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1.
The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challenging task in coastal research. The bathymetric changes result from the combined action of tides, waves, rivers discharge and wind stress in the area of interest. Additionally, an accurate knowledge of the sediment transport is essential to achieve a good morphological characterization. This work establishes the influence of the wave climate on the morphodynamics of the Ria de Aveiro lagoon inlet by analysing the numerical results of the morphodynamic modelling system MORSYS2D. The numerical simulations considered a realistic coupled forcing of tidal currents and waves. The computed sediment fluxes and bathymetric changes are analysed and compared with the erosion and accretion trends obtained from the numerical simulations forced only by tidal currents, in order to establish the wave climate influence. The final bathymetry and the corresponding changes are compared with bathymetric data collected through surveys. It is concluded that: (a) the morphodynamics of the study area is dominated by the wave regime in the lagoon inlet and nearshore areas, while in the inner areas is tidally dominated; and (b) the inclusion of the wave regime forcing constitutes an improvement in order to accurately reproduce the local morphodynamics.  相似文献   

2.
The main objective of this paper is to address the principal mechanisms involved in the medium-term (order of months to years) morphodynamic evolution of estuaries through the application of a process-based numerical modelling. The Teign estuary (Teignmouth, UK) is the selected site. The system is forced by the macrotidal semi-diurnal tide in the English Channel and is perturbed to a minor extent by high river discharge events (freshets). Although waves have a definite influence on the adjacent coastal area, Wells (Teignmouth Quay Development Environmental Statement: Changes to Physical Processes. Report R.984c:140. ABP Marine Environmental Research Ltd., Southampton, 2002b) suggested that swell waves do not enter the estuary. Hence, wave effects are neglected in this study, as only tides and the river discharge are taken into account. The sediment grain size is highly variable, but mainly sandy. Within the frame of the COAST3D project (), four bathymetric surveys of the adjacent coastal area were carried out at a nearly weekly intervals. The outer estuary and the adjacent coastal area were also surveyed every 6 months as part of the COASTVIEW project (). Based on these data and on continuously measured parameters, such as water level, waves, wind and river discharge, numerical modelling of the morphodynamic processes can be tested. To replicate the morphological changes in the medium-term within a feasible simulation time, forcing conditions are reduced through the use of an input reduction method (called ensemble technique). In this study, simulations are based on the coupling between Telemac-2D and its non-cohesive sediment transport module, Sisyphe (version 5.3 for both modules). Three different sediment transport formulae were tested: (1) Engelund and Hansen (A monograph on sediment transport in alluvial streams, 3rd edn. Technological University of Denmark, Copenhagen, 1967) including the modifications proposed by Chollet and Cunge (J Hydraul Eng 17(1):1–13, 1979); (2) Bijker (Mechanics of sediment transport by the combination of waves and current. In: Design and reliability of coastal structures. 23rd international conference on Coastal Engineering, pp 147–173, 1968) and (3) Soulsby (Dynamics of Marine Sands. A manual for practical applications. HR Wallingford, Wallingford, p 142, 1997) modified version of van Rijn [J Hydraul Eng 110(10):1431–1456, 1984a, J Hydraul Eng 110(11):1613–1641, 1984b] formulation. Both a qualitative (i.e. visual comparison) and a quantitative tool [Brier Skill Score (BSS); described in Sutherland et al. in Coast Eng 51:917–939, 2004b] are applied to assess the similarity of simulations when compared to model predictions and observations. Tests confirmed the reliability and time efficiency of the ensemble technique, since it reproduced very well the results of a reference run, a computation based on the observed boundary conditions. For the spring-neap cycle modelled, the BSS was of 0.91 (a perfect modelling would have a BSS of 1), with a reduction in the simulation time on the order of 80%. For the 6-month-period simulation, results were also excellent: BSS=0.92 and a computer time reduction of 85%. In principle, this method has the advantage of being applied to any process-based numerical model.  相似文献   

