Stability analysis of a two-inlet bay system

The stability analysis for a double-inlet bay system is applied to an inlet system resembling Big Marco Pass and Capri Pass on the lower west coast of Florida. Since the opening of Capri Pass in 1967, the length of Big Marco Pass has increased from 2000 m in 1967 to 3000 m in 1988 and the cross-sectional area has decreased from 1200 m² in 1967 to 1000 m² in 1988. Since 1967, the cross-sectional area of Capri Pass has steadily increased and in 1988 was 700 m². Tides off the inlets are of the mixed type with a diurnal range of 1 m. The gross littoral transport rate in the vicinity of the inlets is estimated at 150,000 m³ yr⁻¹.For each inlet the maximum tidal velocities are calculated as a function of the gorge cross-sectional areas using a lumped-parameter model to describe the hydrodynamics of the flow. In the model it is assumed that the bay level fluctuates uniformly and the bay surface area remains constant. The velocities are used to calculate the tidal maximum of the bottom shear stress in each inlet as a function of the cross-sectional areas of the two inlets (=closure surface). Values of the equilibrium shear stress are derived from an empirical relationship between cross-sectional area and tidal prism for stable inlets along the west coast of Florida. Closure surfaces and equilibrium stress values are calculated for values of friction factors ranging from F=4×10⁻³ to F=6×10⁻³. Using the closure surfaces and equilibrium stress values, the equilibrium flow curve for each inlet is determined. The equilibrium flow curve represents the locus of the combination of cross-sectional areas for which the actual bottom shear stress in the inlet equals the equilibrium shear stress.Based on the equilibrium flow curves and the known values of the cross-sectional areas of the two inlets in 1988, it is expected that, ultimately, Big Marco Pass will close and Capri Pass will remain as the sole inlet with a cross-sectional area of 1250 m² and a maximum tidal velocity pertaining to a diurnal tide of 0.85 m s⁻¹.     

Spit and Inlet Morphodynamics of a Tropical Coastal Lagoon

The morphological changes of spits and inlets of the Chilika lagoon, the largest brackish water tropical coastal lagoon in Asia, are investigated using real-time kinematic GPS observation and numerical models during 2009–2013. The seasonal/interannual variations of the spit and inlet cross-sectional areas with varying widths and depths are recorded in association with different physical processes. The results show significant changes in spit morphology: particularly, the south spit accreted continuously, while the middle and north spits eroded. The cross-sectional depth of inlets becomes narrower and deeper during summer and winter seasons, while they are wider and shallower during the monsoon. The model results show that sediment transport rate is larger during monsoon and summer, while it is relatively less during the winter. Alongshore, sediment transport is predominantly northward throughout the study period. The result shows that gain/loss of the spits and closure/opening of inlets are significantly controlled by the high wave power, longshore drifts, and river discharge. The study demonstrates that the combined use of observational and numerical models is very effective to understand the changes of spit and inlet morphology and their impact on ecological conditions of the lagoon environment.     

Stability of tidal inlets—Pass Cavallo,Texas

Many tidal inlets are scoured in loose granular material, and the morphological changes in these inlets are discussed. The changes are the result of the predominantly fortnightly variations in the tide, the seasonal variations in storm activity and the occurrence of extreme meteorological events. The adjustment of an inlet to changes in the hydraulic environment and sudden changes in its morphology associated with extreme meteorological events is primarily via a change in the cross-sectional area. For a single-inlet bay system, the response of the inlet cross-sectional area can be determined using the stability analysis presented by Escoffier (1940). Rather than one inlet, many bays are connected to the ocean by several inlets. In this study, Escoffier's analysis is expanded to include the interaction of these inlets. In the analysis, the sediment carrying capacity of the inlet currents is characterized by the bottom shear stress. The stability analysis is applied to Pass Cavallo, Texas. Assuming the absence of future influences of tropical storms and hurricanes, the analysis shows that as a result of the opening of a companion inlet, Pass Cavallo ultimately will close.     

