Numerical modelling of the extreme wave climate in the Belgian harbours: part 3. Marina of Blankenberge

The design of water and wave retaining walls and flood risk analyses need hydrodynamic boundary conditions. These boundary conditions are needed during a storm with return period 1000yrs and during the super storms which were defined in the risk analysis study. The modelling of the extreme wave climate is decoupled to the wave penetration and the lacal generation of waves by the extreme wind speed. The wave penetration is modelled with Mike 21 BW as was done for Oostende and Zeebrugge. MILDwave is not used this time because non-linear effects (e.g. long wave generation, wave setup) are too important in this case. Instead another nonlinear model SWASH is applied. The modelling of local generation of waves by wind is still done with the spectral model SWAN.First the bathymetry files are created based on the dredging plan of Blankenberge marina, and all the suitable settings used for the Mike 21 BW and the SWASH are investigated. Since SWASH model does not have so much application examples, Wenduine physical model is used to validate the model. Consequently, a sensitivity analysis is conducted for both models to study which parameter is important for the wave climate inside the marina. The most severe offshore wave direction for the design of the wave retaining walls is decided based on the 1000 year storm. After the calculation of the wave penetration in the case of 1000 year storm and +7.9 mTAW storm, locally generated wind waves are also simulated by SWAN. All extreme wind speeds and directions for the 1000-year storm and the super storms are modelled. Finally, long and short wave energy of the wave penetration models is separated and a superposition of the short wave energy and the SWAN model is done to obtain the total extreme wave climate in the marina of Blankenberge. The maximum surface elevation of the long wave energy and the wave setup provide an increase of the still water level to take into account for design purpose

2D overtopping and impact experiments in shallow foreshore conditions

This paper introduces the 2D experiments conducted for the CREST project in the wave flume of Ghent University. The experiments focus on wave interactions with low-crested sea dikes fronted by a shallow foreshore and mildly to steeply sloping beaches, which is a very typical situation along the Belgian coast. Foreshore slopes of 1/20, 1/35, 1/50 and 1/80 were tested for a range of low to high energy wave conditions, a variation in wave steepness and two water levels. The main goal was to obtain a dataset in which the effects of the infragravity waves on the wave-structure interactions (i.e. wave overtopping and impact forces) can be studied. The tests included high spatial resolution surface elevation measurement tests, which is new for beaches including a dike in the inner surf zone. From the first results it became clear that the foreshore slope influences the wave transformation up to the dike toe. The influence is apparent comparing to existing (semi-) empirical models for prediction of the spectral wave period at the dike toe and wave overtopping at the dike crest. The high spatial resolution data show a steep increase in infragravity significant wave height in the very shallow area in front of the dike

2D experiments of wave dynamics in front of and over a sea dike with a very shallow foreshore

This paper introduces the 2D experiments conducted for the CREST project in the wave flume of Ghent University. The experiments focus on wave interactions with low-crested sea dikes fronted by a shallow foreshore and mildly to steeply sloping beaches, which is a very typical situation along the Belgian coast. Foreshore slopes of 1/20, 1/50 and 1/80 were tested for a range of low to high energy wave conditions, a variation in wave steepness and two water levels. The main goal was to obtain a dataset in which the effects of the infragravity waves on the wave-structure interactions (i.e. wave overtopping and impact forces) can be studied. The tests included high spatial resolution surface elevation measurement tests, which is new for beaches including a dike in the inner surf zone. From the preliminary results it became clear that the foreshore slope influences the wave transformation up to the dike toe. The influence is apparent comparing to existing (semi-) empirical models for prediction of the spectral wave period at the dike toe and wave overtopping at the dike crest. The high spatial resolution data show a steep increase in infragravity significant wave height in the very shallow area in front of the dike

Climate warming and atmospheric deposition affect seed viability of common juniper (Juniperus communis) via their impact on the nutrient status of the plant

Global environmental change is increasingly affecting species worldwide. One of the emblematic casualties among plants in several European countries is common juniper (Juniperus communis). Many populations of common juniper throughout its distribution range are declining. The relative lack of viable seed production, resulting in low probabilities for successful natural regeneration, is one of the main reasons for this decline. Climate warming and elevated atmospheric depositions have been shown to negatively affect seed viability of common juniper, but our understanding of the underlying mechanisms remains scarce. One possible pathway is via changes in the plant nutrient status that, in turn, may affect seed viability. Here we took advantage of large-scale gradients in climate and atmospheric depositions between central Sweden and northern Spain, and analysed foliar nutrient concentrations and stoichiometry and seed viability in 20 juniper populations spread across Europe. Our results show that increasing temperatures can negatively affect needle N and P concentrations while enhanced potentially acidifying depositions resulted in lower foliar N and Ca concentrations. Needle C:N ratios increased with higher temperature, acidifying depositions and precipitation. By linking these patterns to seed viability, we found that low needle P, Ca and Mg concentrations were related to low seed viability. Thus, a shortage of these key elements during seed development and seed nutrient storage, can lead to anomalies and seed abortion. These findings help to explain the low seed viability of juniper in Europe and may help to assist land managers to take urgently needed conservation actions