共查询到20条相似文献，搜索用时 31 毫秒
1.
The Dee Estuary, at the NW English–Welsh border, is a major asset, supporting: one of the largest wildlife habitats in Europe, industrial importance along the Welsh coastline and residential and recreational usage along the English coast. Understanding of the residual elevation is important to determine the total water levels that inundate intertidal banks, especially during storms. Whereas, improved knowledge of the 3D residual circulation is important in determining particle transport pathways to manage water quality and morphological change. Using mooring data obtained in February–March 2008, a 3D modelling system has been previously validated against in situ salinity, velocity, elevation and wave observations, to investigate the barotropic–baroclinic wave interaction within this estuary under full realistic forcing. The system consists of a coupled circulation-wave-turbulence model (POLCOMS-WAM-GOTM). Using this modelling system the contribution of different processes and their interactions to the monthly residuals in both elevation and circulation is now assessed. By studying a tidally dominated estuary under wave influence, it is found that baroclinicity induced by a weak river flow has greater importance in generating a residual circulation than the waves, even at the estuary mouth. Although the monthly residual circulation is dominated by tidal and baroclinic processes, the residual estuarine surface elevation is primarily influenced by the seasonal external forcing to the region, with secondary influence from the local wind conditions. During storm conditions, 3D radiation stress becomes important for both elevation and circulation at the event scale but is found here to have little impact over monthly time scales. 相似文献
2.
Several field studies in bays and estuaries have revealed pronounced subsurface maxima in the vertical profiles of the current amplitude of the principal tidal harmonic, or of its vertical shear, over the water column. To gain fundamental understanding about these phenomena, a semi-analytical model is designed and analysed, with focus on the sensitivity of the vertical structure of the tidal current amplitude to formulations of the vertical shape of the eddy viscosity. The new analytical solutions for the tidal current amplitude are used to explore their dependence on the degree of surface mixing, the vertical shape of eddy viscosity in the upper part of the water column and the density stratification. Sources of surface mixing are wind and whitecapping. Results show three types of current amplitude profiles of tidal harmonics, characterised by monotonically decreasing shear towards the surface, “surface jumps” (vertical shear of tidal current amplitude has a subsurface maximum) and “subsurface jets” (maximum tidal current amplitude below the surface), respectively. The “surface jumps” and “subsurface jets” both occur for low turbulence near the surface, whilst additionally the surface jumps only occur if the eddy viscosity in the upper part of the water column decreases faster than linearly to the surface. Furthermore, “surface jumps” take place for low density stratification, while and “subsurface jets” occur for high density stratification. The physics causing the presence of surface jumps and subsurface jets is also discussed. 相似文献
3.
Angela M. Gurnell 《地球表面变化过程与地形》1997,22(10):967-985
Major hydraulic discontinuities along lowland rivers may be caused by water impoundment behind weirs, by tributary floods, and by tides. An analysis of the geometry of 122 surveyed channel cross-sections located on an 18 km reach of the lower River Dee identifies up to three levels in the bank profile representing minima in the width:mean depth ratio, and distinct changes in the geometric properties of the channel to these three levels in a downstrem direction and within four stretches influenced to varying degrees by hydraulic discontinuities created by a weir and by tidal overtopping of the weir. Simple modelling combined with field observations suggest possible processes that may control the observed changes in channel morphology. © 1997 John Wiley & Sons, Ltd. 相似文献
4.
5.
An irregular mesh model of the west coast of Britain is used to examine the sensitivity of tidal residuals to mesh resolution in the region. Computed residuals are compared with earlier published results determined with a high resolution (1 km grid) finite difference model of the eastern Irish Sea. Initial calculations show that tidal residuals are largest in nearshore regions particularly in the vicinity of headlands. Local refinement of the mesh in these regions leads to a more detailed picture of the flow field, particularly adjacent to the coast. Although large scale offshore features of the flow can be resolved using the high resolution finite difference model, such an approach leads to a “stair case” representation of the coastal boundary with an adjacent near coastal region of spurious tidal residuals. By using an irregular mesh that follows the coast, this effect is removed. In the Mersey river region the tidal residual is resolved with a mesh resolution of 120 m, although calculations show that its distribution is particularly sensitive to small scale features of the topography. A variable mesh that can accurately represent the lateral variations in river width and details of topography in both the nearshore and estuarine environment appears essential in modelling the coastal spread of freshwater plumes from rivers and pollutants discharged into the near coastal environment. 相似文献
6.