3.
Sea level change is an important consequence of climate change due to its impact on society and ecosystems. Analyses of tide-gauge data have indicated that the global sea level has risen during the 20th century and several studies predict that the mean sea level will continue to rise during the 21st century, intensifying coastal hazards worldwide. In Portugal, the Ria de Aveiro is expected to be one of the regions most affected by sea level change.The main aim of this study is to evaluate the potential impacts of the mean sea level change on the hydrodynamics and morphodynamics of the Ria de Aveiro. With this purpose, local mean sea level change was projected for the period 2091-2100 relative to 1980-1999, for different Special Report on Emission Scenarios (SRES) scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). These projections revealed an increase in the mean sea level between 0.28 m under scenario B1 and 0.42 m under scenario A2.The results obtained for sea level rise scenario A2 projection were used to force the morphodynamic model MORSYS2D, previously implemented for the Ria de Aveiro. The modelling results were compared with model forecasts for the present sea level. The residual sediment transport and its balance at the lagoon inlet were computed and analysed for both situations. While the residual sediment transport is generally seaward, sediments tend to deposit inside the inlet due to the weak sediment transport at its mouth. The direction of the residual flux will not change with the sea level rise, but sediment fluxes will intensify, and accretion inside the inlet will increase.The rise in mean sea level will also affect the lagoon hydrodynamics. The tidal prism at the lagoon mouth will increase by about 28% in spring tide. In the lower lagoon only a slight increase of the tidal asymmetry is predicted.  相似文献   

4.
In‐channel sand mining by dredge removes large quantities of bed sediment and alters channel morphodynamic processes. While the reach‐scale impacts of dredging are well documented, the effects of the dredged borrow pit on the local flow and sediment transport are poorly understood. These local effects are important because they control the post‐dredge evolution of the borrow pit, setting the pit lifespan and affecting reach‐scale channel morphology. This study documents the observed morphological evolution of a large (1·46 million m3) borrow pit mined on a lateral sandbar in the lower Mississippi River using a time‐series of multibeam bathymetric surveys. During the 2·5 year time‐series, 53% of the initial pit volume infilled with sediment, decreasing pit depth by an average of 0·88 m yr?1. To explore the controls of the observed infilling, a morphodynamic model (Delft3D) was used to simulate flow and sediment transport within the affected river reach. The model indicated that infilling rates were primarily related to the riverine sediment supply and pit geometry. The pit depth and length influenced the predicted magnitude of the pit bed shear stress relative to its pre‐dredged value, i.e. the bed‐stress reduction ratio (R*), a metric that was correlated with the magnitude and spatial distribution of infilling. A one‐dimensional reduced‐complexity model was derived using predicted sediment supply and R* to simulate patterns of pit infilling. This simplified model of borrow‐pit evolution was able to closely approximate the amount and patterns of sediment deposition during the study period. Additional model experiments indicate that, for a borrow pit of a set volume, creating deep, longitudinally‐shorter borrow pits significantly increased infilling rates relative to elongated pits. Study results provide insight into the resilience of alluvial river channels after a disturbance and the sustainability of sand mining as a sediment source for coastal restoration. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

5.
A consistent time series of synoptic and high-frequency bathymetric observations is fundamental to improving our understanding and predictive capabilities regarding the morphological behavior of large coastal inlets. Based on satellite observations, an original approach is proposed to characterize the long-term morphological evolution of the Arcachon lagoon inlet and to describe sediment bypassing and breaching mechanisms. The almost 26-year-long remotely sensed data archive used in this study is built from 78 suitable SPOT images (1986–2012) collected in the framework of the KALIDEOS-Littoral program. Bathymetric information is derived from satellite data using a physics-based model. A validation exercise performed on a large bathymetric survey data set (N?=?43,949) demonstrates that the inversion model performs excellently in estimating the depth of mildly to moderately turbid shallow waters. The performance of the model suggests that the minimum requirements are fulfilled to apply the SPOT-derived bathymetry to morphodynamic applications. We demonstrate that high-spatial-resolution multispectral sensors are well adapted to analyzing the morphological evolution of small- (i.e., sand dunes), medium- (i.e., sandbanks and channels), and large- (i.e., the entire inlet-lagoon system) scale sedimentary structures present in coastal inlets. For the first time, the long-term evolution of a flood and ebb-tidal delta is characterized by observations at a seasonal timescale. Finally, migration rates of sedimentary entities are quantified, and fundamental mechanisms driving the sediment transport cross the inlet are confirmed.  相似文献   

