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A survey of literature is made on reservoir sedimentation, one of the most threatening processes for world-wide reservoir performance. The sedimentation processes, their impacts, and their controlling factors are assessed from a hydraulic engineering point of view with special emphasis on mathematical modelling. The objective of this study is to find the remaining gaps in the understanding of the relevant features, and the needs for further research. The physics of sediment distribution (such as delta formation and density currents) and the present modelling techniques are identified for various types of reservoirs. Attention is also paid to the operational aspects and the environmental impacts of the reservoir on the river-system morphology. Finally the methods to reduce the sediment inflow, to reduce the accumulation, or to remove the deposits are described. Evaluating the state of knowledge it is clear that a large number of physical processes are involved which are not well understood or hard to simulate. Recommended is to develop more comprehensive mathematical models and to do more specific laboratory research.

An analytical mathematical model is presented for flow and salinity in tidal mangrove swamps that is based one-dimensional approaches. The model is designed with the purpose to develop a method for rapid assessment of effects in mangrove swamps due to changes in river discharges that can also be used in situations with few data. A literature study demonstrated that the changes in salinity control the effects in mangrove swamps on the shortest timescale. The flow section of the model is based on linearisation of the momentum equation as introduced by Lorentz (1926). The salinity section of the model for open water in the swamps (creeks) is based on the equation for trapping in tidal swamps originally proposed by Ridd (1990). The salinity section of the model for groundwater is based on the description of hydrodynamic dispersion. A model with predictive value for groundwater salinity could be developed by incorporating the analytical solution of the flow section in the description of hydrodynamic dispersion and by using the solutions for salinity in creeks as boundary condition. The theoretical model can be used in practice with a relatively small set of field measurements and in combination with an existing model for flow and salt transport in rivers and estuaries.

Fairway Maintenance of the river Ijssel The inland trade is a very important economical activity in The Netherland. Therefore to maintain and improve waterways is a common activity. The main problems that threaten the safety in the shipping are the erosion and sedimentation on the banks, especially in the bend banks. So some studies are necessary to know the best method to avoid the sedimentation and erosion in these places. This study is focused in the effect of a sand trap in the River IJssel over the sedimentation and to try to answer questions about its effectiveness and if it is possible to find a better layout for the sand trap. To carry out this research is necessary to set-up a mathematical model which can reproduce the behaviors of the river and the sand trap. So a mathematical model has been built using the Delft3D software. So, the effectiveness of the original sand trap has been studied and three possible alternatives have been studied too. The alternatives are: - Two different sand traps with same volume of the original one, but shallower, longer than the original one and nearest to the sedimentation zone (alternatives A.1 and A.2). - Sand trap with more volume than the original one and nearest to the sedimentation zone ( alternative B). The results of this study show that the effect of the sand trap over the sedimentation in a bend located 2 km downstream of the sand trap is non-existent. Also the results show that the alternatives A.1, A.2 and A.3 are more efficient, it means that they catches more sediments, but they dont produce any effect over the sedimentation zone. To study the effect of a bigger sand trap and nearer to the sedimentation zone is necessary. Also it is recommended to improve the data about sediment transport, bed levels and discharges in the lower stretch of IJssel. These data will be necessary to carry out a better mathematical model.

The study focuses on the impact of human interventions on the natural behaviour of estuaries in response to sea-level rise. In particular it focuses on the affect of managed realignment on the critical sea level rise (SLRcrit) for the Poole Harbour. Numerical model ASMITA (Aggregated Scale Morphological Interaction between a Tidal inlet and the Adjacent coast, Stive and Wang, 1996) is used to study the response of the system to the external forcing (both natural and anthropogenic). ASMITA model schematises the tidal-inlet system and characterises each model element by a single variable volume. Volumetric data of the Poole harbour inlet elements obtained through the digitisation of the historical admiralty charts was used to calibrate the model. The model assumes that the each inlet elements tends towards an equilibrium volume which can be defined using the empirical equations. These equilibrium equations consist of equilibrium parameters that depend on the regional properties like hydrodynamics and topography of the Poole harbour. Once the model is calibrated, simulations were performed with various sea level rise scenarios (historic and future SLR) to observe the natural behaviour of the Poole harbour. Managed realignment is being introduced in the model and a range of values of critical sea-level rise was obtained and compared with the predicted sea-level rise rate given in the literature for the next century. Results suggest that the “hold the line” management scenario (current situation) would not result in the complete loss of inter-tidal flats and the coastal flooding is unlikely to occur over the next century, as a result of critical sea-level rise values exceeds the predicted rate. However research suggests, introducing realignment (coastline retreat management scenario) reduces SLRcrit values for the estuary; thus making the estuary more sensitive to the predicted future SLR rates.

