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CSDMS 2020: Linking Ecosphere and Geosphere

Mangrove Interaction with Tidal Flow, Waves & long term sedimentation: Combining Field Data & Numerical Modelling

Uwe Best

IHE Delft Institute for Water Education, Netherlands
Mick van der Wegen IHE Delft Institute for Water Education Netherlands
Jasper Dijkstra Deltares Netherlands
Dano Roelvink IHE Delft Institute for Water Education Netherlands

The projected increases in the frequency and magnitude of hazards, which threaten the coastal hinterland, heighten the need for an enhanced understanding of the determining mechanisms for mangrove adaptation and their contribution to coastal safety. This research seeks to improve the understanding of the bio-physical processes governing the geomorphological evolution of the mangrove-mudflat system by combining spatially explicit observations of mangrove population dynamics with process-based modelling.

Field observations were taken at the Le Ressouvenir- Chateau Margot mangrove-mudflat, within the 300m wide fringe and on the mudflat extending 6km offshore, along the Guyana coastline. This coastline resides 1m below sea level and, is subject to a semi-diurnal tidal regime with a maximum tidal range of 3.5m during spring tide. Using the data collected on the elevation, vegetation, water level, flow velocities, sediment concentration and wave heights; we developed a 2D depth averaged model using a process-based approach. On a high resolution grid of 10m, the model predicts the geomorphological development from the interaction between the intertidal flow, waves, sediment transport and the temporal and spatial variation in the mangrove growth, drag and bio-accumulation. Here, we coupled Delft3D-FM with a mangrove dynamics model capturing the Avicennia germinans and Laguncularia racemosa species under suitable inundation and competition regimes.

Waves are critical for the transport of mud into the mangrove belt during high tide. Only when approaching spring tide is the inner part of the fringe inundation, creating a heightened platform which governs the species establishment. The channels form the major path for the tidal inflow during the lower tides, while the interior of the forest is an effective sediment sink during the higher tides. Sea level rise scenarios reinforce field observations for mangrove retreat and decay, with tipping points realized after 1.5m to 2.0m.

Results indicate mangrove adaptability, to climate change and anthropogenic threats, hinges on the long term sedimentation responses and system conditions to promote the establishment of stable belt widths.

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Of interest for:
  • Terrestrial Working Group
  • Coastal Working Group
  • Education and Knowledge Transfer (EKT) Working Group
  • Ecosystem Dynamics Focus Research Group
  • Continental Margin Initiative