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1.
W. Gregory Hood 《地球表面变化过程与地形》2006,31(14):1824-1838
The origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes a contrasting depositional model for blind tidal channel origin and development in the Skagit River delta, Washington, USA. Chronological sequences of historical maps and photos spanning the last century show that as sediments accumulated at the river mouth, vegetation colonization created marsh islands that splintered the river into distributaries. The marsh islands coalesced when intervening distributary channels gradually narrowed and finally closed at the upstream end to form a blind tidal channel, or at mid‐length to form two blind tidal channels. Channel closure was probably often mediated through gradient reduction associated with marsh progradation and channel lengthening, coupled with large woody debris blockages. Blind tidal channel evolution from distributaries was common in the Skagit marshes from 1889 to the present, and it can account for the origin of very small modern blind tidal channels. The smallest observed distributary‐derived modern blind tidal channels have mean widths of 0·3 m, at the resolution limit of the modern orthophotographs. While channel initiation and persistence are similar processes in erosional systems, they are different processes in this depositional model. Once a channel is obstructed and isolated from distributary flow, only tidal flow remains and channel persistence becomes a function of tidal prism and tidal or wind/wave erosion. In rapidly prograding systems like the Skagit, blind tidal channel networks are probably inherited from the antecedent distributary network. Examination of large‐scale channel network geometry of such systems should therefore consider distributaries and blind tidal channels part of a common channel network and not entirely distinct elements of the system. Finally, managers of tidal habitat restoration projects generally assume an erosional model of tidal channel development. However, under circumstances conducive to progradation, depositional channel development may prevail instead. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
van Maanen Barend Coco Giovanni Bryan Karin R. Friedrichs Carl T. 《Ocean Dynamics》2013,63(11):1249-1262
Sea-level rise has a strong influence on tidal systems, and a major focus of climate change effect studies is to predict the future state of these environmental systems. Here, we used a model to simulate the morphological evolution of tidal embayments and to explore their response to a rising sea level. The model was first used to reproduce the formation of channels and intertidal flats under a stable mean water level in an idealised and initially unchannelled tidal basin. A gradual rise in sea level was imposed once a well-developed channel network had formed. Simulations were conducted with different sea-level rise rates and tidal ranges. Sea-level rise forced headward erosion of the tidal channels, driving a landward expansion of the channel network and channel development in the previously non-inundated part of the basin. Simultaneously, an increase in channel drainage width in the lower part of the basin occurred and a decrease in the overall fraction of the basin occupied by channels could be observed. Sea-level rise thus altered important characteristics of the tidal channel network. Some intertidal areas were maintained despite a rising sea level. However, the size, shape, and location of the intertidal areas changed. In addition, sea-level rise affected the exchange of sediment between the different morphological elements. A shift from exporting to importing sediment as well as a reinforcement of the existing sediment export was observed for the simulations performed here. Sediment erosion in the inlet and the offshore transport of sediment was enhanced, resulting in the expansion of the ebb-tidal delta. Our model results further emphasise that tidal embayments can exhibit contrasting responses to sea-level rise.
相似文献3.
Barend van Maanen Giovanni Coco Karin R. Bryan Carl T. Friedrichs 《Ocean Dynamics》2013,63(11-12):1249-1262
Sea-level rise has a strong influence on tidal systems, and a major focus of climate change effect studies is to predict the future state of these environmental systems. Here, we used a model to simulate the morphological evolution of tidal embayments and to explore their response to a rising sea level. The model was first used to reproduce the formation of channels and intertidal flats under a stable mean water level in an idealised and initially unchannelled tidal basin. A gradual rise in sea level was imposed once a well-developed channel network had formed. Simulations were conducted with different sea-level rise rates and tidal ranges. Sea-level rise forced headward erosion of the tidal channels, driving a landward expansion of the channel network and channel development in the previously non-inundated part of the basin. Simultaneously, an increase in channel drainage width in the lower part of the basin occurred and a decrease in the overall fraction of the basin occupied by channels could be observed. Sea-level rise thus altered important characteristics of the tidal channel network. Some intertidal areas were maintained despite a rising sea level. However, the size, shape, and location of the intertidal areas changed. In addition, sea-level rise affected the exchange of sediment between the different morphological elements. A shift from exporting to importing sediment as well as a reinforcement of the existing sediment export was observed for the simulations performed here. Sediment erosion in the inlet and the offshore transport of sediment was enhanced, resulting in the expansion of the ebb-tidal delta. Our model results further emphasise that tidal embayments can exhibit contrasting responses to sea-level rise. 相似文献
4.
