Comment on "Wetland Sedimentation from Hurricanes Katrina and Rita"

Törnqvist, Torbjörn E.; Paola, Chris; Parker, Gary; Liu, Kam‐biu; Mohrig, David; Holbrook, John; Twilley, Robert R.

doi:10.1126/science.1136780

Cited by 41 publications

(31 citation statements)

References 12 publications

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“…While storm surge flooding east of the track likely played a role toward increased accretion, this spatial pattern strongly suggests that the higher accretion rates attributed to Isaac were caused largely by overbank flooding from the Mississippi River and its distributaries during and immediately after the event. This provides further evidence of the importance of riverine flooding to land building throughout Southern Louisiana [46]. This study demonstrates the role of hurricanes in land-building in the wetlands of coastal Louisiana by using Hurricane Isaac as an example.…”

Section: Discussionmentioning

confidence: 77%

Wetland Accretion Rates Along Coastal Louisiana: Spatial and Temporal Variability in Light of Hurricane Isaac’s Impacts

Bianchette

Liu

Qiang

et al. 2015

Water

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Abstract:The wetlands of the southern Louisiana coast are disappearing due to a host of environmental stressors. Thus, it is imperative to analyze the spatial and temporal variability of wetland vertical accretion rates. A key question in accretion concerns the role of landfalling hurricanes as a land-building agent, due to their propensity to deposit significant volumes of inorganic sediments. Since 1996, thousands of accretion measurements have been made at 390 sites across coastal Louisiana as a result of a regional monitoring network, called the Coastal Reference Monitoring System (CRMS).We utilized this dataset to analyze the spatial and temporal patterns of accretion by mapping rates during time periods before, around, and after the landfall of Hurricane Isaac (2012). This analysis is vital for quantifying the role of hurricanes as a land-building agent and for understanding the main mechanism causing heightened wetland accretion. The results show that accretion rates averaged about 2.89 cm/year from stations sampled before Isaac, 4.04 cm/year during the period encompassing Isaac, and 2.38 cm/year from sites established and sampled after Isaac. Accretion rates attributable to Isaac's effects were therefore 40% and 70% greater than before and after the event, respectively, indicating the event's importance toward coastal land-building. Accretion associated with Isaac was highest at sites located 70 kilometers from the storm track, particularly those near the Mississippi River and its adjacent distributaries and lakes. This spatial pattern of elevated accretion rates indicates that freshwater flooding from fluvial channels, rather than storm surge from the sea per se, is the main mechanism responsible for increased wetland accretion. This significance of riverine flooding has implications toward future coastal restoration policies and practices.

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Section: Discussionmentioning

confidence: 77%

Wetland Accretion Rates Along Coastal Louisiana: Spatial and Temporal Variability in Light of Hurricane Isaac’s Impacts

Bianchette

Liu

Qiang

et al. 2015

Water

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“…Published estimates of SRE (Nittrouer et al, 1995;Allison et al, 1998;Goodbred and Kuehl, 1998;Törnqvist et al, 2007;Blum and Roberts, 2009;Day et al, 2016;Roberts et al, 2016) vary from 5 to 80 %, a range that is too wide to be useful for planning purposes but which suggests that the specific depositional setting is an important control. Here we propose that vegetated inland deltaic settings that are protected from wave and tide energy can be highly efficient in trapping sediment, especially mud, and thus offer desirable locations for diversions that target mud for coastal restoration.…”

Section: Introductionmentioning

confidence: 99%

“…There are only a handful of studies that have attempted to tie the bulk sedimentary properties of a recent deposit to sediment-transport properties in the river that created it (Törnqvist et al, 2007;Kim et al, 2009;Giosan et al, 2013; The Attakapas Crevasse Splay at Napoleonville, Louisiana. Black dots mark core locations.…”

Section: Measuring Sediment Retention Efficiencymentioning

confidence: 99%

“…A value of 67 % sand for the WLD has been used (Törnqvist et al, 2007;Nittrouer and Viparelli, 2014b), though that value implicitly assumes that the sandy deposits documented in the WLD stratigraphy (Roberts, 1997;Roberts et al, 2003) are composed entirely of sand. Applying a mean sand content of 70 % to the WLD sandy deposits (well above the highest sand content that we have observed in our study area; Table 1) implies a total sand content of 47 %, although substantial work will be needed to confirm this.…”

