Experimental river delta size set by multiple floods and backwater hydrodynamics

Ganti, Vamsi; Chadwick, A. J.; Hassenruck‐Gudipati, Hima J.; Fuller, Brian M.; Lamb, Michael P.

doi:10.1126/sciadv.1501768

Cited by 81 publications

(220 citation statements)

References 45 publications

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“…It has been observed in many natural deltas that flows below flood conditions are able to transport sediment loads. Ganti et al () ran experiments with a single intermittency value where sediment concentrations were varied in order to yield the same transport slope during low flows and high flows, producing a delta that was not erosive with a constrained topset slope. However, these experiments also simply the reality of the nonlinear sediment transport, where lower flows will generally have smaller sediment concentrations and conversely higher flows will generally have greater concentrations (van Rijn, ), suggesting that variable flow conditions can cause a system to transition from aggradations to erosional as overserved in the presented experiments.…”

Section: Discussionmentioning

confidence: 99%

“…The discharge fluctuations in these experiments were important for limiting vegetation colonization and maintaining the distributary network of the delta. Also, Ganti et al () investigated the role of backwater hydraulics on river delta size by comparing experimental deltas produced with constant discharge with one produced over multiple flood cycles with I = 0.27, where sediment and water discharge values were selected to maintain constant transport slopes between high‐ and low‐flow events. Their experiments showed that deltas with constant discharge conditions were not affected by backwater hydraulics, while the delta with multiple floods produced a deposit with a characteristic delta lobe size that was dependent on the backwater conditions.…”

Section: Introductionmentioning

confidence: 99%

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Laboratory Investigation on Effects of Flood Intermittency on Fan Delta Dynamics

2019

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To simplify the complex hydrological variability of flow conditions, experiments on delta evolution are often conducted using a representative channel‐forming flood flow and results are related to field settings using an intermittency factor, defined as the fraction of time in flood. Although this factor provides an approximation of dominant flow conditions and makes modeling deltas easier by turning their complex hydraulics into a single representative value, little is known about how this generalization affects delta processes. We conducted experiments with periodic flow conditions to determine the effects of intermittent discharges on fan deltas. For each run, the magnitude of floods was held constant, but the duration changed, thus varying the intermittency factor, between 1 and 0.2. Floods consisted of higher water and sediment discharge, while base flow periods had lower water discharge and sediment input ceased, causing the system to become erosional during these periods. We find that as the duration of floods decreases, the delta topset is larger in area with a shallower slope due to reworking on the topset during base flow conditions. During base flows, the experimental system adjusts toward a new equilibrium state that in turn acts as the initial condition for subsequent flood periods. These results suggest that the adjustment timescale is a factor in determining the behavior of deltas and their channels. We conclude that both periods of flood when most of the sediment is supplied to the system and periods of base flow when topset sediment is reworked contribute to delta dynamics.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Laboratory Investigation on Effects of Flood Intermittency on Fan Delta Dynamics

2019

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“…Piper et al, 1990)arguably different from the unvegetated deltaic plains of our experiments where longitudinal slopes are on the order of 10 À2 (Figure 6). Martin et al, 2009;Wickert et al, 2013;Kleinhans et al, 2014b;Ganti et al, 2016). Martin et al, 2009;Wickert et al, 2013;Kleinhans et al, 2014b;Ganti et al, 2016).…”

Section: Experimental Delta Morphology and Evolutionmentioning

confidence: 99%

Experimental delta evolution in tidal environments: Morphologic response to relative sea‐level rise and net deposition

