The Eurocodes are design codes, widely accepted throughout Europe, that provide guidelines on how to deal with loads, resistance, and uncertainty. For most type of structures, loads and materials, the Eurocode has been well developed. However, for the loads on coastal structures, caused by wave, water level and current actions, no such Eurocode exists. Therefore, a new Eurocode is in progress. The preliminary version of this Eurocode is titled prEN1991-1-8, and will describe how to deal with hydraulic loads on coastal structures.
The Eurocode has a safety philosophy based upon partial factors and consequence classes, but the extension of this method to hydraulic engineering is not so straightforward. A premature introduction of the new Eurocode could mean that important design aspects related to sea condition parameters, such as extreme value analysis, dependence and wave transformation, are underexposed. In turn, this might give way to unsafe structures. Because of this, it is important to investigate how the semi-probabilistic approach (proposed by prEN1991-1-8) compares to existing design methods, both in terms of safety and in terms of ease of application. The goal of this thesis is to acquire knowledge on how the introduction of the new Eurocode influences the design of coastal structures, and address any inconsistencies and issues in prEN1991-1-8 before the preliminary version is adopted as the definitive version.

The main focus of the research is the re-design of a coastal structure following the instructions in prEN1991-1-8. The breakwaters of IJmuiden are used as a case study for this. Three different approaches are adopted for the design: a deterministic approach, a semi-probabilistic approach and a full probabilistic approach. The breakwater elements that have been extensively examined in this thesis are the armour layer, consisting of either rock or artificial units, the crest height and the crown wall.
Conclusions have been drawn based on any unclarities that are encountered in the design process, and based on comparisons between the semi-probabilistic approach and the two existing design methods, respectively.

The introduction of the new document prEN1991-1-8 should result in more conformity regarding the treatment of sea condition parameters and their accompanying uncertainties in design calculations. However, the new (draft) Eurocode in its current form does not seem to achieve this objective. This conclusion has been drawn based on the practical issues (i.e. room for interpretation in the document and poor descriptions of key concepts) that were encountered in the case study, and because the breakwater design that was arrived at by following the semi-probabilistic approach described in prEN1991-1-8, did not resemble the design outcome obtained with the deterministic and full probabilistic approach.

In addition, the semi-probabilistic approach is still a time-consuming method when applied to breakwater elements, while it is relatively easy to set up a full probabilistic calculation. It is recommended to shift (at least part of) the attention towards the full probabilistic approach, and explore the possibilities of making it the default approach for coastal structures, as it raises fewer questions than the semi-probabilistic approach and deals with uncertainties more extensively.

Nevertheless, it can be viewed as a positive development that there will be one general document to consult for the design of coastal structures. Most importantly, standardised levels of safety and return periods are now available with the introduction of prEN1991-1-8, even though their interpretations are not always straightforward. It is of course also still possible to improve the semi-probabilistic approach as it is currently proposed by prEN1991-1-8. When this is preferred, it is recommended to include a more systematic explanation of the DA-1 format in EN1991-1-8, describing the characteristic values, partial factors and safety margins to be adopted in design without any ambiguity.
... Read more

