259 research outputs found
Assessment of effects of chemical contaminants in dredged material on marine ecosystems and human health
No full textOm te voorkomen dat scheepvaartroutes dichtslibben moeten waterwegen en havens in deltagebieden regelmatig worden gebaggerd. Wereldwijd worden op jaarbasis honderden miljoenen tonnen baggerspecie en sediment verwijderd. Nederland verspreidt jaarlijks meer dan 25 miljoen kubieke meter gebaggerd sediment in de Noordzee. Hierbij is het van belang te kunnen bepalen wat de risico's zijn voor het ecosysteem. Het in sediment identificeren van chemische stoffen die een potentieel risico vormen voor het ecosysteem of voor de menselijke gezondheid is dan ook het onderwerp van veel studies. Dit proefschrift onderzoekt de toepasbaarheid van in vitro, in vivo bioassays en bio-indicatoren als mogelijke beoordelingsinstrument voor het vaststellen van de schadelijke effecten op zeeorganismen van complexe chemische verbindingen in sedimen
Monthly morphological measurements of Vlugtenburg beach (NL) - 2009-2012
No full textThis dataset contains morphological cross shore coastal profiles collected with the Technical University Delft (TUD) Jetski using Real Time Kinematic satellite navigation (RTK-GPS). The data includes the foreshore till the -10m depth, the beach and part of the dune area. The aim to collect this dataset was to study the morphological developments just after a nourishment at Vlugtenberg Beach in the Netherlands.
The data contain 38 combined surveys. A combined survey exists of a jetski and a walking survey. The time entries of the data are organised by the 78 individual surveys. The attached notes contain a table that shows how the time entries of the individual surveys relate to the combined surveys
Navigating Sand and Waves: On the evolution of sand ripples under combined wave and current conditions
No full textSand ripples are small (10 cm height) bed forms which occur in the nearshore and surf zone under the impact of both waves and currents. They impact the roughness of the bed used in models of this zone, and contribute to sediment transport. Predictions of their geometry are important to properly model roughness, so correlations between the waves and ripples need to be established. In this project, data about the instantaneous bed level and wave conditions at two point locations in the surf zone was used to analyze the relationship between wave conditions and ripples on the bed. Values for significant wave height, peak period, skewness, ripple height and ripple period were found over bins of 15 minutes in length. It was found that there are relationships between ripple height and wave height, wave skewness and ripple height. These correlations are strongest for a zero shift in the signals, meaning the ripple height can adjust to the wave height and/or skewness within 15 minutes. These results can be used with further research, which includes local current measurements, to make more accurate estimates of the ripple height.Civil Engineering | Hydraulic Engineerin
Macro-scale performance of a mega-feeder nourishment: Describing and predicting the long-term feeding performance
No full textA mega-feeder nourishment is a concentrated nourishment that disperses over time due to wind, waves, and tide, and as a result ‘feeds’ its adjacent coasts. During the design phase of a nourishment, performance indicators can enable an objective comparison of a mega-feeder nourishment to alternative nourishment strategies, In the case of an existing mega-feeder nourishment, predictions of the performance enable an objective assessment of the need for additional nourishments in the proximity of a mega-feeder nourishment.Today, engineers and policy makers rely on expert judgement when assessing alternative nourishment strategies, or the need for additional nourishments. Currently no tool exists that enables quantification of the performance of a mega-feeder nourishment. Existing models that describe and predict developments of nearshore coastal areas have been applied before to assess the developments of a mega-feeder nourishment, but have not been validated specifically to describe the performance in terms of alongshore feeding. The research question is therefore: "How to describe and predict macro-scale mega-feeder nourishment performance with behaviour-based coastal indicators?"A tool is proposed that enables the quantification of the performance of a mega-feeder nourishment, as well as the validation of models that describe and predict the performance of a mega-feeder nourishment, The tool is specifically aimed at quantifying the performance in terms of the alongshore feeding. The tool comprises of indicators that representatively quantify the contribution of sediment, the region of feeding, and the time it does so.The tool is applied to the Sand Engine, used as a case study to examine the applicability. This Sand Engine, constructed during the spring of 2011, has a nourishment volume of 21.5Mm3, initially spanned a width of 2.4km and extended 1km into the sea. Application of the indicators to the Sand Engine confirmed the performance developed with continuous trends, suggesting the performance can be predicted.From the validation of the model approaches, it is concluded that the analytical model can be used to predict the initial performance of a mega-feeder nourishment, if the longshore spreading is derived from the LST equation by Kamphuis. Second, if the bathymetry is regularly monitored (e.g. semi-annually), the input of the analytical model can be calibrated, enabling long-term predictions of the performance. If more detailed descriptions of the developments of a mega-feeder nourishment are needed, a bruteforce process-based numerical modelling approach can serve as a method to describe and predict the feeding performance of a mega-feeder nourishment.The performance of the Sand Engine is predicted with the validated models up until 2030. The volumetric growth will stagnate on the south, while on the north it is expected to grow up to 4Mm3. The width will increase to approximately 7km. From this, it is concluded that it is unlikely the Sand Engine will meet its original objective of contributing to coastal safety along the Westland coast (17.2km). Further, the half-life of the Sand Engine will be reached near 2030, indicating the actual lifetime is significantly longer than the design lifetime (20 years). Sand Engin
