R-3 Repository :: Browsing by Author "Nittrouer, Jeffrey A."

Browsing by Author "Nittrouer, Jeffrey A."

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Can Reservoir Regulation Along the Yellow River Be a Sustainable Way to Save a Sinking Delta?
(Wiley, 2020) Wu, Xiao; Bi, Naishuang; Syvitski, Jaia; Saito, Yoshiki; Xu, Jingping; Nittrouer, Jeffrey A.; Bianchi, Thomas S.; Yang, Zuosheng; Wang, Houjie
Today's deltas are impacted negatively by (1) accelerated subsidence (e.g., from ground fluid extraction), (2) global eustatic sea level rise, and (3) decreased sediment supply, which increasingly starves these landforms of sediment necessary to sustain their footprint. This growing vulnerability threatens many megacities that have developed due to the rich resources offered by deltas and therefore urgently calls for efforts to maintain sustainability. The Yellow River of China is classic example of such a landform under threat and which requires human intervention to maintain its resilience. Since 2002, the Yellow River Conservancy Commission has enacted an annual water and sediment regulation scheme (WSRS) by coordinated operation of three large reservoirs in the mainstream. Here we evaluate the efficiency and sustainability of this man‐made experiment on delta evolution. The impulsive delivery of muds and sands, within ~20 day intervals (averaged duration of the WSRS), did indeed move the present Yellow River delta from a destructive phase to an accretion phase. With continuous scouring, however, the downstream riverbed erosion efficiency has decreased, due to coarsening of surface bed material sediment. Concomitantly, sediment delivery has decreased, resulting in the present delta once again entering an erosive (destructive) phase, since 2014. From a perspective of delta restoration, the WSRS on the Yellow River is effective but potentially unsustainable. Restoring delta resilience necessitates an enhanced, coordinated effort, relying upon new sciences advances, rather than simply assuming channel scour will address the sediment deficit of the delta.
Coastal Landscape Dynamics: Predicting the Evolution of the Upper Texas Gulf Coast
(Rice University, 2014) Nittrouer, Jeffrey A.; Trueba, Jorge; Shell Center for Sustainability
Coralgal reef morphology records punctuated sea-level rise during the last deglaciation
(Springer Nature, 2017) Khanna, Pankaj; Droxler, André W.; Nittrouer, Jeffrey A.; Tunnell, John W. Jr.; Shirley, Thomas C.
Coralgal reefs preserve the signatures of sea-level fluctuations over Earth’s history, in particular since the Last Glacial Maximum 20,000 years ago, and are used in this study to indicate that punctuated sea-level rise events are more common than previously observed during the last deglaciation. Recognizing the nature of past sea-level rises (i.e., gradual or stepwise) during deglaciation is critical for informing models that predict future vertical behavior of global oceans. Here we present high-resolution bathymetric and seismic sonar data sets of 10 morphologically similar drowned reefs that grew during the last deglaciation and spread 120 km apart along the south Texas shelf edge. Herein, six commonly observed terrace levels are interpreted to be generated by several punctuated sea-level rise events forcing the reefs to shrink and backstep through time. These systematic and common terraces are interpreted to record punctuated sea-level rise events over timescales of decades to centuries during the last deglaciation, previously recognized only during the late Holocene.
Coupling non-uniform channel hydrodynamics and development of fluvial-deltaic stratigraphy, over scales ranging from bedforms to basins
(2020-04-24) Wu, Chenliang; Nittrouer, Jeffrey A.
