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1.
A variable mesh finite element model of the Irish and Celtic Sea regions with/without the inclusion of the Mersey estuary is used to examine the influence of grid resolution and the Mersey upon the higher harmonics of the tide in the region. Comparisons are made with observations and published results from finite difference models of the area. Although including a high resolution representation of the Mersey had little effect upon computed tides in the western Irish Sea it had a significant effect upon tidal currents in the eastern Irish Sea. In addition the higher harmonics of the M2 tide in near-shore regions of the eastern Irish Sea particularly the Solway and Mersey estuary together with Morecambe Bay showed significant small scale variability. The Mersey was used to test the sensitivity to including estuaries because high resolution accurate topography was available. The results presented here suggest that comparable detailed topographic data sets are required in all estuaries and near-shore regions. In addition comparisons clearly show the need for an unstructured grid model of the region that can include all the estuaries. Such an unstructured grid solution was developed here within a finite element approach, although other methods in particular the finite volume, or coordinate transformations/curvilinear grids and nesting could be applied. 相似文献
2.
Three finite element codes, namely TELEMAC, ADCIRC and QUODDY, are used to compute the spatial distributions of the M2, M4 and M6 components of the tide in the sea region off the west coast of Britain. This region is chosen because there is an accurate
topographic dataset in the area and detailed open boundary M2 tidal forcing for driving the model. In addition, accurate solutions (based upon comparisons with extensive observations)
using uniform grid finite difference models forced with these open boundary data exist for comparison purposes. By using boundary
forcing, bottom topography and bottom drag coefficients identical to those used in an earlier finite difference model, there
is no danger of comparing finite element solutions for “untuned unoptimised solutions” with those from a “tuned optimised
solution”. In addition, by placing the open boundary in all finite element calculations at the same location as that used
in a previous finite difference model and using the same M2 tidal boundary forcing and water depths, a like with like comparison of solutions derived with the various finite element
models was possible. In addition, this open boundary was well removed from the shallow water region, namely the eastern Irish
Sea where the higher harmonics were generated. Since these are not included in the open boundary, forcing their generation
was determined by physical processes within the models. Consequently, an inter-comparison of these higher harmonics generated
by the various finite element codes gives some indication of the degree of variability in the solution particularly in coastal
regions from one finite element model to another. Initial calculations using high-resolution near-shore topography in the
eastern Irish Sea and including “wetting and drying” showed that M2 tidal amplitudes and phases in the region computed with TELEMAC were in good agreement with observations. The ADCIRC code
gave amplitudes about 30 cm lower and phases about 8° higher. For the M4 tide, in the eastern Irish Sea amplitudes computed with TELEMAC were about 4 cm higher than ADCIRC on average, with phase
differences of order 5°. For the M6 component, amplitudes and phases showed significant small-scale variability in the eastern Irish Sea, and no clear bias between
the models could be found. Although setting a minimum water depth of 5 m in the near-shore region, hence removing wetting
and drying, reduced the small-scale variability in the models, the differences in M2 and M4 tide between models remained. For M6, a significant reduction in variability occurred in the eastern Irish Sea when a minimum 5-m water depth was specified. In
this case, TELEMAC gave amplitudes that were 1 cm higher and phases 30° lower than ADCIRC on average. For QUODDY in the eastern
Irish Sea, average M2 tidal amplitudes were about 10 cm higher and phase 8° higher than those computed with TELEMAC. For M4, amplitudes were approximately 2 cm higher with phases of order 15° higher in the northern part of the region and 15° lower
in the southern part. For M6 in the north of the region, amplitudes were 2 cm higher and about 2 cm lower in the south. Very rapid M6 tidal-phase changes occurred in the near-shore regions. The lessons learned from this model inter-comparison study are summarised
in the final section of the paper. In addition, the problems of performing a detailed model–model inter-comparison are discussed,
as are the enormous difficulties of conducting a true model skill assessment that would require detailed measurements of tidal
boundary forcing, near-shore topography and precise knowledge of bed types and bed forms. Such data are at present not available. 相似文献
3.
