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U.S.N. Best
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Morphodynamic adaptation timescales of the Guyana mangrove-mudflat system
Are coastlines shaped by migrating mudbanks more resilient against sea level rise?
In developing effective and resilient coastal management strategies, it is critical to consider the coastline's natural spatial and temporal variation. This is particularly relevant for Guyana's wave-exposed mud-dominated coastline, where longshore migrating subtidal mudbanks create a 30-year cycle of accretion and erosion of the coastline, driven by the presence or absence of a mudbank. These cyclic dynamics are integral to the broader coastal system, shaping the development of both the mudflat profile and the opportunistic mangrove vegetation. This study aims to enhance our understanding of the behaviour of mangrove-mudflat systems on the Guyana coast by examining: (1) intertidal sediment dynamics and vegetation dynamics on a mangrove/mudflat profile, (2) the morphodynamics associated with the cyclically varying forcing conditions and (3) the processes involved in the morphodynamic response under sea level rise. We utilized an open-source, 1D, cross-shore model (Mflat) that couples tidal flow, wave action, sediment transport and morphodynamic development to vegetation dynamics, including temporal and spatial growth of the tree population and bio-accumulation. The mudflat dynamics are highly determined by the cyclically varying sediment influx, wave height and period, whereas the mangrove vegetation tends to follow the evolution of suitable intertidal areas rather than impacting morphodynamic changes. An important finding is that the time scale of the cyclically varying boundary conditions (30 years) is much shorter than the system's characteristic morphodynamic adaptation timescale, so no formal equilibrium is reached for a given boundary condition. The cyclic mangrove-mudflat system shows considerable resilience to sea level rise due to the abundance of mud, though it gradually drowns under larger sea level rise scenarios. These insights on the survivability of these intertidal systems are relevant to many other mangrove-mudflats worldwide.
...
In developing effective and resilient coastal management strategies, it is critical to consider the coastline's natural spatial and temporal variation. This is particularly relevant for Guyana's wave-exposed mud-dominated coastline, where longshore migrating subtidal mudbanks create a 30-year cycle of accretion and erosion of the coastline, driven by the presence or absence of a mudbank. These cyclic dynamics are integral to the broader coastal system, shaping the development of both the mudflat profile and the opportunistic mangrove vegetation. This study aims to enhance our understanding of the behaviour of mangrove-mudflat systems on the Guyana coast by examining: (1) intertidal sediment dynamics and vegetation dynamics on a mangrove/mudflat profile, (2) the morphodynamics associated with the cyclically varying forcing conditions and (3) the processes involved in the morphodynamic response under sea level rise. We utilized an open-source, 1D, cross-shore model (Mflat) that couples tidal flow, wave action, sediment transport and morphodynamic development to vegetation dynamics, including temporal and spatial growth of the tree population and bio-accumulation. The mudflat dynamics are highly determined by the cyclically varying sediment influx, wave height and period, whereas the mangrove vegetation tends to follow the evolution of suitable intertidal areas rather than impacting morphodynamic changes. An important finding is that the time scale of the cyclically varying boundary conditions (30 years) is much shorter than the system's characteristic morphodynamic adaptation timescale, so no formal equilibrium is reached for a given boundary condition. The cyclic mangrove-mudflat system shows considerable resilience to sea level rise due to the abundance of mud, though it gradually drowns under larger sea level rise scenarios. These insights on the survivability of these intertidal systems are relevant to many other mangrove-mudflats worldwide.
Wave attenuation potential, sediment properties and mangrove growth dynamics data over Guyana's intertidal mudflats
Assessing the potential of mangrove restoration works
Journal article
(2022)
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U.S.N. Best, Mick van der Wegen, Jasper Dijkstra, J.A.H. Reyns, Bram van Prooijen, D. Roelvink
Coastal mangroves, thriving at the interface between land and sea, provide robust flood risk reduction. Projected increases in the frequency and magnitude of climate impact drivers such as sea level rise and wind and wave climatology reinforce the need to optimize the design and functionality of coastal protection works to increase resilience. Doing so effectively requires a sound understanding of the local coastal system. However, data availability particularly at muddy coasts remains a pronounced problem. As such, this paper captures a unique dataset for the Guyana coastline and focuses on relations between vegetation (mangrove) density, wave attenuation rates and sediment characteristics. These processes were studied along a cross-shore transect with mangroves fringing the coastline of Guyana. The data are publicly available at the 4TU Centre for Research Data (4TU.ResearchData) via https://doi.org/10.4121/c.5715269 (Best et al., 2022) where the collection Advancing Resilience Measures for Vegetated Coastline (ARM4VEG), Guyana, comprises of six key datasets.