This dissertation explores the impact of backwater hydrodynamics on the development of fluvial-deltaic strata across a range of spatiotemporal scales by linking numerical modeling, field observations of channel bathymetry from the modern Mississippi River, and stratigraphic patterns from the ancient Tullig Sandstone of the Western Irish Namurican Basin (Co. Clare, Ireland). The research topics include: (1) assessing the response of channel hydrodynamics to external environmental forcings and associated feedback on stratigraphic development, (2) evaluating bedform dynamics as a function of systematically varying sediment transport conditions within a river backwater reach and determining the impact on cross strata, and (3) inverting stratigraphy to improve accuracy of paleohydraulic reconstructions of ancient fluvial-deltaic systems. The numerical model developed in this study incorporates channel morphodynamics and a grain size-specific sediment transport relation, and allows the tuning of input boundary conditions so to account for geological forcings (e.g., base level change, basin geometry). It is thus capable of simulating not only short-term (seconds to hours) and reach-scale hydrodynamics of fluvial-deltaic system, but also long-term (millennia) and basin-scale patterns of stratigraphy. Simulation results using this newly developed modeling framework reveal that the influence of variable channel hydrodynamics extends beyond the typical backwater length scale of modern fluvial-deltaic systems due to in-channel sedimentation that migrates upstream. Coupled with shoreline movement, the degree of channel deepening enhances downstream, independent of long-term base-level fluctuations. However, channel deepening is not indefinite, because a state of dynamic equilibrium is reached during periods of base-level rise, which generates an autoretreat of the river system and unique (recognizable) basin-scale patterns of stratigraphy. At the bedform scale, dune dynamics and morphology are shown to be impacted by backwater hydrodynamics. An analytical model predicts that the dune-scale cross-set thickness (an important paleohydraulic indicator) increases, and then decreases, progressing downstream towards the river outlet. This trend is opposite to what traditional paleohydraulic reconstruction methods predict, but yet is observed for a modern river (the lowermost Mississippi River), and an ancient fluvial-deltaic system (Tullig Sandstone). These results support the hypothesis that sedimentary strata may preserve distinct signatures of backwater hydrodynamics. This hypothesis is further tested in the Tullig Sandstone, by parameterizing the numerical model from this study to assess predicted patterns and observed patterns of stratigraphy found in rock outcrops. A distinct trend in cross-set thickness is identified and used to improve paleohydraulic reconstruction methods. The physics-based model frameworks presented in this dissertation can be adopted for other settings, and used to constrain planetary surface evolution by assessing the response of fluvial-deltaic systems to internal and external changes in boundary conditions.
Downstream elimination of gravel in multiple distributary channels on the Selenga River delta topset, Russia: a morphodynamics case study of fan delta at the Baikal Rift basin margin
(2015-04-24) Dong, Tian Yang; Nittrouer, Jeffrey A.; Anderson, John B; Dickens, Gerald R
The Selenga River delta, Lake Baikal, Russia, is approximately 600 km² in size and contains multiple distributary channels that receive varying amounts of water and sediment discharge. This delta is positioned along the deep-water (~1600 m) margin of Lake Baikal, a half-graben styled rift basin, qualifying it as a modern analogue of shelf-edge system. This study provides a detailed field survey of channel bed sediment composition, channel geometry, and water discharge. Our data indicate that the delta exhibits downstream sediment fining, ranging from predominantly coarse gravel and sand near the delta apex to silt and sand at the delta-lake interface. An analytical framework is developed utilizing field data to evaluate the downstream elimination of gravel within the multiple distributary channels. Our major findings are: 1.) the Selenga River delta consists of at least eight orders of distributary channels, 2.) with increasing channel order, channel cross-sectional area, width-depth ratio, water discharge, boundary shear stress, and sediment flux all decrease downstream, 3.) the downstream elimination of gravel in distributary channels is caused by reducing boundary shear stress downstream where water discharge is partitioned among bifurcating channels, 4.) Gravel is trapped on the delta topset due to frequent basin subsidence, thus preventing coarse material from being delivered to the axis of the rift basin. The distribution of sediment in deltaic channels and the associated sediment transport processes that construct stratigraphy, combined with the active tectonic setting, allow sedimentary systems like the Selenga delta to be preserved in the long-term geologic record. Therefore, the location of the Selenga River delta along the active Baikal Rift margin renders the opportunity to explore the influence of tectonics and sedimentation on deltaic processes that produce basin stratigraphy.
Effect of freeze-thaw cycling on grain size of biochar
(Public Library of Science, 2018) Liu, Zuolin; Dugan, Brandon; Masiello, Caroline A.; Wahab, Leila M.; Gonnermann, Helge M.; Nittrouer, Jeffrey A.
Biochar may improve soil hydrology by altering soil porosity, density, hydraulic conductivity, and water-holding capacity. These properties are associated with the grain size distributions of both soil and biochar, and therefore may change as biochar weathers. Here we report how freeze-thaw (F-T) cycling impacts the grain size of pine, mesquite, miscanthus, and sewage waste biochars under two drainage conditions: undrained (all biochars) and a gravity-drained experiment (mesquite biochar only). In the undrained experiment plant biochars showed a decrease in median grain size and a change in grain-size distribution consistent with the flaking off of thin layers from the biochar surface. Biochar grain size distribution changed from unimodal to bimodal, with lower peaks and wider distributions. For plant biochars the median grain size decreased by up to 45.8% and the grain aspect ratio increased by up to 22.4% after 20 F-T cycles. F-T cycling did not change the grain size or aspect ratio of sewage waste biochar. We also observed changes in the skeletal density of biochars (maximum increase of 1.3%), envelope density (maximum decrease of 12.2%), and intraporosity (porosity inside particles, maximum increase of 3.2%). In the drained experiment, mesquite biochar exhibited a decrease of median grain size (up to 4.2%) and no change of aspect ratio after 10 F-T cycles. We also document a positive relationship between grain size decrease and initial water content, suggesting that, biochar properties that increase water content, like high intraporosity and pore connectivity large intrapores, and hydrophilicity, combined with undrained conditions and frequent F-T cycles may increase biochar breakdown. The observed changes in biochar particle size and shape can be expected to alter hydrologic properties, and thus may impact both plant growth and the hydrologic cycle.
