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Integrated sedimentological and ichnological studies in deltaic systems are key to determine whether a delta is river‐dominated, tide‐dominated, wave‐dominated or hybrid, and thus predict the distribution of their geometries and main reservoirs. The Austral Basin is one of the most important oil and gas basins from Argentina, and the Upper Cretaceous La Anita Formation has shown excellent attributes as a hydrocarbon reservoir. Analysis of eleven cores, supplemented by a large volume of well logging data and two‐dimensional and three‐dimensional seismic, allowed to recognize a river‐dominated deltaic system affected by hyperpycnal discharges and storm events. Four main facies associations were recognized (offshore, prodelta, delta front and interdistributary bay), being the delta front facies associations, the most recurrent facies and constituting the major reservoir of the La Anita Formation. Three types of deltaic mouth bars have been characterized in the delta front. Type I corresponds to active mouth bars with preservation of sedimentary structures and bioturbated by suspension and deposit feeding organisms. Type II represents the stopped progradation and the abandonment in the construction of mouth bars, which are completely reworked by suspension and deposit feeding organisms and, in some cases, affected by fair‐weather or storm‐wave processes at the top. Type III comprises hyperpycnal mouth bars characterized by transitional and recurrent intervals of sedimentary structures, high concentration of phytodetritus, and paucity of bioturbation. The amalgamation and coalescence of these three types of sandy mouth bars produce lobe‐like geometries and are the main processes of delta front construction and progradation. This proposed model allows to explain the principal mechanism of construction of the delta front and can be applied to the analysis of other reservoirs where mouth bar architectural elements are dominant. [ABSTRACT FROM AUTHOR]

Abstract The sedimentary architecture of fan deltas, which commonly constitute reservoirs, is a primary control on distribution and recovery efficiency of oil and gas. Deep-water fan deltas have been extensively discussed in the literature, whereas the sedimentary architecture of shallow-water fan-delta fronts, especially the characterization of mouth bar, quantification of architectural elements, and factors controlling the various architectural elements, remain poorly understood. Here, based on the integration of field survey and unmanned aerial vehicle (UAV) observation, the sedimentary architecture of Sangyuan section of the Lower Cretaceous Xiguayuan Formation in the Luanping Basin to is qualitatively and quantitatively characterized. Furthermore, factors controlling the architecture of the shallow-water fan-delta front are highlighted. Five facies associations, which differ in both lithofacies and dimensions, were interpreted in gravel-sand deposits of Sangyuan section, and indicate variations in flow conditions during deposition. The width/thickness ratio of facies associations generally increases rapidly as the flow energy and flow concentration decreases from debris flow to traction currents during the evolution of shallow-water fan delta. Both distributary channels and mouth bars dominate facies associations in the shallow-water fan-delta front, accounting for 53.42% and 36.88% of gravel-sand deposits respectively in Sangyuan section. Mouth bar consists of gravel accretions and sand accretions. Grain size of sediments influences the relative strength of the inertial force and bed friction, which determine the effluent behavior in a river-mouth system and the vertical grain-size trend of mouth bar accretions. Gravel accretions are characterized by normal grading, and these are interpreted as the products of inertia-dominated effluent. Sand accretions exhibit coarsening-upward trends in the river-mouth systems where friction-dominated outflow occurred. The overall vertical grain-size trend of mouth bar depends on the stacking pattern of accretions rather than the grading of one accretion.