In this study the river migration model MIANDRAS has been applied to simulations of the planform changes of the river Allier, a tributary of the river Loire in France. The Allier is a very dynamic and natural river system with braided and meandering river sections. Two meandering reaches of the Allier, located between Varennes-sur-Allier and Moulins, have been examined in the present study. MIANDRAS is a numerical model that simulates meandering processes in shallow alluvial rivers with erodible banks. In MIANDRAS the river is schematised as a single meandering channel, as the floodplains are assumed non-conveying. For the prediction of river planform changes, the rate and direction of bank erosion are computed by coupling a steady-state flow and bed topography model with a time-dependent bank erosion model. Sediment gradation, timedependent variations of the bed topography (i.e. migrating bars) and flow exchanges between the main channel and the floodplains are not taken into account. MIANDRAS did not perform satisfactorily in predicting the planform changes of the Allier. The 2(and 3-) dimensional flow processes in flood periods, caused by floodplain constrictions and flow exchange between the main channel and the floodplains, appeared to be an important feature influencing the bank erosion. Therefore, the influence of overbank flow was studied in more detail. The 3-dimensional flow model DELFT3D-FLOW (TRISULA) was used to simulate overbank flow processes in one of the examined reaches of the Allier. The results of the MIANDRAS computations can be explained reasonably well from the results of the overbank flow computations. Near the upstream floodplain constriction, where high bank erosion rates were observed in the prototype river, high velocities occurred in the overbank flow computations. At this location high bank erosion coefficients had to be adopted in the MIANDRAS computations. The relatively low erosion rates at the downstream boundary can be explained by the low velocities occurring in overbank flow. These are due to backwater effects near the downstream floodplain constriction. The small erosion rates at this location resulted in small erodibilities in the MIANDRAS computations. Floodplain bed roughness appears to have a significant influence on velocity directions and magnitudes. The velocity field is correlated to the flow exchange between the main channel and the floodplains. This flow exchange strongly decreases in the case of a higher floodplain bed roughness. These results agree with the results of scale model experiments performed in the Flood Channel Facility at HR Wallingford, England. The results of this study give new indications for the range of applicability of MIANDRAS. Besides the possibility to use MIANDRAS in case of rivers with mainly inbank flow, the model can also be applied to rivers with overbank flow periods, provided that the flow exchange between the main channel and the floodplains is small. A small flow exchange occurs in case of a high floodplain bed roughness, a straight floodplain and main channel, or relatively small flood discharges.

Vermindering door aanpassing van de vormgeving van jachthavens 't Steel en la Bonne Aventure. Jachthavens aan rivieren slibben steeds verder dicht. AIs gevolg hiervan lopen de kosten voor het beheer van een dergelijke haven zo hoog op dat enkele havens misschien zelfs moeten sluiten. Daarom is er landelijk een onderzoek gestart om te bezien of de aanslibbing verminderd kan worden door aanpassing van de vormgeving van de haven. Aanslibbing van een haven is afhankelijk van het uitwisselingsdebiet tussen haven en rivier. In principe komen daar drie mechanismen voor in aanmerking, te weten: • Het getijmechanisme • Het dichtheidsmechanisme • Het stromingsmechanisme In dit onderzoek komt alleen het stromingsmechanisme aan de orde, omdat het getij afwezig is en er verwaarloosbare dichtheidsverschillen zijn tussen water in de rivier en water in de haven. Aan de bovenstroomse zijde van de havenmond ontstaat als gevolg van wervelvorming een menglaag, die een primaire neer aandrijft in de havenmond. Deze primaire neer drijft op zijn beurt weer een secundaire neer aan in het havenbekken. Via dit systeem wordt het sedimentrijke water van de rivier de haven ingebracht, waar het bezinkt. Om te onderzoeken of er maatregelen genomen kunnen worden om de aanslibbing in jachthavens te verminderen is een schaalmodel gebruikt van twee jachthavens aan de Maas te Roermond, 't Steel en La Bonne Aventure. Hierin zijn diverse in dit onderzoek ontwikkelde ingrepen toegepast, zoals een geleidescherm, een paalscherm en een gekromde drempel in de havenmond, en vervolgens is hun effectiviteit gemeten. Het uitgangspunt was de bestaande situatie met een gemiddelde waterstand, maar omdat de Maas nogal eens te kampen heeft met hoogwater is ook de situatie gedurende hoogwater beschouwd. Na het vergelijken van de metingen is gebleken dat het mogelijk is om een aanzienlijke reductie in aanslibbing te bewerkstelligen. Het geleidescherm geeft een reductie van ca. 25%, het paalscherm een reductie van ca. 50%, de gekromde drempel een reductie van ca. 70% en een combinatie van het paalscherm met de gekromde drempel geeft zelfs een reductie van ca. 90%. Deze reducties gelden alleen in de niet-overstroomde situatie. Gesteld kan worden dat het zeker mogelijk is om een vermindering van aanslibbing te realiseren. Hoewel natuurlijk nog afgewacht moet worden wat de reducties in werkelijkheid zullen worden.