Assessment of tidal inlet evolution and stability using sediment budget computations and hydraulic parameter analysis

Research into the response of coastlines to the opening and stabilisation of inlets has been limited by the availability of suitable data, the shortcomings of existing formulae when applied to different inlets, and the difficulties particular to multi-inlet situations. Our appraisal of methodologies for studying inlet dynamics leads us to formulate a new approach for investigating inlet evolution and stability based on combining sediment budget computations (using best estimates and uncertainty analysis) and inlet hydraulic parameter analysis.The approach developed is applied to a stabilised inlet, located within a multi-inlet system (Faro-Olhão Inlet, Ria Formosa, Southern Portugal), which was opened starting 1929 and has since been dredged periodically to maintain navigability. A series of digital maps was produced based on multi-year data acquired from charts, surveys, and aerial photos. The maps were used to compute sediment volumes for six coastal cells delineated on the basis of the morphological features of the inlet. Cell volumes and fluxes were calculated for three periods (1929–1962, 1962–1978, and 1978–2001), and overall sediment budgets were calculated for the latter two periods. Inlet hydraulic parameters measured included tidal prism, inlet channel cross-sectional area and hydraulic radius, and maximum depth of the inlet throat, and were tracked over 9 bathymetric surveys from 1947–2004. The computed budget reveals that the inlet is only at present reaching volumetric equilibrium. However, the analysis of channel cross-sectional area and radius indicates parameter stability around 1978–1985, 20–25 years before the inlet started to reach volumetric equilibrium. It is hypothesised that the observed stability in parameters for the inlet post-1978 is related to the presence of fixed jetties and to a stratigraphic control that prevents further deepening, and not to the achievement of a dynamic equilibrium.The findings indicate that the coupling of sediment budget computation and inlet parameter analysis is useful for understanding historical sediment pathways and magnitudes, and for analysing the evolution of an inlet towards equilibrium. Although the analysis of inlet parameter evolution is valuable for examining the locational/geometrical stability of an inlet, it needs to be used in conjunction with sediment budget computations in order to properly infer inlet equilibrium. Moreover, existing formulae used to infer inlet stability, which relate cross-sectional area to tidal prism, should be reviewed with a view to including other external variables (e.g., stratigraphic controls) and to making their application more flexible to cope with the range of different inlet conditions. For multi-inlet systems, the coupling of morphology and hydrodynamics analysis should be extended to all inlets in order to infer the stability of the overall system based on the distribution of the tidal prism through time and the patterns of inlet circulation and sediment transport.     

Tidal and residual circulations in coupled restricted and leaky lagoons

Finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled “restricted” and “leaky” coastal lagoon system located in the Magdalen Islands, Gulf of Saint-Lawrence. Havre-aux-Maisons Lagoon (HML) is of a “restricted” nature with a neutral inlet in terms of tidal asymmetry. Grande-Entrée Lagoon (GEL) is of a “leaky” nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents. The imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from HML to GEL. The residual circulation is also characterized by strongest values at both inlets, very weak residual currents in HML deep basin and a dipole of residual eddies over the deeper areas of GEL. Further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system.     

Process-based modeling of morphodynamics of a tidal inlet system

The morphodynamic evolution of an idealized inlet system is investigated using a 2-D depthaveraged process-based model,incorporating the hydrodynamic equations,Englund-Hansen’s sediment transport formula and the mass conservation equation.The model has a fixed geometry,impermeable boundaries and uniform sediment grain size,and driven by shore-parallel tidal elevations.The results show that the model reproduces major elements of the inlet system,i.e.,flood and ebb tidal deltas,inlet channel.Equilibrium is reached after several years when the residual transport gradually decreases and eventually diminishes.At equilibrium,the flow field characteristics and morphological patterns agree with the schematized models proposed by O’Brien (1969) and Hayes (1980).The modeled minimum cross-sectional entrance area of the tidal inlet system is comparable with that calculated with the statistical P-A relationship for tidal inlets along the East China Sea coast.The morphological evolution of the inlet system is controlled by a negative feedback between hydrodynamics,sediment transport and bathymetric changes.The evolution rates decrease exponentially with time,i.e.,the system develops rapidly at an early stage while it slows down at later stages.Temporal changes in hydrodynamics occur in the system;for example,the flood velocity decreases while its duration increases,which weakens the flood domination patterns.The formation of the multi-channel system in the tidal basin can be divided into two stages;at the first stage the flood delta is formed and the water depth is reduced,and at the second stage the flood is dissected by a number of tidal channels in which the water depth increases in response to tidal scour.     