Global Coasts: A Baroque Embarrassment of Riches
No full textCoasts form the universal stage on which people interact with the global ocean. Our history is inextricably intertwined with the seashore, being a rich tapestry of archaeological sites that paint a vivid picture of people hunting, foraging, fishing and scavenging at the edge of the sea. Seascapes inspire diverse art forms celebrated through the ages. The world’s sandy beaches have a flummoxing duality of anthropocentric purpose—ranging from the horrors when being theatres of war to first love under a rising moon. ‘Man’s Love of the Sea’ continues to draw people towards the shore: the narrow coastal strip contains everything from holiday cottages to mega-cities. This coastal concentration of the human population is problematic when shorelines erode and move inland, a geological process fastened by climate change. Society’s response is often a heavy investment in coastal engineering to complement and enhance the natural storm protection capacity of beaches and dunes. The coast’s immense cultural, social, and economic significance are complemented by a wealth of natural riches. In the public’s eye, these ecological values can pale somewhat compared with more imminent ecosystem services, particularly protecting human properties from storm impacts. To re-balance the picture, here we illustrate how peer-reviewed science can be translated into ‘cool beach facts’, aimed at creating a broader environmental appreciation of ocean shores. The colourful kaleidoscope of coastal values faces a veritable array of anthropogenic stressors, from coastal armouring to environmental harm caused by off-road vehicles. Whilst these threats are not necessarily unique to coastal ecosystems, rarely do the winds of global change blow stiffer than at the edge of the sea, where millions of people have created their fragile homes on shifting sands now being increasingly eroded by rising seas. Natural shorelines accommodate such changing sea levels by moving landwards, a poignant and powerful reminder that protecting the remaining natural land is primus inter pares in coastal management. There is no doubt that coastal ecosystems and coastal communities face august trials to maintain essential ecosystem services in the face of global change. Whilst bureaucracies are not always well equipped to counteract environmental harm effectively, using measures carrying a social license, many communities and individuals have encouragingly deep values connected to living coastlines. Building on these values, and harnessing the fierce protective spirits of people, are pivotal to shaping fresh models that can enhance and re-build resilience for shores that will continue to be a ‘baroque embarrassment of coastal riches’
Morphodynamic acceleration techniques for multi-timescale predictions of complex sandy interventions
No full textThirty one percent (31%) of the world's coastline consists of sandy beaches and dunes that form a natural defense protecting the hinterland from flooding. A common measure to mitigate erosion along sandy beaches is the implementation of sand nourishments. The design and acceptance of such a mitigating measure require information on the expected evolution at time scales from storms to decades. Process-based morphodynamic models are increasingly applied, together with morphodynamic acceleration techniques, to obtain detailed information on this wide scale of ranges. This study shows that techniques for the acceleration of the morphological evolution can have a significant impact on the simulated evolution and dispersion of sandy interventions. A calibrated Delft3D model of the Sand Engine mega-nourishment is applied to compare different acceleration techniques, focusing on accuracy and computational times. Results show that acceleration techniques using representative (schematized) wave conditions are not capable of accurately reproducing the morphological response in the first two years. The best reproduction of the morphological behavior of the first five years is obtained by the brute force simulations. Applying input filtering and a compression factor provides similar accuracy yet with a factor five gain in computational cost. An attractive method for the medium to long time scales, which further reduces computational costs, is a method that uses representative wave conditions based on gross longshore transports, while showing similar results as the benchmark simulation. Erosional behavior is captured well in all considered techniques with variations in volumes of about 1 million m3 after three decades. The spatio-temporal variability of the predicted alongshore and cross-shore distribution of the morphological evolution however have a strong dependency on the selected acceleration technique. A new technique, called 'brute force merged', which incorporates the full variability of the wave climate, provides the optimal combination of phenomenological accuracy and computational efficiency (a factor of 20 faster than the benchmark brute force technique) at both the short and medium to long time scales. This approach, which combines realistic time series and the mormerge technique, provides an attractive and flexible method to efficiently predict the evolution of complex sandy interventions at time scales from hours to decades.Coastal Engineerin
On the generation of surfable ship waves in a circular pool: Part I: physical background & wave pool design
