· · · Institutional Repository

Quick user guide for Jesew, a computer program for 'Joint Ecological and Socio-economic Evaluation of Water resources development. The program is originally written in Basic (Torno, 1988), but for TU Delft and Unesco-IHE Delft rewritten as a spreadsheet application.

In overwash beaches, response of a barrier profile as a whole to storm wave attacks can be distinguished into seaward and landward parts that are associated with two respective across-shore driving processes i.e. surge erosion, and overwash. Modeling of overwash relies heavily on the specification of wave overtopping from the seaside (see problem schematization in Fig.1). In return, overwash imposes a non-zero landward sediment transport rate and thus significantly modifies also the seaward profile, especially on the beach face area. This defers substantially from cases of high beach profiles where there is no or negligible transport in the landward direction. These two above cross-shore processes are therefore well interrelated and must be convoluted in one single model. In order to form the basis for the development of a numerical model of low-crested sand barriers response to wave attacks, two successive test series were carried out to increase physical insight into wave overwash. Low-crested condition corresponding to moderate to severe overtopping was selected for all the tests.

Lecture notes on dikes and revetments, part on stone pitching revetment design. Design rules for concrete block revetments.

Overzicht van kunstmatige eilanden t.b.v. de oliewinning in arctische gebieden (rond de Noordpool, Beaufort Sea). Includes a risk analysis for such an island

Aan het begin van deze studie bestond onduidelijkheid over de vraag in hoeverre het eventueel falen van een geometrisch open filterconstructie in een open waterloop nu het gevolg zou zijn van onzekerheden met betrekking tot het bij het ontwerp gehanteerde rekenmodel, of juist van onzekerheden met betrekking t o t onnauwkeurigheden bij de bouw van de constructie. Deze studie moest een antwoord op deze vraag geven, alsmede een lijst met een overzicht van de grootste 'boosdoeners'. Deze lijst kan dan fungeren als richtlijn bij het opstellen van een programma voor de bij de huidige stand van zaken meest nuttige vervolgonderzoeken op dit terrein. Bij de start van dit project was sprake van een situatie waarin meerdere rekenmodellen circuleerden voor de beoordeling van de stabiliteit van geometrisch open filterconstructies in open waterlopen. Er bestond veel verwarring over de juistheid van deze modellen. In de inleiding is dit aspect uitgebreid toegelicht. Als gevolg van deze situatie moest deze studie worden begonnen met een analyse van de geldigheid van enkele bestaande rekenmodellen (bijlage A). Door de voorspellingen van deze modellen te vergelijken met de op dat moment beschikbare meetresultaten werd duidelijk dat deze modellen tekort schoten bij de beschrijving van de fysica. Daarom moest eerst een voorstudie worden verricht naar de mogelijkheden voor de opstelling van een rekenmodel dat een betere overeenstemming met de meetresultaten vertoonde. De complete rapportage van deze voorstudie is in dit rapport opgenomen als de bijlagen B t /m E. Het eindresultaat van al deze beschouwingen is daarna samengevat in de eerste paragraaf van hoofdstuk 2.

The Tanjung Perak harbour of the city of Surabaya on the island Java, Indonesia has experienced a considerable growth of container traffic. In order to adequately deal with the expected continuing increase of container traffic in the future, the International container terminal is presently being expanded. In future there will be three independently operating terminals: two terminals for international container traffic (ICT) and one terminal for inter island traffic (IIT). The Inter Island Terminal will handle coasters operating between the larger and smaller (more inland located) ports. The quays of these three terminals will be connected to the container yards by one bridge. Evidently the expansion of the container terminal will create a new situation on the whole terminal, in particular on the bridge connecting the quays to the container yards. The objective of this research is to investigate the capacity of the future container terminal and to analyse possible future bottlenecks (with emphasis on the bridge situation). For this purpose computer simulation models have been created of the three terminals and the bridge. Using simulation models the future terminal operations have been analysed and in the process also an indication of the capacity of the terminal is obtained. The models enabled a better insight of the possible container throughput of the terminal in relation to the efficiency level of terminal operations and upgrading of equipment. The traffic load on the bridge has been investigated by analysing the varying traffic flows generated by the terminal models. Concluding it appears that there are two factors that may limit the anticipated container throughput increases per terminal: the capacity of the portainers and the stacking area of the container yards. In case the container throughput per terminal increases as expected and the efficiency levels can not be improved (thus limiting the production of quay cranes), the possibility of a serious congestion of the terminal may be the result. This would result in increased anchorage waiting times for the vessels and in a further increase of the quay occupancy (more than the present 70%). Also the capacity of the stacking areas may prove to be insufficient to cope with this increased container throughput. These effects also imply that the terminal will not have an adequate safety margin to handle unforeseen delays, for instance equipment breakdown.