An unstructured mesh model of the west coast of Britain, covering the same domain and using topography and open boundary forcing
that are identical to a previous validated uniform grid finite difference model of the region, is used to compare the performance
of a finite volume (FV) and a finite element (FE) model of the area in determining tide–surge interaction in the region. Initial
calculations show that although qualitatively both models give comparable tidal solutions in the region, comparison with observations
shows that the FV model tends to under-estimate tidal amplitudes and hence background tidal friction in the eastern Irish
Sea. Storm surge elevations in the eastern Irish Sea due to westerly, northerly and southerly uniform wind stresses computed
with the FV model tend to be slightly higher than those computed with the FE model, due to differences in background tidal
friction. However, both models showed comparable non-linear tide–surge interaction effects for all wind directions, suggesting
that they can reproduce the extensive tide–surge interaction processes that occur in the eastern Irish Sea. Following on from
this model comparison study, the physical processes contributing to surge generation and tide–surge interaction in the region
are examined. Calculations are performed with uniform wind stresses from a range of directions, and the balance of various
terms in the hydrodynamic equations is examined. A detailed comparison of the spatial variability of time series of non-linear
bottom friction and non-linear momentum advection terms at six adjacent nodes at two locations in water depths of 20 and 6 m
showed some spatial variability from one node to another. This suggests that even in the near coastal region, where water
depths are of the order of 6 m and the mesh is fine (of order 0.5 km), there is significant spatial variability in the non-linear
terms. In addition, distributions of maximum bed stress due to tides and wind forcing in nearshore regions show appreciable
spatial variability. This suggests that intensive measurement campaigns and very high-resolution mesh models are required
to validate and reproduce the non-linear processes that occur in these regions and to predict extreme bed stresses that can
give rise to sediment movement. High-resolution meshes will also be required in pollution transport problems. 相似文献
4.
Storm surge computations for the west coast of Britain using a finite element model (TELEMAC) 总被引：1，自引：1，他引：0
An unstructured mesh finite element model of the sea region off the west coast of Britain is used to examine the storm surge event of November 1977. This period is chosen because accurate meteorological data to drive the model and coastal observations for validation purposes are available. In addition, previous published results from a coarse-grid (resolution 7 km) finite difference model of the region and high-resolution (1 km) limited area (namely eastern Irish Sea) model are available for comparison purposes. To enable a “like with like” comparison to be made, the finite element model covers the same domain and has the same meteorological forcing as these earlier finite difference models. In addition, the mesh is based on an identical set of water depths. Calculations show that the finite element model can reproduce both the “external” and “internal” components of the surge in the region. This shows that the “far field” (external) component of the surge can accurately propagate through the irregular mesh, and the model responds accurately, without over- or under-damping, to local wind forcing. Calculations show significant temporal and spatial variability in the surge in close agreement with that found in earlier finite difference calculations. In addition, root mean square errors between computed and observed surge are comparable to those found in previous finite different calculations. The ability to vary the mesh in nearshore regions reveals appreciable small-scale variability that was not found in the previous finite difference solutions. However, the requirement to perform a “like with like” comparison using the same water depths means that the full potential of the unstructured grid model to improve resolution in the nearshore region is inhibited. This is clearly evident in the Mersey estuary region where a higher resolution unstructured mesh model, forced with uniform winds, had shown high topographic variability due to small-scale variations in topography that are not resolved here. Despite the lack of high resolution in the nearshore region, the model showed results that were consistent with the previous storm surge models of the region. Calculations suggest that to improve on these earlier results, a finer nearshore mesh is required based upon accurate nearshore topography. 相似文献
5.
An unstructured mesh tidal model of the west coast of Britain, covering the Celtic Sea and Irish Sea is used to compare tidal distributions computed with finite element (FE) and finite volume (FV) models. Both models cover an identical region, use the same mesh, and have topography and tidal boundary forcing from a finite difference model that can reproduce the tides in the region. By this means, solutions from both models can be compared without any bias towards one model or another. Two-dimensional calculations show that for a given friction coefficient, there is more damping in the FV model than the FE model. As bottom friction coefficient is reduced, the two models show comparable changes in tidal distributions. In terms of mesh resolution, calculations show that for the M2 tide, the mesh is sufficiently fine to yield an accurate solution over the whole domain. However, in terms of higher harmonics of the tide, in particular the M6 component, its small-scale variability in near-shore regions which is comparable to the mesh of the model, suggests that the mesh resolution is insufficient in the near-coastal regions. Even with a finer mesh in these areas, without detailed bottom topography and a spatial varying friction depending on bed types and bed forms, which is not available, model skill would probably not be improved. In addition in the near-shore region, as shown in the literature, the solution is sensitive to the form of the wetting/drying algorithm used in the model. Calculations with a 3D version of the FV model show that for a given value of k, damping is reduced compared to the 2D version due to the differences in bed stress formulation, with the 3D model yielding an accurate tidal distribution over the region. 相似文献
6.