Worldwide, rubble mound breakwaters are designed and built to shelter and protect coastal areas from overtopping and flooding, especially harbours and shorelines. Rubble mound breakwaters are essential to preserve desired hydraulic conditions within the hinterland, avoiding damage to inhabited or industrial areas. This research focuses on the wave overtopping of rubble mound breakwaters as failure mechanism. To assess the wave overtopping engineers can adopt multiple methods. These methods can be ordered in increasing degree of accuracy and costs: empirical methods, neural networks, numerical models and physical laboratory experiments. The preliminary design phase is a highly iterative process. Using physical laboratory experiments within this phase is an expensive choice, therefore empirical methods are often preferred. Nevertheless, this research revealed that empirical methods, e.g. the so called EurOtop 2018, show significant shortcomings in assessing average overtopping quantities over rubble mound breakwaters, even more when the geometrical complexity of the structure increases (presence of protruding wave wall). This thesis re-calibrated the roughness coefficient proposed by the original EurOtop 2018 approach, referred to as the updated EurOtop 2018 method. Numerical models are proposed as a possible solution between empirical methods (which can be carried out quickly given their low complexity) and physical laboratory experiments (which need more time but are characterised by high accuracy). They have been increasingly used and accepted in the past decades. Following this trend, the Joint Industry Project (JIP) CoastalFOAM was launched with the objective to develop and validate a numerical model (OpenFOAM, waves2Foam, OceanWaves3D and JIP additions; referred to as CoastalFOAM) capable of accurately modelling the wave-structure interaction of rubble mound breakwaters. This research aims to calibrate and evaluate the CoastalFOAM model to assess small to large wave overtopping of rubble mound breakwaters with protruding or non-protruding wave wall, considering 500 waves. The evaluation of CoastalFOAM shows that this numerical model can be used, instead of empirical methods (e.g. updated EurOtop 2018), to assess the average overtopping discharges. CoastalFOAM showed excellent agreement with measurements for large and medium overtopping cases, while resulting less accurate for small overtopping cases. The analysis revealed, however, that the average overtopping discharge as a quantity is not capable of identifying the magnitude of large overtopping events (without modelling all 500 waves). This can be considered critical in determining whether the structure is safe enough in terms of Serviceability Limit State (SLS) or Ultimate Limit State (ULS). Consequently, this thesis proposes a new methodology to assess the maximum overtopping volume within a storm, applying the concept of wave focusing and using the NewWave theory. The input variables for the NewWave profile are extracted from the spectral properties at the toe of the breakwater. A first order wave maker is used to generate the NewWave profile, making the methodology sensitive for the degree of non-linearity of the considered wave conditions. This NewWave methodology offers improved accuracy to assess the maximum overtopping volumes when compared to the EurOtop 2018 approach. Furthermore, this research proposes to apply the inverse EurOtop 2018 technique to assess the average overtopping discharge using the NewWave maximum overtopping volume. However, the accuracy of this methodology is lower than that obtained with the updated EurOtop 2018 guidelines. This study shows that CoastalFOAM can be used, instead of the current empirical methods, to assess the average overtopping discharge within the design cycle of rubble mound breakwaters. However, according to what has emerged, CoastalFOAM shows to be less accurate in calculating small overtopping discharges as opposed to medium and large. On the other hand, when considering the maximum overtopping volume as design criterion the proposed NewWave methodology showed to be the most efficient and accurate. ... Read more

The Twin Dike project is an innovative concept to achieve the required flood safety while being able to preserve valuable areas. A lower, second dike is constructed behind the original existing dike. The original dike is only being strengthened to a minimal extent. The general idea behind this project is to more efficiently use the area near the dike without losing valuable nature or buildings during dike reinforcements. At the same time, this concept is expected to be cheaper, provides the required flood safety and the area between the dikes is used for experimental purposes. Currently, there are no pre-defined methods which can be used to easily assess the safety requirements of multiple lines of dikes. This research investigates if multiple lines can be an attractive alternative for traditional dike reinforcements regarding flood safety and costs, to provide the required protection against floods.

In order to answer the research question, it is analysed how flood defences are currently assessed in the Netherlands. Governing loads and failure mechanisms for the Twin Dike are determined. Using current and experimental methods the loads acting on both dikes are determined. Next, a sensitivity analysis is performed to analyse the sensitivity of various aspects on the results. Finally, a cost-benefit analysis is performed.