The effect of tidal inlets on open coast storm surge hydrographs

Bridge scour modeling requires storm surge hydrographs as open ocean boundary conditions for coastal waters surrounding tidal inlets. These open coast storm surge hydrographs are used to accurately determine both horizontal and vertical circulation patterns, and thus scour, within the inlet and bay for an extreme event. At present, very little information is available on the effect that tidal inlets have on these open coast storm surge hydrographs. Furthermore, current modeling practice enforces a single design hydrograph along the open coast boundary for bridge scour models. This study expands on these concepts and provides a more fundamental understanding on both of these modeling areas.     

Morphodynamic modeling of tidal channel evolution in comparison to empirical PA relationship

Tidal channels and inlets in alluvial environments are interconnected dynamic systems that react to changing physical conditions (such as sea level rise) as well as to anthropogenic impact (such as dredging and bank protection works). Past research resulted in an empirical equilibrium relationship for inlets between the tidal prism (P) and the cross-sectional area in a tidal inlet (A). Constant PA relationships were found along several tidal basins.     

Process-based 2DH morphodynamic modeling of tidal inlets: A comparison with empirical classifications and theories

The economical and ecological importance of tidal inlets has fostered the development of empirical tools for inlet management during the last century. This study aims at confronting these empirical theories with results obtained with a process-based numerical model, MORSYS2D. This 2DH morphodynamic modeling system is applied to an idealized tidal inlet/lagoon system with different combinations of significant wave height, tidal range and tidal prism. The numerical model predictions are compared to the empirical models of Hayes, Bruun, O'Brien and FitzGerald and to morphologies observed at natural tidal inlets. The results present good accordance with observations as well as with some key behaviors predicted with the empirical theories. The predicted morphologies satisfy the relation of O'Brien between the tidal prism and the cross-sectional area, the model reproduces the conceptual model of sand by-passing by ebb-tidal delta breaching of FitzGerald and the classifications of Hayes and Bruun are generally respected. However, some inconsistencies between model results and Hayes classification highlight the limitations of applying this classification, which only considers the yearly-averaged significant wave height and tidal range, to a single tidal inlet case.     

Sea-level and subsidence data from a Late Holocene back-barrier lagoon (Valle Standiana, Ravenna, Italy)

Late Holocene back-barrier sediments have been studied in a former lagoon reclaimed during the last century. Several shallow boreholes were cored, from which nine organic-rich samples were selected for radiocarbon dating, and others for palynological and palaeontological analysis. This enabled the reconstruction of the evolution of a back-barrier coastal basin during the late Holocene coastline progradation. Since late Roman times, the rate of relative sea-level rise (RSLR) has increased from 1.1 mm/yr to over 2 mm/yr, even after removal of the main human impacts during of the last century. This change is ascribed to sediment compaction related to changes in the hydrological regime, and possibly to an isostatic subsidence wave accompanying the northward shift of the Po Delta during the last 2000 years.     

海南岛洋浦港潮汐汊道口门的均衡过水面积

将汊道均衡与潮汐特征，纳潮量，淡水径流量及沉积物搬运格局相联系，确定了洋浦港的均衡条件，根据纳潮盆地的水面面积－水面高程曲线以及相关的特征潮位估算平均纳潮量，利用１９７７－１９７９年波浪观测资料和ＣＥＲＣ公式计算沿岸输沙率；此外，还用改进的Ｇａｄｄ公式确定口门涨、落潮流输沙率，计算中引入汊道口门流速频率分布函数的定义。由此而得洋浦港均衡过水面积为５８００ｍ＾２，与Ｏ＇Ｂｒｉｅｎ方法所得结果相比，本     