Suspended sediment concentrations typically exceeded 1 g L−1 with a maximum of 60 g L−1, implying that we measured merely fluid-mud conditions across a 1 m depth. Time series of wind waves and fluid-mud density variations, recorded simultaneously with tide elevation and suspended sediment data, indicate that wave–fluid-mud interactions in the nearshore may be largely responsible for the accumulation of fine, muddy sediment along the coast. Sediment properties reveal a consolidated underlying bed layer. Vegetation coverage densities in the Avicennia-dominated forest were determined across the vertical with maximum values over the first 20 cm from the bed due to the roots and pneumatophores.
Generalized total wave attenuation rates in the forest and along the mudflat were between 0.002–0.0032 m−1 and 0.0003–0.0004 m−1 respectively. Both the mangroves and the mudflats have a high wave-damping capacity. The wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than wave dissipation inside the mangrove vegetation. Data collected corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves. ...
Suspended sediment concentrations typically exceeded 1 g L−1 with a maximum of 60 g L−1, implying that we measured merely fluid-mud conditions across a 1 m depth. Time series of wind waves and fluid-mud density variations, recorded simultaneously with tide elevation and suspended sediment data, indicate that wave–fluid-mud interactions in the nearshore may be largely responsible for the accumulation of fine, muddy sediment along the coast. Sediment properties reveal a consolidated underlying bed layer. Vegetation coverage densities in the Avicennia-dominated forest were determined across the vertical with maximum values over the first 20 cm from the bed due to the roots and pneumatophores.
Generalized total wave attenuation rates in the forest and along the mudflat were between 0.002–0.0032 m−1 and 0.0003–0.0004 m−1 respectively. Both the mangroves and the mudflats have a high wave-damping capacity. The wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than wave dissipation inside the mangrove vegetation. Data collected corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves. ...
Coastal mangroves, thriving at the interface between land and sea, provide robust flood risk reduction. Projected increases in the frequency and magnitude of climate impact drivers such as sea level rise and wind and wave climatology reinforce the need to optimize the design and functionality of coastal protection works to increase resilience. Doing so effectively requires a sound understanding of the local coastal system. However, data availability particularly at muddy coasts remains a pronounced problem. As such, this paper captures a unique dataset for the Guyana coastline and focuses on relations between vegetation (mangrove) density, wave attenuation rates and sediment characteristics. These processes were studied along a cross-shore transect with mangroves fringing the coastline of Guyana. The data are publicly available at the 4TU Centre for Research Data (4TU.ResearchData) via https://doi.org/10.4121/c.5715269 (Best et al., 2022) where the collection Advancing Resilience Measures for Vegetated Coastline (ARM4VEG), Guyana, comprises of six key datasets.
Suspended sediment concentrations typically exceeded 1 g L−1 with a maximum of 60 g L−1, implying that we measured merely fluid-mud conditions across a 1 m depth. Time series of wind waves and fluid-mud density variations, recorded simultaneously with tide elevation and suspended sediment data, indicate that wave–fluid-mud interactions in the nearshore may be largely responsible for the accumulation of fine, muddy sediment along the coast. Sediment properties reveal a consolidated underlying bed layer. Vegetation coverage densities in the Avicennia-dominated forest were determined across the vertical with maximum values over the first 20 cm from the bed due to the roots and pneumatophores.
Generalized total wave attenuation rates in the forest and along the mudflat were between 0.002–0.0032 m−1 and 0.0003–0.0004 m−1 respectively. Both the mangroves and the mudflats have a high wave-damping capacity. The wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than wave dissipation inside the mangrove vegetation. Data collected corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves.
Suspended sediment concentrations typically exceeded 1 g L−1 with a maximum of 60 g L−1, implying that we measured merely fluid-mud conditions across a 1 m depth. Time series of wind waves and fluid-mud density variations, recorded simultaneously with tide elevation and suspended sediment data, indicate that wave–fluid-mud interactions in the nearshore may be largely responsible for the accumulation of fine, muddy sediment along the coast. Sediment properties reveal a consolidated underlying bed layer. Vegetation coverage densities in the Avicennia-dominated forest were determined across the vertical with maximum values over the first 20 cm from the bed due to the roots and pneumatophores.
Generalized total wave attenuation rates in the forest and along the mudflat were between 0.002–0.0032 m−1 and 0.0003–0.0004 m−1 respectively. Both the mangroves and the mudflats have a high wave-damping capacity. The wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than wave dissipation inside the mangrove vegetation. Data collected corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves.