Flow structure and mean residence time in floodplain river landscapes

The role of riparian zones in rivers and streams are well determined in terms of protecting the aquatic environments they shelter from excessive sedimentation, polluted runoff and erosions thus providing conditions for the promotion of living organisms development. In floodplain river landscapes, the riparian zones are consisting of deep zones or lagoons, surrounded by either submerged and emergent aquatic vegetation with different plant densities and morphologies. Understanding the effect riparian zones have on both the residence time and mixing in the lagoons can increase the knowledge on the fate of the lotic zones in marsh areas being studied. The present study focuses on quantifying the hydrodynamics and residence time in the lagoons under the impact of unidirectional flows. Experimental conditions were set for controlled conditions with canopies of Juncus maritimus with densities of 0-1785 plants m-2, lagoon aspect rations between 0.09 and 0.44, and flows with Reynolds 2560-45040. The experiments proved that the residence time of the flow in the lagoons decreased as the flow velocity increased and as the canopy density increased. In contrast, the residence time increased with the aspect ratio of the lagoon.