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1.
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.  相似文献   

2.
《Marine Geology》2006,225(1-4):23-44
The morphodynamics of inlets and ebb-tidal deltas reflect the interaction between wave and tidal current-driven sediment transport and significantly influence the behaviour of adjacent shorelines. Studies of inlet morphodynamics have tended to focus on sand-dominated coastlines and reference to gravel-dominated or ‘gravel-rich’ inlets is rare. This work characterises and conceptualises the morphodynamics of a meso-tidal sand–gravel inlet at the mouth of the Deben estuary, southeast England. Behaviour of the inlet and ebb-tidal delta over the last 200 yr is analysed with respect to planform configuration and bathymetry. The estuary inlet is historically dynamic, with ebb-tidal shoals exhibiting broadly cyclic behaviour on a 10 to 30 yr timescale. Quantification of inlet parameters for the most recent cycle (1981–2003) indicate an average ebb delta volume of 1 × 106 m3 and inlet cross-sectional area of 775 m2. Bypassing volumes provide a direct indicator of annual longshore sediment transport rate over this most recent cycle of 30–40 × 103 m3 yr− 1. Short-term increases in total ebb-tidal delta volume are linked to annual variability in the north to northeasterly wind climate. The sediment bypassing mechanism operating in the Deben inlet is comparable to the ‘ebb delta breaching’ model of FitzGerald [FitzGerald, D.M., 1988. Shoreline erosional–depositional processes associated with tidal inlets, in: Aubrey, D.G., Weishar, L. (Ed.), Hydrodynamics and Sediment Dynamics of Tidal Inlets. Springer-Verlag Inc., New York, pp. 186–225.], although the scales and rates of change exhibited are notably different to sand-dominated systems. A systematic review of empirical models of sand-dominated inlet and ebb-tidal delta morphodynamics (e.g. those of [O'Brien, M.P., 1931. Estuary tidal prisms related to entrance areas. Civil Engineering, 1, 738–739.; Walton, T.L., and Adams, W.D., 1976. Capacity of inlet outer bars to store sand. Proceedings of 15th Coastal Engineering Conference, 1919–1937.; Gaudiano, D.J., Kana, T.W., 2001. Shoal bypassing in mixed energy inlets: geomorphic variables and empirical predictions for nine South Carolina inlets. J. Coast. Res., 17, (2), 280–291.]) shows the Deben system to be significantly smaller yet characterised by a longer bypassing cycle than would be expected for its tidal prism. This is attributed to its coarse-grained sedimentology and the lower efficiency of sediment transporting processes.  相似文献   

3.
The cross-sectional stability of two tidal inlets connecting the same back-barrier lagoon to the ocean is investigated. The condition for equilibrium is the cross-sectional area tidal prism relationship. In an earlier study [Van de Kreeke, J., 1990. Can multiple inlets be stable? Estuarine, Coastal and Shelf Science 30: 261–273.], using the same equilibrium condition, it was concluded that where two inlets connect the same basin to the ocean ultimately one inlet will close. One of the major assumptions in that study was that the water level in the basin fluctuated uniformly. In hindsight this assumption might be too restrictive. For example, in the Wadden Sea the back barrier lagoon consists of a series of basins, rather than one single basin, separated by topographic highs. These topographic highs limit but do not exclude the exchange of water between the sub-basins. For this reason in the present study, a topographic high in the form of a weir was added, separating the back-barrier lagoon in two sub-basins. The water level in the sub-basins, rather than in the back-barrier as a whole, is assumed to fluctuate uniformly. For this schematization the hydrodynamic equations are solved using a finite difference method. The results, together with the equilibrium condition, yield the equilibrium flow curve for each of the inlets. The intersections of the two equilibrium flow curves represent combinations of cross-sectional areas for which both inlets are in equilibrium. The stability of the equilibriums was investigated using a non-linear stability analysis resulting in a flow diagram. Calculations were carried out for different inlet and weir characteristics. Sinussoidal tides were the same for both inlets. The results show that for relatively large wetted cross-sectional areas over the topographic high, approaching the situation of a single basin, there are no combinations of inlet cross-sectional areas for which both inlets are in a stable equilibrium. This supports the conclusion in the earlier study. For relatively small wetted cross-sectional areas over the topographic high there is one set of stable equilibriums. In that case the two-inlet bay system approaches that of two single-inlet bay systems.  相似文献   

