Velocities derived from X-band radar were compared to depth averaged ADCP measurements in a complex tidal inlet system at Ameland, the Netherlands. Inclusion of depth assimilation and ensemble averaging in radar calculations led to smaller differences between ADCP and radar. The observed differences were clustered and related to water level elevations, wind velocities, wave periods, wave heights, spatial coherence in radar output and error metrics of the radar fitting procedure. Larger waves and higher wind velocities were observed to benefit radar agreement with ADCP results. Rising water levels benefitted agreement in east west direction. Falling water levels benefitted agreement in north south direction. Confidence intervals of the fitting procedure were observed to coincide with differences between ADCP and radar and potential for filtering based on them was shown. Nevertheless, an unclarified tendency towards northwestern bias, which may be specific to the comparison locations, remains. The radar at Ameland monitors the whole inlet system and provides current velocities everywhere in its range. This study shows that its currents are in good agreement with ADCP depth averaged currents throughout most of the tidal cycle. Furthermore, it stresses radar’s potential for better monitoring of the coast and for cost effective coastal field measurements to obtain large datasets, even in hydrodynamically very complex regions. ... Read more

In the Netherlands flood protection is immensely important for the safety of the nation. The shocking outcome of the 1953 flooding proves this point. In modern days, the development of socioeconomic and climate change factors casts doubt on the effectiveness of conventional approaches to flood risk management. Consequently, this project explored new approaches to flood risk management.
An analysis of climate change effects led to estimation of future loading conditions. Subsequently, a detailed hydrodynamic analysis was conducted. It highlighted the significant levels of uncertainty that climate change introduces into loading conditions. Also, it confirmed the team’s perception, that the Westkapelle case region requires additional safety measures to guarantee an acceptable level of safety in the future. But how to guarantee the acceptable level of safety in the most efficient way? The team adopted the concept of robustness to find an answer. In a keynote publication Mens (2015) describes robustness in the following way: "Robust flood risk systems have some degree of resistance and some degree of resilience: the system can withstand some floods (no response), and for other (larger) floods impacts are limited and the system can recover quickly from the flood impact (response and recovery)." The team set out to include robustness as an integral part of the design process to handle uncertainties. The project shall be seen as an explorative study how this can be done, revolving around Westkapelle as a case study that proves the methodology’s feasibility. Robustness and uncertainty were included on multiple levels throughout the design process. Firstly, the range of uncertainties was quantified. Secondly, the effect, that single parameters have on the magnitude of uncertainties, was assessed. Thirdly, the system’s capacity was analysed to find the required overtopping reduction for guaranteeing sufficient safety. Fourthly, constructive measures were assessed on their robustness potential and satisfaction of stakeholder needs via a Multi Criteria Analysis (MCA). The MCA was then employed to select the type of constructive and non constructive measures to achieve the required levels of overtopping and safety. With the information on uncertainties, the measures were combined to form a robust design, consisting of living breakwater, dike heightening, surface protection and two policy measures. Probabilistic analysis was also done to see the sensitivity of the failure probability to sea level rise in different loading and design scenarios. A thorough comparison between the conventional design, that has been applied to the project location, and the robust design followed. The robust design came out on top. Robustness was found to be an effective tool in countering uncertainties. Where conventional design methodologies are lacking flexibility and precision, the robust design methodology makes use of the system and its resilience to find an optimal solution. Its applicability may not be limited to flood risk management only but stretch out to other civil engineering disciplines. ... Read more