Seree Supharatid 《水文研究》2003,17(15):3085-3099
This paper presents the applicability of neural network (NN) modelling for forecasting and filtering problems. The multilayer feedforward (MLFF) network was first constructed to forecast the tidal‐level variations at the mouth of the River Chao Phraya in Thailand. Unlike the well‐known conventional harmonic analysis, the NN model uses a set of previous data for learning and then forecasting directly the time‐series of tidal levels. It was found that lead time of 1 to 24 hourly tidal levels can be predicted successfully using only a short‐time hourly learning data. The MLFF network was further used to establish a stage–discharge relationship for the tidal river. The results show a considerably better performance of the NN model over the conventional models. In addition, the stage–discharge relationship obtained by the NN model can indicate reasonably well the important behaviour of the tidal influences. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
Alexander Port Klaus-Werner Gurgel Joanna Staneva Johannes Schulz-Stellenfleth Emil V. Stanev 《Ocean Dynamics》2011,61(10):1567-1585
Tidal and wind-driven surface currents in the German Bight between shallow mudflats of the North Frisian islands and the island
of Helgoland are studied using coastal high-frequency radar (HFR) observations and hindcasts from a primitive equation numerical
model. The setup of the observational system is described, and estimates of expected measurement errors are given. A quantitative
comparison of numerical model results and observations is performed. The dominant tidal components are extracted from the
two data sources using tidal harmonic analysis and the corresponding tidal ellipses are defined. Results show that the spatial
patterns of different tidal ellipse parameters are consistent in the two data sets. Model sensitivity studies with constant
and variable salinity and temperature distributions are used to study density-related mechanisms of circulation. Furthermore,
the role of the surface wind field in driving the German Bight circulation is investigated using the complex correlation between
wind and surface current vectors. The observed change of the respective correlation patterns from the coastal to open ocean
is shown to be due to a combination of density effects, the coastline and topography. The overall conclusion is that HFR observations
resolve the small-scale and rapidly evolving characteristics of coastal currents well in the studied area and could present
an important component for regional operational oceanography when combined with numerical modelling. Some unresolved issues
associated with the complex circulation and large instability of circulation in front of the Elbe River Estuary justify further
considerations of this area using dedicated surveys and modelling efforts. 相似文献
8.
Daniel J. Twigt Erik D. De Goede Firmijn Zijl Dirk Schwanenberg Alex Y. W. Chiu 《Ocean Dynamics》2009,59(6):1077-1093
Within the hydrodynamic modelling community, it is common practice to apply different modelling systems for coastal waters
and river systems. Whereas for coastal waters 3D finite difference or finite element grids are commonly used, river systems
are generally modelled using 1D networks. Each of these systems is tailored towards specific applications. Three-dimensional
coastal water models are designed to model the horizontal and vertical variability in coastal waters and are less well suited
for representing the complex geometry and cross-sectional areas of river networks. On the other hand, 1D river network models
are designed to accurately represent complex river network geometries and complex structures like weirs, barrages and dams.
A disadvantage, however, is that they are unable to resolve complex spatial flow variability. In real life, however, coastal
oceans and rivers interact. In deltaic estuaries, both tidal intrusion of seawater into the upstream river network and river
discharge into open waters play a role. This is frequently approached by modelling the systems independently, with off-line
coupling of the lateral boundary forcing. This implies that the river and the coastal model run sequentially, providing lateral
discharge (1D) and water level (3D) forcing to each other without the possibility of direct feedback or interaction between
these processes. An additional disadvantage is that due to the time aggregation usually applied to exchanged quantities, mass
conservation is difficult to ensure. In this paper, we propose an approach that couples a 3D hydrodynamic modelling system
for coastal waters (Delft3D) with a 1D modelling system for river hydraulics (SOBEK) online. This implies that contrary to
off-line coupling, the hydrodynamic quantities are exchanged between the 1D and 3D domains during runtime to resolve the real-time
exchange and interaction between the coastal waters and river network. This allows for accurate and mass conserving modelling
of complex coastal waters and river network systems, whilst the advantages of both systems are maintained and used in an optimal
and computationally efficient way. The coupled 1D–3D system is used to model the flows in the Pearl River Delta (Guangdong,
China), which are determined by the interaction of the upstream network of the Pearl River and the open waters of the South
China Sea. The highly complex upstream river network is modelled in 1D, simulating river discharges for the dry and wet monsoon
periods. The 3D coastal model simulates the flow due to the external (ocean) periodic tidal forcing, the salinity distribution
for both dry and wet seasons, as well as residual water levels (sea level anomalies) originating from the South China Sea.
