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Damage characterization of rock slopes
In order to design reliable coastal structures, for present and future scenarios, universal and precise damage assessment methods are required. This study addresses this need, and presents improved damage characterization methods for coastal structures with rock armored slopes. The data used in this study were obtained from a test campaign carried out at Deltares within the European Union (EU) Hydralab+ framework. During these tests, advanced measuring techniques (digital stereo photography) were used, which are able to survey the full extension of the structure and identify local variations of damage. The damage characterization method proposed here is based on three fundamental aspects: clear damage concepts, precise damage parameters, and high resolution measuring techniques. Regarding damage concepts, first, the importance of the characterization width is studied. For damage parameters obtained from the maximum erosion depth observed in a given width (E3D,m), the measured damage increases continuously with increased characterization width. However, for damage parameters obtained from width-averaged profiles (S and E2D), the measured damage reduces with increased characterization width. Second, a new definition of damage limits (damage initiation, intermediate damage, and failure) is presented and calibrated. Regarding the damage parameters, the parameter E3D,5, which describes the maximum erosion depth within the characterization width, is recommended as a robust damage parameter for conventional and non-conventional configurations based on four main characteristics: its low bias, its low random error, the ability to distinguish damage levels, and its validity and suitability for all types of structures (conventional and non-conventional). In addition, the results from this study show that the damage measured with the damage parameter E3D,5 presents an extreme value distribution.
Climate change-driven losses in ecosystem services of coastal wetlands : a case study in the West coast of Bangladesh
Climate change is globally recognized as one of the key drivers of degradation of coastal wetland ecosystems, causing considerable alteration of services provided by these habitats. Quantifying the physical impacts of climate change on these services is therefore of utmost importance. Yet, practical work in this field is fragmented and scarce in current literature, especially in developing countries which are likely to suffer most from the adverse climate change impacts. Using a coherent scenario-based approach that combines assessment of physical impacts with economic valuation techniques, here we quantify potential climate change driven losses in the value of wetland ecosystems services due to relative sea-level rise (RSLR)-induced inundation in the vulnerable Western coastal area of Bangladesh in 2100. The results show a small inundation area in 2100 under the three IPCC climate scenarios of RCP2.6 (with 0.25m of RSLR), RCP6.0 (with 1.18m of RSLR), and RCP8.5 (with 1.77m of RSLR) for the coastal wetland ecosystems including the Sundarbans mangrove forest, neritic system and aquaculture ponds. In all scenarios, RSLR will drive a loss in the total value of ecosystem services such as provision of raw materials, and food provision, ranging from US$ 0–1 million to US$ 16.5–20 million, respectively. The outcomes of this study reveal that RSLR-induced inundation on its own, is unlikely to be a major threat to the wetland ecosystems in Western coast of Bangladesh. This would suggest that other climate change impacts such as coastal erosion, increase in frequency of cyclone events, and sea temperature rise might be the likely primary drivers of change in the value of wetland ecosystems services in this area.
An integrated and interactive toolbox for the design of coastal infrastructure
In order to support clients and stakeholders in the early design phases of interventions in coastal systems, the Coastal Design and Support (CoDeS) tools framework is developed. This framework combines relatively simple tools and empirical relations to assess various aspects of designs and their impacts. The tools are linked to a consistent and easy-to-use Graphical User Interface (GUI) which is applicable around the globe.
How tides and waves enhance aeolian sediment transport at the Sand Motor mega nourishment
In this paper we present a two-dimensional application of the Windsurf modeling framework on the Sand Motor mega-nourishment in The Netherlands that allows for detailed simulation of the interaction between subtidal and subaerial processes.
Undular bore development over a laboratory fringing reef
Several studies have reported the development of undular bores over fringing coral reefs but the importance of this phenomenon for reef hydrodynamics has never been studied. In this study, we investigate undular bore development over reef-type profiles based on a series of laboratory experiments. More specifically, we aim to characterize the conditions under which undular bores develop, and analyse how their development affect the hydrodynamics at the toe of the reef-lined beach and the resulting wave run-up.