This research concludes that erosion of the outer slope and overtopping are governing failure mechanisms for the outer dike of the Twin Dike project. Overtopping volumes are, however, not large enough to cause considerable damage to both the outer and inner dike. Existing assessment methods are not good enough to determine the safety of the Twin Dike project with respect to erosion of the outer slope. A prototype model is used to better analyse the effects of erosion of the outer dike and the consequent loads on the inner dike. The model showed that breaches are formed in the outer dike at conditions which have a higher probability of occurrence than allowed by the safety norms. When a breach occurs the inner dike is not able to withstand the consequential loads. A total system failure immediately occurs.

A sensitivity analysis was performed on the overtopping volumes and erosion model results. Sea level rise was the dominant uncertainty for the overtopping volumes. If sea levels will rise extremely within the design lifetime, overtopping volumes can be three times as large compared to the case with mean sea level rise. However, the overtopping volumes are still low enough such that Twin Dike satisfies the required safety norms. For the erosion model, the average return period for which a breach occurs varies greatly with the uncertainty of various parameters. However, using a case with mean values for all variables, the probability of a breach is still larger than allowed by the safety norms.

Also, a cost-benefit analysis was performed to assess if the Twin Dike project is an attractive solution with regards to costs. In this case, from a cost perspective, multiple lines of dikes are not an optimal solution. ... Read more

Currently, sand retaining rubble mound structures are often constructed with geotextiles, lining the interface between the core material and the sandfill. These geotextiles are placed to make sure the sand from the sandfill is not flushed out through the core by incoming hydraulic forces from the surrounding water. It is proposed that difficulties faced during placement, or uncertainties regarding the correct installation of these geotextiles can be overcome by curtailing the geotextiles. The potential for this abbreviations is stressed by Polidoro et al. (2015) as this author concluded, that at the lower inner corner of rubble mound structures with a closed inner slope, pressures are dampened below a certain estimated critical value. However, no proof was found for the applicability of this critical value. Despite several researches predicting hydraulic loading in rubble mound breakwaters, and studies assessing the stability of sand to stone interfaces, insight in the behaviour of sediments in this particular interface configuration of a sand retaining breakwaters was lacking. Therefore, the aim of this research was to study the behaviour of sediments at the interface to a core in a sandfill. Under supervision of VAN OORD and DELFT UNIVERSITY OF TECHNOLOGY (TU Delft), a physical model is designed to study specifically this interface. The model tests took place in the Fluid mechanics Laboratory at TU Delft, where a relatively small setup (1 * 0.5 * 0.15m) was used to model on a relatively large scale (lambda= 15). An exact scaled representation of a nominal breakwater by Polidoro et al. (2015) was used. In the model both the Development of the interface during placement of the sandfill as the behaviour of the sediments when subjected to hydraulic loading is studied. The research concluded that a stable initial interface was found with a slope of approximately 35degrees. In what extent the infill migrated inward through the core varied depending on the installation
method. When subjected to hydraulic loading, a critical hydraulic gradient was found of 0.05m/m on average and 0.04m/m in the most conservative case. These results were established with a measurement accuracy of » 5% and the consistency over different series of tests was¸ 80%. Sometimes segregation of the stones was observed. The main attribution to the deviations in the measured hydraulic gradients and sediment transport were concluded due to this variation in the positioning of the stones. It is concluded that the current existing literature is able to give reasonable initial approximations of the critical gradient in the system(5¡40% accurate), however, the deviation can be significant and further research by varying more geometrical parameters should conclude if the obtained approximations are constant. Concluding, the results obtained in this research suggest that the critical loading conditions for the interface stability of to a rubble mound in a sandfill are of comparable order to conventional filter criteria and are higher than the currently calculated and measured appearing gradients by for instance Vanneste and Troch (2012) and Polidoro et al. (2015). These results justify the further exploration towards the potential of the abbreviation of geotextiles at the considered interface. In order to guide further research a list of recommendations is given as well as additional model improvements. ... Read more

One sixth of the world's coastline consist of coral reefs and provide natural flood defence for the people who live in the coastal region behind the reef. However, a rising sea level, changing wave conditions and degradation of corals threaten the coastal safety of these reefs.Numerical models can be applied to study the reef-hydrodynamics and the effects of coral degradation on the reef-hydrodynamics. When non-linear processes are important or the individual waves need to be determined, a phase resolving model is preferred. Within this thesis two issues regarding the application of non-hydrostatic models to coral reefs were studied.

