The dunes along the Dutch coast serve as a critical component of flood defense. Storms and a shortage of sediment supply offshore lead to dune and shoreline erosion, posing a hazard to flood safety. To combat coastal erosion, the Dutch government decided in 1990 to proactively nourish the coast. It is expected that as an indirect effect of the sand nourishments, the volume of the dunes will increase. This thesis aims to determine if the influence of the nourishments and storms along the Dutch coast at decadal timescales can be observed.

A conceptual model is presented to address the impact of storms and nourishments. With the model it is argued that storms have little influence whilst nourishments will likely significant influence the long term dune development.

To investigate the impact of storms yearly coastal profile measurements along the entire Dutch coast (JarKus dataset) and storm profile measurements from the storm in 1976 are used. Following the analysis, no correlation is found between the magnitude of the storm impact and the post storm dune development. However, a difference in horizontal dune toe translation (DTT) trend before the storm (1965-1975) and after the storm (1976-1981) is observed. For all coastal regions except the Delta regions, a higher post storm DTT is found.

To investigate the impact of nourishments yearly coastal profile measurements from 1965 to 2022 of more than 1000 transects along the entire Dutch coast are used. Fitting a continuous bi-segmented piecewise linear function showed an average dune volume change (DVC) of 4.5 m3/m/y before the break point year 1993 and 9.3 m3/m/y after 1993 for the entire Dutch coast. These findings align with the fact that large-scale nourishments commenced in 1990.

Furthermore, the nourishment volume is compared to the change in DVC per coastal region to investigate the impact of the nourishments. A Pearson correlation coefficient of r = 0.78 is found between the change in nourishment volume and the change in DVC between the period before and after the breakpoint year. The ratio between nourishment volume and dune growth is 0.24, meaning that if the correlation is causal, 1m³ of nourished volume contributes to 0.24m³ of dune growth.

Based on the data analysis, we conclude that there is no evidence based on the storm measurements in 1976 to suggest that the size of the storm influences dune growth post-storm. However, the measured DTT trend before and after the storm supports the idea that the dune toe tends to return to the pre-storm trend after a storm. Therefore, on a long-term scale, there seems to be no lingering influence of the storm on dune development. Additionally, the data analysis revealed a distinct change in the trend of dune growth in 1993, three years after the start of large-scale nourishments. A strong relationship is found between the amount of nourished sediment and the DVC. These findings supports the idea that nourishments along the Dutch coast have a significant impact on dune development on a decadal timescale.