Coasts, Volume 3, Issue 1 (March 2023) – 6 articles

Among the impacts of climate change in West Africa, coastal erosion is the most threatening disaster apart from floods and the increase in temperatures. The southern coast of the Dakar region, as part of the most threatened coastal zones in West Africa, records the most current coastal damages in Dakar due to its coastline dynamics and low-lying area. This paper investigates the influences of the topography and slope of the beach on shoreline dynamics using remote sensing, cartographic tools and statistical methods such as linear regression. It also states the important role of geomorphologic structures in shoreline dynamics. It was conducted in three littoral cells (Mbao, Bargny and Toubab Dialaw) along the southern coast of Dakar. It helps to understand better the role that topography, slope and geomorphology play in coastal dynamics. The Modified Normalized Difference Water Index (MNDWI) was employed to delineate the coastlines before computing the dynamic rate of the coastline using Digital Shoreline Analysis System (DSAS) software. After that, the topography and slope were determined using a digital elevation model (DEM). Then, the correlation between the coastline dynamic, topography and slope was analyzed using the coefficient of correlation and linear regression model. In the Mbao and Bargny littoral cells where the geomorphology is mostly dominated by soils little or not evolved in situ, there is a significant relationship between the coast line dynamic, topography and slope with a coefficient of correlation of about 0.63 and 0.87, respectively. The relationship is not significant in Toubab Dialaw, where the topography and slope are high, and the geomorphology is mainly characterized by a category of sandstone, with a coefficient of 0.15. We conclude that topography, slope and geomorphology play an important role in the shoreline dynamics in the study area. Full article

Operation of source control measures (SCM) in urban drainage in tropical/transitional climates are still a challenge because of higher rain volumes and more intense rains, as well as constraints from sea-level interference. In this study, the performance of a swale to control runoff was detailed and monitored in such an environment. The data on rain, runoff, and sea levels were acquired at a site located in an island in the south coast of Brazil. The results showed that even with higher rain volumes and more intense rains, the mean capture of the swale was 51.7% of the entrance runoff volume, but it depended on seasonal rain variation and interference of sea/tide level. As a result, the swale might be undersized in summer and oversized in winter. Peak flow retardation was observed in 97% of monitored events. The interference of sea/tide level was not directly correlated with infiltration volumes, but in the principal component analysis, the parameters of sea/tide level, along with the hydrological parameters of rain duration, height, and intensity, explained 60% of the variance in the data. In conclusion, the application of SCMs in tropical regions is suitable, but seasonality should be incorporated in the design. The interference of sea/tide level must be further investigated to verify how to incorporate its influence in the design. Full article

The production and trade of dried fish are important sources of livelihood and employment for poor people engaged in the dried fish value chain. More importantly, half of them are women. Dried fish makes a significant contribution to the food and nutrition security of the poor because it is high in calcium and other vital micronutrients. Despite its importance, work on the dried fish value chain (DFVC) continues to focus on financial value creation and linear interactions among market actors that impede the recognition of human rights, justice, food security, and power across the entire value chain. Such a neoclassical perspective on DFVC tends to undermine the complex human-nature interactions that are contingent upon specific histories, people, places, and practices. Poor fishers and dried fish processors placed at the extractive end of the value chain hold low power in the market and remain vulnerable to changing social-ecological system dynamics. The recent work on a hybrid framework of social-ecological system-oriented dried fish value chain (SESDFVC) makes a departure from the conventional dried fish value chain framework. It values dynamic resource contexts, considers upstream actors as active collaborators, and expands the notion of value to include the social-ecological wellbeing of the value chain actors. This paper, with a mixed method research framework, provides an empirical outlook of the dried fish value chain in relation to SES attributes in the context of the eastern Indian coast of the Bay of Bengal, including Odisha and West Bengal, India. Full article

Hydrobioid gastropods are abundant in coastal systems and ecologically important for ecosystem functioning. We aimed to unravel the relationship between usual and stress-related population attributes of the dominant macrofaunal species Heleobia australis with indicators of environmental quality and coastal pollution. Using Guanabara Bay (GB, Brazil) as a model of a multi-impacted coastal system, our hypothesis is that increased amounts of rainfall during the warm season reduce the bay’s environmental quality and induce shifts in snail population attributes. A suite of environmental variables, population attributes, and sediment quality descriptors was assessed by combining field and laboratory evaluations with literature compilation. Results indicate high organic pollution levels with environmental degradation and reinforce GB status as a severely contaminated system. Some environmental conditions can be applied as seasonal predictors of changes in warm-rainy (rainfall and salinity), intermediate (silicate), and cold-dry seasons (nitrite and nitrate). Three selected usual population attributes (snail density, fecundity, and recruitment) were not affected by changes in environmental conditions, but significant effects were detected on two stress-related attributes (relative penis length index and shell deformity). For the first time, shell deformity was recorded in H. australis snails. Low variation in usual population attributes highlight the high tolerance of H. australis to shifts in environmental conditions. Full article

Oyster farming may impact the estuarine tidal circulation with a series of effects on environmental conditions and cultures’ growth. Hydrodynamic numerical models set up in estuaries integrated the presence of oyster structures by simply increasing the bottom friction coefficient over farming areas. However, for elevated oyster tables in tidal environments, such default calibration ignored the temporal variations of the friction coefficient between the conditions of submerged or unsubmerged structures. Thus, an original formulation of the Chézy coefficient was here proposed to integrate these modulations. Assessed against measured and predicted vertical velocity profiles on a 1/2 scaled model, this formulation was implemented in a simulation of the tidal circulation within the Aber Wrac’h estuary (Brittany, France). Particular attention was dedicated to the changes induced on the current magnitudes and sediment transport. Oyster tables were found to impact current magnitudes in the vicinity of elevated structures, with major differences at times of local peak flood and ebb. These modifications were characterised by (i) a reduction of current magnitudes over oyster farming areas and (ii) a tidal-flow acceleration on both sides of these structures. Increased sediment transport was, therefore, expected in the vicinity of these cultures, with potential implications on seabed morphology and water quality. Full article