Section: Implications For Delta Evolution and Sustainabilitymentioning

confidence: 99%

“…1a) that is often used as a diversion analog. The WLD is sand-dominated (Roberts et al, 2003;Kim et al, 2009) and has been estimated to have an SRE ranging from 5 to 30 % (Törnqvist et al, 2007;Kim et al, 2008;Roberts et al, 2016). Our results demonstrate the essential role that mud plays in vertically aggrading delta plains, and the contrast with the WLD highlights the importance of careful site selection for diversion projects.…”

Section: Introductionmentioning

confidence: 99%

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Efficient retention of mud drives land building on the Mississippi Delta plain

Esposito

Shen

Törnqvist³

et al. 2017

Earth Surf. Dynam.

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Abstract. Many of the world's deltas -home to major population centers -are rapidly degrading due to reduced sediment supply, making these systems less resilient to increasing rates of relative sea-level rise. The Mississippi Delta faces some of the highest rates of wetland loss in the world. As a result, multibillion dollar plans for coastal restoration by means of river diversions are currently nearing implementation. River diversions aim to bring sediment back to the presently sediment-starved delta plain. Within this context, sediment retention efficiency (SRE) is a critical parameter because it dictates the effectiveness of river diversions. Several recent studies have focused on land building along the open coast, showing SREs ranging from 5 to 30 %. Here we measure the SRE of a large relict crevasse splay in an inland, vegetated setting that serves as an appropriate model for river diversions. By comparing the mass fraction of sand in the splay deposit to the estimated sand fraction that entered it during its life cycle, we find that this mud-dominated sediment body has an SRE of ≥ 75 %, i.e., dramatically higher than its counterparts on the open coast. Our results show that transport pathways for mud are critical for delta evolution and that SRE is highly variable across a delta. We conclude that sediment diversions located in settings that are currently still vegetated are likely to be the most effective in mitigating land loss and providing long-term sustainability.

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Sediment transport and topographic evolution of a coupled river and river plume system: An experimental and numerical study

Chatanantavet

Lamb

2014

J. Geophys. Res. Earth Surf.

108

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Sediment transfer from rivers to the ocean is the fundamental driver of continental sedimentation with implications for carbon burial, land use dynamics, and unraveling global climate change and Earth history from sedimentary strata. Coastal rivers are dynamically coupled to their offshore plumes at the river mouth creating regions of nonuniform flow that can dictate patterns of erosion and deposition both onshore and offshore. However, there are limited experimental and modeling studies on sediment transport and morphodynamics of coupled river and river plume systems and their response to multiple flood events. To address this knowledge gap, we developed a quasi-2-D, morphodynamic numerical model and conducted exploratory flume experiments in a 7.5 m long flume where a 10 cm wide river channel was connected to a 76 cm wide "ocean basin." Both the numerical model and the flume results demonstrate that (1) during low-discharge flows, backwater hydrodynamics cause spatial-flow deceleration and deposition in the river channel and the offshore plume area, and (2) during high flows the water surface is drawn down to sea level, resulting in spatial-flow acceleration and bed scour. During high-discharge flows, we also found that the offshore river plume self-channelized owing to both levee formation and bed scour. Our study suggests that coastal rivers may be in a perpetual state of morphodynamic adjustment and highlights the need to link rivers and river plumes under a suite of flow discharges to accurately predict fluvio-deltaic morphodynamics and connectivity between fluvial sediment sources and marine sinks.

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Comment on "Wetland Sedimentation from Hurricanes Katrina and Rita"

Cited by 41 publications

References 12 publications

Wetland Accretion Rates Along Coastal Louisiana: Spatial and Temporal Variability in Light of Hurricane Isaac’s Impacts

Wetland Accretion Rates Along Coastal Louisiana: Spatial and Temporal Variability in Light of Hurricane Isaac’s Impacts

Efficient retention of mud drives land building on the Mississippi Delta plain

Sediment transport and topographic evolution of a coupled river and river plume system: An experimental and numerical study

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