No full textSurfing as a sport is growing. Locations with good surfing conditions are limited and therefore crowded. The growing interest for the sport led to a new concept, surf pools. Surf pools mimic good surfing conditions found along the coast. This thesis is about the technical feasibility of a new surf pool concept, creating surfing waves in a circular pool by towing ship-like hulls around. The hulls are towed along the outer wall of the pool and waves generated by these hulls propagate inwards and break on an island in the middle of the pool. The waves break around the island which theoretically leads to endless surf rides. The initial design as suggested by Webber is based on a pool diameter of 200 m and a water depth of 3 m. The objective of his design to generate 2 m high waves for intermediate to expert surfers. Because of the lack of knowledge about ship induced waves in such an enclosed environment, a physical and a numerical model study are carried out. Various hull sizes are towed in a towing tank and the surface elevations are measured and analyzed. From this physical model study it was concluded that the wave pattern behind a hull is the result of a complex interference pattern and is easily disturbed when the velocity beside the hull becomes large. The difficulties of wave generation by a hull therefore lie in the return currents. The magnitude of the return flow is a function of the blockage, the percentage of the cross section of the pool blocked by the hull. In case the blocking and the velocity are too large, water accumulates in front of the hull and the wave field behind the hull is disturbed, the so-called trans-critical regime. Maximum wave height is found when to towing a hull at the onset of this trans-critical regime. The initial wave pool design is evaluated, and it was concluded that the water depth of 3 m is insufficient to generate the desired 2 m waves. Therefore an amended design is presented. Water depth is increased to 7 m and the generation area is enlarged to reduce the blockage to 5%. The large generation area causes a weak return flow and therefore less turbulence in the pool. In such a cross section it is considered technically possible to generate 2 m high surfable waves.Civil Engineering and Geoscience
Examining parameters that control spreading of a concentrated nourishment
No full textDue to sea level rise and subsidence of land, coastal erosion is a serious problem in the Netherlands. And nourishments are common solutions to mitigate coastal erosion. Over the last decades, many studies have been focusing on individual nourishment performance to help us increase understanding of it. However, it is still not clear for us how the nourishments behave under different parameters (such as water depth of the nourishment crest, wave heights or nourishment size etc). This thesis tests the impact of different parameters on the erosion rate of the nourishments through measured data and numerical model simulations.Civil Engineerin
The Influence of Diffraction on Artificial Pocket Beaches: a Morphological Assessment with XBeach
No full textInformation about the hydrodynamic, sediment transport and morphodynamics is limited in pocket beaches (Dehouck et al., 2009). However, a good understanding is necessary for effective management of coastal areas (Scholar et al., 1998). A small artificial pocket beach has relatively large shadow zones, therefore, diffraction might be an important process. Designs of pocket beaches are now based on equilibrium beaches and morphological changes and sediment losses during storm conditions. The numerical model XBeach is used to predict the beach development and losses. However, so far diffraction has not been included in these simulations. Therefore, the main objective of this research is to gain better insight on the effect of including short wave diffraction in the simulations on the morphological development in pocket beaches. Various modes of XBeach give the opportunity to variate including short wave diffraction or not. A simplified pocket beach and a case study beach has been used to research the influence of short wave diffraction on the morphological development within a storm and the underlying hydrodynamic and sediment transport processes. The simplified beach used, has a length of 500 metres and perpendicular groynes. The shadow zone covered about 30% of the embayment area. The case study beach is a stable designed, real, curved pocket beach in Constanta, Romania, with a similar surface area as the simplified beach but a total shadow area of 40%. In both cases the effect of short wave diffraction appeared to be a wider circulation cell than without diffraction and the outflow velocities along the groyne are lower with diffraction. Sediment transport patterns are similar to the circulation patterns, however, without diffraction an abrupt decrease of sediment transport can be found at the boundary of the shadow zone. Erosion and sedimentation patterns are dispersed gradually over the embayment in case diffraction is included in the simulations. In case diffraction is neglected the transitions of erosion and sedimentation are very abrupt. The exact results of the morphological development in the case study look more reliable than the simplified pocket beach results. Both cases, with and without diffraction, show erosion, however, with diffraction the total loss of sediment is 10% less relative to without diffraction. With diffraction, the exposed shoreline shows less erosion (10%), the shadow shoreline shows more erosion (90%), the shadow embayment shows less sedimentation (30%) and the exposed embayment shows more sedimentation (350%). Without diffraction abrupt vertical changes of about one metre exist at the boundary of shadow to exposed zones. The results with diffraction look promising however, a real validation of the results was not possible with the available data. In conclusion, diffraction appears to be an important phenomenon in relatively small pocket beaches. The sedimentation and erosion pattern is much more gradually dispersed over the area. The main alongshore velocities and sediment transport direction in the exposed zone and the gradual development of sediment transport into the shadow zones cause these gradual transitions. The abrupt transitions in the sediment transport patterns without diffraction result in very abrupt changes in the bed level alterations.Civil Engineerin