Embedding of subsea pipelines for protection purposes is usually done in a ‘Trench – Install – Backfill’ operation. The pipeline can also be embedded after it is installed on the seabed. This method is called post-trenching. When using a trailer suction hopper dredger for post-trenching, a large water jet erodes the soil underneath the pipe creating a temporarily trench in which the pipeline can sink. Large steel pipelines are inflexible and need a considerable free span to sink to the desired depth. The length of the trench is limited as the eroded sand that is brought in suspension starts to settle in the trench when the velocity of the suspension decreases. To be able to predict the length of the trench, the sedimentation velocity in jet induced flow is investigated in this research. The research describes the experiment series that is performed to investigate the behavior of a trench that is created by a vertical jet flow, trailing over a sand bed. The focus is on the sedimentation part of the trench. Concentrations and flow velocities are measured to determine the shape of the trench, the distribution profile and velocity profile. The experiments show a clear relation between the depth of the trench and the length that the trench is open. A deeper trench (due to a higher pressure or lower trail velocity) results in all experiments in a longer trench. The near bed concentration and the sedimentation velocity do not change a lot for different settings of the jet. To see if the theory on the sedimentation process can represent the post-trenching process, a calculation model is made that uses the theoretical concentration profile to calculate the sedimentation velocity. A good similarity was found between the model and the experiments. The experimental research on the sedimentation velocity in a trench that is created in a post-trenching process, indicates that sedimentation velocity is largely independent of the jet parameters. To make the trench longer, it has to be deeper to lengthen the path that the bed has to travel. A test with a second run over the bed proved highly effective due to the high porosity of the sand that settles in the first run, the maximum excavation depth is twice the depth of the first run. By implementing a pipeline in the experiment it is investigated if the pipeline has an influence on the flow conditions and sedimentation velocity.

Sedimentation in reservoirs is a consequence of constructing a barrier in a flowing river, which results in a decrease of the transport capacity of the river. The storage capacity of the reservoir decreases due to the accumulation of sediments and the river downstream starts to erode due to the disturbance of the sediment balance. Water Injection Dredging can be an interesting option in order to counteract these processes. This method injects water in the bottom of the reservoir, creating hereby density currents which are capable of transporting large amounts of sediment. The sediment can in this way be transported towards the dead storage of the reservoir or be sluiced out of the reservoir through the bottom outlets of a dam, which will increase the storage capacity of a reservoir considerably. Because the density current uses gravitation and the natural slope of the reservoir, this method is a relative cheap and quick way to transport sediments. The dredging installation is also relatively simple and basic. If the sediments are sluiced through the dam, the disturbance of the sediment balance in the river can be counteracted. It is however necessary to investigate whether or not the river is capable of dealing with the increased sediment load in the river downstream of the dam. The high production rates of Water Injection Dredging results in high sediments peaks, which the river should be able to transport. Case studies done in the scope of this thesis show that the method can be a competitive and feasible method that can be used to counteract sedimentation problems in reservoirs, if some specifications of the investigated reservoirs were different. If these specific requirements for Water Injection Dredging in reservoir are met, the method can restore the reservoir capacity in a cheap and effective way. More research and testing the method in practice will be necessary however.

In Alberta (Canada) bitumen is extracted from the mined oil sands ore by a process that uses hot water. This process produces large amounts of tailings, which is a mixture of water and sediment particles. These tailings are stored in large ponds to allow the sediments to settle out of suspension. The water is recycled in the hot-water process and the solids are used for land reclamation in the mine site areas that have been mined out. The fine particles in the tailings settle very slowly so companies are trying to find ways to accelerate the dewatering process. A dewatering process consists of three phases: sedimentation, consolidation and ripening when the sediment layer is exposed to air. Samples of the tailings were shipped to Delft University of Technology to perform dewatering experiments. From one of the first experiments it was suspected that the moisture content of the samples was already too low for the sedimentation phase to precede the consolidation phase. The goal of this project was to find out if there is a relation between the moisture content at the transition between the sedimentation and consolidation phases and the liquid limit and liquidity index of the soil. To be able to compare the results with another type of soil, the same tests were performed on river clay. Three sedimentation columns with different moisture contents were prepared for each of the materials and standard tests (BS 1377) were performed on the soils to determine the liquid and plastic limit from which the liquidity index was derived. To further characterize the materials, hydrometer tests were performed. From the British soil classification chart was deduced that the thickened tailings were to be classified as an intermediate plasticity clay and the river clay as a high plasticity clay. The major conclusion that may be drawn from the test results is that the liquidity index at the boundary between sedimentation and consolidation for both materials is around 18 and 19 for both soils. Furthermore the moisture content at the transition from the sedimentation phase to the consolidation phase is around ten times higher than the liquid limits of the materials. Another conclusion is that the consolidation phase shows no acceleration on a logarithmic time scale when it is preceded by the sedimentation phase, where this acceleration is visible when the sedimentation phase does not occur.