Diffusion of a mega feeder nourishment : assessing 5 years of sand engine spreading
Feeder nourishments, where sand quantities of O (10 million m3) are placed locally to feed adjacent coastal stretches, are suggested nowadays as an alternative for local, smaller-scale nourishments (< 1 million m3). The Sand Engine project that is implemented in the Netherlands in 2011 consists of 21.5 million m3 of nourished sediment, and is the largest existing feeder nourishment. In this paper the morphological development of the Sand Engine mega feeder nourishment and the adjacent coastal sections is presented. The alongshore extent of the analysis is 17 km and spans a coastal cell between 2 harbor entrances.
Predicting the reshaping of temporarily exposed bunds with XBeach-G
During coastal construction works, damages often occur to temporary constructions consisting of fine and often wide graded rock material due to exposure to waves. For an exposed breakwater core, it is important to have an idea on how much of the placed material will be moved outside the perimeter, and thus how much material needs to be rehandled before the cover layers can be constructed. For temporary defense works, it is important to know how much material needs to be placed initially in order to offer sufficient protection for a certain period. For both cases, an accurate prediction of the reshaping of such structures is necessary. The reshaping of fine and wide graded temporary structures has been simulated using the process-based model XBeach-G. The results of the model compare well with measured reshaped profiles from physical model tests. XBeach-G appears to be a suitable tool to estimate the reshaping and the resulting volume losses of rock from temporary exposed structures.
Long-term dune evolution under interacting cross-shore and longshore processes
Only few models are available that predict long-term dune evolution. Dune processes are typically modeled at shorter time scales, focusing on storm impact. Meanwhile, long-term coastline evolution models typically ignore exchange of sediment between the beach and the dune. Instead, these models often consider a fixed profile that moves seaward or landward if gradients in the longshore transport are negative or positive, respectively. As a step towards bridging the gap between nearshore, beach, and dune modelling, this study investigates the interaction between longshore transport gradients and the beach and dune evolution on decadal time scales. This aim is addressed by combining an analysis of a 22-year long data set at IJmuiden (The Netherlands) with simulations using a semi-empirical crossshore model, the CS-model.
The relative contribution of sea level rise and storm erosion to long term net coastline recession
The potential Climate change (CC) impacts on coasts and associated socio-economic and environmental risks are widely recognised internationally. One of the most talked about CC impacts is coastline recession. Any increase in mean sea level is expected to result in an upward and landward shift of the entire active profile causing net coastline recession (Bruun, 1962). Another phenomenon that can result in net coastline recession is the cumulative effect of storm erosion. This is due to the hysteresis effect in the storm erosion/dune recovery cycle (Ranasinghe et al., 2012). But what causes more recession: storms or sea level rise? This is a commonly asked question, to which science-backed answers have not been presented to date. This paper addresses this question via the application of a physics based, probabilistic numerical model at a typical swell and storm beaches located in SE Australia and The Netherlands, respectively.
Stability comparison of 9 modern placed block revetment types for slope protections
Placed block revetments are constructed to withstand the wave forces on dikes, especially in regions where rip rap is not locally available, such as the Netherlands. The blocks are placed adjacent to each other on a filter layer to form a relatively closed and smooth surface, which is easy to walk on. Large-scale test in the Delta Flume of Deltares have been carried out to compare the stability of nine types of block revetments, presently on the market in the Netherlands (2016). All tests have been performed with a comparable test setup and test program. The test program consisted of three series of tests. The first two series were short duration tests of 1000 waves with two different wave steepnesses, in which the wave height was increased step-by-step until damage occurred. The third test series was a long duration test lasting for 26 hours, or until damage occurred. The results of the tests have been used to quantify a correction factor in the calculation method. This correction factor, or stability factor, makes that the calculation method gives the same results as the Delta Flume tests, taking a safety margin into account. In this way the type-specific stability of each type of block revetment was better included in the calculation method.