Impacts of Engineered Diversions and Natural Avulsions on Delta-Lobe Stability
(Wiley, 2021) Carlson, Brandee N.; Nittrouer, Jeffrey A.; Swanson, Travis E.; Moodie, Andrew J.; Dong, Tian Y.; Ma, Hongbo; Kineke, Gail C.; Pan, Minglong; Wang, Yuanjiang
Reduced sediment supply and rising sea levels are driving land submergence on deltas worldwide, motivating engineering practices that divert water and sediment to sustain coastal landforms. However, lobe response following channel abandonment by diversions has not been constrained by field-scale studies. Herein, avulsion and engineered diversion scenarios are explored for the Huanghe delta (China), where three lobes were abandoned in the last 40 yr. Two lobes were completely cut off by diversions, and one naturally by an avulsion. Shoreline retreat rates are strikingly different: ∼400 m/yr for diverted lobes and ∼90 m/yr for avulsed lobe. We hypothesize that this variability is linked to vegetal cover across lobes, and therefore the capacity to buffer hydrodynamic reworking of shoreface sediment. Furthermore, the vegetal cover is related to lobe salinity and elevation, which vary by abandonment style. We offer this as a case study to inform about the efficacy of future delta diversions.
Influence of climate-modulated flooding on fluvial morphodynamics and stratigraphy
(2021-04-29) Barefoot, Eric A.; Nittrouer, Jeffrey A.
Contemporary climate change is expected to exacerbate river flooding in the future, but the potential impacts on alluvial landscapes remain ambiguous. There are two main sources of natural observations to bolster this understanding: modern rivers and fluvial stratigraphy. Observations from modern rivers directly connect floods and landscape evolution, but because the data span at maximum a few centuries, the temporal scope is insufficient to constrain the impact of future changes in flood frequency and magnitude. On the other hand, the stratigraphic record is synoptic in scope, but stochastic erosion and deposition render the record incomplete, and thus limit the precision of paleoenvironmental reconstructions. This dissertation sharpens interpretations of the geologic record by improving process-based interpretations of fluvial strata influenced by flooding, particularly by focusing on how changes in flooding intensity manifest in fluvial strata. Two main strategies are used. In the first, a stratigraphic study characterizes the signature of enhanced flooding during an abrupt warming episode in the geologic past, and in the second, experiments were conducted whereby a scaled fan delta was subjected to artificial floods while process responses were observed, and the resulting stratigraphy analyzed. Both the stratigraphic and experimental studies point to the importance of the balance between lateral and downstream sediment transport. It is shown that extreme flooding destabilizes channel banks, and promotes lateral sediment dispersal and floodplain reworking, whereas a total absence of flooding restricts sediment exchange across channel margins and directs sediment downstream. However, incremental increases in flooding do not always result in enhanced sediment exchange. Moderate amounts of flooding act to stabilize channels rather than destabilize them, because sediment delivered to channel margins during floods builds levees that confine flow and limit lateral sediment dispersal in favor of downstream transport. In this way, climate-modulated changes in flooding alter the spatiotemporal distribution of sediment, which is a crucial control enhancing or diminishing the taphonomic potential of paleoclimate records through time. Thus, levee-construction processes are the lynchpin governing fluvial responses to flooding, and are essential for reconstructing past environmental change as well as characterizing future threats to riparian communities.