Rijkswaterstaat and the Dutch contractors have many years of experience in the removal of silt and sand from the Rotterdam harbour. In all those years a great deal of valuable experience has been gained with the behaviour of silt in the harbour. They never succeeded, however in making an estimation/prediction of the amount of sedimentation which has taken place, based on natural parameters like wind river discharge etc.. In this study an attempt is made to build a Neural Network model in order to perform an adequate simulation. A Neural Network is a powerful nonlinear data analysis tool; the network developed for the sedimentation simulation is called Mud Brain. In order to perform the Neural Network analysis it is necessary to make a re-analysis of the existing measurement data. It is also necessary to make an inventory of the knowledge available about the sediment transport to the Maasmond, starting off with the large scale sediment transports in the Southern North sea. A silt and sand transporting residual-current runs parallel to the Belgian and Dutch shoreline, it is mainly driven by the tide but is strengthened by the ruling wind direction which is from the south-west. Sediment supplied through the Channel and eroded from the Vlaamse Banken travels to the to the Wadden Sea and Oester Gronden. While on transport, sediment sometimes settles under tranquil weather conditions, however, most of the sediment is eroded again and travels further north. Due to the unnatural depth, a great deal of sediment is caught in the Maasmond. The material which enters mostly settles in dredging area F. About 40 % of the material is further transported further along to dredging area E (the buffer pit). In their present state, numerical models are not yet able to predict the amounts of sediment settling in the Maasmond, based on certain natural parameters. The best option for a sediment prediction seems to be a statistical analysis on the relation between the amount of sediment and some natural parameters. For most patterns information about the past as well as information about the present is included (except for the first two patterns which already contain a hitorical time span). In order to provide the statistical analysis with the best possible target outputs, a new sedimentation model is drawn up. This model uses the 1.03-level, the 1.2-level, the amounts of dredged material and some consolidation theory in order to calculate the quantities of sediment, which have settled in a certain dredging area, for every week. This reports presents a test for two statistical methods: 1. Linear regression and 2. Neural Network processing. The Neural Network produces results with a 50 % smaller error margin than the linear regression. The Neural Network results are produced with the so-called 'Leave One Out' testing procedure. This procedure is applied to include all available patterns in the test procedure. After post processing the results of the LOO test fall within an accuracy margin of 23,000 TDS and 34 %. When the standard deviation on the amounts of sediment (= 34,000 TDS, target outputs of the model) are taken into account this result seems adequate. The Levenberg-Marquadt algorithm has proven to produce faster and more accurate results in the sedimentation prediction than conventional back propagation. Recurrent networks and data reduction provide valuable tools in making initial estimations of the attainable accuracy and the important parameters. The most promising potentials of Mud Brain are: • An analysis of the relative importance of the different input parameters on the amount of sedimentation • The application of Mud Brain for a sedimentation prediction in order to smooth the dredging logistics. • The combination of Neural Networks and mathematical physical models in a hybrid model. In this combination the neural network can function as a filter on the mathematical-physical model results.

At the Cao Jing district in Shanghai, China, a landreclamation project is planned. The object of this project is to stimulate the natural process of sedimentation. This report comprises the results of a study concerning the optimum lay-out of dikes in the reclamation-area (see Fig. 0.1 and 0.2). In this report particularly the influence of the waves (wind-waves and swell) is discussed. In the foregoing report "LAY-OUT part I" the influence of the tidal motion has been discussed. In this analysis the wave-climate at the Cao Jing district has been calculated on the basis of measurements at cape Nan Hui, concerning the waves and wind-speeds. Next, the optimum dimension of the opening-size is determined, based on wave-diffraction. The optimum dimensions of the field (length and distance) are determined by the admissable fetch-length (for wind-generated waves). Finally the height of the longitudinal dike is optimized, based on wave-transmission.

Siltation of harbour basins and navigation channels is a serious problem in the port of Rotterdam as well in many other harbours all over the world. Due to siltation, basins and channels require frequent maintenance dredging to guarantee safe navigational depths. The costs associated with these dredging activities are quite high. To keep the channels and harbours in Rotterdam navigable, Rijkswaterstaat and the Port of Rotterdam are dredging approximately 15 million m3 of sediment a year. The dredging cost of the Botlek Harbour only is already about 3 million Euros a year. It is a task to keep the costs in the Port of Rotterdam as low as possible to compete with other ports. Reducing maintenance dredging costs is in line with the goal of the Port of Rotterdam to be the most competitive, innovative and sustainable port in the world. Most sedimentation within the maintenance area of the Port of Rotterdam occurs in the Botlek. According data, between 1.5 and 3 million m3/year is dredged in the Botlek Harbour. Although the current dredging philosophy more or less works, the question arises whether there are solutions that are more cost-effective. However, the problem is so complex that it narrowed down for the sake of research quality. The main causes of siltation in general and specifically in the Botlek Area form an important part of the study. Hydrodymical models (SIMONA & Delft3D), were used to gain insight in the sedimentation problem. The focus in this thesis was more on the hydrodynamics. The exchange mechanisms between the river and Botlek Harbour were investigated, which were needed to examine the effectiveness of certain solutions. In practice a lot of solutions are proposed in literature, however in this study only a couple of ‘hard’ measures are investigated. The first possible solution that was examined was the use of a Current Deflecting Wall. It turned out that the hydrodynamics were very sensitive to the configuration of the CDW. While sometimes it would lower the exchange flow, at other cases it would even make the problem worse. The second solution was to make a gap in the Geulhaven dam. However this was not a good solution as high exchange flows occurred. The last proposed solution, the filling of the underwater dam, seemed more feasible as it would decrease the exchange flow according the numerical models. The research has first order results which can be used in further studies. According to this results, certain solutions will decrease the exchange flows. On turn it would very likely result in lower sedimentation rates in the Botlek Area. It is expected that some CDW configurations and the filling of the underwater dam would have a positive effect when it comes to sedimentation. However, this research is the first step of an extensive study that must made to deal with the problem. First of all many things can be done to improve the models, for example by using a higher spatial resolution. Secondly, other sets of conditions must be modelled to see what kind of effect this has on exchange flows. In addition, sediment must be included in the models to have more insight on the sedimentation itself. The next step would be a feasibility study, including a cost benefit analysis. It would be wise to improve the models further and to make a scale model for the most feasible solution. In the ideal case, were all steps are positive and hard conclusion can be made, it would be a good idea for the Port of Rotterdam to start a pilot.