6.
A 2-year investigation into shoreface morphodynamic behaviour off a high-energy headland-embayment coast in Northern Ireland reveals important process–response mechanisms that cannot be explained solely by existing conceptual models. Fourteen sequential bathymetric surveys, conducted every 1–2 months, show that morphologic (seabed) change is not directly related to oceanographic forcing—extensive nearshore and shoreface accretion and erosion occurs under fair-weather, modal and high-energy conditions. The main factors which seem to cause significant change are long-duration (swell) events coupled with onshore winds, availability of (recently) introduced sediment, surges and elapsed time between storms and the next scheduled survey. Several high-energy events over a short time period (<30 days) did not result in extensive seafloor changes, contrary to expectations. Net seabed change over 2 years shows an average to 0.6 m m?2 of shoreface accretion from the nearshore to 24 m depth. Net erosion was not observed anywhere, including the subaerial beach. Geologic evidence strongly suggests that the source of the significant volume (7.7×105 m3) of sediment introduced into the study area must have been derived from the lower shoreface and/or inner shelf, beyond 24 m depth.  相似文献   

7.
Waves with a large incidence angle in deep water can drive a morphodynamic instability on a sandy coast whereby shoreline sand waves, cuspate forelands, and spits can emerge. This instability is related to bathymetric perturbations extending offshore in the shoaling zone. Here, we explore a different mechanism where the large incidence angle is supposed to occur at breaking and the bathymetric perturbations occur only in the surf zone. For wave incidence angles at breaking above ≈?45°, the one-line approximation of coastal dynamics predicts an unstable shoreline. This instability (EHAWI) is scale-free and the growth rate increases without bound for decreasing wavelength. Here we use a 2DH morphodynamic model resolving surf zone instabilities to investigate whether EHAWI could approximate a real instability in nature with a characteristic length scale. Assuming very idealized conditions on the bathymetric profile and sediment transport, we find a 2DH instability mode consisting of shore-oblique up-current bars coupled to a meandering of the longshore current. This mode grows for high-angle waves, above about 30° (offshore) and the maximum growth rate occurs for the angle maximizing the angle at breaking, about 70° (offshore). The dominant wavelength is of the order of the surf zone width. Interestingly, for long sand waves, the growth rate never becomes negative and it matches very well the anti-diffusive behavior of EHAWI. This distinguishes the present instability mode from other modes found in previous studies for other bathymetric and sediment transport conditions. Thus, we conclude that EHAWI approximates a real morphodynamic instability only for quite particular conditions. In such case, a characteristic length scale of the instability emerges thanks to surf zone processes that damp short wavelengths.  相似文献   

8.
This contribution aims to model the dominant processes that control sedimentation within the ocean inlet to intermittently open–closed coastal lagoons; focussing on the role of infilling, backfilling and morphodynamic feedback. The key elements that have been included in the present model are: (1) the delivery of sediment to the mouth of the estuary by littoral processes; (2) sediment transport processes within the inlet due to non-linear tidal flow; and (3) the down-slope diffusion of sediment. The model discussed here includes a simple one-dimensional (1-D), non-linear flow parameterisation that predicts the spatial variability in the magnitude and non-linearity of the tidal flow. The predicted third and fourth velocity moments are used to drive a morphodynamic module. Down-slope diffusion of sediment is dealt with in a separate diffusion term in the bed-evolution equation. Feedback between the evolving morphology and the flow field are integral to the model. Numerical simulations are used to investigate different modes of evolution for this type of inlet system. Inlet closure due to infilling is critically controlled by the balance between sediment addition at the mouth due to littoral processes and the removal of sediment by non-linear tidal flow. Rapid widening or deepening of the inlet at its landward margin leads to the deposition of a flood shoal. Under conditions of high sedimentation (and low diffusion) the flood shoal can become sufficiently well developed to present a physical barrier to sediment entering the lagoon. Under these circumstances backfilling can become significant. The infilling and backfilling processes are ameliorated by efficient down-slope diffusion which is controlled in the present model by a diffusion parameter, D. High diffusion coefficients slow inlet closure and allow sediment to propagate further into the lagoon.  相似文献   

