Two massive beach and nearshore sand nourishment operations were conducted in Dunkirk, northern France, from December to April 2014 in order to reinforce sea dikes that protect the port infrastructures and the city from marine flooding. A comparison of the morphologic evolution of both nourishment sites was carried out to assess the respective persistence of a subtidal versus an intertidal beach nourishment in a microtidal environment, based on an extensive data set of high-resolution topographic measurements of the intertidal beach and bathymetry surveys in the nearshore zone. In addition, offshore wave data were used for analyzing the potential impacts of wave forcing on both nourishments. Our results show that the westernmost part of both nourishment sites experienced significant erosion whereas sediment accumulation took place to the east due to eastward-directed longshore sediment transport. Our data also show that most erosion of the nourishments occurred during energetic wave conditions associated with high water levels for the intertidal/supratidal nourishment. In the case of the nearshore nourishment, a strong correspondence was observed between erosion rates and wave energy during conditions of low water levels, which may be explained by an increase in wave-induced bottom stress with decreasing water depths. Overall, the subtidal nourishment site lost more sediments than the intertidal beach nourishment, with a loss of more than 6.5 x 10^5 m^3 of sand between March 2014 and March 2017 compared to a loss of 1.85 x 10^5 m^3 of sand at the Dunkirk beach during the same period. The subtidal nourishment experienced more erosion than the beach nourishment due to wave-induced bottom currents combined with strong tidal flows on the shoreface.

Coastal regions are confronted with mounting peril stemming from wave-driven erosion, a consequence of rising sea levels and heightened storm severity. This underscores the necessity for pioneering approaches to safeguard shorelines with greater efficacy. The preservation of coastal areas is imperative not only for the protection of human settlements and infrastructure but also for the preservation of vital ecosystems such as wetlands, mangroves, and coral reefs. Additionally, coastal regions often serve as economic hubs, supporting various industries such as tourism, fishing, and shipping. Thus, the implementation of innovative coastal protection measures is essential not only to safeguard lives and property but also to preserve biodiversity, sustain economic activities, and ensure the resilience of coastal communities in the face of climate change. Traditional breakwaters demonstrate effective wave-dampening capabilities. However, as water depth rises, the associated construction expenses escalate significantly, posing a challenge to their practical implementation in engineering projects. Furthermore, these structures impede natural water circulation within the protected zone, leading to heightened concerns regarding pollution and sediment accumulation. Floating breakwaters offer an attractive alternative to fixed structures, as they are minimally impacted by seabed conditions, variations in tides and sea level rise. With their low profile, they have minimal visual impact on the horizon, especially in areas with significant tidal fluctuations. Additionally, they are environmentally friendly as they cause minimal disruption to water circulation. Importantly, they can be easily repositioned, relocated, or removed with little effort. This study focuses on the potential of Triply Periodic Minimal Surface (TPMS) floating breakwaters that boast intricate geometry and structural integrity, enhancing the dissipation and dispersion of wave energy to mitigate shoreline erosion. With the anticipation that the findings of this study will contribute to the development of innovative coastal protection solutions, we aim to strike a balance between environmental sustainability and effective wave attenuation, ensuring the safeguarding of coastal ecosystems while implementing robust coastal defense measures.

The Quebec Ministry of Public Safety initiated the Coastal Erosion and Submersion Prevention Program to evaluate, develop and fund solutions to Quebec coastal communities facing significant coastal hazards during strong storms in the maritime estuary and the gulf of the St-Lawrence. For a given community, the first stage of the Program is to carry out a solution options study to identify the best intervention based on several criteria (cost, resiliency, civil protection, environmental impact, social acceptability, emergency, etc.). Among the studied options, coarse material beach nourishment appears to be more and more considered as an interesting alternative due to its resiliency (more stable than traditional sand nourishment), lower adverse impact on the beach and on the adjacent coastline than rock revetments or groynes. However, being made of granular material exposed to highly variable hydrodynamic forcing, this type of works remains mobile and is characterized by complex hydro-sediment dynamics. Hence, to end up with a durable design adapted to local marine conditions in the long term, accounting for climate change effects, the designer must rely on strong field data and detailed hydrosediment modeling studies. Through the course of five case study, the presentation will highlight some of the challenges and the added value of carrying out such modeling work.