Auswirkungen von Stürmen auf kurz- und mittelfristige Morphodynamik in einer gezeitendominierten Küstenregion

A storm event over shallow nearshore coastal waters or shallow inland water bodies can generate large water fluctuations if the storm is sufficiently strong. It can cause both a rise (set-up) and fall (set-down) of the water level. Generally, as a result of the water level fluctuations and the associated changes in the wave conditions the morphology will change at temporal and spatial scales. The main concern of this work is to study the storm events and their effects on the short- and the medium-term morphological developments in the central Dithmarschen Bight, German North Sea. In this study, the morphological changes on the short- and the medium-term will be a result of a singular event from a few hours to days and from a few weeks to months, respectively. In previous works, the individual process models (flow, wave and sediment transport) have been extensively calibrated and validated against measurements. In this work a morphodynamic model for the Dithmarschen Bight region has been setup. The morphodynamic model is based on Delft3D model developed by WL-Delft Hydraulics in which the on-line approach was applied. The Dithmarschen Bight morphodynamic model implies a morphological acceleration factor. Moreover, the sediment transport model concerns the sediment distribution for cohesive and non-cohesive sediments for the Dithmarschen Bight. In the short-term morphodynamic model the simulations were obtained by nesting the Dithmarschen Bight Model (DBM) in the German Bight Model (GBM), which in turn is nested in the northwest European Continental Shelf Model (CSM). For the Dithmarschen Bight model the bathymetry update takes place every computing time step of the flow simulation and the analysis was focused on two severe events that took place in January 1994 and December 1999. In the medium-term morphodynamic model an input filtering approach has been applied in which a limited number of representative conditions by means of tides, wave climates and storm conditions were defined. The interactions between the flow, sediment and wave models were obtained every time step of the flow model, however, the bathymetric update will take place each morphological acceleration factor value. The performance of the short-term morphodynamic model showed that the maximum morphological changes take place during the storm event (the peak of the storm) with about 1m depth of erosion in the Tertiussand sandbank at most. It has been also noted that the morphological changes due to the tide alone were relatively small within the period considered. The morphological changes due to the two storms events indicate that more significant changes took place during the storm of December 1999 and lower morphological activity was observed from the storm of January 1994. The medium-term morphodynamic model showed that the tide is the main driving force for the initiation of the tidal channels and the storms are responsible for the erosion of the tidal flats. The model also showed no indication that the storm sequences and the chronologies of the wave climates have major effects on the morphodynamics for the simulation period. The evaluation of the differences between the cases simulated including only the tides and those including tides and storms together showed that there are increases in erosion and sedimentation of about 0.4m in the Tertiussand sandbank and about 1m in the Piep tidal channel after including the storms

A TIDAL FLOW MODEL OF THE WESTERN COAST OF LIBYA

This paper presents the hydrodynamics on the western coast of Libya. The investigated area, which is a part of the Mediterranean Sea, is one of the most critical and active coastal region in the country. A 2Dh process-based model for flow based on the Delft3D modelling system from Deltares is constructed for the study area. Extensive field data concerning the tidal constituents were used. The flow model that is necessary to understand the hydrodynamics of the area was calibrated and validated using the field measurements. In this paper, only the water levels and tidal components for the astronomical tide are presented. Calibration and validation of the numerical flow model show that the results of the water level represent the field conditions well. The present study gives insight into the basic hydrodynamic processes of the investigated area. It should help designers and the decision-makers maintain the region for any other economic and social activities. The flow model for the investigated area can be also coupled with any other models like wave, sediment transport, morphodynamic and water quality. &nbsp

Effect of storm events on the morphodynamics of tidally-dominated coastal environment