9.
The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi-natural system to evaluate large-scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be >30 years (starting from the mid-1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large-scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd.  相似文献   

10.
The artificial gravel augmentation of river channels is increasingly being used to mitigate the adverse effects of river regulation and sediment starvation. A systematic framework for designing and assessing such gravel augmentations is still lacking, notably on large rivers. Monitoring is required to quantify the movement of augmented gravel, measure bedform changes, assess potential habitat enhancement, and reduce the uncertainty in sediment management. Here we present the results of an experiment conducted in the Rhine River (French and German border). In 2010, 23 000 m3 of sediments (approximately the mean annual bedload transport capacity) were supplied in a by‐passed reach downstream of the Kembs dam to test the feasibility of enhancing sediment transport and bedform changes. A 620‐m‐long and 12‐m‐wide gravel deposit was created 8 km downstream from the dam. Monitoring included topo‐bathymetric surveys, radio‐frequency particle tracking using passive integrated transponder (PIT) tags, bed grain size measurement, and airborne imagery. Six surveys performed since 2009 have been described (before and after gravel augmentation, and after Q2 and Q15 floods). The key findings are that (i) the augmented gravel was partially dispersed by the first flood event of December 2010 (Q1); (ii) PIT tags were found up to 3200 m downstream of the gravel augmentation site after four years, but the effects of gravel augmentation could not be clearly distinguished from the effects of floods and internal remobilization on more than 3500 m downstream; (iii) linear and log‐linear relationships linking bedload transport, particle mobility, and grain size were established; and (iv) combined bathymetry and PIT tag surveys were useful for evaluating potential environmental risks and the first morpho‐ecological responses. This confirmed the complementary nature of such techniques in the monitoring of gravel augmentation in large rivers. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

11.
Abstract

A measurement campaign was carried out in the Upper Tana basin (Kenya) to quantify soil erosion and reservoir sedimentation rates, including a bathymetric reservoir survey and sediment load sampling during one year. Then, distributed soil erosion modelling was performed to study sediment budgets throughout the basin and to evaluate the potential of upstream erosion control through vegetated contour strips and check dams. Finally, the areas where these measures would be most effective were identified and local stakeholder associations to implement them were prioritized. The influence of the scale of implementation was evaluated by using the model to consider three adoption scenarios. This study illustrates the relevance of distributed erosion models to target erosion control measures when sufficient information on the eroding areas is available from field surveys. Bathymetric surveys were fundamental to validate the long-term model response, while point measurements were valuable to verify the spatial variability of model predictions.

Editor Z.W. Kundzewicz; Associate editor G. Mahé

Citation Hunink, J.E., Niadas, I.A., Antonaropoulos, P., Droogers, P., and de Vente, J., 2013. Targeting of intervention areas to reduce reservoir sedimentation in the Tana catchment (Kenya) using SWAT. Hydrological Sciences Journal, 58 (3), 600–614.  相似文献   