Finotello

Lentsch

Paola

2019

Earth Surf Processes Landf

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Tide‐influenced deltas are among the largest depositional features on Earth and are ecologically and economically important as they support large populations. However, the continued rise in relative sea level threatens the sustainability of these landscapes and calls for new insights on their morphological response. While field studies of ancient deposits allow for insight into delta evolution during times of eustatic adjustment, tide‐influenced deltas are notoriously hard to identify in the rock record. We present a suite of physical experiments aimed at investigating the morphological response of tide‐influenced deltas subject to relative sea‐level rise. We show that increasing relative tidal energy changes the response of the delta because tides effectively act to remove fluvially deposited sediment from the delta topset. This leads to enhanced transgression, which we quantify via a new methodology for comparing shoreline transgression rates based on the concept of a ‘transgression anomaly’ relative to a simple reference case. We also show that stronger tidal forcing can create composite deltas where distinct land‐forming processes dominate different areas of the delta plain, shaping characteristic morphological features. The net effect of tidal action is to enhance seaward transfer of bedload sediment, resulting in greater shoreline transgression compared to identical, yet purely fluvial, deltaic systems that exhibit static or even regressive shorelines. © 2019 John Wiley & Sons, Ltd.

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“…Generally, the evolution of river deltas comprises the abandonment of old delta lobes and creation of new (active) delta lobes due to river avulsion (Ganti et al, ; Jerolmack & Swenson, ). The growth of the active river delta lobes is further shaped by the competing fluvial and marine forcings (Galloway, ).…”

Section: Introductionmentioning

confidence: 99%

“…Additional factors such as sediment grain size (Caldwell & Edmonds, ; Orton & Reading, ), vegetation (Nardin et al, ), and the unsteadiness of river discharge (Shaw & Mohrig, ; Wright & Coleman, ) have also been found to play an important role in controlling delta morphodynamics. Regarding the effects of unsteady river discharge on delta morphological evolution, some recent studies have explored the effects of interannual variability of river discharge on delta channel avulsion (Chatanantavet et al, ; Ganti et al, ) and delta growth rate (Rosen & Xu, ). River floods and associated sediment pulses into the delta have been considered as the major factors that affect the growth of delta as well as the supported saltmarsh (Mudd, ; Rosen & Xu, ).…”

Section: Introductionmentioning

confidence: 99%

Long‐Term Cumulative Effects of Intra‐Annual Variability of Unsteady River Discharge on the Progradation of Delta Lobes: A Modeling Perspective

et al. 2019

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Rivers, regardless of their scales and geographic locations, are characterized with natural and human‐induced variability in their discharges. While previous studies have established the effects of both interannual and intra‐annual variabilities of unsteady river discharge on delta morphological evolution, the long‐term cumulative effects of intra‐annual unsteadiness on the progradation of delta lobes has remained hitherto elusive. To address this issue, numerical experiments using simplified unsteady discharges were performed in Delft3D and compared with those assuming constant bank‐full discharges. A modified box model was further used to explore the effects of varying intra‐annual unsteadiness on the progradation of delta lobes at reduced computational cost. While the overall trends of the progradation and the ultimate area created were found to be similar between the unsteady discharge scenarios and their corresponding constant bank‐full discharge scenarios, the nuances of intermittent zig‐zag variation in natural delta lobe area were well reproduced by model simulations assuming unsteady river discharges. In addition, long‐term predictions suggested the potential existence of a tipping point in the area growth trajectory beyond which the delta lobe area declines during periods of low discharge. When confounding factors such as waves and variable sediment capture ratio were further taken into consideration, simulation results for unsteady river discharge scenarios exhibit significant deviations from constant bank‐full discharge scenarios. The implications of the modeling results for delta protection and restoration measures, such as the water‐sediment regulation scheme in the Yellow River and artificial channel diversions in the Mississippi River Delta, are also discussed.

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Experimental river delta size set by multiple floods and backwater hydrodynamics

Abstract: Experimental delta lobe size is controlled by bed adjustment to transient floods within the backwater zone.

Cited by 81 publications

References 45 publications

Laboratory Investigation on Effects of Flood Intermittency on Fan Delta Dynamics

Laboratory Investigation on Effects of Flood Intermittency on Fan Delta Dynamics

Experimental delta evolution in tidal environments: Morphologic response to relative sea‐level rise and net deposition

Long‐Term Cumulative Effects of Intra‐Annual Variability of Unsteady River Discharge on the Progradation of Delta Lobes: A Modeling Perspective

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