The model is calibrated and its performance extensively assessed against field measurements, resulting in a mean root mean
square (RMS) error of below 6% for water levels over the entire Pearl River Delta. The model also represents both the discharge
distribution over the river network and salinity transport processes with good accuracy, resolving the discharge distribution
over the main branches of the river network within 5% of reported annual mean values and RMS errors for salinity in the range
of 2 ppt (dry season) to 5 ppt (wet season). 相似文献
9.
Conceptual models of circulation theorise that the dominant forces controlling estuarine circulation are freshwater discharge from the riverine section (landward), tidal forcing from the ocean boundary, and gravitational circulation resulting from along-estuary gradients in density. In micro-tidal estuaries, sub-tidal water level changes (classified as those with periods between 3 and 10 days) with amplitudes comparable to the spring tidal range can significantly influence the circulation and distribution of water properties. Field measurements obtained from the Swan River Estuary, a diurnal, micro-tidal estuary in south-western Australia, indicated that sub-tidal water level changes at the ocean boundary were predominantly from remotely forced continental shelf waves (CSWs). The sub-tidal water levels had maximum amplitudes of 0.8 m, were comparable to the maximum tidal range of 0.6 m, propagated into the estuary to its tidal limit, and modified water levels in the whole estuary over several days. These oscillations dominated the circulation and distribution of water properties in the estuary through changing the salt wedge location and increasing the bottom water salinity by 7 units over 3 days. The observed salt wedge excursion forced by CSW was up to 5 km, whereas the maximum tidal excursion was 1.2 km. The response of the residual currents and the salinity distribution lagged behind the water level changes by ∼24 h. It was proposed that the sub-tidal forcing at the ocean boundary, which changed the circulation, salinity, and dissolved oxygen in the upper estuary, was due to a combination of two processes: (1) a gravity current generated by a process similar to a lock exchange mechanism and (2) amplified along-estuary density gradients in the upper estuary, which enhanced the gravitational circulation in the estuary. The salt intrusions under the sub-tidal forcing caused the rapid movement of anoxic water upstream, with significant implications for water quality and estuarine health. 相似文献
10.
DSQ水管仪和SSQ-2I水平摆效能对比研究 总被引：1，自引：1，他引：0
SSQ-2I型水平摆仪器和DSQ水管仪同属倾斜类前兆仪器,两者观测原理不同,但观测物理量一致.相对于水管仪而言,SSQ-2I型水平摆属于新型仪器,有关其运行效能的评价很少.延庆地震台从2007年开始两种仪器同场地观测,通过年变幅度、滤波残差、周期分析、Venedikov调和分析、相关性分析、抗干扰能力等角度,对两种仪器... 相似文献
11.
In urban drainage modelling, uncertainty analysis is of undoubted necessity. However, uncertainty analysis in urban water-quality modelling is still in its infancy and only few studies have been carried out. Therefore, several methodological aspects still need to be experienced and clarified especially regarding water quality modelling. The use of the Bayesian approach for uncertainty analysis has been stimulated by its rigorous theoretical framework and by the possibility of evaluating the impact of new knowledge on the modelling predictions. Nevertheless, the Bayesian approach relies on some restrictive hypotheses that are not present in less formal methods like the Generalised Likelihood Uncertainty Estimation (GLUE). One crucial point in the application of Bayesian method is the formulation of a likelihood function that is conditioned by the hypotheses made regarding model residuals. Statistical transformations, such as the use of Box–Cox equation, are generally used to ensure the homoscedasticity of residuals. However, this practice may affect the reliability of the analysis leading to a wrong uncertainty estimation. The present paper aims to explore the influence of the Box–Cox equation for environmental water quality models. To this end, five cases were considered one of which was the “real” residuals distributions (i.e. drawn from available data). The analysis was applied to the Nocella experimental catchment (Italy) which is an agricultural and semi-urbanised basin where two sewer systems, two wastewater treatment plants and a river reach were monitored during both dry and wet weather periods. The results show that the uncertainty estimation is greatly affected by residual transformation and a wrong assumption may also affect the evaluation of model uncertainty. The use of less formal methods always provide an overestimation of modelling uncertainty with respect to Bayesian method but such effect is reduced if a wrong assumption is made regarding the residuals distribution. If residuals are not normally distributed, the uncertainty is over-estimated if Box–Cox transformation is not applied or non-calibrated parameter is used. 相似文献
12.