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
7.
The problem of resolving or parameterising small-scale processes in oceanographic models and the extent to which small-scale
effects influence the large scale are briefly discussed and illustrated for a number of cases. For tides and surges in near-shore
regions, the advantages of using a graded mesh to resolve coastal and estuarine small-scale features are demonstrated in terms
of a west coast of Britain unstructured mesh model. The effect of mesh resolution upon the accuracy of the overall solution
is illustrated in terms of a finite element model of the Irish Sea and Mersey estuary. For baroclinic motion at high Froude
number, the effect of resolving small-scale topography within a non-hydrostatic model is illustrated in terms of tidally induced
mixing at a single sill, or two closely spaced sills. The question of how to parameterise small-scale non-linear interaction
processes that lead to significant mixing, in a form suitable for coarser grid hydrostatic models, is briefly considered.
In addition, the importance of topographically induced mixing that occurs in the oceanic lateral boundary layer, namely, the
shelf edge upon the large-scale ocean circulation is discussed together with the implications for coarse grid oceanic climate
models. The use of unstructured grids in these models to enhance resolution in shelf-edge regions in a similar manner to that
used in storm surge models to enhance near coastal resolution is suggested as a suitable “way forward” in large-scale ocean
circulation modelling. 相似文献
8.
The storm surge period of 13–16 November 1977 when there was a major positive surge followed by a negative surge in the Irish
Sea is investigated using a two-dimensional unstructured mesh model of the west coast of Britain. The model accounts for tidal
and external surge forcing across its open boundaries which are situated in the Celtic Sea and off the west coast of Scotland.
Although this period has been examined previously using a uniform finite-difference model, and a finite element model, neither
of these could resolve the Mersey estuary which is the focus of the present study. By using a finite element model with very
high mesh resolution within the Mersey, the spatial variability of surge elevations and currents within the Mersey to rapidly
changing surge dynamics can be examined. The mesh in the model varies from about 7 km in deep water, to the order of 100 m
in the Mersey, with the largest mesh length reaching 17 km in deep offshore regions, and smallest of order 26 m occurring
in shallow coastal regions of the Mersey estuary. The model accounts for wetting/drying which occurs in shallow water coastal
areas. Calculations showed that during the positive surge period, the amplitude and speed of propagation of the surge was
largest in the deep water channels. This gave rise to significant spatial variability of surge elevations and currents within
the estuary. As wind stresses decreased over the Irish Sea, a negative surge occurred over Liverpool Bay and at the entrance
to the Mersey. However, within the Mersey there was a local positive surge which continued to propagate down the estuary.
This clearly showed that although the large scale response of the Irish Sea to changing wind fields occurred rapidly, the
response in the Mersey was much slower. These calculations with a west coast variable mesh model that included a high-resolution
representation of the Mersey revealed for the first time how elevations and currents within the Mersey responded to Irish
Sea surges that rapidly changed from positive to negative. 相似文献
9.
An unstructured grid storm surge model of the west coast of Britain, incorporating a high-resolution representation of the
Mersey estuary is used to examine storm surge dynamics in the region. The focus of the study is the major surge that occurred
during the period 11–14 November 1977, which has been investigated previously using uniform grid finite difference models
and a finite element model of the west coast of Britain. However, none of these models included the Mersey estuary. Comparison
of solutions in the eastern Irish Sea with those computed with these earlier models showed that, away from the Liverpool Bay
region, the inclusion of the Mersey estuary had little effect. However, at the entrance to the Mersey, its inclusion did influence
the solution. By including a detailed representation of the Mersey estuary within the model, it was possible to conduct a
detailed study of storm surge propagation in the Mersey, which had never previously been performed. This detailed study showed
for the first time that the surge’s temporal variability within the estuary is influenced by surge elevation at its entrance.
