Projections of high rates of sea level rise have stimulated proposals for adaptation strategies with increasingly high nourishment volumes along sandy beaches. An underlying assumption is that coastal profiles respond rapidly to nourishments by redistributing sediments towards a (new) equilibrium shape. However, this perception may not be valid when high volumes of nourishment are applied, as the profile shape may then undergo significant deformation. Current state-of-the-art modelling techniques often concentrate on a single spatio-temporal scale, either lacking the necessary temporal horizon or failing to provide the required level of cross-shore detail. This article introduces Crocodile, a diffusion based cross-shore model designed to bridge the gap between short- and long-term nourishment modelling. The model simulates the effects of nourishment strategies on coastal volume, coastline position and beach width over a decadal timeframe. It incorporates different elements which compute cross-shore diffusion, sediment exchange with the dune and longshore sediment losses. To test the model performance, a series of idealized nourishment scenarios are examined, along with three case studies along the Dutch coast with different nourishment strategies over the past few decades. The modelled coastal volume, shoreline position and beach width strongly resemble the observations with only a 12% overestimation in profile volume and 13% underestimation in beach width. Averaged over selected periods of nourishment, trends and trend reversals between different strategies are well replicated with slight overestimation for coastal volume trends by 1.5m³/m/yr(10%), while beach width trends are underestimated by 0.2m/yr (15%). Given that the added nourishment volumes are typically in the order of 100m³/m, these model errors are considered sufficiently low to conclude that Crocodile effectively simulates variations in coastal volume, coastline position and beach width over a decadal timeframe in response to different nourishment strategies. Therefore, Crocodile can facilitate the evaluation of future nourishment strategies.

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Accelerated sea level rise prompts the upscaling of nourishment strategies, either through larger individual nourishment volumes or increased frequency of implementation. In such strategies, the nourished sand may lack time to effectively redistribute in the designated timeframe, leading to significant deformation of the profile over multiple nourishment cycles. This study quantifies subsequent effects, focusing on profile steepening, nourishment lifetimes, and the feasibility of operational objectives. We simulated two common nourishment strategies at a Dutch case study location using the cross-shore morphological model Crocodile over a 50-year timespan under sea level rise rates of 2–32 mm/year. The choice of strategy led to a variation of up to 75% in the total amount of sand used. Our results show increasing profile deformation with nourishment volume applied and duration of the nourishment strategy, with sand accumulating in the nourished section and little dissipation to the lower shoreface. The consequent profile steepening leads to reduced nourishment lifetimes by up to 30%. Additionally, under high sea level rise rates, more erosive coasts experience a reduction in nourishment lifetimes to annual intervals, while less erosive areas require up to four times more sand than currently needed. These findings illustrate key dilemmas in the formulation of future nourishment strategies and highlight the importance of optimizing these strategies to account for sea level rise.

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The aim of this technical note is to describe the Cycle 46 reference configuration of the HARMONIE-AROME convection-permitting numerical weather prediction model. HARMONIEAROME is one of the canonical system configurations that is developed, maintained, and validated in the ACCORD consortium, a collaboration of 26 countries in Europe and northern Africa on shortrange mesoscale numerical weather prediction. This technical note describes updates to the physical parametrizations, both upper-air and surface, configuration choices such as lateral boundary conditions, model levels, horizontal resolution, model time step, and databases associated with the model, such as for physiography and aerosols. Much of the physics developments are related to improving the representation of clouds in the model, including developments in the turbulence, shallow convection, and statistical cloud scheme, as well as changes in radiation and cloud microphysics concerning cloud droplet number concentration and longwave cloud liquid optical properties. Near real-time aerosols and the ICE-T microphysics scheme, which improves the representation of supercooled liquid, and a wind farm parametrization have been added as options. Surface-wise, one of the main advances is the implementation of the lake model FLake. An outlook on upcoming developments is also included.@en

Projections of high rates of sea level rise have stimulated proposals for adaptation strategies with increasingly high nourishment volumes. Nourishment strategies involving higher sand volumes can be accomplished by increasing the volume of individual nourishments or by decreasing the time interval between successive nourishments. The optimal placement of the sediment volumes in the cross-shore and alongshore to attain our coastal management goals is still under debate. From a long term, large scale perspective only the added sediment volume may be considered, regardless of the placement. A widely accepted perception is that coastal profiles respond to nourishment by rapid equilibration to an equilibrium shape including the added sand volume. However, the timescale of the redistribution of the sediment may be slower than the desired spreading rate of the added sediment, causing sediment to accumulate at some parts of the profile, while leaving other elevations sediment starved. This research aims to examine decadal-scale coastal profile response to nourishment strategies upscaled with sea level rise (SLR) whereby potential nourishment strategy impacts for beach width (fluctuations), dune growth potential and momentary coastline are mapped. @en