Exploring decadal beach profile dynamics in response to nourishment strategies under accelerated sea level rise

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.