This varies with time as a function of spatial and temporal variations of wind stress over the west coast of Britain. Within
the Mersey, calculations show that the spatial variability is mainly determined by changes in bottom topography, which had
not been included in earlier finite difference models. However, since water depth is influenced by variations in tidal elevation,
this, together with tide surge interaction through bottom friction and momentum advection, influences the surge. The ability
of the finite element model to vary the mesh in near-shore regions to such an extent that it can resolve the Mersey and hence
the impact of the Mersey estuary upon the Liverpool Bay circulation shows that it has distinct advantages over earlier finite
difference models. In the absence of detailed measurements within the Mersey at the time of the surge, it was not possible
to validate predicted surge elevations within the Mersey. However, significant insight into physical processes influencing
the surge propagation down the estuary, its reflection and spatial/temporal variability could be gained. 相似文献
10.
A pilot Coastal Observatory has been established in Liverpool Bay which integrates (near) real-time measurements with coupled
models and whose results are displayed on the web. The aim is to understand the functioning of coastal seas, their response
to natural forcing and the consequences of human activity. The eastern Irish Sea is an apt test site, since it encompasses
a comprehensive range of processes found in tidally dominated coastal seas, including near-shore physical and biogeochemical
processes influenced by estuarine inflows, where both vertical and horizontal gradients are important. Applications include
hypernutrification, since the region receives significantly elevated levels of nutrient inputs, shoreline management (coastal
flooding and beach erosion/accretion), and understanding present conditions to predict the impact of climate change (for instance
if the number and severity of storms, or of high or low river flows, change). The integrated measurement suite which started
in August 2002 covers a range of space and time scales. It includes in situ time series, four to six weekly regional water
column surveys, an instrumented ferry, a shore-based HF radar system measuring surface currents and waves, coastal tide gauges
and visible and infra-red satellite data. The time series enable definition of the seasonal cycle, its inter-annual variability
and provide a baseline from which the relative importance of events can be quantified. A suite of nested 3D hydrodynamic,
wave and ecosystem models is run daily, focusing on the observatory area by covering the ocean/shelf of northwest Europe (at
12-km resolution) and the Irish Sea (at 1.8 km), and Liverpool Bay at the highest resolution of 200 m. The measurements test
the models against events as they happen in a truly 3D context. All measurements and model outputs are displayed freely on
the Coastal Observatory website () for an audience of researchers, education, coastal managers and the public. 相似文献
11.
《Continental Shelf Research》2006,26(12-13):1519-1541
Initially a brief overview of the problem of computing the wind-induced circulation on the west coast of Britain is reviewed together with storm surge modelling. To date this work has primarily been performed with finite difference models. However, here new work is presented using a finite element model with a range of mesh refinements in shallow water regions to examine the influence of mesh resolution upon the wind-induced circulation off the west coast of Britain. Steady state current fields are computed for uniform westerly and southerly winds and compared with a uniform grid (of order 7 km) finite difference model solution. Calculations show that in deep water regions away from the coastal influence, the large-scale circulation features in the finite element solution are in good agreement with those found in the finite difference model. This suggests that they can be adequately resolved on a 7 km mesh. In the nearshore region and within estuaries a significantly finer mesh is required, with the variable mesh finite element model showing significant small scale variability in the nearshore area. Refining the mesh in the Mersey and using an accurate topographic data set, shows that although the larger scale features in the estuary can be resolved in the coarser mesh model, accurate topography is required to model their exact location. In addition smaller scale features are found that were not resolved in the coarser mesh models. Due to the effects of “wetting and drying” and the importance of non-linear processes in shallow regions difficulties occurred in de-tiding the full solution in order to determine the wind forced residual. Determining the wind forced solution in shallow water from a calculation in which wind and tidal forcing are included poses problems as to how to “de-tide” the solution in such a highly non-linear region. An approach based upon the harmonic analysis of the total solution, rather than subtracting a “tide only” solution is shown to be most effective and has implications for storm surge prediction.General and specific conclusions on the importance of highly accurate bathymetry, good mesh resolution and de-tiding method upon the accuracy of the wind forced solution in nearshore regions are summarized in the final part of the paper. The implications for storm surge prediction together with suggestions for future research to enhance the accuracy of storm surge prediction, namely “the way forward” are given at the end of the paper. 相似文献
12.
