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Over recent years, many coastal engineering projects have employed the use of soft solutions as these are generally less environmentally damaging than hard solutions. However, in some cases, local conditions hinder the use of soft solutions, meaning that hard solutions have to be adopted or, sometimes, a combination of hard and soft measures is seen as optimal. This research reviews the use of hard coastal structures on the foreshore (groynes, breakwaters and jetties) and onshore (seawalls and dikes). The purpose, functioning and local conditions for which these structures are most suitable are outlined. A description is provided on the negative effects that these structures may have on morphological, hydrodynamic and ecological conditions. To reduce or mitigate these negative impacts, or to create new ecosystem services, the following nature-based adaptations are proposed and discussed: (1) applying soft solutions complementary to hard solutions, (2) mitigating morphological and hydrodynamic changes and (3) ecologically enhancing hard coastal structures. The selection and also the success of these potential adaptations are highly dependent on local conditions, such as hydrodynamic forcing, spatial requirements and socioeconomic factors. The overview provided in this paper aims to offer an interdisciplinary understanding, by giving general guidance on which type of solution is suitable for given characteristics, taking into consideration all aspects that are key for environmentally sensitive coastal designs. Overall, this study aims to provide guidance at the interdisciplinary design stage of nature-based coastal defence structures.

Coastal erosion is a natural process, whose intensity and occurrence have increased due to natural and anthropogenic factors. To protect the coasts, the use of hard infrastructure is a widespread practice that can be effective, mostly at a local scale. However, recent evidence also shows that downstream erosion can be accelerated in adjacent zones. Because of this, natural barriers such as coastal dunes and their plant cover have gained attention, but there is a general lack of information about the role that different species (and combinations of species) play in coastal protection. The aim of this study was to explore if the functional richness of plant species helps reduce wave erosion on embryo coastal dunes. In a wave flume, we set up a 1:1 scale artificial dune covered with different combinations of plant species (Ipomoeae pes-caprae, Sesuvium portulacastrum, and Sporobolus virginicus) and exposed it to simulated “storm waves”. We found that erosion was reduced in dunes covered by plants, but such protection was species-specific and the effectiveness of protection varied over time. Ipomoea was the most effective specie for protection. Differences between species and combinations of species were associated with their physical attributes such as growth form and plant architecture. Although we found that there are species that offer little or no protection from hydrodynamic forces, they may still be important for coastal protection through their ability to build embryo dunes through eolian processes. Indeed, naturebased coastal protection is likely to be an effective alternative to engineered solutions at many sites, but the protection provided is species-specific.

Reefs are known to provide coastal protection and important ecosystem services for many coastlines around the world. Physical processes such as wave damping, sediment transport and nearshore hydrodynamics are closely related to the coastal protection services provided by reefs. The steep-fronted bathymetries of reefs cause abrupt wave transformations and wave damping alongshore, while reef roughness has an important contribution to coastal protection. Five Latin-American case studies are presented to illustrate the coastal protection offered by reefs and their contribution to wave damping. The methodologies applied (e.g. numerical modelling, field measurements) and reef conditions (e. g. reef degradation scenarios and contribution of reef roughness) are listed. Considerable efforts have been made towards diagnosing, understanding and modelling the hydrodynamic transformations induced by reefs. Based on physical and field surveys, roughness and friction parameters were derived in order to implement calibrated and validated numerical models. Discussion on the advantages and disadvantages of the different models applied in the study cases is provided as well as on the needs of highlighting physical processes and the analysis of reef hydrodynamics for supporting appropriate ecosystem-based management.

Shoreline change is an important morphological feature used to identify impacts on coastal processes caused by coastal infrastructure or natural conditions (e.g., storms or sea level rise), providing insightful information for coastal and shoreline management. While shoreline measurements are not always available, remote sensing data can provide shoreline position in scarce data areas, as well as in large and inaccessible regions. Nevertheless, few studies have used multi-temporal remote sensing data to study gradual changes for time frames of less than 10 years due to the low spatial resolution for detecting small changes. In this study, we explore the use of image data fusion from the Satellite Pour l’Observation de la Terre-5 (SPOT-5), taking into account the accuracy of shoreline mapping to detect changes in both disturbed and undisturbed coasts during 10 years in the northwestern Yucatan coast. Our results show that using image data fusion in SPOT-5 images is a feasible method to detect shoreline change trends in a relatively short time frame. Based on the proposed method, we were able to identify the factors leading to shoreline trends. This methodology proves useful for shoreline management and is appropriate for the planning of future developments in areas for which data are scarce.

Change is inherent in coastal systems, which are amongst the most dynamic ones on Earth. Increasing anthropogenic pressure on coastal zones interferes with natural coastal dynamics and can cause ecosystem imbalances that render the zones less stable. Furthermore, human occupation of coastal zones often requires an uncharacteristic degree of stability for these inherently dynamic coastal systems. Coastal management teams face multifaceted challenges in protecting, rehabilitating and conserving coastal systems. Diverse monitoring schemes and modelling tools have been developed to address these challenges. In this article, we explore various perspectives: the integration of biophysical, ecological and social components; the uncertainties of diverse data sources; and the development of flexible coastal interventions. We propose general criteria and guidance for an Ecosystem-based Management (EbM) to coastal management, which aims primarily at adaptation to global change and uncertainties, and to managing and integrating social aspects and biophysical components based on the flows of energy and matter.