The sedimentary architecture of fan deltas, which commonly constitute reservoirs, is a primary control on distribution and recovery efficiency of oil and gas. Deep-water fan deltas have been extensively discussed in the literature, whereas the sedimentary architecture of shallow-water fan-delta fronts, especially the characterization of mouth bar, quantification of architectural elements, and factors controlling the various architectural elements, remain poorly understood. Here, based on the integration of field survey and unmanned aerial vehicle (UAV) observation, the sedimentary architecture of Sangyuan section of the Lower Cretaceous Xiguayuan Formation in the Luanping Basin to is qualitatively and quantitatively characterized. Furthermore, factors controlling the architecture of the shallow-water fan-delta front are highlighted. Five facies associations, which differ in both lithofacies and dimensions, were interpreted in gravel-sand deposits of Sangyuan section, and indicate variations in flow conditions during deposition. The width/thickness ratio of facies associations generally increases rapidly as the flow energy and flow concentration decreases from debris flow to traction currents during the evolution of shallow-water fan delta. Both distributary channels and mouth bars dominate facies associations in the shallow-water fan-delta front, accounting for 53.42% and 36.88% of gravel-sand deposits respectively in Sangyuan section. Mouth bar consists of gravel accretions and sand accretions. Grain size of sediments influences the relative strength of the inertial force and bed friction, which determine the effluent behavior in a river-mouth system and the vertical grain-size trend of mouth bar accretions. Gravel accretions are characterized by normal grading, and these are interpreted as the products of inertia-dominated effluent. Sand accretions exhibit coarsening-upward trends in the river-mouth systems where friction-dominated outflow occurred. The overall vertical grain-size trend of mouth bar depends on the stacking pattern of accretions rather than the grading of one accretion. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Sedimentological Society of Japan / Taisekigaku Kenkyu is the property of Sedimentological Society of Japan and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An estuarine turbidity maximum (ETM) functions as a filter and plays a key role in transporting suspended sediment. The features of ETM and their formation mechanisms vary with different types of estuaries. Their responses to morphological factors require further study. In this study, the Modaomen Estuary of the Pearl River was selected to examine the formation mechanisms of the ETM and roles of the mouth bar. Hydrodynamics, suspended sediment concentration, and sediment size distribution were measured via cruise shipboard in the mouth bar zone during the dry season of 2020, which indicated that the ETM occurred in the central and western bars. Furthermore, numerical modeling of an idealized estuary based on Delft3D was performed to explore the effects of the existence of a mouth bar on the dynamic structures causing the ETM, including saltwater intrusion, residual longitudinal circulation, and bed sediment resuspension. The results indicated that the existence of a mouth bar contributed to the occurrence of double residual circulations and enhanced bed shear stress on the mouth bar, which favor the ETM formation. In general, two different dynamic regimes were responsible for the ETM formation, that is, sediment trapping by saltwater intrusion and sediment resuspension induced by tidal currents. The mouth bar played a key role in these two mechanisms, including altering the estuarine circulation and bed shear stress. The results contribute to a better elucidation of the ETM formation in estuaries and provide scientific guidelines for estuarine management and engineering. Plain Language Summary: In estuaries, sediment can accumulate forming a sediment‐rich zone with high suspended sediment concentration. The occurrence and distribution of sediment‐rich zones affect water quality and ecological systems in estuary, as well as dredging and shipping needs, which has attracted significant interests of scientists and engineers. We have conducted a field survey to investigate the locations of the sediment‐rich zone and their causes. And we find that high sediment concentration mainly occurs on a shallow depth zone in estuary, which is caused by saltwater intrusion and sediment resuspension. Furthermore, we use a computer model to explore the roles of shallow topography on the accumulation of massive sediment. The results indicate that the shallow topography enhances the impacts of saltwater intrusion and sediment resuspension on sediment accumulation, favoring the occurrence of sediment‐rich zones. These findings have important scientific implications for estuarine management and engineering efforts. Key Points: Formation of turbidity maximum in different mouth bar zones was caused by estuarine circulation and sediment resuspension varying with timeSill topography favored the formation of double estuarine circulation and subsequently trapped sediment on the mouth barExistence of mouth bar enlarged the bed shear stress and then strengthened sediment resuspension caused by tidal current scouring [ABSTRACT FROM AUTHOR]

