94 research outputs found
Velocity profiles of sea currents
No full textSome monitoring surveys were carried out in spring seasons, during March 2003, along the Southern Adriatic coast. A vessel mounted acoustic Doppler current profiler was used to measure the vertical distributions of current velocities in some selected stationing points. At the same time and locations also a CTD recorder was used to measure water temperature and salinity. The aim of the paper is to investigate these field measurements of sea currents and to model the measured velocity vertical profiles by means of some classical empirical laws, thus testing their ability to reproduce the velocity field. The analyzed data refer to a complex domain, characterized by an irregular bathymetry and a roughness due to non uniformseabed vegetation. Consequently the validity of the theoretical velocity laws along with their classic parameter values has not necessarily to be expected. Therefore, a modified form of the velocity-defect law is here proposed
Machine-learning and physics-based numerical modelling for flood level forecasting in rivers: insights from a case study in Italy
No full textThis paper considers the case study of the Parma River (Italy) to highlight drawbacks in data-driven methods for flood forecasting, in particular their limited flexibility in accounting for possible modifications in the river geometry or roughness, in comparison with physics-based models, which can be updated quite easily
Idealised modelling of estuarine development affected by human interventions and climate change
Get PDFEstuaries worldwide are facing the challenge of coping with changing climates. Insufficient supply of sediment to overcome sea-level rise can increase flood risk and saltwater intrusion and drowning of ecosystems. To explore how estuarine eco-morphology is affected by large-scale human interventions and climate change, an idealised eco-morphological model is developed and validated. The model represents the Nieuwe Waterweg estuary in the Rhine-Meuse Delta. Short-term simulations (1 year) are performed after human-induced changes and projected climate changes are implemented in the model.The model is able to represent annual morphological trends. Results show the sensitivity of the system towards channel depth and the presence and size of wetlands. Simulations will be repeated with projected future climate forcings, enabling assessment of estuarine development after large-scale changes for the present and the future
Evaluation of emerging behaviours on anthropogenic shores with a cellular automata model
Get PDFThis study aims to develop a model to explore the emerging morphological development of anthropogenic shores. We extended an existing Cellular Automata model for the combined development of Dunes, Beaches and Vegetation (DuBeVeg) by including longshore sediment transport and coastline retreat, sand armouring of the beach, and the formation of beach scarps due to wave action. These processes were combined with aeolian, hydrodynamic, groundwater, and vegetation dynamics that were already represented in the model. The extended model was evaluated for a schematized version of the Sand Motor, a mega-nourishment in front of the Dutch coast. The simulated scale and types of dunes compared well with the real dunes that have developed on the Sand Motor since its construction in 2011. These preliminary results show that the extended model can represent the development of mega-nourishments realistically and can be used to assess the goals of such anthropogenic shores for different configurations and scenarios
Bioengineering in front of a river dike:Wave attenuation by vegetation
Get PDFBioengineering is a novel way to reduce the application or dimensions of hard constructions. In the Dutch Noordwaard polder a vegetation field is proposed in front of a planned dike to damp waves such that the desired dike height can be reduced. To investigate the impact of vegetation on waves, the description for wave attenuation as derived by Mendez and Losada (2004) was implemented in the wave model SWAN. The SWAN-VEG model was tested by performing a sensitivity analysis and by calibration and validation on experimental flume data. The model showed expected behavior and calibrated values for the drag coefficient gave reasonable correlations between predicted and measured wave attenuation, except for a plant with flexible floating leaves. Application of the model to the Noordwaard polder showed that a field of willows is able to reduce wave heights by 70% under extreme conditions. This allows a lower dike that fits better into the landscape while maintaining the required safety standard
Modeling oxidation ditches using the IAWPRC activated sludge model with hydrodynamic effects
No full textA mathematical model is presented to predict the concentrations of the active heterotrophic biomass, the readily biodegradable substrate (soluble COD) and the dissolved oxygen (DO) in a completely aerobic oxidation ditch. The model involves the one-dimensional convection-dispersion equations for biomass, COD and DO. Hydrodynamic effects are represented in the model by the values of the average flow velocity and the dispersion coefficient. Biological processes are described in the model according to the IA WPRC activated sludge model, using typical values for the model parameters at 10°C. The equations are solved with the finite volume method. The application of the model leads to the following conclusions: (i) Steady state biomass concentrations are almost constant throughout the ditch. (ii) Steady state COD concentrations in the ditch are very low, and COD removal efficiency is practically independent of the values of the flow velocity and the dispersion coefficient. The distribution of the COD concentration in the ditch is less uniform, when small values of the dispersion coefficient are used. (iii) The distribution of the DO concentration in the ditch is very sensitive to the values of the flow velocity, the dispersion coefficient and to the capacity of the rotors. DO concentrations increase when the dispersion coefficient decreases or the flow velocity increases. (v) Daily sludge production, oxygen requirements and sludge age are calculated equal to 0.44 g (g COD removed)‒1, 0.56 g (g incoming COD)‒1 and 6.3 days, respectively.</jats:p
Verification and application of a mathematical model for the assessment of the effect of guiding walls on the hydraulic efficiency of chlorination tanks
No full textA mathematical model is applied to the tank of Kipseli in Athens, Greece, which is used for storage, balancing and emergency chlorination. A Flow-Through Curve (FTC) experiment is performed for the initial geometry of the tank. The shape and the characteristics of the FTC show a very poor hydraulic efficiency, with extensive short-circuiting, intense mixing and low detention times. To improve the hydraulic efficiency of the tank the use of four alternative arrangements of guiding walls is examined by the model. Prior to its application, the model is verified by comparing the predicted FTC with the experimental. A satisfactory agreement is observed between the calculated and the experimental curves. Then the model is applied to calculate the flow field and the FTC for the four arrangements. Calculations are compared and the arrangement which shows the highest hydraulic efficiency is proposed for construction.</jats:p
Modelling of oxidation ditches using an open channel flow 1-D advection-dispersion equation and ASM1 process description
No full textA river water quality model is presented for the prediction of the concentration fields of the water quality variables in an oxidation ditch performing carbon oxidation, nitrification and denitrification. The model involves the one-dimensional convection-dispersion equations for all the variables, which are described in the IAWPRC Activated Sludge Model No 1. The model is applied to a typical oxidation ditch to show that all variables, with the exception of DO, are uniformly distributed in the ditch; thus permitting the characterisation of the oxidation ditch as a completely mixed reactor. The DO concentration, which controls the reaction rates of almost all the processes, shows a plug flow behaviour. The potential of the present model to be used to improve the DO control system of the ditch and to perform real time predictions is also demonstrated. All calculations have been performed with a PC.</jats:p
Prediction of hydrodynamic characteristics of oxidation ditches using the k-ε turbulence model
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