Impacts of Engineered Diversions and Natural Avulsions on Delta‐Lobe Stability

Carlson, Brandee; Nittrouer, Jeffrey A.; Swanson, Travis; Moodie, Andrew J.; Dong, Tian Y.; Ma, Hsi-Pin; Kineke, Gail C.; Pan, Minglong; Wang, Yuanjiang

doi:10.1029/2021gl092438

Cited by 7 publications

(11 citation statements)

References 52 publications

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“…The Phase II process and associated degrading evolution of the DF waned following 2000 CE (Figure 5f), which suggested that the DKL is approaching a morphological equilibrium after ∼20-year of evolution. This hypothesis is also supported by previous shoreline studies (e.g., Carlson et al, 2021) which suggested that the rate of 9 (i.e., two sediment gravity flow [SGF]-related units formed a wedge downlap on the middle and lower delta front with many submarine channels at/near the landward termini of the SGF units) are also observable at other regions of our focused area, suggesting a widespread phenomenon. In panel (a), the SGF-related units off Diaokou lobe also experienced postdepositional sediment loss.…”

Section: Discussionsupporting

confidence: 91%

The Impact of Gravity‐Driven Sedimentation on Reshaping the Huanghe (Yellow River) Delta Front

et al. 2022

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Many of the world's mega‐river deltas are currently degrading due to a shortage of sediment supply feeding their construction. Here, using bathymetric and seismic data, the geomorphological/sedimentary evolution on and near a recently abandoned (1976 CE) Huanghe delta lobe is investigated. The delta front (DF) exhibits a lobe switching‐controlled pattern of progradation followed by mass wasting on the upper front, and redeposition at the seaward toe of the front; the latter process appears to be associated with sediment failure and contributes to delta degradation. During degradation, mass wasting‐driven deepening of the upper DF was initially up to ∼0.86 m/yr from 1978 to 1985 CE, slowed to ∼0.12 m/yr from 1985 to 2000 CE, and has been negligible since. In either prograding or degrading, gravity‐driven sedimentation results in a downlapping seismic unit superimposed on the bottomset of an earlier converging clinoform, with numerous buried/exposed submarine channels at its seaward terminus. These units exhibit a shore‐parallel elongated and continuous geometry, suggesting lateral spreading, which we attribute to alongshore hydrodynamic (especially tidal) remolding. Our findings underscore the significance of sediment gravity flows in the evolution of a degrading delta front, particularly as a principal mechanism of downslope mass transport that gentled (halving the gradient) and reshaped the DF over time. Gravity‐driven accumulations sourced from upper DF collapse can account for ∼1/3 of the previous DF and laterally extend over an unexpectedly large area (∼60‐km long) through hydrodynamic redistribution. Both processes should be considered for modeling other subaqueous deltas.

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Section: Discussionsupporting

confidence: 91%

The Impact of Gravity‐Driven Sedimentation on Reshaping the Huanghe (Yellow River) Delta Front

et al. 2022

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“…More efforts, resources, and engineered diversions will be necessary to prevent avulsion as channels aggrade more quickly and farther upstream during sea‐level rise (Kim et al., 2009; Moodie & Nittrouer, 2021; Temmerman & Kirwan, 2015). Modified deltas may also be at risk of unexpected new avulsion sites if levee and dam infrastructure has sufficiently altered backwater effects and aggradation patterns since the last avulsion (Carlson et al., 2021; Chadwick & Lamb, 2021; Moodie & Nittrouer, 2021).…”

Section: Discussionmentioning

confidence: 99%

Effect of Sea‐Level Change on River Avulsions and Stratigraphy for an Experimental Lowland Delta

et al. 2022

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Lowland deltas experience natural diversions in river course known as avulsions. River avulsions pose catastrophic flood hazards and redistribute sediment that is vital for sustaining land in the face of sea‐level rise. Avulsions also affect deltaic stratigraphic architecture and the preservation of sea‐level cycles in the sedimentary record. Here, we present results from an experimental lowland delta with persistent backwater effects and systematic changes in the rates of sea‐level rise and fall. River avulsions repeatedly occurred where and when the river aggraded to a height of nearly half the channel depth, giving rise to a preferential avulsion node within the backwater zone regardless of sea‐level change. As sea‐level rise accelerated, the river responded by avulsing more frequently until reaching a maximum frequency limited by the upstream sediment supply. Experimental results support recent models, field observations, and experiments, and suggest anthropogenic sea‐level rise will introduce more frequent avulsion hazards farther inland than observed in recent history. The experiment also demonstrated that avulsions can occur during sea‐level fall—even within the confines of an incised valley—provided the offshore basin is shallow enough to allow the shoreline to prograde and the river to aggrade. Avulsions create erosional surfaces within stratigraphy that bound beds reflecting the amount of deposition between avulsions. Avulsion‐induced scours overprint erosional surfaces from sea‐level fall, except when the cumulative drop in sea‐level is greater than the channel depth and less than the basin depth. Results imply sea‐level signals outside this range are removed or distorted in delta deposits.

