The researchers studied how tides and river flow affect water and sediment movement in the Guadiana estuary in Portugal. They collected data on currents, salinity, turbidity, and sediment levels during different tidal and river flow conditions. They found that faster currents flow out to sea during ebb tides, especially when the river is high. The amount of freshwater and tidal range control how well the water mixes and stratifies. Sediment levels in the estuary change with tidal currents and river flow, with sand being carried out to sea over time. The researchers also observed a salt wedge moving in during floods and the turbidity maximum shifting downstream with higher currents.