Modelling travel and residence times in the eastern Irish Sea 总被引：2，自引：0，他引：2
The Irish Sea, which lies between 51 degrees N-56 degrees N and 2 degrees 50'W-7 degrees W, provides a sheltered environment to exploit valuable fisheries resource. Anthropogenic activity is a real threat to its water quality. The majority of freshwater input down rivers flows into the eastern Irish Sea. The structure of the water circulation was not well understood during the planning of Sellafield nuclear plant outfall site in the eastern Irish Sea. A three-dimensional primitive equation numerical model was applied to the Irish Sea to simulate both barotropic and baroclinic circulation within the region. High accuracy was achieved with regard to the prediction of both tidal circulation and surface and nearbed water temperatures across the region. The model properly represented the Western Irish Sea Gyre, induced by thermal stratification and not known during planning Sellafield. Passive tracer simulations based on the developed hydrodynamic model were used to deliver residence times of the eastern Irish Sea region for various times of the year as well as travel times from the Sellafield outfall site to various locations within the Irish Sea. The results indicate a strong seasonal variability of travel times from Sellafield to the examined locations. Travel time to the Clyde Sea is the shortest for the autumnal tracer release (90 days); it takes almost a year for the tracer to arrive at the same location if it is released in January. Travel times from Sellafield to Dublin Bay fall within the range of 180-360 days. The average residence time of the entire eastern Irish Sea is around 7 months. The areas surrounding the Isle of Man are initially flushed due to a predominant northward flow; a backwater is formed in Liverpool Bay. Thus, elevated tracer concentrations are predicted in Liverpool Bay in the case of accidental spills at the Sellafield outfall site. 相似文献
13.
A finite element model (namely TELEMAC) with a range of mesh refinements and assumptions of coastal water depths is used to
determine an optimal mesh for computing the M
2 tide in a region of significant geographical extent. The region adopted is the west coast of Britain covering the Irish and
Celtic Seas. The nature of the spatially varying topography and tidal distribution, together with a comprehensive set of measurements
and existing accurate finite difference model makes it ideal for such a study. Calculations show that a water-depth dependent
criterion for determining element size gives an optimal distribution over the majority of the region. However, local refinements
in narrow channels such as the North Channel and Bristol Channel are required. Although the specification of a zero coastal
water depth, leads to a fine near coastal grid, this does not yield the most accurate solution. In addition the computational
cost is high. In practice in a large area model the use of a non-zero coastal water depth yields optimum accuracy at minimal
computational cost. However, calculations show that accuracy is critically dependent upon nearshore water depths. Comparison
with the finite difference model shows that the bias in elevation amplitude in the finite difference solution is removed in
the finite element calculation. 相似文献
14.
A three-dimensional finite volume unstructured mesh model of the west coast of Britain, with high resolution in the coastal regions, is used to investigate the role of wind wave turbulence and wind and tide forced currents in producing maximum bed stress in the eastern Irish Sea. The spatial distribution of the maximum bed stress, which is important in sediment transport problems, is determined, together with how it is modified by the direction of wind forced currents, tide–surge interaction and a surface source of wind wave turbulence associated with wave breaking. Initial calculations show that to first order the distribution of maximum bed stress is determined by the tide. However, since maximum sediment transport occurs at times of episodic events, such as storm surges, their effects upon maximum bed stresses are examined for the case of strong northerly, southerly and westerly wind forcing. Calculations show that due to tide–surge interaction both the tidal distribution and the surge are modified by non-linear effects. Consequently, the magnitude and spatial distribution of maximum bed stress during major wind events depends upon wind direction. In addition calculations show that a surface source of turbulence due to wind wave breaking in shallow water can influence the maximum bed stress. In turn, this influences the wind forced flow and hence the movement of suspended sediment. Calculations of the spatial variability of maximum bed stress indicate the level of measurements required for model validation. 相似文献
15.
We applied a three-dimensional general ocean and coastal circulation model to the Irish Sea in order to determine water renewal time scales in the region. The model was forced with meteorological data for 1995, a year with relatively warm summer and when extensive hydrographic surveys were conducted in the Irish Sea. We investigated intra-annual variability in the rates of net flow through the Irish Sea and carried out several flushing simulations based on conservative tracer transport. The results indicate that the net northward flow of 2.50 km3/d is seasonally highly variable and under certain conditions is reversed to southward. The variability in obtained residence times is high; baroclinic effects are significant. Obtained results point at the importance of spatial and temporal consideration for transport of pollutants in the shelf seas. Implications for management are numerous and involve activities such as transport, fishing, use of resources, nature conservation, monitoring, tourism and recreation. 相似文献
16.