Korte beschrijvingen van kustwaterbouwkundige software met verwijzingen naar achtergronddocumenten

This report describes the process of the design of the “Waterdraer”, a new connection between the Mfolozi and the St Lucia estuary. The different process steps of Systems Engineering have been used as a guideline during the design. In short, the main goal of the Waterdraer is to transport fresh water into St Lucia without a long extensive back up of water in the Mfolozi. In the beginning of the report the following research question was defined: · What is the most optimal solution for restoring and enhancing some of the features of the original ecologic St Lucia estuary system, in relation to the short term possibilities? The St Lucia estuary and surroundings are part of the GEF project in the iSimangaliso Wetland Park. The GEF project involves many different stakeholders and complex problems. Even in the short term there are a lot of interests at stake. First, there is the need for fresh water into the St Lucia estuary, the Narrows, and lakes. Secondly, there are the sugarcane farmlands that should be “protected” against flooding. Thirdly, there is a need for biologic and ecologic exchange between the sea and iSimangaliso Wetland Park. Finally there is a need for an open St Lucia mouth connection for local fishery. The difficulty of these problems is that they are all interdependent. However, the four problems are also conflicting with one another. The current situation shows that the old Back Channel is not sufficient enough to provide enough water inflow without backing up water in the Mfolozi floodplain. Even when the Mfolozi berm height is sustained the discharge of the “natural” weir in the old Back Channel is too low. As a result the water levels could rise too fast and would lead to an artificially or even a natural breach. Even a small flood could not be sustained to prevent a (artificially) breach of the berm. An open Mfolozi berm results in the malfunctioning of the old Back Channel. In the past years a lot of knowledge about the problems and systems has been gained. Mismanagement during the past 50 years becomes gradually accepted and the iSimangaliso Wetland Park authority has changed the management strategy of the iSimangaliso Wetland Park. One of the preferred long term options is bringing back the combined mouth dynamics. Currently, this is not an option because management conflicts and uncertainties about such impact are unsolved. The improved Back Channel (the Waterdraer) anticipates to the customer needs by providing an easy implementable short term solution. The Waterdraer its main goal is to bring enough fresh and sediment free water into St Lucia to counteract the hypersalinity during droughts. In addition, it should limit the effects of flooding on the lower floodplains. The Waterdraer variant consists of the widening of the recently excavated new Back Channel. The bottom level is decreased towards 0m GMSL, which is assumed to be the current height of the “main” channel of the Back Channel. The threshold of (artificially) breaching the Mfolozi berm is set at +1.8m above GMSL. The proposed threshold level is depended on two factors. Firstly the amount of flooding allowed on the floodplains and secondly the largest flood wave that has to be retained. A new weir inside the new Back Channel is designed as the control notch of the system. The weir creates a “controllable” situation and minimizes the effects of sediment transport. The crest height and width of the overflow determine the size of the flow into St Lucia. The width of the weir is based on the maximum flow velocity at which erosion occurs in mangrove forests, and on the minimum flow required to fulfill the requirements. A stilling basin of soft materials (logs) is designed to dissipate the energy of the water that flows over the weir. Modelling in SOBEK shows that the improved Back Channel could have provided a flow of approximately 64Mm3 considering the discharge of the last 4. months. The latter is based on the condition that the maximum water level behind the Mfolozi berm would be increased to +1.8m GMSL. An interesting remark is that the water level has not exceeded +1.5m GMSL during this period. In addition, the artificial breach of the Mfolozi berm in July 2011 has been kept out the model in order to simulate the natural situation of the Mfolozi mouth. Lawrie and Stretch (2011) mention that hypersaline conditions in the St Lucia lakes can be prevented if the Back Channel provides a water inflow of at least 5Mm3/month, which is 60Mm3/year. The SOBEK model and a simple water balance model suggest that even small floods (single peak flood waves with a peak height . 75m3/s) are retained behind the berm. Finally, the Waterdraer could drop water levels in the Mfolozi from +1.8m GMSL back to + 1.5m GMSL in five days if such a flood occurs. Floods above 75m3/s result in a natural breach which means long flooding periods on the floodplains are no longer present. In short, the Waterdraer offers an easy implementable short term solution that counteracts hypersalinity in the St Lucia lakes. Furthermore, it minimizes the effects of flooding on the floodplains that lie above +1.5m GMSL. Due to the retention basin behind the Mfolozi berm sediment inflow into the Narrows is reduced to acceptable levels. The effect on marine distribution is considered to be minimal. In comparison with a combined mouth the new Back Channel does not provide enough inflow to breach the St Lucia mouth by itself.