Tidal channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of intertidal landforms. In muddy coastlines, the morphology of tidal channels and adjacent marshes strongly depends on the supply of fine sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fluxes in muddy coastlines, we measured tidal velocity and sediment concentration in Little Constance Bayou, a tidal channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the channel, thus allowing the quantification of feedbacks between waves and sediment fluxes. Results indicate that the sediment concentration in the channel is directly related to the wave height in the adjacent bay during flood and high slack water, whereas the concentration during ebb depends on local channel velocity. Moreover, the sediment flux during ebb is of the same order of magnitude as the sediment flux during the previous flood, indicating that only a small fraction of transported sediments are stored in the marsh during a tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
5.
Daniel J. Nowacki Andrea S. Ogston Charles A. Nittrouer Aaron T. Fricke Nils E. Asp Pedro Walfir M. Souza Filho 《地球表面变化过程与地形》2019,44(9):1846-1859
Mainstem–floodplain material exchange in the tidal freshwater reach of major rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environments. This knowledge gap prompts investigation of floodplain-incising tidal channels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current-induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level. © 2019 John Wiley & Sons, Ltd. 相似文献
6.
Estuaries typically show converging planforms from the sea into the land. Nevertheless, their planform is rarely perfectly exponential and often shows curvature and the presence of embayments. Here we test the degree to which the shapes and dimensions of tidal sandbars depend on estuary planform. We assembled a dataset with 35 estuary planforms and properties of 190 tidal bars to induce broad‐brush but significant empirical relations between channel planform, hydraulic geometry and bar pattern, and tested a linear stability theory for bar pattern. We found that the location where bars form is largely controlled by the excess width of a channel, which is calculated as the observed channel width minus the width of an ideal exponentially widening estuary. In general, the summed width of bars approximates the excess width as measured in the along‐channel variation of three estuaries for which bathymetry was available as well as for the local measurements in the 35 investigated estuaries. Bar dimensions can be predicted by either the channel width or the tidal prism, because channel width also strongly depends on local tidal prism. Also braiding index was predicted within a factor of 2 from excess width divided by the predicted bar width. Our results imply that estuary planform shape, including mudflats and saltmarsh as well as bar pattern, depend on inherited Holocene topography and lithology and that eventually convergent channels will form if sufficient sediment is available. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
7.
Weina Zhang Xiaohe Zhang Huiming Huang Yigang Wang Sergio Fagherazzi 《地球表面变化过程与地形》2020,45(11):2613-2630
We use a hydrodynamic model applied to an idealized fan-shaped basin to explore the morphology and dynamics of radial sand ridges in a convergent coastal system. A positive morphological feedback between channel incision and flow redistribution is responsible for the formation of the channel-ridge pattern. The selection mechanism of bottom wavelength is associated with flow concentration in the deeper part of the channels. Our results are compared to sediment and hydraulic dynamics in the radial sand ridges (RSRs) in China. In a convergent, sloping basin the tangentially averaged tidal velocity peaks at 47 km from the apex. This distance is similar to the arc distance, 62 km, where the RSRs are most incised. An offshore shift in tidal phase results in stronger flows near the north coastline, explaining the presence of asymmetric channel patterns. A numerical stability analysis indicates that small radial oscillations with a wavelength of 10° to 15° maximize the velocity in the troughs. This oscillation wavelength also emerges in the RSRs, which display a peak in spectral energy at a radial wavelength between 25° to 37.5°. High-resolution numerical simulations in the RSRs confirm that flow concentration occurs in the deeper part of the channels, keeping them flushed. We therefore conclude that the RSRs display morphometric characteristics similar to other tidal incisions, like tidal inlets and intertidal channels. This result further supports the dominant role of tidal prism and related peak velocities in incising coastal landscapes. © 2020 John Wiley & Sons, Ltd. 相似文献
8.