This is not the main report, but the partial report. Portugal has a coast of approximately 800 km containing a lot of interesting coastal phenomena, such as estuaries, land spits, rock coasts, lagoons, cliffs and rias (areas af sandbanks and canals in open connection with the sea). Also a lot a different harbours can be found along this coast. The problems encountered during the desk studies and the visits vary drastically, from the closure of a river by sedimentations of the littoral drift in Praia de Areia Branca, to the stability of the tetrapods on the rubble mound breakwater in Nazaré. For the lay out of a fishing harbour and the handling of the fish, the D.G.P has developed a procedure which is applied in many harbours. Erosion and sedimentation form the problem in Aveiro where also a new commercial dock is just finished. Viano do Castello is the harbour in the north of Portugal where the river bed was changed as one of the necessary works in order to enlarge the capacity of the harbour. A new coal terminal is almost finished in Sines harbour as the first phase of the master plan for the development of this area. The breakwater which is exposed to very severe storm conditions is protected with blocks up to 72 tons, to resist the design waves of 11 meters! The development of the harbour of Portimao in the Algarve was done in only 10 years, including a fishing dock, a commercial and tourist dock and a naval quay. The entrance of the Ria de Faro suffered from severe erosion after the entrance was stabilized by the construction of two breakwaters. The repairing is in full action at the moment. The harbour of Lisbon contains a lot of different harbour activities, but will concentrate in fut ure on the development of containers, cereal, and tourism.

Student project report, in cooperation with Smith-Warner International Ltd. (SWIL), Kingston, Jamaica. At this moment the shipping channels in Kingston Harbour, Jamaica, slowly accrete. When the harbour is expanded, the local and global sediment transport is likely to change. During this project it is investigated whether these changes are significant and if they will have a negative influence on the Kingston Harbour area. Also the increase of flood risk for the area surrounding Hunts Bay is investigated. This investigation is done by modeling the hydrodynamics of the Kingston Harbour area with MIKE21 and Delft3D, where after both modeling programs are compared to each other. For the input data for the models, research has been done concerning the boundary conditions. This data is gathered from several projects done in the past about other areas in the harbour and fieldwork in Hunts Bay. During the year, most of the wind comes from the east and south-east direction. There are also two mayor streams which debouch into Hunts Bay, namely the Sandy Gully and the Rio Cobre. Since there is only discharge known about the Rio Cobre (daily values from 1985 to 2010), only the Rio Cobre is taken into account. The maximum measured value was 563 m3/s (during hurricane IVAN) and the average value is about 12 m3/s. For the sediment input data some fieldwork is done in Hunts Bay to gather information about the type of soil. From this it is concluded that it is silt, which is confirmed after a lab research of the sediment. However these accurate soil properties couldn’t be implemented into the models due to the lack of time. During the fieldwork also a bathymetric survey was done, which showed that Hunts Bay is sedimented compared to the previously used bathymetric data, gathered from admiralty charts in 2000. Calibration of both models is done by comparing it with the measured water level and flow velocities underneath the Causeway Bridge. Since this is the only point where data was available for, the calibration kept global, and should be improved in the future. The modeling showed that most of the sediment transport into the shipping channel is caused by the high discharge of the Rio Cobre. Ivan showed the most extreme sedimentation and the biggest change due to the expansion. In the present situation the shipping channel is gradually silting, with two areas where the siltation is concentrated. With the first phase expansion these ‘mountainous’ areas will be much more concentrated. However it can be concluded that the changes in the sediment transport due to the first phase expansion are not significant and will not lead to more problems than there are without this expansion. For this problem a sediment trap is proposed. At first it was placed just eastward of the Causeway Bridge, but this didn’t solve the problem and it would be in the way for the phase two expansion. Therefore a sand trap is designed in Hunts Bay, just westward of the Causeway Bridge. This location is really effective, since it stores the sediment from the rivers. This solution prevents the shipping channel to silt. Again, since the lack of reference data, on the size of the pit nothing can be said.

