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dc.rights.licenseCC-BY-NC-ND
dc.contributor.advisorXie, D.
dc.contributor.advisorPrice, T. D.
dc.contributor.authorBelonje, R.G.
dc.date.accessioned2020-02-20T19:06:35Z
dc.date.available2020-02-20T19:06:35Z
dc.date.issued2019
dc.identifier.urihttps://studenttheses.uu.nl/handle/20.500.12932/35284
dc.description.abstractMangrove forests are dominant ecosystems covering the intertidal zone of shorelines at tropical and subtropical latitudes. They provide valuable ecosystem services and functions, such as carbon sequestration and coastal protection. However, mangrove forests are being threatened by human activity and climate change, reducing the resilience of the ecosystem. Gaining further understanding about the hydro-morphodynamic processes and vegetation dynamics governing mangrove systems will prove essential in governing and protecting these ecosystems. As mangrove forests are located on the coast, they are subject to wave action. While much research has gone into how mangroves attenuate waves, little research has gone into how wave action affects the development of mangrove coasts. Wave action has a significant effect on the coastal hydro-morphodynamics, which affect mangrove forest resilience and development. Therefore, research on the interactions between wave action and mangrove system development will prove beneficial in gaining further understanding on the functioning of mangrove ecosystems. A hydro-morphodynamic model is used to study the effect of wave action on mangrove coasts. The model simulates bio-geomorphic feedbacks between mangrove vegetation and coastal hydro-morphodynamic processes. The approach uses the Delft3D-FLOW hydro-morphodynamic model including the roller model simulating waves, and a dynamic vegetation model in MATLAB. Forty model scenarios are run, with three variables changing between model runs: wave height, vegetation presence and sea level rise. Four different wave height scenarios are included: no waves, small waves with a significant wave height of 0.3 m, medium-sized waves with a significant wave height of 0.5 m and large waves with a significant wave height of 1.0 m. For each of these wave heights, two scenarios are run with varying vegetation presence. One scenario is run including vegetation and one scenario is run excluding vegetation. To conclude, five different sea level rise scenarios are considered for each wave height and vegetation presence scenario. These scenarios consist of no sea level rise, slow linear sea level rise, fast linear sea level rise, slow exponential sea level rise and fast exponential sea level rise. The results show that wave action has a significant effect on the hydro-morphodynamics and vegetation dynamics of the mangrove system. Waves increase the bed shear stress and the suspended sediment concentration, which enhance the erosion and sedimentation, respectively. They also transport sediment from the seaward boundary towards the coast through Stokes drift. The balance between erosion and sedimentation is influenced by the wave height. Small waves cause coastal progradation, medium-sized waves can cause either coastal progradation or coastal regression, while large waves cause coastal regression. Mangrove vegetation affects the hydro-morphodynamics through two processes. Firstly, the vegetation traps sediment through the dampening of currents, which enhances sedimentation within the mangrove forest. Secondly, it influences the tidal asymmetry. This increases the ebb-tidal dominance, which enhances erosion. Which of these processes is dominant depends on the wave height. While without waves the presence of vegetation inhibits coastal progradation, it has the opposite effect when medium-sized waves are introduced to the system. Mangrove vegetation only survives within a specific relative hydroperiod, which is governed by the amount of time a location is inundated relative to the amount of time it is dry. Because waves cause increased coastal progradation, the bed level at a location changes faster than without waves, and the relative hydroperiod changes with it. This causes vegetation to get less time to mature while a location contains its optimal hydroperiod. Through this mechanism, waves put additional stress upon growing vegetation, with higher waves causing lower vegetation number and total vegetation biomass. However, this affects small trees relatively more than large trees, since smaller trees are more vulnerable. This causes the average vegetation biomass to increase under the influence of wave action. Sea level rise influences the coastal hydrodynamics by increasing the water depth. The faster the sea level rises, the more it affects the morphological change, increasing the peak bed level. Whether the sea level rise is linear or exponential influences the final shape of the bed profile, changing the curvature of the plateau. In the current model set-up, the sediment supply is sufficient for the mangrove system to keep up with all tested sea level rise scenarios, which means the vegetation is not significantly affected by sea level rise. In conclusion, wave action, mangrove vegetation and sea level rise all affect the development of the coastal system. However, their contributions are not equal. Wave action affects the coastal dynamics the most, followed by the mangrove vegetation and finally sea level rise. Waves also have a significantly larger effect on the vegetation parameters than sea level rise. This information can be used to improve management strategies for coastal mangrove systems, both in the present and when devising strategies for the future, when climate change will become more important.
dc.description.sponsorshipUtrecht University
dc.language.isoen_US
dc.titleModelling the effect of wave action on sediment transport, morphological evolution and vegetation dynamics in coastal mangrove systems
dc.type.contentMaster Thesis
dc.rights.accessrightsOpen Access
dc.subject.keywordswaves; mangroves; sea level rise; coastal morphodynamics; ecomorphodynamics; ecomorphodynamic modelling; delft3d
dc.subject.courseuuMarine Sciences


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