A high-resolution geophysical investigation of sediment distribution controlled by catchment size and tides in a multi-basin turbid outwash fjord: Simpson Bay,Prince William Sound,Alaska

Surficial sediment distribution within Simpson Bay is a function of antecedent bedrock and recently deposited glacial geology, as well as active physical processes both within Simpson Bay and Prince William Sound (PWS). Simpson Bay is a turbid, outwash fjord located in northeastern PWS, Alaska. Freshwater from heavy precipitation, and the melting of high alpine glaciers enter the bay through bay head rivers and small shoreline creeks. The catchment has a high watershed/basin surface area ratio (∼8:1), and easily erodible bedrock that contribute to high sediment loads. The system can be divided into three discrete basins, each with specific morphologic and circulatory characters. Side scan sonar, swath bathymetry, and seismic profiles reveal that bathymetric highs are areas of outcropping glacial surfaces. High backscatter coupled with surface grab samples reveal these surfaces to be composed of coarse sediment and bedrock outcrops. Bathymetric lows are areas of low backscatter, and grab samples reveal these areas to be ponded deposits of organic-rich estuarine muds. The data provide evidence of terminal morainal bank systems, and glacial grounding line deposits at the mouth of the bay and rocky outcrops were identified as subsurface extensions of aerial rocky promontories. Radioisotope analyses of short cores reveal that the bay has an average accumulation rate of approx. 0.5 cm year⁻¹, but that this varies in function of the watershed/basin surface area ratios of the different basins. The interaction of tidal currents and sediment source drives sediment distribution in Simpson Bay. Hydrographic data reveal high spatial variability in surface and bottom currents throughout the bay. Subsurface currents are tide dominated, but generally weak (5–20 cm s⁻¹), while faster currents are found along shorelines, outcrops, and bathymetric highs. Bathymetric data reveal steep slopes with little to no modern sediment throughout the bay, suggesting lack of deposition due to tidal currents.     

Changes in Venice Lagoon dynamics due to construction of mobile barriers

The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon's inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios.     

Morphological response of tidal basins to human interventions

This study focuses on the prediction of the long-term morphological evolution of tidal basins due to human interventions. New analytical results have been derived for an existing model [ASMITA, Aggregated Scale Morphological Interaction between a Tidal inlet and the Adjacent coast; Stive, M.J.F., Capobianco, M., Wang, Z.B., Ruol, P., Buijsman, M.C., 1998. Morphodynamics of a Tidal Lagoon and adjacent Coast. 8th International Biennial Conference on Physics of Estuaries and Coastal Seas, The Hague, September 1996, 397–407.]. Through linearisation of the model equations a set of time scales is obtained that describe the main features of the morphological evolution of tidal inlets. The magnitude of these system time scales is determined by inlet geometry and sediment exchange processes. The nature and degree of interventions determine which time scales are dominant. We focus on five different tidal inlets in the Wadden Sea. For these inlets, the system time scales have been estimated. The model has been applied to simulate the morphological response of the Marsdiep and Vlie inlets to the closure of the Zuiderzee in 1932. In this way, the model and associated system time scales for each of these inlets have been validated. Results show that in both inlets, the channels display the largest adaptation time. It will take at least a century before the channels and hence the tidal inlet systems reach a new morphological equilibrium.     

Modeling regional sediment transport and shoreline response in the vicinity of tidal inlets on the Long Island coast,United States

A new numerical model was developed to simulate regional sediment transport and shoreline response in the vicinity of tidal inlets based on the one-line theory combined with the reservoir analogy approach for volumetric evolution of inlet shoals. Sand bypassing onshore and sheltering effects on wave action from the inlet bar and shoals were taken into account. The model was applied to unique field data from the south coast of Long Island, United States, including inlet opening and closure. The simulation area extended from Montauk Point to Fire Island Inlet, including Shinnecock and Moriches Inlets. A 20-year long time series of hindcast wave data at three stations along the coast were used as input data to the model. The capacity of the inlet shoals and bars to store sand was estimated based on measured cross-sectional areas of the inlets as well as on comprehensive bathymetric surveys of the areas around the inlet. Several types of sediment sources and sinks were represented, including beach fills, groin systems, jetty blocking, inlet bypassing, and flood shoal and ebb shoal feeding. The model simulations were validated against annual net longshore transport rates reported in the literature, measured shorelines, and recorded sediment volumes in the flood and ebb shoal complexes. Overall, the model simulations were in good agreement with the measured data.     