The Lai Giang inlet located in Binh Dinh province incorporates various features of the estuaries in the Central part of Vietnam. Belonging to the micro-tidal and wave-dominant coast and influenced by the monsoon regime, the inlet has a seasonal character. During the dry season, as the river flow diminishes, the wave action causes high level of sedimentation and closes up the inlet eventually. In flood season, as the river discharge is high, the channel is scoured and the inlet begins to migrate. The high sedimentation level and migration of the Lai Giang inlet has been a serious problem of Binh Dinh province for a long time, because it is the only exit for the floodway. It is an anchorage and also the connection between the sea and the aquaculture area of Hoai Nhon district. The high level of sedimentation at the entrance of the inlet prevents river flood from flowing smoothly, thus leading to overflow in lowlands and navigation issues. In recent decades, the exploitation and protection of Lai Giang area have been studied in various forms of scientific researches and projects by different scientists and local professional agencies. However, the studies have only focused on hydraulics, hydrology and on adjusting the flow of Lai Giang river. There are only general and basic studies on the entrance of the inlet. The main objective of this research is to understand the morphological behaviour of Lai Giang inlet. The specific interest is focused on the main factors which are the tidal characteristic, the wave climate and the river flow during the flood season, and the interaction between all these factors that influence the morphological changes. The study starts with the collecting and analysing all the documentations to come up with a conceptual model of the Lai Giang inlet to explain how the sedimentation and the migration processes happen. Then, the Delft3D modelling software, which can model (tidal) flow, waves and sediment transport, has been applied to confirm the hypothesis and gain further knowledge. According to the data analysis, the conceptual model as well as the descriptive and quantitative result of the model, we can make the following main conclusions: 1. The wave climate in this area has seasonal characteristic and is dominated by two main directions; Northeast and Southeast in winter and summer monsoon, respectively. 2. During the summer monsoon, the longshore sediment transport moves towards the north, bypasses the entrance of the inlet and gradually builds up on the down-drift spit due to the Southeast Wave. 3. During winter monsoon, the Northeast wave intensifies the southward longshore sediment transport leading to the large amount of sedimentation in front of the inlet. At the same time, the significant river flow flushes away the sediment deposits at the main ebb channel located nearer to the up-drift spit. Thus the sedimentation could not take place at the up-drift spit. The sediment displacement at the up-drift and down-drift spit made the inlet migrate to the north gradually. Finally, the possibility to stabilize the inlet is discussed to give the optimum solution for this area.

Om flora en fauna de kans te geven zich langs scheepvaartwegen te vestigen en voort te planten zijn natuurvriendelijke oevers nodig. Voor kanalen is een speciale natuurvriendelijke oever ontworpen : de natte strook. Tijdens onderzoeken naar het functioneren van de natte strook is een verondieping hiervan geconstateerd, hetgeen, in verband met ecologische doelstellingen van de natte strook, niet wenselijk is. Het onderzoek, waarvan in dit rapport verslag is gedaan, had als doelstellingen : - het analyseren van de oorzaak en aard van de sedimentatie; - het voorspellen van de sedimentatie; - het ontwikkelen van oplossingen die de sedimentatie voorkomt of vermindert; Voor het analyseren van de oorzaak en aard van de sedimentatie is een procesanalyse gedaan. Hieruit bleek dat de waterstandsverandering ten gevolge van een passerend schip de maatgevende oorzaak van wateruitwisseling, tussen natte strook en kanaal, is. Verder bleek uit de procesanalyse dat het slib in de natte strook hoofdzakelijk bestaat uit zwevende sediment dat tijdens een scheepspassage wordt opgewoeld en vervolgens vanuit het kanaal de natte strook instroomt. Het voorspellen van de sedimentatie is gedaan met behulp van twee eendimensionale berekeningen. Deze berekeningen bleken, in vergelijking met praktijkgevallen, voor twee extreme gevallen goede resultaten op te leveren. Deze extreme gevallen zijn: een natte strook met een enkele opening in de vooroever en een natte strook met een poreuze vooroever. Voordat met het ontwikkelen van oplossingen, die het probleem van sedimentatie voorkomen of verminderen, is begonnen, is eerst gekeken naar het sedimenttransportproces van en naar de natte strook. Uit dit proces blijkt dat, ten gevolge van een scheepspassage, eerst sediment-arm water de natte strook uitstroomt en wordt vervangen door sediment-rijk water vanuit het kanaal. De oplossingen die bedacht zijn om de sedimentatie te verminderen, zijn de volgende : - het verminderen van wateruitwisseling door de openingen verder uit elkaar te plaatsen; - de valsnelheid van de deeltjes in het water te verkleinen; - het sediment in een beperkt en gecontroleerd gebied laten neerslaan door het maken van een slibvang achter de opening.