Jesse R. Fleri Sara Lera Alessandro Gerevini Lorie Staver William Nardin 《地球表面变化过程与地形》2019,44(11):2223-2235
Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine-grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high-resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco-geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood-ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In-situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea-level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience. © 2019 John Wiley & Sons, Ltd. 相似文献
9.
Aaron T. Fricke Charles A. Nittrouer Andrea S. Ogston Daniel J. Nowacki Nils E. Asp Pedro W. M. Souza Filho 《地球表面变化过程与地形》2019,44(1):204-218
Depositional environments along the tidal river downstream of Óbidos have been proposed as important sinks for up to one third of the sediment discharge from the Amazon River. However, the morphology of the intertidal floodplain and the dynamics of sediment exchange along this reach have yet to be described. River-bank surveys in five regions along the Amazon tidal river reveal a distinct transition in bank morphology between the upper, central and lower reaches of the tidal river. The upper tidal-river floodplain is defined by prominent natural levees that control the transfer of water and sediment between the mainstem Amazon River and its floodplain. Greater tidal influence in the central tidal river suppresses levee development, and tidal currents increase sediment transport into the distal parts of the floodplain. In the lower tidal river, the floodplain morphology closely resembles marine intertidal environments (e.g. mud flats, salt marshes), with dendritic tidal channels incising elevated vegetated flats. Theory, morphology and geochronology suggest that the dynamics of sediment delivery to the intertidal floodplain of the Amazon tidal river vary along its length due to the relative influence and coupling of fluvial and tidal dynamics. © 2018 John Wiley & Sons, Ltd. 相似文献
10.
Lisanne Braat Jasper R. F. W. Leuven Ivar R. Lokhorst Maarten G. Kleinhans 《地球表面变化过程与地形》2019,44(2):417-432
Human interference in estuaries has led to increasing problems of mud, such as hyper-turbidity with adverse ecological effects and siltation of navigation channels and harbours. To deal with this mud sustainably, it is important to understand its long-term effects on the morphology and dynamics of estuaries. The aim of this study is to understand how mud affects the morphological evolution of estuaries. We focus on the effects of fluvial mud supply on the spatial distribution of mudflats and on how this influences estuary width, depth, surface area and dynamics over time. Three physical experiments with self-forming channels and shoals were conducted in a new flume type suitable for tidal experiments: the Metronome. In two of the experiments, we added nutshell grains as mud simulant, which is transported in suspension. Time-lapse images of every tidal cycle and digital elevation models for every 500 cycles were analysed for the three experiments. Mud settles in distinct locations, forming mudflats on bars and sides of the estuary, where the bed elevation is higher. Two important effects of mud were observed: the first is the slight cohesiveness of mud that causes stability on bars limiting vertical erosion, although the bank erosion rate by migrating channels is unaffected. Secondly, mud fills inactive areas and deposits at higher elevations up to the high-water level and therefore decreases the tidal prism. These combined effects cause a decrease in dynamics in the estuary and lead to near-equilibrium planforms that are smaller in volume and especially narrower upstream, with increased bar heights and no channel deepening. This trend is in contrast to channel deepening in rivers by muddier floodplain formation. These results imply large consequences for long-term morphodynamics in estuaries that become muddier due to management practices, which deteriorate ecological quality of intertidal habitats but may create potential area for marshes. © 2018 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. 相似文献
11.
12.
Lagoonal tidal inlets are a typical morphology of the Central Coast of Vietnam. Recently, navigation channels in these inlets have become increasingly threatened by siltation. This study analyses the relations between sediment distribution and transport trends (using the technique of Sediment Trend Analysis-STA■) in the lagoonal system of the De Gi inlet and then proposes appropriate countermeasures against sand deposition in the navigation channel. The STA identified three types of transport trends in the De Gi inlet, namely dynamic equilibrium, net accretion, and net erosion. Processes associated with the tidal prism have resulted in trends of sediment transport and deposition across the flood and ebb tidal shoals, which maintain a present cross-sectional area of about 1000m^2. However, longshore sediment transport from north to south resulting from northeast waves cause additional sand deposition in the channel. In addition, the effects of refraction associated with a nearby headland and jetty also increase sedimentation. These processes provide the main reasons for sediment deposition in the De Gi inlet. Short term and regular dredging helps to maintain the navigation channel. A system comprised of three jetties (north, south, and weir) is necessary to ensure the longterm cross-sectional stability of the navigation channel. 相似文献
13.