Spatial and Temporal Entry Patterns of Fish Larvae into North Carolina Estuaries: Comparisons Among One Pelagic and Two Demersal Species

A sampling programme targeting larvae of winter spawning fishes immigrating from the oceanic domain into the Pamlico-Albemarle Sounds system (NC, U.S.A.) was performed at the four major inlets of the lagoon system. Sampling yielded abundant catches of three species, a Clupeid (Atlantic menhaden,Brevoortia tyrannus) and two Sciaenids (Atlantic croaker,Micropogonias undulatusand spot,Leiostomus xanthurus). In this article, the author documents the differences in the mechanisms developed for estuarine recruitment among the three species. Abundance at the tidal inlets was dependent upon numerous factors, such as sampling month, inlet, luminosity, tide flow direction and depth. The spatial and temporal positioning of the larvae differed among the species and affected their capabilities to be transported through the inlets. More specifically, spot and croaker migrated vertically within the water column in accordance with the direction of the water flow. Sciaenids minimized the outwelling effects of ebb tides by migrating into the slowest ebbing currents, near the bottom. Menhaden did not rely on vertical migrations for estuarine transport and retention. For this species, landward transport is provided either when dusk and flood onset are coincident or through non-tidal flows developing under meteorological forcing. The Sciaenids were less, or not, dependent upon these conditions. In one inlet, the retention was dependent upon the strength of the flooding and ebbing flows. In this case, the retention of the pelagic species was lower than the retention of demersal species.     

Field and model data analysis of sand transport patterns in Texel Tidal inlet (the Netherlands)

Texel inlet, the largest inlet in the Dutch Wadden Sea, has undergone drastic changes in the morphology of basin, ebb-tidal delta and adjacent coastlines after closure of a major part of its back-barrier basin. Despite intensive monitoring and analysis, present observation-based conceptual models lack the subtle physics necessary to explain the sand exchange between inlet, ebb-tidal delta and adjacent coastlines.Fundamental understanding of the inlet dynamics and evolution is obtained by integrating field and model data analysis. The state-of-the-art process-based model Delft3D Online Morphology has been used to generate synoptic data of high spatial and temporal resolution over the inlet domain. It is shown that the Delft3D Online Morphology model is capable of the quasi real-time simulation of the dominant flow and transport patterns over a 3-month period on the scale of the inlet. The high-resolution numerical model results prove to be a valuable tool in identifying the main transport patterns and mechanisms in the inlet domain. Qualitative transport patterns in Texel Inlet and its associated ebb-tidal delta are derived by integration of the observations and model results.The present ebb-tidal delta developments are best described as a second-stage self-organizing phase of redistribution and recirculation of sediments to obtain a natural dynamic equilibrium state, adapted to the changed configuration of the main-ebb channels. Sand is transported from the abandoned ebb-delta front (western margin of Noorderhaaks) and along the adjacent coastlines into the basin where it partly settles. Ebb-tidal currents redistribute sand back from the basin mainly onto the southern ebb-tidal delta shoals. Large gross transport rates, but small morphological changes, point to sediment recirculation. Sediment import into the basin results from net flood dominated transport due to tidal asymmetry, landward directed wind- and wave-driven flow, and larger flood transport capacities due to wave effects (e.g. enhanced bed shear stresses and stirring of sediment) that exceed the net ebb-dominated tidal residual transports.     