The morphodynamics of shallow, vertically well-mixed estuaries, characterised by tidal flats and deeper channels, have been
investigated. This paper examines what contributes to flood/ebb-dominant sediment transport in localised regions through a
2D model study (using the TELEMAC modelling system). The Dyfi Estuary in Wales, UK has been used as a case study and, together
with idealised estuary shapes, shows that shallow water depths lead to flood dominance in the inner estuary whilst tidal flats
and deep channels cause ebb dominance in the outer estuary. For medium sands and with an artificially ‘flattened’ bathymetry
(i.e. no tidal flats), the net sediment transport switches from ebb-dominant to flood-dominant where the parameter a/h (local tidal amplitude ÷ local tidally averaged water depth) exceeds 1.2. Sea level rise will reduce this critical value
of a/h and also reduce the ebb-directed sediment transport significantly, leading to a flood-dominated estuarine system. A similar
pattern, albeit with greater transport, was simulated with tidal flats included and also with a reduced grain size. This suggests
that analogous classifications for flood/ebb asymmetry of the tide in estuaries as a whole may not represent the local sediment
transport in sufficient detail. Through the Dyfi simulations, the above criterion involving a/h is shown to be complicated further by augmented flow past a spit at the estuary mouth which gives rise to a self-maintaining
scour hole. Simulations of one year of bed evolution in an idealised flat-bottomed estuary, including tidal flow past a spit,
recreate the flood/ebb dominance on either side of the spit and the formation of a scour hole in between. The erosion rate
at the centre of the hole is reduced as the hole deepens, suggesting the establishment of a self-maintaining equilibrium state. 相似文献
13.
The validation and subsequent application of the current three-dimensional numerical hydrodynamic model of Chesapeake Bay is presented. The numerical model solves conservation equations for water mass, momentum, salinity, and heat on a boundary-fitted grid in the horizontal plane and a Cartesian z-grid in the vertical. A generalized ADI finite difference scheme is employed in conjunction with mode splitting technique, solving external and the internal modes. The 10-year boundary conditions including tide, slinity, temperature, wind, heat exchange coefficient, river and non-point source flows were constructed. Model validation was accomplished by demonstrating the model's ability to reproduce observed data over time scales ranging from tidal to seasonal periods. The major parameters compared include tidal elevation, intra-tidal and residual velocities, salinity, temperature, stratification, and flux calculated through the Bay mouth.After validation, the model was applied to simulate bay hydrodynamics for the 10 years of 1985–94. These results were used to drive the three-dimensional water quality model of Chesapeake Bay, which is discussed in a companion paper. 相似文献
14.
The basic features of the hydrological regime and morphodynamics of the mouth area of the Garonne and Dordogne rivers and its part, i.e., the Gironde Estuary, are discussed. The main attention is given to the analysis of water circulation and sediment dynamics in the Gironde Estuary under the joint impact of seasonal river flow and tidal fluctuations. In addition to this, the estuary evolution during the Holocene period and regularities of present-day erosional and accumulative processes are characterized. 相似文献
15.
16.
A new method of integrating satellite remote sensing data and inundation models allows the mapping of extensive tidal mudflats
in a sub-Arctic estuary, Cook Inlet (CI), Alaska. The rapid movement of the shorelines in CI due to the large tides (~10 m
range) is detected from a series of Landsat imagery taken at different tidal stages, whereas GIS tools are used to identify
the water coverage in each satellite image and to extract the coordinates of the shoreline. Then, water level along the shoreline
for each satellite image is calculated from the observed water level at Anchorage and the statistics of an inundation model.
Several applications of the analysis are demonstrated: 1. studying the dynamics of a tidal bore and the flood/ebb processes,
2. identifying climatic changes in mudflats morphology, and 3. mapping previously unobserved mudflat topographies in order
to improve inundation models. The method can be used in other regions to evaluate models and improve predictions of catastrophic
floods such as those associated with hurricane storm surges and tsunamis. 相似文献
17.
Scales and structure of frontal adjustment and freshwater export in a region of freshwater influence
Sea surface temperature satellite imagery and a regional hydrodynamic model are used to investigate the variability and structure
of the Liverpool Bay thermohaline front. A statistically based water mass classification technique is used to locate the front
in both data sets. The front moves between 5 and 35 km in response to spring–neap changes in tidal mixing, an adjustment that
is much greater than at other shelf-sea fronts. Superimposed on top of this fortnightly cycle are semi-diurnal movements of
5–10 km driven by flood and ebb tidal currents. Seasonal variability in the freshwater discharge and the density difference
between buoyant inflow and more saline Irish Sea water give rise to two different dynamical regimes. During winter, when cold
inflow reduces the buoyancy of the plume, a bottom-advected front develops. Over the summer, when warm river water provides
additional buoyancy, a surface-advected plume detaches from the bottom and propagates much larger distances across the bay.