We revisit the surge of November 1977, a storm event which caused damage on the Sefton coast in NW England. A hindcast has been made with a coupled surge-tide-wave model, to investigate whether a wave-dependent surface drag is necessary for accurate surge prediction, and also if this can be represented by an optimised Charnock parameter. The Proudman Oceanographic Laboratory Coastal Modelling System-Wave Model (POLCOMS-WAM) has been used to model combined tides, surges, waves and wave-current interaction in the Irish Sea on a 1.85 km grid. This period has been previously thoroughly studied, e.g. Jones and Davies [Jones, J.E., Davies, A.M., 1998. Storm surge computations for the Irish Sea using a three-dimensional numerical model including wave-current interaction. Continental Shelf Research 18(2), 201–251] and we build upon this previous work to validate the POLCOMS-WAM model to test the accuracy of surge elevation predictions in the study area. A one-way nested approach has been set up from larger scale models to the Irish Sea model. It was demonstrated that (as expected) swell from the North Atlantic does not have a significant impact in the eastern Irish Sea. To capture the external surge generated outside of the Irish Sea a (1/9° by 1/6°) model extending beyond the continental shelf edge was run using the POLCOMS model for tide and surge. 相似文献
17.
A non-linear three-dimensional unstructured grid model of the M2 tide in the shelf edge area off the west coast of Scotland is used to examine the spatial distribution of the M2 internal tide and its higher harmonics in the region. In addition, the spatial variability of the tidally induced turbulent
kinetic energy and associated mixing in the area are considered. Initial calculations involve only tidal forcing, although
subsequent calculations are performed with up-welling and down-welling favourable winds to examine how these influence the
tidal distribution (particularly the higher harmonics) and mixing in the region. Both short- and long-duration winds are used
in these calculations. Tidal calculations show that there is significant small-scale spatial variability particularly in the
higher harmonics of the internal tide in the region. In addition, turbulence energy and mixing exhibit appreciable spatial
variability in regions of rapidly changing topography, with increased mixing occurring above seamounts. Wind effects significantly
change the distribution of the M2 internal tide and its higher harmonics, with appreciable differences found between up- and down-welling winds and long- and
short-duration winds because of differences in mixing and the presence of wind-induced flows. The implications for model validation,
particularly in terms of energy transfer to higher harmonics, and mixing are briefly discussed. 相似文献
18.
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
19.
The tsunami event generated by the great Sumatra–Andaman earthquake on 26 December 2004 was simulated with the recently developed model TsunAWI. The model is based on the finite element method, which allows for a very flexible discretization of the model domain. This is demonstrated by a triangulation of the whole Indian Ocean with a resolution of about 14 km in the deep ocean but a considerably higher resolution of about 500 m in the coastal area. A special focus is put on the Banda Aceh region in the Northern tip of Sumatra. This area was heavily hit by the tsunami and the highest resolution in this area is about 40 m in order to include inundation processes in the model simulation. We compare model results to tide gauge data from all around the Indian Ocean, to satellite altimetry, and field measurements of flow depth in selected locations of the Aceh region. Furthermore, we compare the model results of TsunAWI to the results of a nested grid model (TUNAMI-N3) with the same initial conditions and identical bathymetry and topography in the Aceh region. It turns out that TsunAWI gives accurate estimates of arrival times in distant locations and in the same mesh gives good inundation results when compared to field measurements and nested grid results. 相似文献
20.
Perturbation of regional ocean tides due to coastal dikes 总被引：1，自引：0，他引：1
The tidal regime modeling system for ocean tides in the seas bordering the Korean Peninsula is designed to cover an area that is broad in scope and size, yet provide a high degree of resolution in coastal development areas, including the Saemangeum area in the eastern Yellow Sea and the Ariake Sea in Japan, where serious environmental problems have occurred after the completion of interior tidal dikes. With this simulation system, we have estimated the changes in tidal regime due to barriers at Saemangeum and Isahaya Bay in the Ariake Sea. Some results in terms of perturbations in tidal elevations due to the construction of coastal dikes are presented and discussed. 相似文献