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“…At present, shorelines of many deltas in the world are experiencing land loss due to declining sediment supply and accelerating rates of sea‐level rise (Blum & Roberts, 2009; Syvitski & Saito, 2007). Because large river deltas are densely populated and are transportation hubs and industrial and commercial centers, artificial bifurcation have been implemented, or are being considered, as a viable engineering tool to divert flow and sediment for combating coastal land loss, especially on those densely populated deltas such as the Yellow River delta (Carlson et al, 2021; Syvitski & Saito, 2007) and the Mississippi River Delta (Shaw et al, 2021; Wang & Xu, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…The outcome of sediment division through artificial bifurcation can be affected by a number of factors, such as channel slope (Iwantoro et al, 2021), friction factor (Edmonds & Slingerland, 2008), Shields number (Bolla Pittaluga et al, 2003), bed sediment sorting (Kleinhans et al, 2008), aspect ratio upstream channel (Bolla Pittaluga et al, 2015), elevation before sediment loss (Carlson et al, 2021), and tidal amplitudes (Ragno et al, 2020). Differences in bed composition between the old channel and the new branch are also relevant, which can affect long-term bifurcation stability.…”

mentioning

confidence: 99%

“…Because large river deltas are densely populated and are transportation hubs and industrial and commercial centers, artificial bifurcation have been implemented, or are being considered, as a viable engineering tool to divert flow and sediment for combating coastal land loss, especially on those densely populated deltas such as the Yellow River delta (Carlson et al, 2021;Syvitski & Saito, 2007) and the Mississippi River Delta (Shaw et al, 2021;.…”

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confidence: 99%

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Artificial bifurcation effect on downstream channel dynamics of a large lowland river, the Atchafalaya

Wang

et al. 2021

Earth Surf Processes Landf

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Artificial river bifurcations have been widely created for different purposes. Yet, long‐term dynamics in the bifurcated channels and natural channels downstream of the artificial bifurcation nodes are not well investigated. Herein, we employed an approach combining three decades (1977–2006) of bathymetric survey records, geographic information system (GIS) application, and bed material transport modeling to investigate riverbed dynamics in an artificially bifurcated channel and the downstream natural channel of the Atchafalaya River, the largest distributary of the Mississippi River. Decadal changes in the riverbed volume were determined, and erosion/deposition patterns in these channels were assessed. Hydraulic properties under low, medium, and high flow conditions were quantified to analyze main factors affecting the long‐term trend of channel dynamics. Our study found that flow from the Atchafalaya River into the artificially bifurcated Wax Lake outlet channel (WLOC) steadily increased. Hydraulic gradient, stream power, and shear stress under all flow conditions of the WLOC were greater than those of the Atchafalaya River natural mainstem channel (ARMC) downstream of the artificial bifurcation. On average, 52% of the total bed material loads (BMLs) from the Atchafalaya entered the steeper and straight WLOC with 41% of the river's flow from 1977 to 2006. Despite the higher sediment inflow, the WLOC degraded with an average rate of −0.12 × 105 m3 km−1 yr−1, while the ARMC downstream of the bifurcation aggraded substantially with an average rate of 0.38 × 105 m3 km−1 yr−1 over the three decades. The disproportional flow–sediment ratio and channel erosion‐aggradation patterns below the artificial bifurcation were apparently a reflection of the difference in the river hydraulic properties. These findings imply that lowland alluvial river diversions for introducing sediment to build new land in world's sinking deltas need to develop sustainable solutions in order to avoid causing severe bed scouring in one but excessive deposition in the other channel downstream of the bifurcation.

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Impacts of Engineered Diversions and Natural Avulsions on Delta‐Lobe Stability

Cited by 7 publications

References 52 publications

The Impact of Gravity‐Driven Sedimentation on Reshaping the Huanghe (Yellow River) Delta Front

The Impact of Gravity‐Driven Sedimentation on Reshaping the Huanghe (Yellow River) Delta Front

Effect of Sea‐Level Change on River Avulsions and Stratigraphy for an Experimental Lowland Delta

Artificial bifurcation effect on downstream channel dynamics of a large lowland river, the Atchafalaya

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