Modeling flow and sediment transport dynamics in the lowermost Mississippi River, Louisiana, USA, with an upstream alluvial-bedrock transition and a downstream bedrock-alluvial transition: Implications for land building using engineered diversions
(Wiley, 2015) Viparelli, Enrica; Nittrouer, Jeffrey A.; Parker, Gary
The lowermost Mississippi River, defined herein as the river segment downstream of the Old River Control Structure and hydrodynamically influenced by the Gulf of Mexico, extends for approximately 500?km. This segment includes a bedrock (or more precisely, mixed bedrock-alluvial) reach that is bounded by an upstream alluvial-bedrock transition and a downstream bedrock-alluvial transition. Here we present a one-dimensional mathematical formulation for the long-term evolution of lowland rivers that is able to reproduce the morphodynamics of both the alluvial-bedrock and the bedrock-alluvial transitions. Model results show that the magnitude of the alluvial equilibrium bed slope relative to the bedrock surface slope and the depth of bedrock surface relative to the water surface base level strongly influence the mobile bed equilibrium of low-sloping river channels. Using data from the lowermost Mississippi River, the model is zeroed and validated at field scale by comparing the numerical results with field measurements. The model is then applied to predict the influence on the stability of channel bed elevation in response to delta restoration projects. In particular, the response of the river bed to the implementation of two examples of land-building diversions to extract water and sediment from the main channel is studied. In this regard, our model results show that engineered land-building diversions along the lowermost Mississippi River are capable of producing equilibrated bed profiles with only modest shoaling or erosion, and therefore, such diversions are a sustainable strategy for mitigating land loss within the Mississippi River Delta.
Modeling the influence of large woody debris on delta morphology and longshore sediment transport using the Brazos delta
(2015-06-09) Huff, Sarah Anne; Nittrouer, Jeffrey A.; Anderson, John B.; Lorenzo-Trueba, Jorge; Masiello, Carrie A.
Large woody debris' (LWD) role in coastal sediment dynamics is understudied, but yet is an extremely important consideration in the face of modern climate change and coastal erosion. In addition to amplified aeolian sediment capture due to increased roughness of the shoreface, LWD has implications for reduction of sediment transport capacity along the shoreface. Here, we examine the impact of increased woody debris concentration within the littoral zone and relate this to differential longshore sediment transport rates. We hypothesize that woody debris concentration and longshore sediment transport can be linked through a dimensionless index for use in most longshore sediment transport equations. Using a numerical model constrained by data collected from field studies, our results show that increased woody debris at the shoreface is inversely related to longshore sediment transport rates. Increased roughness due to woody debris results in a loss of stress available to mobilize sediment. Our model allows for first-order predictions of longshore sediment transport based on woody debris concentrations at the shoreline. Field surveys of the modern Brazos river delta in the Gulf of Mexico reveal an abundance of large woody debris along the coastline and within the delta matrix. There is a multitude of aerial photographs and bathymetric maps documenting the relative stability of the modern Brazos River deltas despite variable sediment discharge and the same wave climate that resulted in rapid erosion of the pre-engineered-diversion old Brazos delta. Despite their similar sediment volume and wave climate characteristics, the two deltas show very different morphologies in times of relaxed sediment discharge. With our model, we propose that the large quantities of woody debris sequestered on the modern delta may result in minimal longshore sediment transport along the delta, thereby preserving delta morphology amongst an energetic wave climate.
Morphodynamic modeling of channel fill and avulsion timescales during early Holocene transgression using Trinity River, TX incised valley stratigraphy
(2015-04-24) Moran, Kaitlin Moran Elizabeth; Nittrouer, Jeffrey A.; Anderson, John B; Droxler, Andre W; Lorenzo-Trueba, Jorge; Perillo, Mauricio M
The Trinity River and the sediments that infill its incised valley system are well-constrained in terms of time and space properties of the sediment deposits and resulting stratigraphy. The Trinity River is an excellent natural laboratory to test fluvial morphodynamic concepts that could be used to examine the processes of incised valley infill. We develop a numerical model that links sediment transport processes and the production of stratigraphy to evaluate the effects of Holocene transgression on the development of Trinity stratigraphy. We simulate the mechanics of channel fill and avulsions for the Trinity River, by coupling fluid flow, sediment transport and channel response, constrained by modern and early Holocene conditions. Our results show how non-uniform flow produces loci of sediment deposition, which backstep within the channel as base-level rises, and coincide with the avulsion locations. There is an upstream retreat as the rate of base-level rise increases (transgression). Additionally, we show how including a floodplain parameter within the model framework influences the calculated time for avulsion by changing the amount of sediment deposited within the channel. Our model is applied over century to millennial timescales, and is utilized to evaluate basin scale patterns of known stratigraphic variability. Because the model is well-constrained, our results have application for predicting stratigraphy for other fluvial-deltaic systems undergoing transgression. This is especially important for predicting the valley infill of systems that lack the robust constraint exhibited by the Trinity incised valley system.
Optimized river diversion scenarios promote sustainability of urbanized deltas
(National Academy of Sciences, 2021) Moodie, Andrew J.; Nittrouer, Jeffrey A.
