Aina Barcelona presents her Degree Final Project entitled “Gravity Current Hydrodynamics and Sediment Transport in A Fragmented Wetland Vegetation”, within the Biology Degree of the University of Girona. This project has been conducted within the FragmentUm Project of the Environmental Physics Research Group of the University of Girona. The advisor of the Degree Final Project is Dr. Teresa Serra.

Abstract of the Degree Final Project:

Coastal ecosystems (marine littoral regions, wetlands and deltas) are regions of high biological productivity. Also, there are one of the most threatened ecosystems in the world for the human pressure. One of these ecosystems being threatened by increasing human pressure are wetlands, which are lands permanently or seasonally inundated. These regions are characterized by the presence of aquatic vegetation adapted to the high salinity and climatic variations. Wetland canopies have a buffering function on atmospheric and hydrodynamic variations. Specially, they reduce the velocity of the current during sea storms, or the runoff after raining periods, favoring the sediment retention.

Gravity currents are the results of the sediment resuspension and transport in the system. From laboratory experiments, different phases are described for gravity currents: inertial regime, drag dominated regime, self-similar phase and viscous regime.

The focus of this work is the study of the effect of the presence of a gap (non-vegetated zone) parallel to the direction of the main current on the sedimentation and hydrodynamics of a gravity current. The aims of this study are to determine the gravity current behavior in the vegetated region compared to the region without vegetation (the gap), to determine the effect of the gap size on the gravity current’s evolution and finally, to determinate the effect of the gap sizes on the sedimentary rates from the gravity current.

Experiments were carried out in the laboratory with four different sediment concentrations; four different canopy densities (884, 354, 177 and 0 plants·m^-2) and three different gap widths (H/2, H and 1.5H where H is the height of the water).

This work shows that the gravity current’s evolution and its sedimentary rates depend on the fractional volume occupied by the vegetation. The current dynamics in experiments with wider gaps is similar to the non-vegetated case, whereas for smaller gaps current dynamics is similar to the fully vegetated case. In addition, the gravity current has the same behavior both in the vegetated region and in the gap.