Due to the large bottom gradient in front of a reef, the offshore boundary has to be located in deep water, which means that frequency dispersion becomes important. The accuracy of frequency dispersion within non-hydrostatic models depends on the number of vertical layers. However, the addition of a vertical layer increases the computational time extremely. Therefore, a reduced two layer non-hydrostatic model (XBeach-nh+) was developed with the assumption of a constant non-hydrostatic pressure in the lower layer. In theory, XBeach-nh+ is capable of modelling the wave transformation from deep to shallow water, but the applied boundary conditions cannot force deep water waves. On top of that XBeach-nh+ has never been properly validated for reef environments.

Furthermore, the corals (growing on the reef flat) have a large effect on the reef-hydrodynamics by dissipating a large part of the wave energy. There exist different formulations to include vegetation into a non-hydrostatic wave model, but these formulations are mainly applicable for cylinder shaped geometries, whereas corals are more complex in shape. Apart from the shape, the in-canopy velocity can be significantly different from the free stream velocity. Therefore, a porous in-canopy model was implemented to model the in-canopy velocity, which was used to determine the canopy-induced force on the depth-averaged flow computation.

Firstly, the inclusion of the second reduced layer improves the dispersion relation up to a relative depth ($kh$) of 5 for linear waves. A simulation of biochromatic waves over a plane beach showed that XBeach-nh+ is capable of modelling the energy transfer between the major wave components. Both steeping and reflection of the sub-harmonic were modelled according to the measurements. Furthermore, the validation of random waves over a fringing reef showed the capability of XBeach-nh+ to model the reef-hydrodynamics for different wave conditions (rel. bias of -0.003 for total wave height, -0.081 for LF-waves and -0.103 for the setup). Moreover, the addition of the second reduced layer gives a more robust prediction for all modelled wave conditions, whereas the one-layer model contains more scatter.

Secondly, the in-canopy model captures the canopy-induced force when the canopy parameters were known. Both the in-canopy flow of unidirectional and oscillating flow fields was accurately modelled when the results were compared to the measured velocity though cylinders and corals. Although, the canopy parameters were not always known, it was shown that an un-calibrated in-canopy model, based on porosity and canopy height, gives a competitive result compared to a fully calibrated shear stress formulation. The applicability of XBeach-nh+ in 2-dimensional domain with a coral covered reef flat was shown by modelling a 5 day Swell event at Ningaloo Reef. Reasonably accurate results were achieved when using the in-canopy model, based on the canopy properties. ... Read more