Optimizing Shoreface Nourishment Design Using The Concept Of Equilibrium Beach Profiles: A Case Study In Nags Head
No full textIntroduction and Problem Description: The autonomous nearshore morphodynamics along the Nags Head shoreline are characterized by consistent erosional behavior. The use of shoreface nourishments to counteract this erosion along shorelines has received considerable attention in the past, having the advantage of reduced cost compared to beach nourishments. Although shoreface nourishments are thus an increasingly interesting option for coastal managers, their design is often highly empirical and based on guidelines. A better understanding of the way a shoreface nourishment interacts with the antecedent bathymetry and respective forcing agents (i.e. - waves and tides) may help to reduce the degree of empiricism and possibly optimizing nourishment design in terms of longevity and shoreline sedimentation. Rather than using design guidelines, the present research aims to relate nourishment design to beach profile shaping parameters like wave climate and sediment characteristics.Representation of beach profiles based on local wave dissipation, wave reflection and sediment characteristics have previously been studied in the form of equilibrium beach profiles (EBP). Recently major improvement in beach profile representations are made by including wave reflection in the energy balance, resulting in a two-sectioned EBP. After local site-specific parameter calibration, the vertical deviation between the initial profile and analogous calibrated EBP (z_{ebp} - z_{ini}) should indicate where a scarcity of sediment along the cross-shore profile is. Shoreface nourishments are then designed by filling in the vertical gaps between these two profiles. A hypothesis was postulated stating that the optimal form for a shoreface nourishment follows the equilibrium beach profile the best. The differences in impact conventional nourishment designs (based on guidelines) have on either cross-shore and longshore transport rates are computed and compared to an EBP-based design in two separate modeling studies.Effects on cross-shore transport: Beach profile morphology and the response to shoreface nourishments are modeled in the 1D cross-shore profile model UNIBEST-TC. Three distinct conventional designs which have found recent applications are selected and based on either; extension of the outer bar, creating a new outer bar or filling in the trough shoreward of the outer bar. Analysis of the model results show that all four nourishment designs are incorporated well in the cross-shore morphodynamics as compared to the situation prior to construction. The EBP-design shows strongest reduction of offshore directed transport, followed by designs based on filling in the trough, creating a new outer bar or extending the existing outer bar. Therefore the model simulations suggest that a nourishment design with the largest vertical deviations from the EBP may be the least effective to counteract coastal erosion. This partially confirms the postulated hypothesis that cross-shore transport rates are lowered most efficient while using the concept of EBP to design shoreface nourishments. Effects on longshore transport: The coastal area flow model Delft3D was utilized for a series of numerical modeling simulations to examine the potential dependencies between nourishment design and post-dredging longshore transport rates and local gradients. Model results show a similar outcome as the cross-shore profile model, where the EBP-design results in the lowest longshore transport rates. Closer examination of the simulations, especially concerning the local gradients and longshore transport rates, show that the EBP-design reduces longshore gradients by a factor two up to four compared to conventional nourishment designs. The EBP-design therefore shows less sediment transport and local gradients because of a divergence of non-linear local sediment transport rates over the coastal zone. Confirming earlier studies that local longshore gradients dominate coastal change at the scale of nourishments and the hypothesis that shoreface nourishment design based on the concept of EBP is a more efficient way compared to conventional designs.Practical applications: The results and theory demonstrate how the incoming wave climate and sediment characteristics are responsible for both the EBP shape and sediment transport. Since the erosion rates at the project site show local longshore variability, and the EBP shape remains constant even though using the same characteristics, the deviation between the initial- and EBP profile should indicate a gradient in longshore transport rates as well. Knowing this, the overall longshore gradient can be estimated using only one survey dataset. This could lead to a preliminary nourishment design, based on only one bathymetry survey and project budget. Approximation of longshore transport gradients could strongly improve the nourishment lifetime, especially in remote locations.The constant longshore shape of the EBP with respect to MSL is furthermore efficient in reducing the local longshore transport gradients. Since the EBP-model is used as a template to fill in the vertical deviations between the initial profile and EBP, the longshore variabilities are spread out over the project site creating a less obstructive flow, thereby reducing longshore transport rates as well. Whereas conventional nourishment designs follow the original longshore variabilities and only enhance them, resulting in strong 3D bathymetrical features corresponding to coastal erosion as well
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