4.
A large deficit in the coastal sediment budget, high rates of relative sea-level rise (~0.9 cm/year), and storm-induced current and wave erosion are forcing barrier shoreface retreat along the periphery of the Mississippi River delta plain. Additionally, conversion of interior wetlands to open water has increased the bay tidal prism, resulting in degradation of barrier islands due to inlet widening, formation of new inlets, and sediment sequestration at ebb-tidal deltas. Single-beam bathymetric surveys along a 165-km stretch of south-central Louisiana barrier coast, from Raccoon Point in Terrebonne Parish to Sandy Point in Plaquemines Parish, were conducted in 2006. These data, combined with historical bathymetry from three time periods (dating to the 1880s), provide a series of digital elevation models that were used to calculate sediment volumetric changes and determine long-term erosional-depositional trends. Dominant patterns during the 125-year period include (1) erosion of ~1.6 × 109 m3 from the shoreface, forcing up to 3 km of shoreface retreat, (2) sediment deposition in coastal bights and at ebb-tidal deltas, and (3) a combined increase in tidal inlet cross-sectional area from ~41,400 m2 to ~139,500 m2. Bathymetric and shoreline change datasets separated by shorter time periods (sub-annual) demonstrate that these long-term trends are driven by processes associated with major hurricane impacts, and that rates of shoreface erosion are an order of magnitude greater during active hurricane seasons compared to long-term trends.  相似文献   

5.
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.  相似文献   

6.
The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.  相似文献   

7.
Between 1970 to 2000, the annual mean suspended matter (SPM) concentrations in the Vlie and Marsdiep tidal inlets of the Wadden Sea varied over five times. The present paper examines the possible relationship between SPM in the Wadden Sea and changing river Rhine discharges and dredging operations. The major short-term variations in annual mean SPM in part of the Wadden Sea appears to be a non-linear, exponential, function of river Rhine discharge and dredge spoil disposal (110 km to over 200 km from the area in front of the Dutch coast near the river Rhine outlet). Correlation coefficients (with SPM as the fixed and dredge disposal as the independent variable) ranged from R=0·8 (deep tidal inlet of Marsdiep) to R=0·2 (shallow inner area of Vlie) and weakened mainly as a function of distance to the disposal site. The best correlation with river discharge was for Marsdiep tidal inlet (r=0·45), indicating the superior effect of dredge disposal over river discharge-related processes. Taking the estimated regression equation as an explorative model, indicates that, without any disposal of dredge spoil, the expected SPM concentration levels in the tidal inlets of the Wadden Sea will be <15 g m−3 (comparable to the 1950s). The overall mean (and the highest mean) annual concentrations for the investigation period reached 42 (90) g m−3 at Marsdiep and 35 (75) g m−3 at Vlie. Assuming a 10% (220 m−3 s−1) increase in river Rhine discharge over the next 50 years, and unchanged dredging policy and other circumstances, SPM concentrations would increase 5–15% for Marsdiep and Vlie. Compared with the calculated (12·4 g m−3 SPM in Marsdiep and 14·8 g m−3 SPM in Vlie) and measured (15 g m−3 SPM in Marsdiep) background SPM concentrations, the expected overall mean increase since 1950 is at least 250% of background. The natural variation in river Rhine discharge will cause further inter-annual variation. Changes in SPM concentrations, due to expected changes in wind climate, combined with river discharge are estimated to increase SPM concentrations 20% above the present situation. The possible implications of changes in land use in combination with further increasing river discharge, changed wind fields and increased temperature are discussed. An important management conclusion is that increasing mean river discharge will significantly increase the need for dredging and spoil disposal, and result in further elevated SPM concentrations in the Dutch coastal zone and the Wadden Sea. The presented relationships offer possibilities for developing new management strategies in relation to dredging and its effects.  相似文献   

