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- The Guadiana river deltaPublication . Morales, Juan A.; Garel, ErwanThe Guadiana Estuary is a good example of rock bounded estuary which consists of a single narrow estuarine channel with a meandering morphology imposed by faults systems affecting the hard geology of the substrate. Only along the last kilometers of the estuarine channel, the valley opens when Cenozoic Guadalquivir Basin formations appear. In this area, the Guadiana develops a prograding coastal system constituted by successive sandy barriers separated by salt marshes which configure a wave dominated delta. This progradation is possible thanks an interaction of the coastal agents which enhanced the silting in addition to a good availability of sediments. This chapter explains an explanation of the dynamic functioning of the open coastal environment, so as the resulting facies model.
- Present dynamics of the Guadiana estuaryPublication . Garel, ErwanEstuaries offer natural protection from energetic ocean waves, and have been used as natural harbour and inland waterways since the beginning of civilisation. Nowadays, most of the largest cities in the world are located on estuaries that must cope with increasing economic and industrial developments. These sheltered coastal areas are also one of the most productive types of ecosystems on Earth and are of considerable value for humans and wildlife. Understanding the dynamics of estuaries is fundamental to maintain a balance between exploitation and conservation. In particular, the assessment of various features of uttermost socio-ecological importance (such as water quality, flood risk, ecosystem health and morphodynamics) must rely on a thorough knowledge of the operating hydrodynamic and sediment transport processes.
- Export of dissolved and suspended matter from the main estuaries in South Portugal during winter conditionsPublication . Correia, C.; Torres, A. F.; Rosa, A.; Cravo, Alexandra; Jacob, J.; de Oliveira Junior, L.; Garel, ErwanEstuaries are essential drivers of primary productivity in coastal waters through the export of dissolved and suspended material. This study aims at quantifying this fertilization process at the two main estuaries in South Portugal, where typical low river discharge conditions occur in winter due to strong flow regulation by upstream dams and seldom-local rain events. Data were collected across the channel of the lower Arade (10/01/2018) and Guadiana (04/02/2019) estuaries during a semi-diurnal tidal cycle with intermediate tidal ranges (1.5 m and 2.2 m, respectively). Current velocity records were completed with hourly water quality measurements (temperature, salinity, pH, dissolved oxygen, suspended solids, chlorophyll a and nutrients) for determination of the along channel fluxes and residual mass transport of dissolved and suspended matter across the channel sections. The results show that the two estuaries were characterized by distinct water circulation patterns and tidal properties (e.g., standing wave at the Arade, mixed wave at the Guadiana). The concentration of dissolved and particulate matter displayed a general similar anti-phase pattern of variations with tidal height at both sites. The corresponding fluxes were generally strongest during the ebb phase. Thus, the residual mass transport was seaward, indicating that both estuaries contribute to fertilize adjacent coastal waters by exporting nutrients (order of kg), chlorophyll a (order of kg) and suspended solids (up to tons). Moreover, transport differences at both estuaries reflect specific discharge flow and environmental conditions as well as contamination sources close to the study areas. In particular, the signatures of a discharge event from a water treatment plant at the Arade and of coastal upwelling at the Guadiana were identified.