12.
《国际泥沙研究》2021,36(6):723-735
This numerical modeling study (i) assesses the influence of the sediment erosion process on the sediment dynamics and subsequent morphological changes of a mixed-sediment environment, the macrotidal Seine estuary, when non-cohesive particles are dominant within bed mixtures (non-cohesive regime), and (ii) investigates respective contributions of bedload and suspended load in these dynamics. A three dimensional (3D) process-based morphodynamic model was set up and run under realistic forcings (including tide, waves, wind, and river discharge) during a 1-year period. Applying erosion homogeneously to bed sediment in the non-cohesive regime, i.e., average erosion parameters in the erosion law (especially the erodibility parameter, E0), leads to higher resuspension of fine sediment due to the presence of coarser fractions within mixtures, compared to the case of an independent treatment of erosion for each sediment class. This results in more pronounced horizontal sediment flux (two-fold increase for sand, +30% for mud) and erosion/deposition patterns (up to a two-fold increase in erosion over shoals, generally associated with some coarsening of bed sediment). Compared to observed bathymetric changes, more relevant erosion/deposition patterns are derived from the model when independent resuspension fluxes are considered in the non-cohesive regime. These results suggest that this kind of approach may be more relevant when local grain-size distributions become heterogeneous and multimodal for non-cohesive particles. Bedload transport appears to be a non-dominant but significant contributor to the sediment dynamics of the Seine Estuary mouth. The residual bedload flux represents, on average, between 17 and 38% of the suspended sand flux, its contribution generally increasing when bed sediment becomes coarser (can become dominant at specific locations). The average orientation of residual fluxes and erosion/deposition patterns caused by bedload generally follow those resulting from suspended sediment dynamics. Sediment mass budgets cumulated over the simulated year reveal a relative contribution of bedload to total mass budgets around 25% over large erosion areas of shoals, which can even become higher in sedimentation zones. However, bedload-induced dynamics can locally differ from the dynamics related to suspended load, resulting in specific residual transport, erosion/deposition patterns, and changes in seabed nature.  相似文献   

13.
The 1999 jökulhlaup at Sólheimajökull was the first major flood to be routed through the proglacial system in over 600 years. This study reconstructed the flood using hydrodynamic, sediment transport and morphodynamic numerical modelling informed by field surveys, aerial photograph and digital elevation model analysis. Total modelled sediment transport was 469 800 m3 (+/‐ 20%). Maximum erosion of 8.2 m occurred along the ice margin. Modelled net landscape change was –86 400 m3 (+/‐ 40%) resulting from –275 400 m3 (+/‐ 20%) proglacial erosion and 194 400 m3 (+/‐ 20%) proglacial deposition. Peak erosion rate and peak deposition rate were 650 m3 s‐1 (+/‐ 20%) and 595 m3 s‐1 (+/‐ 20%), respectively, and coincided with peak discharge of water at 1.5 h after flood initiation. The pattern of bed elevation change during the rising limb suggested widespread activation of the bed, whereas more organisation, perhaps primitive bedform development, occurred during the falling limb. Contrary to simplistic conceptual models, deposition occurred on the rising stage and erosion occurred on the falling limb. Comparison of the morphodynamic results with a hydrodynamic simulation illustrated effects of sediment transport and bed elevation change on flow conveyance. The morphodynamic model advanced flood arrival and peak discharge timings by 100% and 19%, respectively. However, peak flow depth and peak flow velocity were not significantly affected. We suggest that morphodynamic processes not only increase flow mass and momentum but that they also introduce a feedback process whereby flood conveyance becomes more efficient via erosion of minor bed protrusions and deposition that infills or subdues minor bed hollows. A major implication of this study is that reconstructions of outburst floods that ignore sediment transport, such as those used in interpretation of long‐term hydrological record and flood risk assessments, may need considerable refinement. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
Tidal changes in the Ria de Aveiro lagoon, Portugal, show an average increase of 0.245 m in M2 amplitude and an average 17.4° decrease in M2 phase, over 16 years (1987–2004). This paper investigates the causes of these changes using: (a) an analytical model and (b) hydrodynamic (vertically integrated) model of the Ria de Aveiro lagoon.  相似文献   