Over the past decades the north-eastern coast of Brazil has been degrading due to erosion. This degradation has both natural- and men-made causes. Brazil has no specific laws and acts which relate to coastal protection and management up to this date. Beaches in the metropolitan area of Recife show variety in beach width according to the seasons. However the local factors play such a significant role in this, that it is not possible to establish a direct link between the seasons and beach width. Since the beginning of the 20th century, men has built structures all along this coast without proper guidelines. Wrong implementation of the structures has ,most probable, made matters worse. Another aspect is that men built structures (1970) on the backshore creating less back buffer which resulted in relative erosion. This paper entails the study of the coast of metropolitan Recife which is 45 km long. The goal of this study is to assess the area: to create solutions for their problems. The paper consist of two parts, part A and part B. Part A consists of a study of the entire coast of metropolitan Recife. Part B focuses on Boa Viagem, an area of 2.78 km within the metropolitan area of Recife. In order to assess the entire area more suffiecient, the area has been split up into 7 parts, from north to south: Janga, Casa Caiada, Bairro Novo, Fortim, Boa Viagem, Piedade and Candeias. All these areas have been studied in order to find the cause of erosion, and possible solution. This has been done by preliminary assessment, where the current structures are observed; a problem assessment, this study emphasizes each area’s problem and probable causes; and finally a solution assessment where possible solutions are represented. The total area of the coast of metropolitan Recife consists of men-made hard structures such as groynes, breakwaters and revetment. But has also natural breakwaters such as reefs. The presence of the latter makes study of this coast highly complex. The area has one major and one minor source of sediment. The major is the sediment that is transported in the littoral drift. The minor source is sediment being discharged by the rivers in the area. The sediment is fine to medium size sand. The current level of “protection” is highly ineffective and has made matters worse in many cases such as Casa Caiada. The level of protection can be classified as poor. Initially, the area was thought be a flood risk, however, closer inspection has revealed that coastal flooding is a non-issue in the metropolitan area of Recife. The amount of erosion cannot be limited but only displaced if hard measures are deployed. If sediment is trapped in one area, another area will be adversely affected. The only solution to sediment deficiency is introducing additional sediment in the area. Part B focusses on Boa Viagem, an area of 2.78 km long with probably the most economic value. The coast of Boa Viagem has healthy beaches but also shows signs of erosion. The area consist mostly of reefs, but also has revetments and a harbor. Different solutions for Boa Viagem have been presented, via a Multi Criteria Analysis one has concluded that a solution of only nourishment will be applied. The nourishment will be dredged by a hopper, 10 km off the coast. The hopper transports the sand with the aid of a pumping system through a 2.5 km piping system to the beach. The nourishment will be spread by a bulldozer and a scraper. In order to maintain the beach, re-nourishment will be done every 5 years. The total amount of initial nourishment is 1.2 million m³ sand. And for re-nourishment 0.5 million m³ sand has been calculated. The whole operation cost R$ 143 mln ( € 60 mln ) during a period of 50 years, this includes: initial nourishment, re-nourishments and interest etc.