There are plans for the construction of a multi-purpose dam in the White Volta River near Pwalugu in northern Ghana. The reservoir that will be formed should be beneficial for hydropower generation, irrigation and fishery. Up to now there has been no research into the morphological consequences of the creation of this reservoir. In this study the rate and location of sedimentation in the reservoir and the erosion of the riverbed downstream of the dam are investigated. Sedimentation could lead to a loss of storage capacity having less water available for hydropower generation and irrigation purposes. Delta deposition (i.e. sedimentation of coarse sediment in the upstream part of the reservoir) could lead to higher water levels in the river upstream, causing an increased risk of flooding. Erosion of the riverbed downstream of the dam could lead to decreased water levels in the downstream reach. This could provoke riverbank collapse and have negative effects on agriculture due to lowering of groundwater levels. Possibly bridges downstream could be damaged by scouring of the foundations. The aim of this research is to understand the large-scale morphological processes and to give first order estimations of the morphological changes. Additionally, the sediment balance of the White Volta catchment is investigated to estimate landscape erosion. The method consists of a literature study, a field study and a morphological model (SOBEK) of the White Volta River. The total sedimentation in the intended reservoir has been analysed by determining the yearly sediment transport of the White Volta River. The estimation is based on field measurements, conducted in September 2011 at a location close to the proposed dam site, supplemented with a literature study and theoretical transport formulas. The yearly average sediment inflow appeared to be ± 1 million ton/year. The theoretical trap efficiency of the reservoir is nearly 100%, so it is assumed that all sediment will be deposited. If all sediment settles in the active storage of the reservoir, this would mean a storage loss of 3% per 100 years. The impact of this storage loss on the functions of the reservoir is considered negligible. The delta deposition (i.e. sedimentation of coarse material) and the erosion downstream of the dam have been estimated using SOBEK RE, a 1D software package capable of solving the hydrodynamic, sediment transport and morphological equations. The model parameters followed from the field research. The delta deposition depends on the water level variation in the reservoir. If the water level varies between maximum and minimum operative level, the reservoir will vary in length over 40 km and most of the delta deposition will occur in this region. The delta deposition is propagating in both upstream and downstream direction. Due to upstream propagation the riverbed level upstream of the reservoir will also increase. After 50 years, the effect is restricted to ± 30 cm just upstream of the lake and has damped out at the border of Burkina Faso. The water levels will slightly increase during high flows. More research is needed to analyse the increased risk of flooding. Erosion of the riverbed downstream of the dam will occur. The released flow through the dam is expected to be sediment-free. As the sediment concentration is lower than the sediment carrying capacity, the river will take up sediment and the bed will experience erosion. The riverbed level could decrease by 20-30 m in 50 years just downstream of the dam. The erosion rate is reducing in downstream direction, but propagating in time. After ± 30 years a bridge near Pwalugu could be affected. The erosion could be limited locally if any coarse layers are present beneath the riverbed. The erosion rate depends on the released flow through the dam, which is determined by the operational strategy. Spillage could occur when the reservoir gets completely filled. These high flows will have a substantial negative effect on the erosion. Spillage cannot be completely prevented, but the risk could be reduced by ensuring that the lake is at minimum level at the start of the rain season. The drawback of this solution is a decreased energy generation, as the lake will not fill up completely during dry years. The sediment balance of the White Volta catchment is based on sediment deposition and erosion rates. During the dry season there is a supply of Saharan dust into the catchment by so-called Harmattan winds. During the rain season eroded material is flowing out of the catchment as suspended sediment in the White Volta River. The Harmattan dust deposition rate has been derived from literature. The sediment deposition and erosion rate are equal (± 15 mm/1000 years), therefore there is no net landscape erosion in the White Volta catchment. Some parts might be eroding and some parts accumulating, but on average there is equilibrium. To analyse if there are areas more prone to erosion, the origin of deposited sediment on the riverbanks was analysed. This sediment has been collected during the field research in September 2011 and subsequently the texture and mineralogy have been analysed. This has been compared to the composition of the soil in the catchment and the composition of Harmattan dust. Both compositions were derived from literature. The texture of the deposited sediment on the riverbanks appeared to be mainly silt and clay. The mineralogy of the sediment is quartz, feldspar and kaolinite. As these minerals are abundant in the soil as well as in Harmattan dust, no definite conclusions can be drawn on the origin of the sediment. The general conclusion is that the creation of a reservoir will have morphological effects in the reservoir and downstream of the dam. In the intended reservoir sedimentation will occur, but the effect on the functions of the reservoir is negligible. Delta deposition will mainly occur within the reservoir and partly in the upstream riverbed. As the sand will be spread out over a large distance the riverbed increase will be limited. The effect on the water levels in the river should be further investigated. There will be significant erosion of the riverbed close to the dam. In the future the riverbed erosion could damage Pwalugu bridge. Other negative consequences such as bank collapse and the draw down of groundwater levels could occur locally. Applying sediment management strategies could reduce the impact on the river morphology. Possible measures to reduce the erosion and sedimentation rates include dredging or sluicing of high-turbidity currents. The factors that are most determining the results of this study are the riverbed composition and the suspended sediment load. In order to obtain more accurate results, model refinement should start with collecting more data in the field.

