Observations of destratification events in a highly stratified bay in the Ebro Delta

Coastal environments are regions characterized by complex hydrodynamics with high temporal variability in water circulation due to environmental drivers such as local wind, freshwater inflow, or tidal variations. This research investigates the hydrodynamics of destratification events in a highly stratified micro-tidal coastal estuary, such as is the Fangar Bay (Ebro Delta, NW Mediterranean). The bay's hydrodynamics are mainly driven by local wind events and modulated by water column stratification, which is dominant and controlled by freshwater inputs and oscillatory motions. The study here presented is based on the time-series analysis of two ADV (Acoustic Doppler Velocimeter), combined with temperature and salinity profiles, deployed within the bay during the Spring of 2023. Results show a clear destratification of the water column after intense wind episodes, mostly from the northwest, which alter the response of the velocity field and re-distribute the constituents of the water column through mixing and dispersion. The high-frequency analysis of the recorded velocities suggests a differential pattern between upper (fresher) and lower (saline) layers of the water column, with significant implications for aquaculture and water quality.

Keywords: destratification, estuary, hydrodynamics, mixing, measurements

Funding: This work has been funded by the R+D+I project ECO-BAYS (PID2020-115924RB-I00) financed by MCIN/AEI/10.13039/501100011033.  

Acknowledgements: To project REST-COAST (H2020-101037097-REST-COAST) from the European Union’s Horizon 2020 program.