The Durban bight has a very dynamic and variable coastline which is constantly under attack by the Indian Ocean. To protect the Durban harbour from this energetic ocean, already in 1855 breakwaters have been constructed to protect the harbour and prevent sedimentation inside. The construction of these breakwaters and eventually extending these breakwaters towards the sea has influenced the sediment flow in front of the Durban beaches enormously. The natural sediment flow along the coast from South to North has been interrupted and this has changed the surroundings. The beaches of Durban are constantly eroding and nourishments are necessary every year to restore the beaches and preserve the safety of the citizens of Durban. The Durban Harbour has agreed to dredge all the available sand that is trapped by the breakwaters and deliver the sand back into the beach system. The Municipality of Durban has responded to this development by constructing a sand distribution system at the beaches, to nourish the sand in an optimal way. New nourishment pipelines have been constructed through three piers at the central part of the Durban coast to supply the sand directly in the surf zone. Although the rough sea is responsible for the erosion at the beaches, the sea also provides nice surf conditions. If the bathymetry has the right shape, perfect surf waves can appear. A combination of nourishments done by the Durban Harbour and the construction of the new nourishment pipelines can lead to the necessary change in bathymetry, resulting in the perfect surf waves. To investigate the consequences of the nourishments on the surf conditions and the movement of the sediment, a Delft3D computer model has been set up. Different nourishment scenarios have been investigated, as well as the available recorded data regarding the tide, the wave and the wind conditions. The total input data have been reduced in size towards representative parameters and converted to corresponding Delft3D input files. After running the constructed model with different scenarios for a simulation period of 15 days, the results have been checked on two different aspects. First of all the effect of the nourishments through the piers on the bathymetry is analysed. An overview of the most important model outcomes is bundled in the additional document ‘Modelling nourishments through the Durban piers, Figures’. The nourishments tend to move onshore and therefore into the coastal cells between the piers. Offshore transport doesn’t seem to be an issue for the dominant wave conditions, but during north-easterly and north-north-easterly waves it is advised not to carry out nourishments. The just nourished sediment might be transported offshore in that situation. The added sediment is partly used to fill up scour holes just north of each pier, but it also leads to the creation of a shallow area north of the tip of each pier. When every year a volume of 250,000 m3 of sand is supplied to the Durban bight, the coastal cells remain more or less in equilibrium, given that 40% of the total amount is nourished through the piers. The second part concerns the effects on the surf conditions. When analysing the physical wave parameters, no major changes can be noticed. However, the model is only run for 15 days, during which one nourishment is simulated. The results do show some subtle trends, which could lead to a bigger influence when successive nourishments are carried out. Waves start to break at the newly created shallow areas during low tide. This has a positive effect on the surf conditions, since the waves will break in a more favourable way. In case of multiple nourishments, the shallow areas will probably become shallower, so then the positive effect can be noticed during high tide as well. Furthermore, the orientation of the coastline between the piers will obtain a slight obliqueness with respect to the dominant wave direction. This causes the waves not to break at once along the whole wave crest, but more gradually from one side to the other, so that surfers can ride a wave uninterruptedly for a longer period of time. Finally a number of recommendations is given, which result from the whole process that the project has gone through. A few adjustments to the model might lead to a major improvement of the performance. Two of the most important recommendations concern a more detailed way of modelling the piers in the model and the inclusion of wind.