Fateme Yousefi Lalimi Marco Marani James Brendan Heffernan Andrea D'Alpaos A. Brad Murray 《地球表面变化过程与地形》2020,45(6):1456-1468
The formation and evolution of tidal platforms are controlled by the feedbacks between hydrodynamics, geomorphology, vegetation, and sediment transport. Previous work mainly addresses dynamics at the scale of individual marsh platforms. Here, we develop a process-based model to investigate salt marsh depositional/erosional dynamics and resilience to environmental change at the scale of tidal basins. We evaluate how inputs of water and sediment from river and ocean sources interact, how losses of sediment to the ocean depend on this interaction, and how erosional/depositional dynamics are coupled to these exchanges. Model experiments consider a wide range of watershed, basin, and oceanic characteristics, represented by river discharge and suspended sediment concentration, basin dimensions, tidal range, and ocean sediment concentration. In some scenarios, the vertical accretion of a tidal flat can be greater than the rate of sea level rise. Under these conditions, vertical depositional dynamics can lead to transitions between tidal flat and salt marsh equilibrium states. This type of transition occurs much more rapidly than transitions occurring through horizontal marsh expansion or retreat. In addition, our analyses reveal that river inputs can affect the existence and extent of marsh/tidal flat equilibria by both directly providing suspended sediment (favoring marshes) and by modulating water exchanges with the ocean, thereby indirectly affecting the ocean sediment input to the system (favoring either marshes or tidal flats depending on the ratio of the river and ocean water inputs and their sediment concentrations). The model proposed has the goal of clarifying the roles of the main dynamic processes at play, rather than of predicting the evolution of a particular tidal system. Our model results most directly reflect micro- and meso-tidal environments but also have implications for macro-tidal settings. The model-based analyses presented extend our theoretical understanding of marsh dynamics to a greater range of intertidal environments. © 2020 John Wiley & Sons, Ltd. 相似文献
14.
The effect of bidirectional flow on tidal channel planforms 总被引：1，自引：0，他引：1
Salt marsh tidal channels are highly sinuous. For this project, ?eld surveys and aerial photographs were used to characterize the planform of tidal channels at China Camp Marsh in the San Francisco Bay, California. To model the planform evolution, we assume that the topographic curvature of the channel centreline is a key element driving meander migration. Extraction of curvature data from a planimetric survey, however, presents certain problems because simple calculations based on equally distanced points on the channel axis produce numerical noise that pollutes the ?nal curvature data. We found that a spline interpolation and a polynomial ?t to the survey data provided us with a robust means of calculating channel curvature. The curvature calculations, combined with data from numerous cross‐sections along the tidal channel, were used to parameterize a computer model. With this model, based on recent theoretical work, the relationship between planform shape and meander migration as well as the consequences of bidirectional ?ow on planform evolution have been investigated. Bank failure in vegetated salt marsh channels is characterized by slump blocks that persist in the channel for several years. It is therefore possible to identify reaches of active bank erosion and test model predictions. Our results suggest that the geometry and evolution of meanders at China Camp Marsh, California, re?ect the ebb‐dominated regime. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
15.
