GEOMBEST++

Geomorphic model of barrier, estaurine, and shoreface translations plus dynamic marsh plus waves. GEOMBEST++ is a morphological-behaviour model that simulates the evolution of coastal morphology and stratigraphy resulting from changes in sea level and sediment volume within the shoreface, barrier, and estuary. GEOMBEST++ builds on previous iterations (i.e. GEOMBEST+) by incorporating the effects of waves into the backbarrier, providing a more physical basis for the evolution of the bay bottom and introducing wave erosion of marsh edges.

marshbarrier islandwave erosionoverwashsea level rise

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Contributor(s)

Initial contribute: 2021-09-09

Authorship

:  
Duke University
:  
rebecca.lauzon@duke.edu
:  
UNC Chapel Hill
:  
laura.moore@unc.edu
:  
Duke University
:  
abmurray@duke.edu
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Classification(s)

Application-focused categoriesNatural-perspectiveOcean regions

Detailed Description

English {{currentDetailLanguage}} English

GEOMBEST+ is a 2-D morphological behavior model representing the evolution of a cross-shore transect from the base of the shoreface to the mainland and including a barrier, marsh, and bay. GEOMBEST+ combines the conservation of mass with geometric constraints on sediment availability and placement, given some commonly employed assumptions (chiefly involving equilibrium elevations and shapes of some parts of the cross-shore profile, representing negative morphodynamic feedbacks). GEOMBEST+ facilitates exploration of barrier island evolution on long timescales, as influenced by spatially varying stratigraphy and topography/bathymetry, possibly representing real world settings (e.g., Moore et al., 2010). With the addition of back-barrier processes represented in the model (Walters et al., 2014), and the improvements to those processes in this work, GEOMBEST++ offers an opportunity to further examine the interactions between barriers and back-barrier environments. A more detailed model description, including model assumption.

Bay bottom erosion in GEOMBEST+ is depth dependent, decreasing with depth until reaching zero at the equilibrium depth (equation (1)). Because the equilibrium depth of a bay is dynamic in natural systems, varying with the size of the waves and the amount of fine-grained sediment input (Fagherazzi et al., 2007), we replace the previous formulation with a more physically based one driven by shear stress. In GEOMBEST++, we calculate wave height and wave period using the relationships between wave height and energy developed by Young and Verhagen (1996) and then use the orbital velocity (ub; based on linear wave theory)—a function of bay depth, fetch, and wind speed—to calculate the shear stress (τ) according to


(Dean & Dalrymple, 1991), where ρ is water density and fw is a friction factor equal to 0.03. (We experimented with different values of fw, but changing this value did not affect the results significantly, so for simplicity we chose a reasonable constant value for a smooth bed; Wikramanayake & Madsen, 1991.) Gross bay bottom erosion (EB; replacing equation (1)) is

then related to the difference between shear stress and the critical shear stress τc through


Where a is a constant equal to 4.12 × 10?4kg/(m2· s · Pa; Mariotti & Fagherazzi, 2010) and τc is 0.2 Pa (consistent with values used in Mariotti and Fagherazzi, 2013, and Fagherazzi and Wiberg, 2009). For simplicity and to enhance the clarity of insight, we assume an equant basin and do not consider anisotropic wind. Instead, we use the cross-shore bay width as the fetch. If there was a predominant wind direction, the two sides of the marsh/bay could experience different amounts of erosion, which would introduce a translation of the bay (which we do not investigate in this work) and a change in size. As in GEOMBEST+, the gross sediment deposition rate (AB) within the bay (representing riverine and/or net coastal sediment input) is obtained by distributing the net import of sediment to the bay (QB) over the width of the bay. The gross bay bottom erosion rate (EB, equation (3)) depends on sediment characteristics (through τc) and on wave characteristics and depth (through τ). Net erosion or deposition is determined by the difference between AB and EB. Because EB decreases with depth, bay depth tends to converge to a steady state value in which deposition balances erosion plus RSLR (Fagherazzi et al., 2007). For greater depths, deposition outpaces erosion (AB>EB and net

deposition occurs), and the depth shallows toward the equilibrium (and vice versa). We use this dynamic formulation to calculate equilibrium depth (at which EB+ RSLR rate =AB) in the model. The time to reach this equilibrium sets the time step for the back-barrier component of the model, meaning that the bay adjusts to equilibrium instantaneously in the model (i.e., we do not resolve smaller timescales). This treatment represents the results of previous modeling showing that the timescale for approaching equilibrium depth is very small compared to the timescale for changes in bay width (Mariotti & Fagherazzi, 2013).

Quoted from : Effects of Marsh Edge Erosion in Coupled Barrier Island-Marsh Systems and Geometric Constraints on Marsh Evolution

模型元数据

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Rebecca Lauzon, Laura Moore,, Brad Murray (2021). GEOMBEST++, Model Item, OpenGMS, https://geomodeling.njnu.edu.cn/modelItem/b6ba8b57-953c-4c00-a065-509b505f4dcf
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Contributor(s)

Initial contribute : 2021-09-09

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Authorship

:  
Duke University
:  
rebecca.lauzon@duke.edu
:  
UNC Chapel Hill
:  
laura.moore@unc.edu
:  
Duke University
:  
abmurray@duke.edu
Is authorship not correct? Feed back

History

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Yihan Zhang
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2021-09-09
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