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732A state-of-the-art process-based model is applied to hindcast morphological developments resulting from severe storms in a study area on the German North Sea coast. The applied morphodynamic model is based on coupled flow, wave and sediment transport models via a bed evolution model. Owing to the complex geomorphological conditions in the study area, a curvilinear grid with an enhanced grid resolution of about 20m along the coastline was implemented. The effectiveness of the model for simulating morphological changes during storm conditions is demonstrated by a qualitative comparison of model results with measurements. This comparison yields good agreement regarding trends and the order of magnitude of bed elevation changes. Comparisons among the modelled morphological changes resulting from severe storms in the study area serve to improve our understanding of the dominating processes during storm events. The bed elevation changes in the study area due to storms were found to be of the order of several decimetres. It was also found that sudden increases in westerly wind speeds in conjunction with neap tides result in enhanced erosive activity

Numerical Simulation of Climate Change Impacts on the Coast of Oman

It is well known that there is an apparent increase in the intensity and frequency of extreme weather events, such as tropical cyclones (IPCC, 2023). This will lead to a significant effect not just on the infrastructure and the economic activities but also on the coastal environments. On the other hand, an increase in the population along the coastal areas in such a country as the Sultanate of Oman will also increase the risk and the hazard. It has been noticed extremely heavy rainfall during the most recent tropical cyclone, Shaheen (October 3 2021). It is also recorded along the Omani coast's extremely high waves during this storm event. Some other tropical cyclones in the past also indicated an essential effect on the Omani coast (Shawky et al., 2021). In this regard, the development of a fundamental understanding of the hydrodynamic behaviour along the coastal system during these events has been necessary. Moreover, the tropical cyclone track and wind speeds have been recorded only for a few temporal spans. This leads to better reliable estimations of such a kind of event. The state-of-the-art process-based numerical model will be utilized to hind cast the hydrodynamic developments from several tropical cyclone events along the Omani coast. A well-calibrated and validated flow model has been set up using Deft3D, a world leader's software (Lesser et al., 2004). Furthermore, the impact of wind-induced waves has been investigated using the SWAN wave model (Booij et al., 1999; Ris et al., 1999). In this paper, four well-known tropical cyclones in the Indian Ocean will be simulated. The four tropical cyclones were selected due to their historical significance and the amount of destruction they caused on the Omani coast. The investigation results showed significant tropical cyclones' effects on the Omani coasts due to their intensity and the cyclones' pattern. Overall, the numerical models that are showing good descriptions of climate change can be valuable tools for comprehending and predicting the influences of climate change on the Omani coast and can be employed to support in the decision-making

Study of Turbulence in Open Channels Using Two-Equation Models

Prediction of the sediment transport in streams requires an accurate estimation of bed shear stress (for bed load) and eddy viscosity (for suspended load). In general, shallow water models employ empirical relationships to estimate the bottom shear stress. However, with the advancement of computing systems, the utilization of advanced turbulence models is getting common. In this paper, a number of model versions are reviewed based on their predictive abilities against the well-known bottom boundary layer properties in open channels and computational economy. Qualitative and quantitative comparisons have been made to infer that the choice of model versions should be based on the field application. For example, the bottom shear stress is very well predicted by the k-? model whereas the cross-stream velocity profile and turbulent kinetic energy are predicted more efficiently by k-? model versions. This study may be useful for researchers and practicing engineers in selecting a suitable two-equation model for calculating various bottom boundary layer properties

A case study of sediment transport in the Paranagua Estuary Complex in Brazil

This paper presents transport of a mixture of cohesive sediments and sand in the Paranagua Estuarine Complex in the south of Brazil. The estuary houses a navigation channel from the Atlantic Ocean to a busy harbour. The channel requires frequent dredging owing to sediment deposition to maintain navigable depth for vessels. A three-dimensional process-based model for sediment transport coupled with wave-current models based on the Delft3D modelling system is constructed for the estuary. Extensive field data concerning current velocity, water level, salinity and suspended sediment concentration were collected. The flow model that is necessary to run the sediment transport model was calibrated and validated using field measurements. In this paper only the results concerning the sediment motion are presented. Calibration and validation of the numerical model show that the results of sediment transport represent the field conditions well. Additional support for the validity of the computed results is provided by field data pertaining to bathymetry acquired in 2005 and 2006. The present study gives insight into the motion of cohesive sediments and the morphological behaviour of the estuary, and should help operators maintain the channel for navigation