In the past two decades, the dynamic sedimentation process of the Yangtze Estuary has been seriously disturbed by coupled human interventions from the river basin to the estuary, especially the impoundment of the Three Gorges Dam in 2003 and the large-scale Deep-water Navigational Channel (DNC) regulation project in 1998–2010. This study investigated the changes in sedimentary dynamic and geomorphological processes in the turbidity maximum zone (TMZ) by analyzing the historical and present data for current, salinity, suspended sediment, and bathymetry. The results show that the decreased riverine sediment input caused a lagging decrease in suspended sediment concentration in the TMZ during the flood seasons. The DNC caused changes in the flow structure, sediment transport, and geometry of the TMZ in the North Passage (NP) and the South Passage (SP). In the NP, decreased ebb transport in the upper reaches led to landward migration of the TMZ during low discharges, while increased ebb transport in the middle and lower reaches caused the seaward migration of the TMZ during high discharges. As the associated topography of the TMZ, the mouth bar in the NP was mostly removed by channel dredging. However, rapid deposition at the location of the previous mouth bar indicates the formation of an incipient bar. In the SP, increased ebb transport after the DNC-induced disappearance of the TMZ and the mouth bar in the upper reaches and the seaward migration of the TMZ in the middle and lower reaches. Therefore, we found that the construction of dams and large-scale estuarine projects changed the sediment dynamics and geomorphological processes of the TMZ and even affected the long-term evolution of the estuary. Construction regulation projects in the TMZ, intended to narrow the cross-section and enhance seaward sediment transport, may produce the opposite effect. Before and after engineering projects, their impacts on estuarine processes need to be carefully estimated. [ABSTRACT FROM AUTHOR]

Abstract Mouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings.

Abstract Modern and ancient analogues are often consulted by geologists to help understand subsurface systems. While modern analogues provide information on the areal relationship between facies, ancient systems provide detailed data on the vertical facies variations, typically along a two‐dimensional outcrop. Combining data from modern and ancient systems effectively requires translating areal morphology, which is often still evolving, to the related sediments preserved in three dimensions. Process‐based models simulate both depositional processes while preserving stratigraphy. These models can be employed to unravel the relationship between sediment supply and preserved deposits in natural systems and to help integrate field data. Four synthetic deltas were modelled using different sediment supply compositions, from coarse to very fine sand systems. The resultant sedimentary deposits are classified into architectural elements, and the grain size composition of each architectural element is studied over time. Facies that are extensive in their horizontal dimensions are often less abundant in three‐dimensional preserved deposits. Between deltas, grain size compositions of a specific architectural element type (e.g. mouth bars) are more similar than their corresponding sediment supply compositions. This is due to selective deposition of grain size classes across each architectural element type. This selective deposition causes overrepresentation of the same range of grain sizes, even for systems with different sediment supply compositions. When a particular supply composition does not contain enough of the overrepresented grain size class for a particular architectural element, that element will be under‐supplied and constitute a smaller proportion of the overall delta deposits. It is imperative to account for over‐representation of grain size classes in particular architectural elements when estimating palaeo‐sediment supply, delta architecture and morphology from field data. Even when data availability/accessibility does not allow the inclusion of distal deposits in field studies, process‐based simulations can contribute valuable information on sediment sorting patterns in three dimensions.

Investigation of the process sedimentology of mouth bar deposition demonstrates a link to the seasonality associated with abrupt climate warming events during the early Eocene. While a relationship between fluvial sedimentology and climate events has been established previously, such documentation within mouth bar deposits is missing. Deltaic mouth bars of the Douglas Creek Member of the Green River Formation in the Uinta Basin record a fluvial–lacustrine response to abrupt warming events associated with the Early Eocene Climatic Optimum. This study ties the observed sedimentology of these mouth bars and their deposition via hyperpycnal currents to these climatic events. Detailed measured sections and analysis of stratigraphic architecture of outcrops in the eastern Uinta Basin document the sedimentology and stratigraphy of delta mouth bar complexes. Internal structures include climbing ripple cross‐lamination, convolute bedding, and those associated with transitional to upper‐flow regime bedforms such as planar laminations with normal grading and convex‐upward stratifications. The dominance of upper‐flow regime bedforms as well as interpreted long run out distances suggests that density currents deposited mouth bars tens of kilometres from the shoreline under Froude supercritical flow conditions. The highly seasonal climate regime of the early Eocene, capable of producing high‐sediment yield flooding events, likely provided the mechanism for hyperpycnal current formation within a relatively freshwater lake and controlled the timing of mouth bar deposition. Discrete lacustrine carbonate‐dominated packages separate periods of episodic fluvial discharge, recording reduced fluvial deposition between warming events. The established link between the occurrence of upper‐flow regime bedforms and the timing of climate warming events suggests that these climate conditions may be important for their formation and preservation. The study has implications for expanding existing mouth bar depositional models to include climatically controlled upper‐flow regime bedforms. [ABSTRACT FROM AUTHOR]