The coastal waters of Nigeria are a difficult environment to build structures to control the local morphology and hydrodynamic conditions to ones desire. This difficulty is a consequence of the persistent high-energy swell wave climate and Longshore Sediment Transport (LST) in the order of one million cubic metres per
year. Besides these tough conditions, the costs of conventional coastal mitigation solutions are high because of the lack of suitable material (rock) close by. These characteristics of the Nigerian coast led to the interest, whether it is possible to design and construct a ’Sand Breakwater’ for a planned port on the Nigerian coastline at Badagry. A ’Sand Breakwater’ is the complete construction which functions as the protection of the port and creates shelter from incoming waves for ships inside, consisting out of components (partly) made out of sand and hard structures. Especially the very uni-directional and consistent character of the wave climate creates an opportunity to embrace natural processes in the design. In addition, much sand needs to be dredged for the creation of the approach channel along with the port’s basin. This volume of sand might possibly be re-used for a sand breakwater.
This report presents the feasibility of a sand breakwater on the Nigerian coastline at Badagry. This feasibility is determined both morphologically and economically. Long term coastline development was modelled with the one-line coastline evolution model LITPACK. Results show that the persistent uni-directional character of the wave climate prevailing at the coast of Badagry forces an equilibrium coastline orientation of 277.5 degrees with respect to True North (TN). Because of this, all other orientations of coast rather than the equilibrium orientation are vulnerable and will develop to the equilibrium orientation over time. The implementation of this equilibrium orientation in the design along with some hard structures led to multiple long term morphological
stable conceptual variants for a sand breakwater. The coastline impacts of these variants west of the sand breakwater were examined on large scale. In 38 years after construction a maximum of 20 meters coastline retreat occurs, which is considered acceptable. After this period, only shoreline accretion takes place.
To establish complete conceptual designs, the cross-shore profiles are first determined. The submerged part of the profile up to the top of the intertidal profile is constructed by integration of measured data in the design. The emerged part of the profile concerns the cross-section of a dune and was the critical part for the designing objective. To determine these profiles, first the design crest height is determined by applying maxmimum acceptable overtopping volumes (Tilmans, 1983). Knowing the design crest height, the dune width is determined by modelling storm impact. This width is established by examining storm impact and determine what minimal required width needs to be present for the sand breakwater to live up to its design criteria.
Storm impact for the found conceptual variants is examined with the numerical software XBeach to determine cross-shore sediment transport during storm impact. The impact of storms with shorter return periods results to be relatively high in comparison to the storms with longer return periods. This is taken into account by adapting the design conditions. The design storm conditions are based on the impact of a storms with a 1/100 year return period along with an expansion for a consecutive storm with a return period of 1/1 year. With this
storm impact known, the required crest width is determined and with that the minimal required cross-shore profiles for the multiple variants are established. Consequently, besides long term morphologically stable, the conceptual designs are capable to design storm impact, confirming the morphological feasibility.
In order to define the economical feasibility of a sand breakwater, a comparison between the different conceptual variants and a conventional design is made. This comparison is conducted via a rough cost comparison along with examining future prospects. In order to be able to make this cost comparison, rough volume estimations are done for all conceptual variants and conventional design. These volume estimations combined with unit prices lead to a rough cost comparison. From this rough cost comparison appears that a sand breakwater
showed to be in the same price range as a conventional design.
Three future prospects of a sand breakwater are determined. First of all the by-pass of sand is compared for the conceptual designs to the conventional design. The characteristic LST is problematic due to the occurrence of sand by-passing causing sedimentation in the approach channel and port. One of the conceptual variants shows that a sand breakwater is proven to be able to provide a period without by-passing of sand in the same order of magnitude as a conventional design.
Another future prospect is the required maintenance necessary to execute for the sand breakwater. The XBeach results of lower storm conditions show that maintenance costs are high. However, these results are assumed to be heavily overestimated. Results with more specific ’Nigerian conditions’ create reason to believe that maintenance for lower storm conditions will be much lower and in acceptable range.
The last future prospect concerns the accreted land which arises due to the blockage of LST. A sand breakwater creates the possibility of acquiring land for new port space which is not possible with a conventional breakwater. In addition, the value of a Building with Nature component is present in this project and could enhance its economical interest.
Not only the morphological but also the economical feasibility of a sand breakwater is confirmed. The ’Sand Breakwater’ succeeded to convert the drivers of the problem to its solution, leading to an innovative and in all likeliness even more cost-effective solution compared to the traditional approach. ... Read more