On the potential of plant species invasion influencing bio‐geomorphologic landscape formation in salt marshes 
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下载免费PDF全文 Christian Schwarz Tom Ysebaert Wouter Vandenbruwaene Stijn Temmerman LiQuan Zhang Peter M. J. Herman 《地球表面变化过程与地形》2016,41(14):2047-2057
Species invasions are known to change biotic and abiotic ecosystem characteristics such as community structure, cycling of materials and dynamics of rivers. However, their ability to alter interactions between biotic and abiotic ecosystem components, in particular bio‐geomorphic feedbacks and the resulting landscape configuration in tidal wetlands, such as tidal channels have not yet been demonstrated. We studied the impact of altered bio‐geomorphic feedbacks on geomorphologic features (i.e. tidal wetland channels), by comparing proxies for channel network geometry (unchanneled flow lengths, fractal dimension) over time between non‐invaded and invaded salt marsh habitats. The non‐invaded habitats (the south of eastern Chongming Island, Yangtze estuary, China) show little change in network geometry over time with a tendency for an increased drainage density. The invaded site (salt marshes in the north of eastern Chongming Island invaded by the exotic plant species Spartina alterniflora) showed a decreasing tendency in channel drainage density throughout and after the species invasion. This suggests that species invasions might not only affect biotic ecosystem characteristics, but also their ability to change bio‐geomorphic feedback loops, potentially leading to changes in existing geomorphologic features and therefore landscape configuration. Our results further suggest that the species invasion also altered sediment composition. Based on observations we propose a mechanism explaining the change in channel drainage density by an alteration in plant properties. The physical and physiological characteristics of the invading species Spartina alterniflora clearly differ from the native species Scirpus mariqueter, inducing different bio‐geomorphic feedback loops leading to the observed change in salt marsh channel configuration. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
16.
Flood and ebb currents provide different contributions to the initiation and evolution of tidal channel networks, generating diverse network structures and channel cross-sections. In order to separate the effects of these contributions, a physical model of a sloping tidal-flat basin was set up in the laboratory. Depending on the degree of tidal asymmetry imposed offshore, either flood or ebb currents can be enhanced. The experimental results show that the ebb current has a higher capability to initiate and shape tidal networks than the flood current. Headward erosion is mainly induced by the ebb flow. The slightly inclined flat surface tends to reduce the energy of the flood current and to enhance the ebb current, thus prolonging the duration of morphodynamic activity as well as sediment motion. Overall, flood-dominated tides favour the formation of small-scale channel branches in the upper basin zone, while long lasting ebb-dominated tides result in more complex, wider and deeper tidal networks. © 2019 John Wiley & Sons, Ltd. 相似文献
17.
Tidal inlets interrupt longshore sediment transport, thereby exerting an influence on adjacent beach morphology. To investigate the details and spatial extent of an inlet's influence, we examine beach topographic change along a 1.5 km coastal reach adjacent to Matanzas Inlet, on the Florida Atlantic coast. Analyses of beach morphology reveal a behavioral change between 0.64 and 0.86 km from the inlet channel centerline, interpreted to represent the spatial extent of inlet influence. Beyond this boundary, the beach is narrow, exhibits a statistically significant inverse correlation of shoreline position with offshore wave conditions, and has a uniform alongshore pattern in temporal behavior, as determined from empirical orthogonal function (EOF) analysis. On the inlet side of the boundary, the beach experiences monotonic widening (with proximity to the inlet), lacks spatial consistency in correlation between shoreline position and wave conditions, and exhibits an irregular pattern in spatial EOF modes. We augment the field observations with numerical modeling that provides calculations of wave setup and nearshore current patterns near the inlet, highlighting the effects of the ebb‐tidal delta on the assailing waves. The modeling results are verified by a natural experiment that occurred during May 2009, when a storm‐produced sedimentary mass accreted to the lower beach, then subsequently split into two oppositely directed waves of sediment that migrated away from the initial accretion site in the subsequent months. Our results suggest that the ebb‐tidal delta produces a pattern of wave setup that creates a pressure gradient driving an alongshore flow that opposes the longshore currents derived from breaking of obliquely oriented incident waves. The resulting recirculation pattern on the margin of the ebb‐tidal delta provides a mechanism through which the inlet influences adjacent barrier island beach morphology. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
18.
Intermittently open/closed estuaries (IOCE) are a dynamic form of estuary characterised by periodic entrance closure to the ocean. Entrance closure is a function of the relative balance between on and offshore sediment transport with closures occurring during periods of low fluvial discharge whereby the estuary ebb‐tidal prism is reduced. Although the broad scale processes of entrance closure are becoming better understood, there remains limited knowledge on channel morphodynamics during an individual closure event. In this study, the entrance dynamics of three IOCE on the coast of Victoria, Australia, were monitored over a daily timescale following both artificial and natural openings. The influence of changing marine and fluvial conditions on the relative sedimentation rate within the entrance channel was examined. IOCE in Victoria showed two distinct modes of entrance closure: (a) lateral accretion, whereby the estuary gradually closes by longshore drift‐driven spit growth during low river flows; and (b) vertical accretion, where the channel rapidly aggrades under high (> 2 m), near‐normal waves. During storms, when fluvial discharge and wave heights simultaneously increase, large swells will not always close the mouth due to an increase in the ebb‐tidal prism. The estuary water depth and the maximum channel dimensions following opening were not proportional to the opening duration, with this being a function of the wave and fluvial conditions occurring following lagoon drainage. Based on the findings of this work, implementing a successful artificial entrance opening is dependent on reduced onshore sedimentation rates which occur when wave energy is low (< 2 m Hs) relative to river flow. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
19.
