Island Edge Morphodynamics along a Chronosequence in a Prograding Deltaic Floodplain Wetland

Bevington, A.; Twilley, Robert R.

doi:10.2112/jcoastres-d-17-00074.1

Cited by 33 publications

(51 citation statements)

References 27 publications

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“…On the channel-side and inner-side margins of the high marsh platform (Salix nigra and Polygonum spp., respectively), the normalized significant mutual information decreases relative to Colocasia but remains high compared to the low island interiors, where exposure to deeper waters or a wider range of flow velocities may coincide with more variability in sediment delivery or erosion. In particular, Salix nigra exhibits both areas of erosion and of deposition ( Figure S5), consistent with observations and models of high-velocity routing of water around island heads and edges, which triggers erosion, together with deposition on the natural levees (Bevington & Twilley, 2018;Olliver & Edmonds, 2017;Wagner et al, 2017).…”

Section: Delta-scale Resolution Of Ecogeomorphic Feedbacks With Inforsupporting

confidence: 86%

Ecogeomorphic Feedbacks that Grow Deltas

Larsen

Wagner

2018

JGR Earth Surface

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Coastal river deltas are complex and dynamic ecosystems where vegetation plays an essential role in influencing, as well as being influenced by, physical processes, creating ecogeomorphic feedbacks between vegetation canopy characteristics and topography. However, this feedback is poorly understood. This knowledge gap is due to difficulties in detecting and quantifying the interactions that define the feedback. Emerging technology and data analysis techniques like transfer entropy have made it possible to overcome former difficulties associated with sampling constraints and delineate bidirectional feedback within many vegetation classes at the delta scale. Here the transfer entropy analysis was consistent with widespread understanding of marsh zonation, yet produced additional insight into which vegetation classes specifically had a dominant impact on topographic change. Ecogeomorphic feedback was resolvable only within native vegetation classes (Nelumbo and Polygonum) that occur over low to moderate elevations within the Wax Lake Delta Louisiana. In contrast, nonnative vegetation classes (Colocasia and Eichhornia) were not as effective at accreting sediment as native classes. The transfer entropy analysis suggests that different vegetation communities play functionally different roles in landscape evolution that should be differentiated in ecogeomorphic models. Within such models, it would be most imperative to resolve detailed flow characteristics at lower to low‐middle island elevations. Furthermore, within elevation zones, it is likely important to differentiate between the roles of multiple vegetation communities rather than treating the entire elevation zone as a single ecogeomorphic entity.

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Section: Delta-scale Resolution Of Ecogeomorphic Feedbacks With Inforsupporting

confidence: 86%

Ecogeomorphic Feedbacks that Grow Deltas

Larsen

Wagner

2018

JGR Earth Surface

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“…Four key observations from these systems motivate our modeling approach. First, the distributary channel network is composed of many branching distributary channels separating shallow unchannelized interdistributary regions composed of islands, low‐lying natural levees, marshes, shallow bays, and a gradually basinward sloping delta front (Bevington & Twilley, ; Edmonds et al, ; Shaw et al, , ). Second, repeat bathymetric surveys have shown that relatively deep distributary channels prograde by eroding into relatively shallow delta front deposits (Shaw & Mohrig, ).…”

Section: Introductionmentioning

confidence: 99%

Distributary Channel Networks as Moving Boundaries: Causes and Morphodynamic Effects

Shaw

Mahon

et al. 2019

JGR Earth Surface

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We propose an exploratory model to describe the morphodynamics of distributary channel network growth on river deltas. The interface between deep channels and the shallow, unchannelized delta front deposits is modeled as a moving boundary. Steady flow over the unchannelized delta front is friction dominated and modeled by Laplace's equation. Shear stress along the network boundary produces nonlinear erosion rates at the interface, causing the boundary to move and network elements (channels and branches) to form. The model was run for boundary conditions resembling the Wax Lake Delta in coastal Louisiana, 20 parameterizations of sediment transport, and 3 parameterizations of discharge. In each case, the model produced a complex channel network with channel number, width, bifurcation angle, and channel shape depending on the sediment transport formula. For reasonable sediment transport parameters and gradually increasing water discharge, the model produced network characteristics and progradation rates similar to the Wax Lake Delta. This suggests that the model contains the processes responsible for network growth, despite its abstract formulation. Key Points:• Prograding distributary channel networks of varying morphology can be modeled as a simple moving boundary • Nonlinearities in the sediment transport formula dictate channel width, number of branches, bifurcation angle, and channel shape • Evolution is dictated by network morphology, sediment transport, and water discharge Supporting Information:• Supporting Information S1

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“…We suggest that this is a consequence of channels prograding radially and becoming further apart with distance from the delta apex. Field and remote sensing studies of the Wax Lake Delta have confirmed that island aggradation rates decrease and timescales of emergence increase with distance from the edges of the primary channels (Bevington and Twilley, 2018;Olliver and Edmonds, 2017;Wagner et al, 2017). We reason that increased island width limits vertical accretion because suspended sediment from the channels must travel farther through a vegetated island.…”

Section: Delta Area Growthmentioning

confidence: 82%

“…The difference arises because the Wax Lake Delta has an extensive delta front that lies below low tide. While the subaerial and shallow land areas are where marshes are established (Johnson et al, 1985), the subaqueous delta forms the platform upon which subaerial islands grow (Cahoon et al, 2011;. Hence, the subaqueous platform extent is important as a leading indicator of future marsh growth, necessary data for navigation, and the key area metric for estimating delta volume and volume change (Geleynse et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Measuring subaqueous progradation of the Wax Lake Delta with a model of flow direction divergence

et al. 2018

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Abstract. Remotely sensed flow patterns can reveal the location of the subaqueous distal tip of a distributary channel on a prograding river delta. Morphodynamic feedbacks produce distributary channels that become shallower over their final reaches before the unchannelized foreset slopes basinward. The flow direction field over this morphology tends to diverge and then converge, providing a diagnostic signature that can be captured in flow or remote sensing data. A total of 21 measurements from the Wax Lake Delta (WLD) in coastal Louisiana and 317 measurements from numerically simulated deltas show that the transition from divergence to convergence occurs in a distribution that is centered just downstream of the channel tip, on average 132 m in the case of the WLD. These data validate an inverse model for remotely estimating subaqueous channel tip location. We apply this model to 33 images of the WLD between its initiation in 1974 and 2016. We find that six of the primary channels grew at rates of 60–80 m yr−1, while the remaining channel grew at 116 m yr−1. We also show that the subaqueous delta planform grew at a constant rate (1.72 km2 yr−1). Subaerial land area initially grew at the same rate but slowed after about 1999. We explain this behavior as a gradual decoupling of channel tip progradation and island aggradation that may be common in maturing deltas.

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Island Edge Morphodynamics along a Chronosequence in a Prograding Deltaic Floodplain Wetland

Cited by 33 publications

References 27 publications

Ecogeomorphic Feedbacks that Grow Deltas

Ecogeomorphic Feedbacks that Grow Deltas

Distributary Channel Networks as Moving Boundaries: Causes and Morphodynamic Effects

Measuring subaqueous progradation of the Wax Lake Delta with a model of flow direction divergence

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