Socioeconomic viability of fluvial-deltaic systems is limited by natural processes of these dynamic landforms. An especially impactful occurrence is avulsion, whereby channels unpredictably shift course. We construct a numerical model to simulate artificial diversions, which are engineered to prevent channel avulsion, and direct sediment-laden water to the coastline, thus mitigating land loss. We provide a framework that identifies the optimal balance between river diversion cost and civil disruption by flooding. Diversions near the river outlet are not sustainable, because they neither reduce avulsion frequency nor effectively deliver sediment to the coast; alternatively, diversions located halfway to the delta apex maximize landscape stability while minimizing costs. We determine that delta urbanization generates a positive feedback: infrastructure development justifies sustainability and enhanced landform preservation vis-à-vis diversions.
Predicting Water and Sediment Partitioning in a Delta Channel Network Under Varying Discharge Conditions
(Wiley, 2020) Dong, Tian Y.; Nittrouer, Jeffrey A.; McElroy, Brandon; Il'icheva, Elena; Pavlov, Maksim; Ma, Hongbo; Moodie, Andrew J.; Moreido, Vsevolod M.
Channel bifurcations control the distribution of water and sediment in deltas, and the routing of these materials facilitates land building in coastal regions. Yet few practical methods exist to provide accurate predictions of flow partitioning at multiple bifurcations within a distributary channel network. Herein, multiple nodal relations that predict flow partitioning at individual bifurcations, utilizing various hydraulic and channel planform parameters, are tested against field data collected from the Selenga River delta, Russia. The data set includes 2.5 months of time‐continuous, synoptic measurements of water and sediment discharge partitioning covering a flood hydrograph. Results show that width, sinuosity, and bifurcation angle are the best remotely sensed, while cross‐sectional area and flow depth are the best field measured nodal relation variables to predict flow partitioning. These nodal relations are incorporated into a graph model, thus developing a generalized framework that predicts partitioning of water discharge and total, suspended, and bedload sediment discharge in deltas. Results from the model tested well against field data produced for the Wax Lake, Selenga, and Lena River deltas. When solely using remotely sensed variables, the generalized framework is especially suitable for modeling applications in large‐scale delta systems, where data and field accessibility are limited.
Testing morphodynamic controls on the location and frequency of river avulsions on fans versus deltas: Huanghe (Yellow River), China
(American Geophysical Union, 2014) Ganti, Vamsi; Chu, Zhongxin; Lamb, Michael P.; Nittrouer, Jeffrey A.; Parker, Gary
A mechanistic understanding of river avulsion location and frequency is needed to predict the growth of alluvial fans and deltas. The Huanghe, China, provides a rare opportunity to test emerging theories because its high sediment load produces regular avulsions at two distinct nodes. Where the river debouches from the Loess Plateau, avulsions occur at an abrupt decrease in bed slope and reoccur at a time interval (607 years) consistent with a channel-filling timescale set by the superelevation height of the levees. Downstream, natural deltaic avulsions reoccur at a timescale that is fast (7 years) compared to channel-filling timescale due to large stage-height variability during floods. Unlike the upstream node, deltaic avulsions cluster at a location influenced by backwater hydrodynamics and show evidence for episodic downstream migration in concert with progradation of the shoreline, providing new expectations for the interplay between avulsion location, frequency, shoreline rugosity, and delta morphology.
The exceptional sediment load of fine-grained dispersal systems: Example of the Yellow River, China
(AAAS, 2017) Ma, Hongbo; Nittrouer, Jeffrey A.; Naito, Kensuke; Fu, Xudong; Zhang, Yuanfeng; Moodie, Andrew J.; Wang, Yuanjian; Wu, Baosheng; Parker, Gary
Sedimentary dispersal systems with fine-grained beds are common, yet the physics of sediment movement within them remains poorly constrained. We analyze sediment transport data for the best-documented, fine-grained river worldwide, the Huanghe (Yellow River) of China, where sediment flux is underpredicted by an order of magnitude according to well-accepted sediment transport relations. Our theoretical framework, bolstered by field observations, demonstrates that the Huanghe tends toward upper-stage plane bed, yielding minimal form drag, thus markedly enhancing sediment transport efficiency. We present a sediment transport formulation applicable to all river systems with silt to coarse-sand beds. This formulation demonstrates a remarkably sensitive dependence on grain size within a certain narrow range and therefore has special relevance to silt-sand fluvial systems, particularly those affected by dams.

Browsing by Author "Nittrouer, Jeffrey A."

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