
文摘The accuracy and efficiency of a class of finite volume methods are investigated for numerical solution of morphodynamic problems in one space dimension.The governing equations consist of two components,namely a hydraulic part described by the shallow water equations and a sediment part described by the Exner equation.Based on different formulations of the morphodynamic equations,we propose a family of three finite volume methods.The numerical fluxes are reconstructed using a modified Roe’s scheme that incorporates,in its reconstruction,the sign of the Jacobian matrix in the morphodynamic system.A well-balanced discretization is used for the treatment of the source terms.The method is wellbalanced,non-oscillatory and suitable for both slow and rapid interactions between hydraulic flow and sediment transport.The obtained results for several morphodynamic problems are considered to be representative,and might be helpful for a fair rating of finite volume solution schemes,particularly in long time computations.
基金National Natural Science Foundation of China(NSFC,Grant Nos.41976156 and 51620105005)Jiangsu Marine Science and Technology Innovation Programme(Grant No.HY2018-1).
文摘The morphodynamic responses of tidal networks to anthropogenic reclamation and de-reclamation projects are investigated through a three-stage numerical simulation.In the first stage,the natural development of tidal networks is modelled in an open coast without any anthropogenic interventions.At the beginning of the second stage,parts of the computational domain are enclosed by sea dikes,which represents the implementation of the reclamation project.These sea dikes are removed or opened in the third stage to simulate the recovery of the tidal networks after de-reclamation.Each stage was set to last 100 years.The model results indicate that land reclamation can lead to three effects on tidal network morphology:(i)completely terminating the development of channels inside the projected area,(ii)hindering the development of the channel network in front of the dikes,and(iii)turning the channel direction near the corners of the dikes.When removing all the sea dikes,the previously reclaimed areas are quickly occupied by tidal networks.However,the morphology cannot be fully restored to its original natural state,although the entire reclaimed areas are returned.The effects of opening breaches are relatively slow,and tree-like network structures are formed inside the reclaimed areas.
基金Foundation： National Natural Science Foundation of China, No.41501208 The Global Change Program of Ministry of Science and Technology of China, No.2016YFA0600503 The U.S. National Science Foundation, No.ATM-0502489
文摘Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dune chronologies and the complexity of paleo-dune deposits as paleoenvironmental records. This paper addresses questions on the paleoenvi- ronmental implications of dune chronostratigraphies that have been raised by those reviews, in the specific case of crescentic dunes, using a case study from the Mu Us dune field, north-central China. The processes of turn-over and stabilization of relatively small crescentic dunes are first investigated by observational evidence. In combination with the analysis of a simplified sand preservation model and stratigraphic records, the effect of dune morphody- namics on sand preservation is demonstrated. It is especially evident that thick, nearly in- stantaneously deposited sand units record dune stabilization near the very end of a dune activity episode, while thin sand units may signal the preservation of sand deposited earlier in episodes of activity. Interpreting the distribution of luminescence ages that indicate sand deposition over time is not as simple as assumed in some previous work. Low frequency of sand ages could indicate an interval of either dune field stabilization or extensive dune activity but poor sand preservation. A peak of sand age frequency likely represents a shift in dune field activity towards stabilization, not a peak of active dune extent, especially if it partially overlaps with an independently identified interval of stabilization （e.g. one recorded by pa- leosols）. The nature and magnitude of these biases in the distribution of sand ages over time are strongly affected by the magnitude of net sand accumulation, which is in turn related to sand supply, transport capacity and sand availability, and ultimately climate change. Rela- tively short dune stabilization and turn-over time （101 to 102 yrs） indicate that dune geomor- phic processes can quickly respond to short-term disturbance, but the chronology of that response must be interpreted in light of how those processes influence age distributions.
