The coastline near Domburg, in the southwest delta of the Netherlands, has been preserved with sand for three decades. Maintenance was conducted on the beach between the low water line and the dune foot every 4 years. To extent this interval, a shoreface nourishment was implemented in 2017 and was supplemented with a beach nourishment in 2019. Such a parallel shoreface bar is not a naturally occurring morphological feature, as the Domburg coast only features transverse bars. This research investigates the hydrodynamic and morphological effects of different nourishment strategies at the Domburg coast. The study focusses on the application of the shoreface nourishment, as this strategy has not been previously applied at a coast without shore-parallel bars. The study aims at gaining more insight and knowledge on important mechanisms responsible for the spreading of nourished sediment, because this is not fully understood. Additionally, the performance of a numerical model to hindcast erosion and sedimentation in coastal zones is evaluated. To this end, a morphological analysis based on measurements and a model analysis are conducted for three nourishment scenarios. The morphological analysis uses an extensive dataset of bathymetric surveys to compute volume changes, sediment fluxes, bar migration rates, momentary coastline (MKL) positions and nourishment longevities (defined as the period that the volume in between the dune foot and mean low water level is greater than before nourishment). The numerical model analysis is based on the output of a morphostatic XBeach model with simplified boundary conditions which computes the hydrodynamics and sediment transports. The longevity of beach nourishments was found to be on average 3.3 years and the MKL regressed 3.9m/yr on average two years after construction. The eroded sediment did not accrete on the shoreface but was likely transported in the direction of the net sediment transport. The model output indicates that a beach nourishment only has a significant local effect on the hydrodynamics and transport rates. The shoreface nourishment transforms from a landward skewed triangular shape into a more rounded body without the formation of a trough. The bar migrates onshore but not alongshore and the bar volume remains constant. The model shows a contraction of the tidal flow due to the shoreface bar, increasing the seaward velocity and causing a sheltered zone at the leeside and downdrift of the bar. Consequently, the alongshore transport gradients are increased. This causes extra erosion on the shoreface seaward of the bar while accretion is seen at the downdrift shoreface. The shoreface bar contributes little to the offshore dissipation of wave energy. No evidence for a wave-driven salient effect was found at Domburg from the model output. The longevity of the 2019 beach nourishment is not prolonged by the presence of a shoreface bar, as this was found to be 3.1 years. Likewise, the MKL measured a regression of 4.3m/yr, similar to previous beach nourishments. Positively, the shoreface bar captures eroding beach sediment because accretion was found in the surf zone, as opposed to the 2014 beach nourishment. Therefore, a shoreface nourishment is moderately beneficial on maintaining the MKL but contributes to the sediment balance of the coastal cell. Additionally, an alternative nourishment strategy was evaluated through the numerical model. A mega nourishment to the west of Domburg is a viable option as it is likely to feed the updrift and downdrift coastlines which have a sediment demand. It is recommended to further evaluate this nourishment strategy with different numerical models.

In the past decades, beach nourishments have been widely applied along the coast of the Netherlands. Different studies on beach nourishment have been conducted over the years. Most of these studies regard the design, execution method, morpho- and hydrodynamic behaviour, and ecological impact. However, the relationship between the design aspects and the longevity of beach nourishment is not well understood. Here we show with the multiple linear regression (MLR) model that the design aspects volume per metre, height and length of beach nourishment are of interest to analyse the relationship with beach nourishment longevity in the central Holland coast. The storm variables were negligible according to the model since the regression coefficients are insignificant. After numerous reruns of the MLR model, it was noticed that the regression coefficient of design volume per metre is fluctuating. This could indicate a positive, negative, or even no distinct correlation between the design volume per metre and longevity. Therefore, no clear conclusions could be drawn on the design of nourishment volume per metre in order to extend a longer beach nourishment longevity. According to the MLR model, the design length has a positive regression coefficient and design height a negative regression coefficient. These signs suggest that a lower design height elevation and longer design length will result in a longer beach nourishment longevity. The computed beach nourishment longevities of the 7 locations (Julianadorp, Callants-oog, Bergen aan Zee, Egmond aan Zee, Bloemendaal aan Zee, Scheveningen, and Ter Heijde) along the central Holland coast showed that the average longevity of each location could not be interpreted with certainty. This outcome results from the given confidence level of the longevities and the number of beach nourishments used for the computation. Nevertheless, these computed longevities showed that a typical beach nourishment longevity along the central Holland coast is in the range of 3 and 3.5 years. Further, it was observed that computed beach nourishment longevities along the central Holland coast have increased between 1990 and 2020. The increase of beach nourishment longevity coincided with a policy shift in 1999 when shoreface nourishment became a common practice. Therefore, this data suggests that the presence of shoreface nourishment had a positive impact on the longevity of beach nourishments. Despite this result, no certain conclusion could be drawn as the positive contribution can also be caused by increasing nourishment volume through the years. Overall, data-driven research forms the basis of this study and provides a first qualitative insight into the relationship between design aspects and beach nourishment longevity of the central Holland coast.