The harbor of Surgidero de Batabano is a harbor that lies in the Gulf of Batabano in the South-Western part of Cuba. It serves as a connection between the main land of Cuba and the islands 'Isla de la Juventud' and Cayo Largo. The Batabano harbor suffers from sediment accretion. The accretion of sediment is harmful to port operations, since the depth of the quays and approach channel decreases gradually and ships are no longer able to enter the harbor. Since 1959 maintenance dredging is required every 4 years inside the manoeuvre area of the harbor, along the quay and inside the approach channel, in order to keep the harbor available for shipment. This is a costly operation. The Cuban harbor authority, APN (Autoridad Portuaria Nacional), want this problem to be solved. When considering the problems described above, the goal of this project is defined by the following: 'To reduce the frequency of dredging of accreted sediment in the harbor of Surgidero de Batabano, while keeping in mind costs, future plans, impact on the environment as well as local facilities'. Furthermore it is very important to calculate the amount of sediment accreting in the harbor and its origins. This information is useful when considering the solutions for the problems. During the analysis of the project, the project site has been investigated by literature and a site visit. The boundary conditions have been determined and the technical demand have been specified. The desires of the APN have been taken into account as well. Using all information obtained in the project analysis, the sediment transport processes inducing the accretion of sediment in the harbor have been analysed. Using theory, calculations and computer simulations, it was discovered that a combination of alongshore and cross-shore sediment transport governing the accretion in the harbor: - Alongshore transport of sediment along the coast, mainly from East to West, generated by normal wave conditions from an East/South-East direction. Sediment transported by this alongshore current, will be deposited in between the breakwaters; - Cross-shore transport of sediment perpendicular to the coast, where both sediment from deeper waters as well as accreted alongshore sediment in front of the harbor is transported by normal and extreme conditions. With the source of sediment known, several preliminary designs were created. Using a Multi Criteria Analyses, cost estimation and risk evaluation 4 preliminary designs were selected to be designed in further detail; extension of the existing Eastern breakwater, extension of the Western breakwater, a combination of these two and the current solution (remain dredging every 4 years). The main reasons for selecting these designs are: efficiency against accretion one the one hand and the wishes of the APN on the other hand. In order to obtain an optimal solution, the above mentioned designs were varied in layout. From these 9 layout options the 4 best options were selected as final designs to be further elaborated. These were a Western breakwater (attached and detached), an Eastern breakwater and a combination of a Western- and an Eastern breakwater. Using theory, calculations and computer simulations, the effectiveness against accretion in the harbor was estimated. Every design was evaluated using an Multi Criteria Analyses (MCA). The costs of each design has been determined. Using both costs and the MCA the best design was selected. The design to be recommended, is the combination of an extension of the existing Eastern breakwater and the expansion of the Western breakwater. Though this is not the cheapest option nor the most effective against accretion of sediment, the combination of these factors give the best overall results for a life span of 50 years. Another great advantage of this design, is the fact it can be built in two phases: first the Eastern and last the Western breakwater. In this was APN will be able to spread the costs of the construction of the design over a longer time.

As one of the most fast growing species on earth, microalgae provides great potential to satisfy the ever increasing demand in food, energy and material in a sustainable way. The focus for this thesis work is on one of the most important bottle neck of microalgae harvest process: microalgae dewatering, by CFD modeling of the flow and sedimentation separation in Evodos SPT centrifuge. Various microalgae dewatering technologies have been reviewed and evaluated. Compare to traditional conical disk centrifuge Evodos SPT centrifuge provides 10% to 20% energy consumption, removing up to 95% extracellular water and other benefits i.e. mechanical simplicity and process flexibility etc. In the model, the fluid dynamic behaviors of multiphase flow has been considered. In this research a complete 3D CFD model of the Evodos centrifuge consisting of five sub components have been built. The particle behavior for the centrifugation separation is based on DPM (Discrete Phase Model) in Fluent. The result of the 3D CFD model gives a clear overview of the pathline, flow pattern and pressure profile inside the centrifuge as well as separation efficiency on particle sizes. The model has been validated through visual result from algae separation test runs, theoretical equations and starch test run measurements. A test and sample taking with starch solution has also been carried out on Evodos site in Breda. This thesis work laid a good foundation for future studies in the CFD modeling of Evodos SPT centrifuge and similar machines. The future focus should be on optimizing the geometry of the parallel plates, impeller chamber for separation efficiency; understanding the effects and impacts of operation conditions and further develop the multiphase model.

The sedimentation behavior of silt particles in the hindered settling regime has been considered. Therefore, laboratory experiments are carried in especially designed settling columns. Silt-water mixtures are prepared and allowed to settle at various initial concentrations. During the settling process, a continuous vertical concentration profile is measured. Settling velocities are obtained from these profiles and are compared with the widely used Richardson and Zaki (1954) expression. This comparison showed that the Richardson and Zaki expression underestimates the settling velocities for the finest silts at high concentrations. For the coarsest silt the Richardson and Zaki expression performed will with the measured data. We anticipate that this is the effect of the particle size on the apparent viscosity of the settling silt-water mixture.