Manado City is growing, its population is increasing. This demands the city to grow outside its borders and even into the sea by using land reclamation. Introducing new challenges or making challenges bigger, which are already present. Not only growth is present in the city, going forward and becoming better and better is an on-going fight for cities. The city came up with a vision “Manado, Model City of Eco Tourism” and a mission “Make Manado a City of Happiness” for their future. Introducing a study on this subject and to anticipate on the city’s goals, the research question is stated as; What are the options to supplement Manado’s vision and mission, making the city more safe and attractive for tourists and citizens? Within this research, two other challenges regarding Manado city will be investigated as well. In the year of 2003 a major flood occurred in the city, causing great damage to the city with many casualties. Nowadays, the risk of flooding is still present. Secondly, a challenge arises at the border of the city . The coastline of Manado suffers from erosion at specific locations, possibly caused by development of the reclaimed land in the past. Narrowing the research, an analysis will be made upon selected subjects. Analysing the coastal protection, river floods and the city’s Vision and Mission gives a clear view of the current state and what could be expected from the future. The goal is to come to a sound idea of the needs and possibilities related to coastal protection, Kota Manado and its Vision and Mission. Working towards advices, different time paths and desires are noticed. Besides recommendations, which can be adopted at any time, found solutions are divided in short, mid and long term time spans. On short term the rivers and garbage have to be handled and nuisance of either one increases day by day. At many places the river is blocked. Removing these blockages is a good start. In addition, the embankments and beds can be ‘smoothened’, to improve the river’s flow. Besides the river attention on the short term, garbage clogs up the city. Waste Management Control is already improving. Clean ups have to be supported by the government, giving a good example to its citizens. By these measures a start is made to work towards real solutions, coming to an Improved Garbage Service. As mentioned before, improving the Waste Management Control is a continuing process. Besides the short term, this solution has a mid-term basis too. By adaption of the 3R-principle, garbage will be even less. This principle represents the Reduction, Reuse and Recycle of materials. The amount of waste will reduce and the city will be cleaner, although it will take a while to adopt. Measurements need to be coordinated and monitored. Making so-called Pre-Project-Planning gives benefits to make them successful. This should not only be used in this case, but also for regular Civil Engineering projects. Erosion is another problem Manado City is facing nowadays. However, its effects evolve more slowly and are thereby less noticeable. The coastline of Manado can be divided in three sections. Section one consists of the Southern part of the coastline and the municipality is already undertaking action to stop the erosion. The adopted measures are well designed and thought through. Even on places where there’s little area to construct a protection, the chosen measure could also be used.Section two is located near the boulevard area. Large land reclamations are constructed along the shore. The reclaimed areas are well protected by big stones and do not suffer from any erosion. These large land reclamations, however, do have side effects. One of them is the change in the current, leading to a flow towards the ’Bunaken’ coral reef area. This flow transports a lot of sediment, dust and garbage and killing a lot of fish and coral. So, for future land reclamations, an investigation into these effects must be done if the city really cares about its environment and wants to prevent it from destroying. Section three is situated in the North of Manado. The protection of the northern coastline consists of vegetation and Mangroves. Due to certain changes in the past, among others construction of reclaimed areas, part of the northern shoreline started to erode. The continuing process of erosion can be resolved on a mid-term base. With solutions like, for instance Mangroves, it can stop the erosion and improve the environmental value of the coastline as well, leading to an eco-friendly solution. A sustainable future for the city of Manado is obtained by their vision “Manado Model City for Ecotourism” and mission “To Make Manado City a city of Happiness”. The government cannot do this on its own. Involving and, most important, convincing the local community of the vision and mission will speed up the progression. This combines the short and long term philosophy. On short notice the local community has to be convinced and at the same time, the long term vision and mission can be fulfilled too. Manado City has a great amount of opportunities to fulfil their mission and are they are well available. Even small improvements can make a change. A good example to use the opportunities and to anticipate on the mission and vision of the city is to construct several parks or a beach in the centre of town. A park or a beach can be created to attract not only tourists but also local citizens. For tourists, including divers, it will be a welcoming relaxing spot to comfort their stay in Manado. So in this way it will give the mission and vision of Manado a tremendous boost.

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.

In dit rapport worden een- en twee-dimensionale wiskundige modellen ontwikkeld, waarmee concentratieverdelingen van al dan niet afbreekbare, geloosde stoffen in een rivier kunnen worden bepaald (tussen de geloosde stof en het ontvangende rivierwater bestaan geen dichtheidsverschillen). De modellen hebben betrekking op continue en momentane (kortstondige) lozingen. Bij de twee-dimensionale modellen zijn aIleen lozingen aan de oever van de rivier in beschouwing genomen. Met behulp van de respectieve modellen zijn cone entratieverdelingen berekend voor een en/ of twee trajecten van de Nederlandse Maas. Omdat de modellen uitgaan van een prismatische rivier met een constante dwarsdoorsnede en een over de breedte van de rivier constante watersnelheid, zijn de betreffende trajecten voor de uitvoering van de berekeningen als zodanig geschematiseerd. Door analyse van de resultaten van de berekeningen zijn de consequenties van een gekozen bemonsteringsprogramma voor het uiteindelijk gevonden kwaliteitsbeeld van een rivier nagegaan. Bij de opzet van een bemonsteringsprogramma kunnen twee uitgangspunten worden gehanteerd: - er wordt op vaste punt en langs de rivier gemeten - er wordt vanaf een varend schip gemeten.

For the generation of second-order random waves in a flume the control signal for the wave board has to be correct up to second order. An expression for this control signal is derived with the perturbation method of multiple scales. It is much less complex and requires less computation time than the expressions obtained from the full second-order theory. A verification of the new method for second-order sub harmonics is provided for bichromatic and continuous first-order spectra. The data are analysed with the complexharmonic principal-component analysis to reduce the influence of noise. The validity of the new method is confirmed.