8.
Broad classification of New Zealand inlets with emphasis on residence times   总被引：5，自引：5，他引：0  
Thirty‐two New Zealand coastal inlets are tentatively classified into seven groups with probable similar circulation patterns, based on ratios of their physical parameters: volume, tidal compartment, entrance width, surface area, length, and average width. Eighteen of these have a predominant tidal flow, shown from their small ratio (ß < 4) of tidal compartment to total volume, and the cross‐sectional areas of their entrances are controlled by the tidal flow: Moutere, Waimea, Aotea, Whanganui, Avon‐Heathcote, Tauranga, Parengarenga, Porirua‐Pauatahanui, Kawhia, Nelson, Rangaunu, Raglan, Whangarei, Bluff, Otago, Hokianga, Manukau, and Whangaruru. The other fourteen range from long narrow sounds with probable strong vertical circulation (e.g., Pelorus Sound) to large bays with strong mean horizontal circulations (e.g., Tasman and Hawke Bays).

Examples of residence time calculated in inlets with ß > 4 are given for Tasman Bay, a bay with a mean horizontal circulation, which has a residence time of 1–3 months, and Pelorus Sound, an inlet with a vertically complex circulation, which has a residence time of about 20 d.  相似文献   

9.
We used naturally occurring radium isotopes as tracers of water exchange in Apalachicola Bay, a shallow coastal-plain estuary in northwestern Florida. The bay receives fresh water and radium from the Apalachicola River, and mixes with Gulf of Mexico waters through four inlets. We deployed moored buoys with attached Mn-fibers at several stations throughout the estuary during two summer and two winter periods. After deployment for at least one tidal cycle we measured the ratio of the two short-lived radium isotopes 223Ra (half-life = 11 d) and 224Ra (3.6 d) to estimate “radium ages” of the water in the bay.During our four seasonal deployments the river discharge ranged from 338 to 1016 m3 s− 1. According to our calculations the water turnover time in the bay during these samplings ranged from 6 to 12 days. Age contours in the bay showed that winds and tides as well as river discharge influence the water movement and the residence time of freshwater in the bay. We also calculated the mean age of river water in the bay which was between 5 to 9 days during the studied periods. We suggest that this approach can be used to quantify transport processes of dissolved substances in the bay. For example, soluble nutrient or pollutant transport rates from a point source could be examined. We conclude that the radium age technique is well suited for flushing rate calculations in river dominated shallow estuaries.  相似文献   

10.
Seagrass landscapes are coastal environments that support diverse and abundant faunal communities. This study investigated infaunal assemblage patterns in fragmented and continuous Zostera muelleri habitat in southeastern New Zealand. Intertidal macroinvertebrate assemblages were examined in fragmented seagrass habitat (containing discrete patches varying in size from 1 to 200 m2) and continuous meadows (>1000 m2), in a small and a large tidal inlet. Community indices differed between seagrass habitat types and the total number of taxa was significantly lower at fragmented seagrass sites in one of the inlets. The total number of individuals and diversity were significantly different between fragmented and continuous seagrass habitat in both inlets, but diversity values showed inconsistent patterns between inlets. Multivariate analysis confirmed that different seagrass habitat types support distinct macrofaunal assemblages in each inlet and position on the shore was identified as the single most important variable explaining dissimilarities in assemblage compositions. These findings confirm the influence of seagrass habitat size on infaunal assemblages and also highlight the importance of spatial position of seagrass habitat in intertidal areas.  相似文献   

11.
象山港潮滩坡度对潮动力影响的数值研究   总被引：2，自引：0，他引：2  
象山港属于狭长型半封闭港湾，湾内分布有大面积潮滩。多年以来象山港内实施了大量海岸工程及养殖工程，湾内潮滩坡度发生了显著变化。基于非结构网格和有限体积数值模式（FVCOM）建立象山港三维潮动力模型，研究湾内不同区域潮滩坡度变化对象山港潮动力过程的影响机理。结果表明：潮滩坡度下降将增大湾内纳潮量，进而增大M2分潮振幅和迟角，反之则反。铁港潮滩坡度的减小（增大），将改变底部耗散项，进而增大（减小）M4分潮振幅。由于M2和M4分潮的振幅在湾顶较大，所以湾顶（铁港）潮滩坡度对象山港潮动力过程的影响明显大于侧岸（西沪港）。西沪港潮滩坡度对象山港潮动力过程的影响是局部的。铁港、西沪港潮滩坡度对湾内潮汐不对称、余流及潮能影响显著。铁港潮滩坡度的改变均会减弱湾内落潮占优程度。西沪港区域潮滩坡度的减小将减弱湾内落潮占优趋势，反之则反。铁港和西沪港潮滩坡度的减小，将增大余流大小及潮能密度，进而潮能耗散增大，反之则反。研究结果对河口海岸潮滩区域的工程建设及生态修复有重要参考价值。  相似文献   