15.
Numerical modelling of morphodynamics—Vilaine Estuary   总被引：1，自引：0，他引：1  
The main objective of this paper is to develop a method to simulate long-term morphodynamics of estuaries dominated by fine sediments, which are subject to both tidal flow and meteorologically induced variations in freshwater run-off and wave conditions. The method is tested on the Vilaine Estuary located in South Brittany, France. The estuary is subject to a meso–macrotidal regime. The semi-diurnal tidal range varies from around 2.5 to 5 m at neap and spring, respectively. The freshwater input is controlled by a dam located approximately 8 km from the mouth of the estuary. Sediments are characterised as mostly fines, but more sandy areas are also found. The morphology of the estuary is highly influenced by the dam. It is very dynamic and changes in a complicated manner with the run-off from the dam, the tide and the wave forcing at the mouth of the estuary. Extensive hydrodynamic and sediment field data have been collected in the past and provide a solid scientific basis for studying the estuary. Based on a conceptual understanding of the morphodynamics, a numerical morphological model with coupled hydrodynamic, surface wave and sediment transport models is formulated. The numerical models are calibrated to reproduce sediment concentrations, tidal flat altimetry and overall sediment fluxes. Scaling factors are applied to a reference year to form quasi-realistic hydrodynamic forcing and river run-off, which allow for the simulations to be extended to other years. The simulation results are compared with observed bathymetric changes in the estuary during the period 1998–2005. The models and scaling factors are applied to predict the morphological development over a time scale of up to 10 years. The influence of the initial conditions and the sequence of external hydrodynamic forcing, with respect to the morphodynamic response of the estuary, are discussed.  相似文献   

16.
Morphodynamic models are used by river practitioners and scientists to simulate geomorphic change in natural and artificial river channels. It has long been recognized that these models are sensitive to the choice of parameter values, and proper calibration is now common practice. This paper investigates the less recognized impact of the choice of the model itself. All morphodynamic models purport to simulate the same flow and sediment dynamics, often relying on the same governing equations. Yet in solving these equations, the models have different underlying assumptions, for example regarding spatial discretization, turbulence, sediment inflow, lateral friction, and bed load transport. These differences are not always considered by the average model user, who might expect similar predictions from calibrated models. Here, a series of numerical simulations in meandering channels was undertaken to test whether six morphodynamic codes (BASEMENT, CCHE‐2D, NAYS, SSIIM‐1, TELEMAC‐2D and TELEMAC‐3D) would yield significantly different equilibrium bathymetries if subjected to identical, initial flow conditions. We found that, despite producing moderately similar velocity patterns on a fixed‐flat bed (regression coefficient r of 0.77 ± 0.20), the codes disagree substantially with respect to simulated bathymetries (r = 0.49 ± 0.31). We relate these discrepancies to differences in the codes' assumptions. Results were configuration specific, i.e. codes that perform well for a given channel configuration do not necessarily perform well with higher or lower sinuosity configurations. Finally, limited correlation is found between accuracy and code complexity; the inclusion of algorithms that explicitly account for the effects of local bed slope and channel curvature effects on transport magnitude and direction does not guarantee accuracy. The range of solutions obtained from the evaluated codes emphasizes the need for carefully considering the choice of code. We recommend the creation of a central repository providing universal validation cases and documentation of recognized fluvial codes in commonly studied fluvial settings. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

17.
The response of the tidal system in the southern North Sea to morphodynamic changes was investigated in a modelling study using fine resolution bathymetric observations available for 1982–2011. The Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) was set up for the different sets of bathymetries. One set of bathymetry was compiled from a large number of bathymetric measurements over many years, while the other two reflected bathymetry state in the area of Wadden Sea during 2000 and 2011, respectively. The temporal and spatial evolution of bathymetry was dominated by migration of tidal channels. The M4 tide showed larger sensitivity to bathymetric change in the Wadden Sea than the M2 tide, whereas the structure of the latter remained rather robust. The largest change of the tidal wave due to the differences in bathymetries was located off the North Frisian Wadden Sea. Traces of changes were also found far away from the regions of their origin because the tidal waves in the North Sea propagate the local disturbances basin-wide. This illustrated an efficient physical mechanism of teleconnectivity, i.e. effecting the local responses to the larger-scale or remote change of ocean bottom caused by erosion and deposition. The tidal distortion resulting from the relatively small bathymetric changes was substantial, particularly in the coastal zone. This is a manifestation of the nonlinear tidal transformation in shallow oceans and is crucial for the sediment transport and the morphodynamic feedback, because of the altered tidal asymmetry.  相似文献   