Constructing a dam across a tidal basin has alway been a long-term integral solution to many water related problems of the surrounding area such as flooding, river control and fresh water storage. However, immense challenges are accompanied with the closure works of large basins. This research treats the closure strategy to close the Gulf of Khambhat in India. The project is known as "Kalpasar", which aims to create of a fresh water reservoir in the Gulf of Khambhat by constructing a 35 km dam across the estuary. The Kalpasar project
has been on the Indian Governments agenda since 1986. Royal Haskoning was involved in the pre-feasibility study, which was presented in 1998. However, due to an alignment change to a more northern position, earlier proposed closure work designs are now considered out of date.
To avoid irrelevance of this research through time and assist the Kalpasar development project with optimizing a new design for the closure works, this research treats the development of a fundamental parametric optimization tool to quickly perform a first-order evaluation of possible closure strategies on costs.
The tool as a product along with case results are delivered to the Kalpasar development project for further design optimization.
Closing the tidal basin involves closing a certain wet cross section along the chosen dam alignment through which large tidal currents penetrate caused by tidal differences up to 11 m. Complexity is caused by increasing tidal flow velocities due to increasing constriction of the wet cross section during the closure. The developed optimization tool can evaluate and compare six pre-programmed strategies to close a multi-sectional wet cross section in time on costs of three fundamental design requirement or "cost factors": Required dam material, bed protection and equipment. Using a multi-sectional storage model to compute the flow velocities in the gap, the channels and tidal flats can be individually modeled after which they are linked as a system. The model reacts as a system to changes in flow area by closing certain cross sections (a channel or a tidal flat). The individual cross sections can be closed strategically by defining their closure method (horizontal, vertical or sudden), execution phase and construction capacity. These are called "strategic input parameters". Defined for all sections, they determine the closure sequence of the system in time. Optimization is achieved when the strategic input parameters define a closing sequence which minimizes the combined cost of all cost factors.
Subsequent to the storage model, three computational models are introduced to quantify the required dam material, bed protection and equipment. Based on earlier research, the material model utilizes only quarried rock for gradual closures and sluice caissons for sudden closures. The equipment model utilizes large dump trucks for horizontal closures and ships or a temporary cable-way/bridge system for vertical closures. The construction capacity is linked to material and bed protection models, since both design requirements are time dependent. Increasing construction capacity can therefore decrease these requirements.
Since subsequent models largely depend on the flow velocity, an attempt to validate and calibrate the storage model was performed using results from previous research and a 2D-H Delft3D model. Deviations with respect to the Delft3D model were significantly large (factor 2-3), because storage models can only be utilized if the basin size and the remaining gap are small (usability limits). Therefore, calibration was performed by introducing an artificial contraction factor to compensate for the error in the flow velocity. An exponential relation was determined linking the error to the constriction percentage of the gap. With increasing constriction percentage, the error decreased due to increasing validity of the storage model usability limits. The artificial contraction factor can be used to optimize the closure of the Gulf of Khambhat. However, for general use, the model should be calibrated to each specific site.
Case study results show that using multiple cross sections to model the bathymetry with respect to a single cross section, the optimal strategy can change from fully vertical to a combination of horizontal and vertical with a specific capacity. Utilizing the developed model for the Kalpasar case is therefore recommendedbecause the complex bathymetry creates many possible strategies and can’t be reliably modeled with single cross-sectional models. The strategy that showed the most potential for further optimization is: First closing the tidal flats horizontally by forward dumping of rocks, while closing the channels up to 40% of their depth with dumping ships after which the remaining gap is closed vertically by a cable-way or bridge system. This strategy is commonly suggested by existing literature, thereby increasing reliability and validity of the optimization model.
A second case study showed negative effects of increasing construction capacity on the total cost. However, these case results are based on assumed costs and cost functions for equipment, which should be verified by contractors first. Bed protection requirements did decrease significantly by increasing construction capacity, showing potential for development of high capacity closure equipment to avoid these costs. Further future development should focus on vertical closure equipment to decrease both material and bed protection costs.
To conclude the recommendations, more case studies should be performed to quantify influences of parameters already included in the model, such as the permeability of the dam, the presence of a tidal power facility and the use of a sudden caisson closure to relieve the final closure. Secondly, further validation of the storage model is essential to generate more reliable results. Furthermore, research should be performed into cost functions of several existing or new high capacity equipment for vertical closures, relating costs to construction capacity to improve usability of the optimization model.
... Read more

