INSTANTANEOUS AND RESIDUAL FLOW AT THE MOUTH OF A DRAINED LAGOON

摘要

The tidal circulation and the temporal variability of water temperature and salinity, as measured at the closed by a barrier entrance canal of a drained lagoon (Drana, Evros Delta System, North-east Greece), was described using self-recording instrumentation for six different tidal periods. The study was part of a re-flooding program for the ecological restoration of Drana Lagoon, aiming at understanding tidal circulation and estimating the instantaneous and residual currents and fluxes of water and salt. Hydrography of the area appears directly influenced by the closed barrier and the outflow of freshwater from Sarahtametros drainage canal, producing near-zero velocity values during flood (0.031 m s~(-1)) and slightly higher ebb currents (0.067 m s~(-1)). Tidal elevation showed semi-diurnal unequal tides, influencing strongly salinity variability. The Eulerian residual transport term had in all cases an outward direction with a mean value of 0.021 m s~(-1), while the Stokes drift term was found to push inwards with near zero values (0.002 m s~(-1)). The residual flux of salt was mostly due to the advective term (0.412 g m~(-2) s~(-1)) with seaward direction, while tidal pumping had an inward direction and very low values (0.001-0.226 g m~(-2) s~(-1)).