18.
A previously developed Cryptosporidium transport model is solved numerically to investigate the transport and interactions between Cryptosporidium, water and surface sediment and to estimate the risk of surface water contamination by Cryptosporidium. The primary objective of this study is to expand the work of Yeghiazarian (Ph.D. dissertation, Cornell University 2001)where the analytical solution of the Cryptosporidium transport model was obtained for a simple case of specific attachment of Cryptosporidium oocysts to fine soil particles wherein some parameters have zero values. However, some studies have shown several cases where these parameters are not zero. This necessitated further study to generate a solution to the complete Cryptosporidium transport model. Utilizing the finite difference method, the Cryptosporidium transport model is solved numerically for the general case of a system with any parameter values. Previously, first- and second-order reliability methods (FORM and SORM) were employed for risk assessment using analytical transport results (Yeghiazarian, Ph.D. dissertation, Cornell University, 2001), but in this work, FORM and SORM are applied to the numerical solution of the Cryptosporidium transport model to estimate the risk of Cryptosporidium contamination in surface water. The risk of surface water contamination is estimated by the probability that the Cryptosporidium concentration in surface water at a given time and location exceeds a safety threshold. The numerical solution is interfaced with the general-purpose reliability code, CALREL, to estimate the probability of failure on one hillslope. The sensitivity of system reliability to process parameters is reported.  相似文献   

19.
A comparison of 1927, 1970 and 2002 bathymetric surveys in the Lagoon of Venice was used to reconstruct historical changes in sedimentation. A detailed GIS-based analysis of the charts revealed the timing and pattern of geomorphic changes and allowed calculation of sediment deposition and erosion for the entire lagoon and each of its four sub-basins: Treporti, Lido, Malamocco and Chioggia.  相似文献   

20.
A correct understanding of the hydrodynamics and morphodynamics of tidal basins is of fundamental importance for the fate of the Venice Lagoon, Italy. If on one hand, the development of sophisticated numerical models is called for in order to reproduce the complexity of the mechanisms governing the morphodynamic evolution of many natural environments, including lagoons, on the other hand, a clear knowledge of the reliability and limits of the results provided by these models is crucial in order to establish the condition under which they can be safely applied. To this aim, researchers involved in numerical modeling in the framework of the recent Corila research programmes, agreed to perform an accurate comparison of results provided by three different numerical models, applying them to the test case offered by the experimental investigations performed under controlled conditions by Tambroni et al. (2005a). Here, we consider the following numerical models: (i) a 2D finite element hydrodynamic model coupled with a 2D finite volume morphodynamic model (5 and 3); (ii) a 2D finite element morphodynamic model (Ferrarin et al., 2008); (iii) a 2D depth-averaged model for the inlet region, coupled with a 1D model for the channel (Tambroni et al., 2005b). A first set of simulations concerns the fixed bed case and shows that all the models provide similar results: in particular, they are able to predict the observed free surface oscillations satisfactorily, while comparison with the measured velocity field is less satisfactory. Moreover, as far as the flow field at the inlet is concerned, the models describe accurately the potential flow into the channel during the flood phase, while they are not able to adequately reproduce the occurrence of the fine structure of the shear layers shed by the inlet edges during the ebb phase. This limit is related to the shallow water character of the models. As for the morphodynamics, the long term equilibrium configurations of the bottom of the channel and of the near inlet region show qualitative agreement with the experimental observations, although in this case the differences between the results provided by the distinct numerical approaches are more marked.  相似文献   

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