Om aan de woningvraag te voldoen werd in 2000 de bouw van eilandengroep IJburg gestart in het IJmeer-Markermeer. IJburg bestaat uit twee fases die achtereenvolgend aan elkaar zouden worden aangelegd. In 2002 betrokken de eerste bewoners hun huizen op de eerste fase van IJburg. Momenteel is het laatste eiland van fase 1 nog onbebouwd en is gepland dat in 2023 wordt gestart met extra bebouwing van huizen op de tweede fase. Echter, verdere beslissingen met betrekking tot de gehele aanleg van IJburg in de tweede fase is op dit moment nog uiterst onzeker. Omdat het huidig waterbouwkundig ontwerp nog steeds uit gaat van de definitieve situatie van fase 1 en fase 2, is onderzoek naar het effect van het uitblijven van het Buiteneiland op de waterveiligheidsstatus nodig. Daarnaast is vanaf januari 2017 een nieuwe waterkeringsnormering en veiligheidsfilosofie voor dijken, dammen en duinen in Nederland wettelijk van kracht. Hieruit is de volgende hoofdvraag ontstaan voor het onderzoek: “Wat is het effect van de implementatie van de nieuwe normering voor primaire waterkeringen en het uitgestelde besluit van B&W voor het eiland Buiteneiland op de waterveiligheidsstatus in IJburg, welke BwN alternatieven bestaan er om de waterveiligheid in IJburg te garanderen, en welk alternatief wordt geadviseerd voor Gemeente Amsterdam?” Om de waterveiligheidsstatus van IJburg te beoordelen worden scenario’s opgesteld waarbij de twee ontwikkelingen in acht worden genomen: uitgesteld besluit met betrekking tot het aanleggen van Buiteneiland en de implementatie van de nieuwe normering voor primaire keringen in Nederland. De waterveiligheidsstatus wordt beoordeeld aan de hand van het berekenen met een vereiste kruinhoogte volgens Ontwerp Instrument 2014. De berekeningen worden uitgevoerd aan de door Rijksoverheid beschikbaar gestelde programma’s als Hydra Modellen en PC Overslag. Geconcludeerd kan worden dat de waterveiligheidsstatus onveilig en ‘worst case’ scenario als 0-alternatief wordt gesteld bij het ontwerpen van de BwN alternatieven. Om de eisen, randvoorwaarden en wensen, oftewel oplossingsrichtingen, voor de alternatieven vast te stellen wordt er een gebiedsanalyse, ecologische analyse en een stakeholderanalyse uitgevoerd. Hierbij wordt onderscheid gemaakt tussen de primaire functie waterveiligheid en de secundaire functies ecologie en recreatie. Uit de oplossingsrichtingen ontstaan een vijftal oplossingen, genoemd: IJmeer Wadden, Zanddam, Zandeiland, Groenstrand en Natuureiland. In de waterbouwkundig ontwerpen van de BwN alternatieven voor dijkverhoging wordt uitgegaan van natuurlijke elementen zoals wind, stroming, flora en fauna waardoor voordelen kunnen worden geboden voor zowel natuur, recreatie als kostenreductie. De alternatieven berusten op twee verschillende principes om de waterveiligheid te waarborgen zonder dat de kruinhoogte van de primaire waterkering moet worden verhoogd: dempen van golfslag door infrastructuur waarbij een schaduwzone in de IJburgbaai wordt gecreëerd en aanleggen van een zandige vooroever voor de huidige kering. De dagelijkse windcondities spelen een belangrijke rol in de ontwerpen betreffende onverdedigde zandige taluds. De zandige taluds bieden zowel voordelen voor natuur (land-waterovergangen en rust- en ruiplaatsen voor watervogels) als recreatie (windsurf-, kitesurf-, zwemmogelijkheden en creatie van stadsstrand). Daarnaast is het gebruik van zand in de ontwerpen gewenst doordat zand beschikbaar komt uit een ander project binnen IJburg. Hierdoor worden kosten gereduceerd en werk met werk gemaakt. Naast zand is er ook nagedacht om met slibmateriaal te werken. Het slibmateriaal is aanwezig in het systeemgebied en overmatig slib is ongewenst door het negatieve effect op de waterkwaliteit. Door het opnemen en verwerken van slibachtig materiaal wordt de waterkwaliteit verbeterd, natuurgebied ontwikkeld en een oplossing geboden op de waterveiligheidsproblematiek. Een laatste belangrijk aspect om voordelen te behalen in tegenstelling tot traditionele dijkverhoging, is het inspelen met het ontwerp op mogelijke beleidsplannen betreft de configuratie van eilanden. Dit wordt gedaan door het creëren van tijdelijke ontwerpen met een mogelijkheid tot permanent karakter. ... Read more