On the stability relationships between tidal asymmetry and morphologies of tidal basins and estuaries 下载免费PDF全文
下载免费PDF全文 Zeng Zhou Giovanni Coco Ian Townend Zheng Gong Zhengbing Wang Changkuan Zhang 《地球表面变化过程与地形》2018,43(9):1943-1959
Simple stability relationships are practically useful to provide a rapid assessment of coastal and estuarine landforms in response to human interventions and long‐term climate change. In this contribution, we review a variety of simple stability relationships which are based on the analysis of tidal asymmetry (TA). Most of the existing TA‐based stability relationships are derived using the one‐dimensional tidal flow equations assuming a certain regular shape of the tidal channel cross‐sections. To facilitate analytical solutions, specific assumptions inevitably need to be made, for example by linearizing the friction term and dropping some negligible terms in the tidal flow equations. We find that three major types of TA‐based stability relationships have been proposed between three non‐dimensional channel geometric ratios (represented by the ratio of channel widths, ratio of wet surface areas and ratio of storage volumes) and the tide‐related parameter a/h (i.e. the ratio between tidal amplitude and mean water depth). Based on established geometric relations, we use these non‐dimensional ratios to restate the existing relationships so that they are directly comparable. Available datasets are further extended to examine the utility of these TA‐based relationships. Although a certain agreement is shown for these relationships, we also observe a large scatter of data points which are collected in different types of landscape, hydrodynamic and sedimentological settings over the world. We discuss in detail the potential reasons for this large scatter and subsequently elaborate on the limited applicability of the various TA‐based stability relationships for practical use. We highlight the need to delve further into what constitutes equilibrium and what is needed to develop more robust measures to determine the morphological state of these systems. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
20.
Modelling the relative dominance of wave erosion and weathering processes in shore platform development in micro‐ to mega‐tidal settings 下载免费PDF全文
下载免费PDF全文 In this paper we use a numerical model to explore the relative dominance of two main processes in shore platform development: wave erosion; weathering due to wetting and drying. The modelling approach differs from previous work in several aspects, including: the way that it accounts for weathering arising from gradual surficial intertidal rock degradation; subtidal profile shape development; and the consideration of a broad erosion parameter space in which, at either end of the erosion spectrum, shore platform profiles are produced by waves or weathering alone. Results show that in micro‐tidal settings, wave erosion dominates the evolution of (i) shore platforms that become largely subtidal and (ii) sub‐horizontal shore platforms that have a receding seaward edge. Weathering processes dominate the evolution of sub‐horizontal shore platforms with a stable seaward edge. In contrast, sloping shore platforms in mega‐tidal settings are produced across the full range of the process‐dominance spectrum depending on the how the erosional efficacy of wave erosion and weathering are parameterized. Morphological feedbacks control the process‐dominance. In small tidal environments wave processes are strongly controlled by the presence/absence of an abrupt seaward edge, but this influence is much smaller in large tidal environments due to larger water depths particularly at high tides. In large tidal environments, similar shore platform profile geometries can be produced by either wave‐dominant or weathering‐dominant process regimes. Equifinality in shore platform development has been noted in other studies, but mainly in the context of smaller‐scale (centimetre to metre) erosion features. Here we draw attention to geomorphic equifinality at the scale of the shore platform itself. Progress requires a greater understanding of the actual mechanics of the process regimes operating on shore platforms. However, this paper makes a substantial contribution to the debate by identifying the physical conditions that allow clear statements about process dominance. © 2018 John Wiley & Sons, Ltd. 相似文献