Doel van het onderzoek is de bestudering van wiskundige modellen, waarmee bij overwegend zwevend transport, bodemveranderingen in rivieren kunnen worden voorspeld (morfologische berekeningen). Voor een goed begrip van morfologische processen in (alluviale) rivieren is kennis van het sedimenttransport van groot belang. Bodemveranderingen hangen nl. direkt samen met veranderingen in het transport. Voor zwevend transport is dit een tijdafhankelijk proces: bij een niet-stationaire en niet-uniforme stroming kan de bodem zich niet direkt aanpassen aan de veranderende stromingsomstandigheden, er treedt vertraging op. Deze wordt in de beschouwde wiskundige modellen beschreven met de diffusie-convectie vergelijking voor turbulent transport. De hiermee samenbangende literatuur over water- en sedimentbeweging in rivieren is zeer uitgebreid. Een overzicht hiervan kan men bijv. vinden in Vreugdenhil (1973) voor de waterbeweging, en in Graf (1971) en Raudkivi (1976) voor het sedimenttransport. Literatuuronderzoek op het gebied van diffusie en suspensie van sediment is bijvoorbeeld verricht door yan Wijngaarden (1973) en door Delvigne en Karelse (1978). Morfologische berekeningen worden behandeld door de Vries (1977), terwijl in het handboek van Jansen (1979) een overzicht wordt. gegeven. Een zeer fundamentele behandeling van twee-fase n stromingen bij hoge sedimentconcentraties is bijvoorbeeld te vinden in Buyevich and Shchelchkova (1978), die ook een goed overzicht geven van de literatuur en de mogelijkheden op dit gebied. In par. 2 van dit rapport wordt een afleiding gegeven van een diffusieconvectievergelijking voor turbulent transport, met alsbelangrijkste veronderstelling dat de slipsnelheid van de sedimentdeeltjes nul is. Essentieel in het probleem is dan de formulering van de randvoorwaarde voor de concentratie bij de bodem, en de daarmee samenhangende vraag of en in hoeverre de afgeleide vergelijking nog geldig is in de grenslaag bij de bodem, waar hoge sedimentconcentraties optreden. Daartoe is in par. 3 een tweetal modellen voor evenwichtstransport nader onderzocht, waarbij geen (kunstmatig) onderscheid wordt gemaakt tussen zwevend transport en bodemtransport. Er is een vergelijking. gemaakt met een drietal, uit de literatuur bekende, transportformules, met als resultaat dat de overeenstemming veelal slecht is. De onderzochte modellen zijn dan ook als zodanig niet bruikbaar voor het voorspellen van transporten. Tenslotte worden er in par. 4 enige suggesties gegeven voor verder onderzoek op dit gebied.

Report on destructive overtopping tests executed with the wave overtopping simulator along the coast of Vietnam to investigate the strength of the inner slopes of grass dikes. This report presents measurement and observation results obtained during destructive tests with the simulator in Do Son, Thinh Long and Thai Thuy. After the first chapter, Chapeter 2 discribes all test sections in detail and test scenario. The method and results of hydraulic measurements are presented in Chapter 3. Chapter 4 and Chapter 5 introduce the slope profiles and photograph of grass slopes. The formation and development of the damages induced by wave overtopping are discussed in Chapter 6. Chapter 7 deals with the resistance against wave overtopping and critical velocity of different grass covered slopes which were tested with the simulator. Finally, Chapter 8 are conclusions and future research, respectively. Detail of hydraulic measurement performed at three sea dikes are given in Appendix A. Data of the slope profiles measured at Thinh Long and Thai Thuy are presented in Appendix B. Appendix C contents of the photograph of the damages on the slope sections at Thinh Long and Thai Thuy sea dike. Characteristics of soil and grass taken at test sections are given in Appendix D. Appendix E summarises brief specifications of all test sections.

