Worldwide, artificial nourishments are being considered as one of the main coastal erosion mitigation measures. However, this solution is not permanent, since the natural removal of sediments that occurs after the sand deposition leads to the need of re-nourishment projects; thus, its performance and longevity dependent on several design parameters (placement site and extension alongshore, frequency, and volume, etc.) In this work, a methodological approach for cost–benefit assessment is applied to analyze the performance of artificial nourishments from a physical and economical point of view, by analyzing the effectiveness of different scenarios. The study was developed considering two study areas: a hypothetical situation (generic study area) and a real coastal stretch (Barra-Vagueira, located in the Portuguese west coast). The findings show the complexity in defining the best nourishment option, being dependent on the wave climate, site specific conditions, and main goal of the intervention. The proposed cost–benefit approach allows one to obtain and compare the physical and economic performance of artificial nourishments to mitigate coastal erosion, aiding the decision-making processes related to coastal planning and management.

Serious erosion problems related to significant negative sediments budgets in the coastal systems are referred worldwide. Artificial nourishments are a coastal erosion mitigation strategy that allow for a decrease in those negative budgets by adding sediment to the coastal system. Thus, it is essential to understand and adequately model the shoreline response after a nourishment operation, in order to support the definition of the best intervention scenarios. The main goal of this work was to study the artificial nourishment effects on the longshore sediment transport and consequently on the morphological evolution at the intervention site and nearby areas, in a time horizon of 5 years. The longshore transport of the nourished sediments was evaluated, aiming to contribute to the evaluation of the sediment’s permanence at the deposition site and the frequency required for new nourishments. The shoreline evolution numerical long-term configuration (LTC) model was applied in order to evaluate the spatial and temporal distribution of the nourished sediments along the coast, considering different types of beaches and incident wave climates. The adopted approach is generic and supported by simple numerical models, which can be useful for preliminary site-specific evaluations. The results show that the nourishment impact is mainly observed nearby the intervention site. It is highlighted that higher longshore sediment transport rates are associated with more energetic wave climates, but not necessarily with incident waves more oblique to the shoreline.

Coelho, C.; Ferreira, M., and Marinho, B., 2020. Numerical modelling of artificial sediment nourishment impacts. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 209–213. Coconut Creek (Florida), ISSN 0749-0208.In general, coastal erosion problems are related to significant sediments deficits. A possible coastal erosion mitigation strategy involves restoring the sediments balance through artificial nourishments. However, the complexity of the physical processes in the coastal zones challenges the numerical tools prediction capacity. This is usually overcome through numerical modelling of the shoreline evolution and the cross-shore profile along time, as an attempt to anticipate the performance of nourishments operations. The coastal morphology depends on the sediments dynamics and the incident wave climate is considered the main modelling agent responsible for the potential sediment transport capacity. The cross-shore sediment transport is usually associated to the shortterm behaviour of the morphological evolution of the beach (seasonal changes) and the longshore sediment transport is related to the long-term changes (towards an equilibrium state). Typically, these distinct sediment transport components are studied and modelled separately due to the incompatibility of their time scales of interest.This work was developed to numerically model the impact of artificial nourishments. LTC (Long-Term Configuration, Coelho, 2005) and CS-model (Larson et al., 2016) were both applied to analyse the spatial and temporal distribution of sediments induced by artificial nourishments along and across the shore, considering different intervention scenarios. LTC was applied to evaluate the nourishments impact in the shoreline evolution and to quantify the volume of nourished sediments in different longshore locations along time. The CS-model was used to analyse the performance of multiple intervention scenarios, varying the cross-shore location, frequency and volume of the artificial nourishments. The performance of this type of intervention generally represents a smaller shoreline retreat and an increase of the cross-shore profile volumes during a limited period of time. The project results aim to increase numerical modelling capabilities, helping on the selection of optimal artificial nourishment schemes and the establishment of more efficient coastal management policies.

Beach–dune systems are highly dynamic features of the coastal system, the evolution of which is influenced by several processes that occur at very different spatial and temporal scales. To mitigate shoreline retreat that threatens extensive coastal areas worldwide, coastal erosion mitigation measures are implemented, aiming to make coastal areas resilient to the effects induced by coastal erosion and the anticipated climate change related to storms, flood events and sea level rise. Numerical modelling can support planned and sustainable coastal management from a medium-to-long-term perspective (decades). This research focuses on presenting contributions regarding the numerical modelling of subaerial beach dynamics (berm width and dune systems interactions) from a medium-term perspective. The method applied is based on a combination of the results of two simplified numerical models (the LTC and CS-Model). The results demonstrate the potential of the proposed combined model for medium-term projections, allowing for the interpretation of beach–dune dynamics and the evaluation of the importance of longshore and cross-shore sediment transport processes.