Modeling interrelationships between morphological evolution and grain-size trends in back-barrier tidal basins of the East Frisian Wadden Sea

In terms of grain size, surficial sediment distribution patterns in back-barrier tidal basins (e.g., the East Frisian Wadden Sea, Germany) often show a landward fining trend from the sea boundary to the mainland shore. In addition to the cross-shore patterns, there are lateral grain-size trends toward the watersheds of the basins and toward the watersheds of tidal flats bordered by tidal channels on either side. In the present study, interrelationships between morphological evolution and grain-size trends in the back-barrier tidal basins of the East Frisian Wadden Sea were simulated for a period of 60 years by a process-based forward modeling approach using the Delft3D system. The model outputs show that grain size displays a shoreward fining trend within the basin area, which is consistent with in situ observations; such a trend can be interpreted by the shoreward decrease in the cross-shore maximum velocity. Moreover, the model predicts lateral grain-size trends similar to those observed in the tidal basins: coarser sediment remains in the inlets and channels, while finer sediment settles at the tidal watersheds and on the tidal flats between channels. The spatial patterns of tidal flat sediment grain size within the tidal basins are thus related to the distance from the sea boundary and from the tidal channels. The modeling exercise also indicates that the development of the grain-size pattern observed in the East Frisian Wadden Sea is accomplished within a few decades, and that the time periods required to reach equilibrium are much shorter for grain size than for bed elevation. Evidently, spatial grain-size information can be used to assess sediment transport and morphological adaptation processes as, for example, attempted in sediment trend analysis procedures.     

有多个出口的北极地区微潮咸水湖的天气导致的次潮流

Estuarine processes in the arctic lagoons are among the least studied but important subjects, especially considering the rapid warming of arctic water which may change the length of ice-free period in the summer. In this paper, wind-driven exchange flows in the micro-tidal Elson Lagoon of northern Alaska with multiple inlets of contrasting widths and depths are studied with in situ observations, statistical analysis, numerical experiments, a regression model on the basis of dynamics, and remote sensing data. Water velocity profiles were obtained from a bottom deployed acoustic Doppler current profiler(ADCP) in the northwestern Eluitkak Pass connecting the Beaufort Sea to the Elson Lagoon during a 4.9 day ice-free period in the summer of 2013. The subtidal flow is found correlated with wind(R~2 value ～96%). Frequently occurring east, northeast and north winds from the arctic atmospheric high-and low-pressure systems push water from the Beaufort Sea into the lagoon through the wide inlets on the eastern side of the lagoon, resulting in an outward flow against the wind at the narrow northwestern inlet. The counter-wind flow is a result of an uneven wind forcing acting through the asymmetric inlets and depth,an effect of "torque" or vorticity. Under northwest wind, the exchange flow at the northwestern inlet reverses its direction, with inward flows through the upwind northwestern inlet and outward flows through the downwind eastern inlets. A regression model is established based on the momentum equations and Taylor series expansions. The model is used to predict flows in July and August of 2015 and July of 2017, supported by available Landsat satellite images. About 73%–80% of the time the flows at Eluitkak Pass are out of Elson Lagoon for the summer of 2015 and 2017. Numerical experiments are conducted to corroborate the findings and illustrate the effects under various wind conditions. A quasi-steady state balance between wind force and surface pressure gradient is confirmed.     

Impact of pulsed Atlantic water inflow into the Alboran Basin at the time of the Zanclean flooding

The study of more than 500 single- and multichannel seismic records enabled the generation of a detailed palaeo-bathymetric map of the Messinian surface over most of the Alboran Basin, Western Mediterranean. This regional surface is characterized by several erosional features (channels, terraces and canyons) and topographic highs (structural, volcanic and diapiric in origin). The most prominent feature is the incised Zanclean Channel crossing the entire basin, its entrenchment having been associated with the opening of the Strait of Gibraltar and subsequent inflow of Atlantic waters. The incision depth of the channel is variable, suggesting local variations in the erosive capacity of the Atlantic inflow, conditioned mainly by the regional basin topography and the local presence of topographic highs. Adjacent to this channel along the Spanish and Moroccan margins, and near the Strait of Gibraltar, several submarine terraces developed at different depths suggest a pulsed flooding of the Alboran Basin. There could have been two major inflow phases of Atlantic water, one shortly before and another during the Zanclean flooding, the latter accompanied by periods of relative sea-level stillstands that enabled terrace development. Alternatively, these features were all generated during the main flooding evident and subsequent pulsed infilling of the basin.