The area around Ho Chi Minh City (HCMC) faces flooding and salt intrusion problems. Flooding problems are caused by intensive rainfall in the city, high river discharges and high tides on sea. Dr. Hoc, the vice-minister of MARD (Vietnamese Ministry of Agriculture and Rural Development) proposed to construct a hydraulic structure downstream of HCMC. This will solve both the flooding and siltation problem. A possibility is to construct a dam between Vung Tau and Go Cong. This solution has been worked out into a preliminary design, which includes a design for the cross section and an investigation into the closure method. The hydraulic system where the project will be constructed consists of the Saigon - Dong Nai river system and the East Sea, and can be classified as an estuary with a (mainly semi-diurnal) mixed tide. Waves are moderate in the area. A dam will be constructed between Go Cong and the Dong Nai navigation channel. Over the Dong-Nai navigation channel to Vung Tau a bridge is planned, to minimise navigation delays and changes in tidal and salinity range in the Can Gio mangrove forest. To make a closed basin, Can Thanh will be connected with the dam near the Dong Nai navigation channel. Ship locks and discharge sluices will be constructed at the sides of the existing navigation channel in the Soi Rap. The final closure of the dam will take place in the Soi Rap navigation channel. A road on the dam will connect Vung Tau with Go Cong. Because there is no subsoil information available at the location of the dam, the soil layering and parameters are estimated based on information from locations in the vicinity of the dam. Three different soil profiles were drawn up. Measures have to be taken to increase the bearing capacity of the subsoil and decrease settlements during the lifetime of the dam. If thick layers of weak subsoil is present, drainage in combination with pre-loading will be the best solution. In case of a stronger subsoil partial replacement with sand is favourable. To build the dam, the use of local material is a cheap and easy solution. Near Vung Tau a number of areas are present where sand can be obtained. Rock can be found in mountains in the neighbourhood of Vung Tau. Since there is already a stone quarry in this area, it is assumed that the rock is of good quality. By means of a Multi Criteria Analysis it was found that a building a dam with a sand core is the best solution in this project. Degradation or even failure of (elements of) the structure may occur as a result of loadings during the operational phase or in accidental situations. The principal failure mechanisms for the VT-GC dam are checked. Slope, crest and toe protections were designed to prevent failure. Two designs were made for the cross section of the dam: one with an outer slope revetment made of asphalt and one for an outer slope revetment made of rock. The biggest differences in these designs can be found in the crest height and layer thicknesses. The construction of the dam should start with the construction of the bridge and work islands. Next, the discharge sluices and navigation locks will be made in building pits. Then the dam will be constructed. This starts with the foundation and scour protection which will be constructed using barges. Waterborne equipment is preferred because of the easier logistics and larger capacities. The core material, filter layers, underlayer, toe and armour layer will be constructed layer by layer to be able to raise the relatively steep slopes. Where water depths are too low, cranes operating from pontoons or rolling equipment can be used. After completion of the core and revetment, the crest is constructed and the dam can be finished with the construction of the road. The closure of the final gap is a very important aspect within the construction of the dam. A storage area approach is used to determine the system behaviour during closure. High velocities in the final gap make it impossible to close the gap with sand. A bottom protection is necessary in the final gap to prevent a scour hole, caused by high velocities, from developing too close to the dam. The gap is closed with coarser material than sand. A combination of vertical and horizontal closure will be used. First barges dump stones to a level of MSL -5 m. When the water is too shallow, dumping will continue from the sides of the closure gap. The final dam profile in the closure gap will be similar to the regular dam sections. A general estimation of the cost for the total project, based on costs in reference projects, is 3.1 billion US dollar. The Dong Thap Muoi region is a very important agricultural area for the production of rice. Due to the low river discharges and the large influence of the tide, the salt concentrations in the Vam Co rivers are high, causing problems for the farmers. An estimation of the salt intrusion length was made using a predictive steady-state salt intrusion model, according to Savenije. Unfortunately it was not possible to perform salinity measurements in the Vam Co River, so data from three fixed measurement stations was used. With this data, it was possible to fit the model roughly but more data is needed to make the model more accurate. Student report for a Master Project.

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This progress report refers to part the work done within the framework of the Dutch Center for Coastal Research (NCK). The primary objective of our research is to develop knowledge and methods for the prediction of the hydrodynamic conditions for the Dutch coast taking into account the morphodynamic behaviour in the nearshore zone. In general the progress reports descibe results, developments and new ideas obtained during our research. Most results have a preliminary status and should be not be used without prior consent of the authors. The various topics described in the progress reports are brought together to gain more insight in the proces to reach the primary objective. More detailed analysis of the various topics are or will be given in the form of journal papers. In addition attention is given to the (potential) links with work done by others.