12.
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.  相似文献   

13.
The “Furkert‐Heath” relationship for tidal inlet stability reviewed   总被引：1，自引：1，他引：0  
The “Furkert‐Heath” relationship is a commonly used method of assessing the stability of New Zealand inlets. However, the equation published by Heath in 1975 was incorrectly calculated which has led to misinterpretation of data in some cases. Recalculation resulted in a new linear relation, presented here, between the inlet gorge cross‐sectional area A and tidal prism O. Misuses of the “Furkert‐Heath” equation are identified including: extrapolating predictions beyond the data field; neglecting errors inherent in measurement of A and O; method of characterising sedimentation regime; neglecting confidence limits of data; using A‐O relationships as the sole indicator of inlet stability; and applying the relationship to inlets other than barrier‐enclosed inlets.  相似文献   

14.
Reynolds stress and TKE production in an estuary with a tidal bore   总被引：4，自引：0，他引：4  
We report new measurements of the turbulent properties of the flow in a tidally energetic estuarine channel of almost uniform cross-section. A high-frequency (1.2 MHz), bottom-mounted Acoustic Doppler Current Profiler (ADCP) has been used to observe the velocity field at a sampling rate of 10 Hz in parallel with measurements of the surface elevation by tide gauges. Our data have been analysed using the Variance Method to determine turbulent kinetic energy (TKE), shear stress and TKE production over the tidal cycle with a time resolution of 60 s. During the highly energetic but brief flood period, when the surface axial velocity reaches 2 m s−1, we observed large values of stress (>2 Pa) and shear production (5 W m−3). TKE is also input through the release of energy in the bore itself which results in a brief but intense injection of energy at the bore front with large transient TKE levels (100 J m−3). Subsequent input by shear production maintains TKE levels which are generally lower (20 J m−3) than the strong peak associated with the bore for the rest of the flood. On the ebb, the flow is relatively tranquil with maximum speeds 0.5 m s−1 and peak TKE production rates of 0.1 W m−3.The flow and elevation data have also been used to estimate the energy fluxes into and out of the estuary. Short (1 h), intense energy inputs (8 MW at springs) on the flood flow are largely balanced by longer, less intense seaward energy flow on the ebb. The net energy input is found to be 0.1 MW at springs which is consistent with estimates of upstream dissipation. Peak dissipation in the bore itself may exceed the mean energy input but it is active only for a small fraction of the tidal cycle and its average contribution does not exceed 12% of total dissipation.  相似文献   

15.
Dense aggregations of the hexactinellid sponge, Pheronema carpenteri, were encountered in the Porcupine Seabight at depths between about 1000 and 1300m. In restricted areas within this bathymetric range the sponges attain numerical abundances of more than 1.5m−2 and an estimated biomass of up to 372g m−2 wet weight or about 10g m−2 ash-free dry weight.These recently acquired samples, together with historical data, suggest that Pheronema occurs close to, but not within, regions of the upper continental slope where the bottom topography is expected to result in significant enhancement of the near-bottom tidal current velocities. It is suggested that the sponges may not be able to withstand the enhanced currents, but may nevertheless be dependent upon the resuspended or undeposited organic matter carried to them from these regions of increased tidal energy.  相似文献   

