University of Twente Student Theses
Incorporating cross-shore dynamics in ShorelineM for the long-term development of Mangrove-Mud coastlines
Potman, Serg (2024) Incorporating cross-shore dynamics in ShorelineM for the long-term development of Mangrove-Mud coastlines.
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| Abstract: | Mangrove forests around the world play a crucial role in creating resilience to climate change and in sequestering carbon. The mangrove forests stabilize coastlines, reduce erosion, increase the biodiversity and protect people along the coast. The conditions of these forests are getting worse by human impacts (clearance and conversion) and impacts as erosion and inundation. In terms of area the mangrove forests lose terrain by these conditions (an area of 1.17×104 km2 of mangroves is lost since 1996). To model the long-term development of mangrove ecosystems, the transport and deposition processes of sediments around and within these ecosystems are important. The spatial distribution of the sediments needs to incorporated in a more realistic way in models, to better model the development of mangrove-mud coastlines for the long-term. A model that is used for modelling this long-term development is ShorelineM. By its relatively simple principles of gradient driven alongshore transport and its low computational costs, this model can supply fast simulations for the long-term longshore development of mangrove-mud coastlines. However, the model has shortcomings in the cross-shore fluxes and the representation of mangroves needs improvements. To represent the forest dynamics in a more realistic way, cross-shore morphodynamics of mangrove forests and establishment, growth and mortality of vegetation should be included. This may be possible by incorporating the cross-shore mangrove growth model MFlat, which includes the sediment- and morphodynamics of mangrove forests and the establishment, growth and mortality of mangrove trees. The goal of this study was to investigate the capability of incorporating cross-shore dynamics from MFlat into the 1D longshore model ShorelineM to model the long-term development of mangrove-mud coastlines. The most important limitations in ShorelineM are: the cross-shore distribution and entrainment of sediment; the assumed cross-shore shape and the absence of changes of the shape of the cross-shore profile in the mangrove zone, which influences the tidal prism and the cross-shore fluxes. The cross-shore profile of the mangrove zone is a uniformly sloped area, whereas in reality convex-up or concave-up profiles are formed. These cross-shore dynamics (profile changes and fluxes) can be resolved by MFlat, in which the cross-shore dynamics can be simulated in a realistic way, which has already been shown at the Guyana coast. In MFlat, the morphology of mangrove forests is growing towards an equilibrium state based on the given conditions, which is in this study reached after roughly 40 years (for constant boundary conditions and with no mangroves at the start of the simulation). For conditions with a high boundary sediment concentration (cbcs = 0.50 g/l) and a low wave height (Hrms = 0.10 m), the mangrove- and mudflat width after 40 years is almost 3500 m (which is the model domain). For conditions with a low sediment concentration there is almost no mangrove development. From MFlat, the equilibrium width after 40 years of simulating with different wave heights and sediment concentrations is used to inform ShorelineM. The development of the mangrove- and mudflat width in ShorelineM is based on the mangrove/mudflat width and the simulation length of the MFlat simulations. Implementing the width of the mangrove- and mudflat area from MFlat-simulations into ShorelineM improves the development of the mangrove- and mudflat width and capability of ShorelineM to model the coastline development for 40 years. This is done for an idealized testcase at the Guyana coast with cyclic sediment conditions, and is compared to the original model with cyclic sediment conditions. However, as cross-shore dynamics are complex and include multiple processes, more morphodynamic processes should be implemented to further increase the model performance, such as incorporation of profile changes and a non-linear relationship of the development of the mangrove- and mudflat width. As in the current version, only a linear relationship of the development of the mangrove- and mudflat width is taken into account. Implementing cross-shore dynamics from MFlat into ShorelineM in the way presented above, shows promising results and keeps the simulation time in ShorelineM low. With some extensions/ improvements (as a change of the profile shape) the model can be an useful tool for coastal planning. |
| Item Type: | Essay (Master) |
| Clients: | Deltares |
| Faculty: | ET: Engineering Technology |
| Subject: | 56 civil engineering |
| Programme: | Civil Engineering and Management MSc (60026) |
| Link to this item: | https://purl.utwente.nl/essays/104825 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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