Influence of a flooding event discharge on accretion in wetlands

Flooding events in wetlands transport sediment particles landwards and can increase accretion in some areas of the wetland or resuspend the sediment in other areas. In this study a flooding event with different water discharges was analyzed in a laboratory simulated wetland to determine the effect stem density has on particle trapping. The discharge that entered the simulated wetland was a particle laden barotropic current that initially produced a pulse that traveled through the wetland. After the first pulse, a baroclinic current, with a different timescale to the initial pulse, developed. Three stem densities, along with the ‘without plant case’, were considered. A semi-empirical model was formulated to explain the propagation of the water pulse. The model predicted the velocity of the pulse dampening in the presence of the simulated vegetation, by using the roughness parameter that had been found to increase with stem density. The baroclinic current propagated at a lower velocity than the pulse did, and its velocity decreased with stem density. As less sediment was found in the wetland with denser canopies, this indicates that the presence of a canopy acts as a barrier to sediment transportation. Furthermore, a greater amount of sediment was deposited in regions at the foot of the denser vegetated wetland zone and the sediment deposition also increased with the water discharge.