Rocking behavior of breakwater research was conducted by Centre for Civil Engineering Research and Codes workgroup CUR C70 (1989) and after that no further validation of the research work has been done. In order to understand the rocking behavior and validate the previously conducted research CUR C70 (1989) wave flume test has been conducted in similar setup. One of the important parameter of rocking behavior is the magnitude of impact velocity and the distribution of this impact velocity stochastically and spatially. This research investigates the order of the magnitude of the impact velocity and distribution of the impact velocity comparing, validating and concluding new findings those were not incorporated in CUR C70 (1989) research.

During this research a new type of sensor Tinyduino has been used inside a cube to measure the acceleration and angular velocity of the cubes. Eight of these sensors were used in eight different cubes. All the sensors were tested properly in Deltares to check the sensors working properly and better understanding the sensors. Before this research two test programs were performed by Deltares in tetrapod in double layer using this Tinyduino sensor in stand alone mode but the data were not analyzed. This research analyzed the data for the tetrapods provided by Deltares and compared with CUR 70 (1989). During this analysis and the testing of the sensors it is found that angular velocity measurement can be much more reliable than acceleration hence the angular velocity measurement is used during data processing of instrumented cubes in double layer.

For experiments eight instrumented cubes were placed using very flexible wire in a randomly placed double layer cubes with same size and almost similar density over a permeable filter layer. The slope 1:1.5 is used for the experiment same as the CUR C70 (1989) research conducted. The cubes were placed in one constant level but the water level is varied in order to demonstrate different slope position. Three slope position Y/Dn=0, Y/ Dn =-2 and Y/ Dn =-4 is used during the research program. Three different wave heights and two wave steepness were used during this test program. Due to time limitation 18 test setups within two days were performed. The data were collected real-time using wire and saved in text file simultaneously with eight instrumented cubes stored in a laptop provided by Deltares.

After the test program all the data is processed with matlab script and analyzed. The result of the analysis showed that the order of the magnitude of impact velocities is same as the CUR C70 (1989) research. It has also been found that the impact velocities are also dependent on the wave steepness which was not included in the CUR C70 (1989) research. So it is recommended for future work to update the equation incorporating wave steepness. Another important parameter is number of collision which was assumed to be 3 times is CUR C70 (1989) but found incorrect during this thesis. It is concluded that number of collision is dependent wave height, wave steepness, position over slope and also exposure to wave attack. It is also found that the number of collision is continuous during wave attack after a certain impact velocity.

One of the finding of CUR 70 (1989) was the location of maximum impact velocity over slope. It was concluded in CUR 70 (1989) that the maximum impact velocity lies on Y/Dn=0 meaning on the water level but during this research all the sample those worked observed that the maximum impact velocity is located on Y/Dn =-2 over the slope under the water level.

For future research work it is recommended to use different types of armor unit in single layer to understand the rocking behavior and also it is recommended using the Tinyduino sensors which provides accurate data on movement of the armor units.
... Read more