Decoupled from near-bed processes, the position of the surface front is more variable. Fortnightly stratification and re-mixing
over large areas of Liverpool Bay is a potentially important mechanism by which freshwater, and its nutrient and pollutant
loads, are exported from the coastal plume system. Based on length scales estimated from model and satellite data, the erosion
of post-neap stratification is estimated to be responsible for exporting approximately 19% of the fresh estuarine discharge
annually entering the system. Although the baroclinic residual circulation makes a more significant contribution to freshwater
fluxes, the episodic nature of the spring–neap cycle may have important implications for biogeochemical cycles within the
bay. 相似文献
18.
We present sea level observations derived from the analysis of signal-to-noise ratio (SNR) data recorded by five coastal GPS stations. These stations are located in different regions around the world, both in the northern and in the southern hemisphere, in different multipath environments, from rural coastal areas to busy harbors, and experience different tidal ranges.The recorded SNR data show periodic variations that originate from multipath, i.e. the interference of direct and reflected signals. The general assumption is that for satellite arcs facing the open sea, the rapid SNR variations are due to reflections off the sea surface. The SNR data recorded from these azimuth intervals were analyzed by spectral analysis with two methods: a standard analysis method assuming a static sea level during a satellite arc and an extended analysis method assuming a time dependent sea level during a satellite arc.The GPS-derived sea level results are compared to sea level records from co-located traditional tide gauges, both in the time and in the frequency domain. The sea level time series are highly correlated with correlation coefficients to the order of 0.89–0.99. The root-mean-square (RMS) difference is 6.2 cm for the station with the lowest tidal range of 165 cm and 43 cm for the station with the highest tidal range of 772 cm. The relative accuracy, defined as the ratio of RMS and tidal range, is between 2.4% and 10.0% for all stations.Comparing the standard analysis method and the extended analysis method, the results based on the extended analysis method agree better with the independent tide gauge records for the stations with a high tidal range. For the station with the highest tidal range (772 cm), the RMS is reduced by 47% when using the extended analysis method. Furthermore, the results also indicate that the standard analysis method, assuming a static sea level, can be used for stations with a tidal range of up to about 270 cm, without performing significantly worse than the extended analysis method.Tidal amplitudes and phases are derived by harmonic analysis of the sea level records. Again, a high level of agreement is observed between the tide gauge and the GPS-derived results. Comparing the GPS-derived results, the results based on the extended analysis method show a higher degree of agreement with the traditional tide gauge results for stations with larger tidal ranges. Spectral analysis of the residuals after the harmonic analysis reveals remaining signal power at multiples of the draconitic day. This indicates that the observed SNR data are to some level disturbed by additional multipath signals, in particular for GPS stations that are located in harbors. 相似文献
19.
从水位观测数据中排除非构造因素影响的状态空间分析方法 总被引：1，自引：0，他引：1
为了更有效地利用地下水位观测数据开展地震预测,需要排除其它因素对地下水位的干扰.降雨、气压和潮汐是影响地下水位的3个重要的非构造应力因素,对此建立状态空间模型以提取与地震有关的水文异常.这个模型把观测到的地下水位时间序列分解为气压响应、潮汐响应、降雨响应、噪声因子和水位残差5个因子,运用状态空间分析方法,从地下水位的实际观测数据中分解出气压、潮汐和降雨等主要的非构造因素对地下水位的影响,从而得到构造应力影响下的地下水位数据,以便于提取与地震活动有关的异常信息. 相似文献
20.
A three-dimensional hydrodynamic model is used to investigate intra-tidal and spring–neap variations of turbulent mixing, stratification and residual circulation in the Chesapeake Bay estuary. Vertical profiles of salinity, velocity and eddy diffusivity show a marked asymmetry between the flood and ebb tides. Tidal mixing in the bottom boundary layer is stronger and penetrates higher on flood than on ebb. This flood–ebb asymmetry results in a north–south asymmetry in turbulent mixing because tidal currents vary out of phase between the lower and upper regions of Chesapeake Bay. The asymmetric tidal mixing causes significant variation of salinity distribution over the flood–ebb tidal cycle but insignificant changes in the residual circulation. Due to the modulation of tidal currents over the spring–neap cycle, turbulent mixing and vertical stratification show large fortnightly and monthly fluctuations. The stratification is not a linear function of the tidal-current amplitude. Strong stratification is only established during those neap tides when low turbulence intensity persists for several days. Residual circulation also shows large variations over the spring–neap cycle. The tidally averaged residual currents are about 50% stronger during the neap tides than during the spring tides. 相似文献