16.
Lugworms are important members of the macrobenthos of sheltered intertidal sediments, and this study assessed the abundance and distribution of Abarenicola affinis in Otago, southern New Zealand. Using a faecal cast:lugworm ratio (1.00:1.09) revealed a patchy distribution across inlets, with an overall mean abundance of 11.1 individuals/m2 (range: 3.8 to 21.3 individuals/m2). Distribution patterns varied among inlets, with lugworms mostly confined to the high intertidal zone, but spread across all intertidal zones in one inlet. The lugworm habitat was characterised by muddy to medium sand (55–233 µm mean grain size) with low organic matter (< 2%) and chlorophyll a (1–12 µg/g dry sediment) contents. Depending on the inlet, lugworm abundance was related to sediment parameters, indicating that their distribution across Otago inlets is habitat dependent. The present findings also indicate that factors other than those measured contribute to A. affinis distribution and abundance patterns in this region.  相似文献   

17.
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.  相似文献   

18.
Studies of mixing were done at the northern flank of Georges Bank in the summer and autumn of 1988. Two time-series of the evolution and intensity of microstructure were examined over a tidal period in the context of tidal forcing and the evolution of the density and velocity field at the site. From the CTD, ADCP and microstructure observations (EPSONDE) on Georges Bank, several interesting features of the mixing processes were found. High dissipation and diffusivity regions appear near the bottom of the Bank. Turbulence near the bottom is highest in intensity and reaches farthest from the bottom at peak tidal flow and diminishes in intensity and vertical extent as the flow decreases. The thickness of the bottom turbulent layer has its maximum value when the flow is strongest and the stratification is weakest. Characterization of the dissipation rate and turbulent diffusivities in respect to buoyancy frequency N, current shear S, Richardson Number Ri and ε/νN2 was done. Dissipation and χT showed little dependence on shear or N2 but decreased at larger Ri. χt was found to be higher in regions of higher N2 and increased as ε/νN2 increased. KT, K and Kν, were all highest near the bottom in excess of 10−2m2s−1 and decreased towards the surface. There was little suggestion of a dependence of mixing efficiency on S2, Ri or ε/νN2, but some indication that Γ decreases with decreasing N2.  相似文献   

19.
Through the water areas extracted from remote sensing images and the combination of the methods for establishing the formula for calculating tidal influx with tidal data, the tidal influx of the Haikou Bay, Hainan Province was found to be 5.14×107m3 in 1990, 5.80×107m3 in 1984 and 5.05×107m3 in 1965, respectively.After the analysis of the morphological and tidal range factors which determine tidal influx, this paper presents the trend of the changes in tidal influx caused by the changes in the morphological factors of the Haikou Bay.It is found that a decreasing trend was shown with a depressive rate of 2×10-3during the period from 1965 to 1984, and an increasing trend with an incremental rate of 1×10-3 during the period of 1984-1990.The main reason for the appearance of the decreasing trend before 1984 is the natural deposition and silting-up of the bay sediments; after 1984, the dredging and expansion of the Haikou Port and the Haikou New Port which caused an increase in water area at the mean low tide are the leading factor which causes the increase in tidal influx.  相似文献   

20.
Simulations of the time and depth-dependent salinity and current fields of the Columbia River Estuary have been performed using a multi-channel, laterally averaged estuary model. The study simulated two periods. The first, in October 1980, with low riverflow of about 4,000m3s−1, which showed marked changes in the salinity intrusion processes between neap and spring tides; and second, in spring 1981, with high riverflow varying between 7,000 and 15,000m3s−1, which showed the rapid response of the salinity intrusion to changes in riverflow and that vertical mixing did not change character with increasing tidal energy because of the maintenance of stratification by freshwater flow. An extreme low flow simulation (riverflow of 2,000m3s−1) showed a more partially mixed character of the estuary channels with tidal dispersion of salt across the Taylor Sands from the North Channel to the upper reaches of the Navigation Channel. Asymmetries in the non-linear tidal mean flows, in the flood and ebb circulations, and salinity intrusion characteristics between the two major channels were observed at all riverflows. The model confirms Jay and Smith's (1990) analysis of the circulation processes in that tidal advection of salt by the vertically sheared tidal currents is the dominant mechanism by which the salinity intrusion is maintained against large freshwater flows. An accurate finite-difference method, which minimized numerical dispersion, was used for the advection terms and was an important component in reasonably simulating the October neap-spring differences in the salinity intrusion. The simulations compare favorably with elevation, current and salinity time series observations taken during October 1980 and spring 1981.  相似文献   

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