Improved understanding of mouth bar morphodynamics, and the resulting stratigraphic architectures, is important for predicting the loci of deposition of different sediment fractions, coastal geomorphic change and heterogeneity in mouth bar reservoirs. Facies and architectural analysis of exceptionally well‐exposed shallow water (ca 5 m depth) mouth bars and associated distributaries, from the Xert Formation (Lower Cretaceous), of the Maestrat Basin (east‐central Spain), reveal that they grew via a succession of repeated autogenic cycles. An initial mouth bar accretion element forms after avulsion of a distributary into shallow standing water. Turbulent expansion of the fluvial jet and high bed friction results in rapid flow deceleration, and deposition of sediment in an aggradational to expansional bar‐form. Vertical bar growth causes flattening and acceleration of the jet. The accelerated flow scours channels on the bar top, which focuses further expansion of the mouth bar at individual loci where the channels break through the front of the mouth bar. Here, new mouth bar accretion elements form, downlapping and onlapping against a readily recognizable surface of mouth bar reorganization. Vertical growth of the new mouth bar accretion elements causes flattening and re‐acceleration of the jet, leading to channelization, and initiation of the next generation of mouth bar accretion elements. Thus the mouth bar grows, until bed‐friction effects cause backwater deceleration and super‐elevation of flow in the feeding distributary. Within‐channel sedimentation, choking and upstream avulsion of the feeding channel, results in mouth bar abandonment. In this study, mouth bars are formed of at least two to three accretion elements, before abandonment happened. The results of this study contrast with the notion that mouth bars form by simple vertical aggradation and radial expansion. However the architecture and facies distributions of shallow water mouth bars are a predictable product of intrinsic processes that operate to deposit them. [ABSTRACT FROM AUTHOR]

In the past two decades, the dynamic sedimentation process of the Yangtze Estuary has been seriously disturbed by coupled human interventions from the river basin to the estuary, especially the impoundment of the Three Gorges Dam in 2003 and the large-scale Deep-water Navigational Channel (DNC) regulation project in 1998–2010. This study investigated the changes in sedimentary dynamic and geomorphological processes in the turbidity maximum zone (TMZ) by analyzing the historical and present data for current, salinity, suspended sediment, and bathymetry. The results show that the decreased riverine sediment input caused a lagging decrease in suspended sediment concentration in the TMZ during the flood seasons. The DNC caused changes in the flow structure, sediment transport, and geometry of the TMZ in the North Passage (NP) and the South Passage (SP). In the NP, decreased ebb transport in the upper reaches led to landward migration of the TMZ during low discharges, while increased ebb transport in the middle and lower reaches caused the seaward migration of the TMZ during high discharges. As the associated topography of the TMZ, the mouth bar in the NP was mostly removed by channel dredging. However, rapid deposition at the location of the previous mouth bar indicates the formation of an incipient bar. In the SP, increased ebb transport after the DNC-induced disappearance of the TMZ and the mouth bar in the upper reaches and the seaward migration of the TMZ in the middle and lower reaches. Therefore, we found that the construction of dams and large-scale estuarine projects changed the sediment dynamics and geomorphological processes of the TMZ and even affected the long-term evolution of the estuary. Construction regulation projects in the TMZ, intended to narrow the cross-section and enhance seaward sediment transport, may produce the opposite effect. Before and after engineering projects, their impacts on estuarine processes need to be carefully estimated.

River plumes are an important component of estuarine circulation and have a vital role in the transport of estuarine material and momentum balance. However, little information is available on the influence of mouth bars on estuarine plumes. To address this, momentum balance analysis was carried out using the ocean numerical model, to analyze the dynamic characteristics of the Pearl River plumes. The results show that the Pearl River plumes may be divided into three dynamic regions: near-, mid-, and far-field region. In the near-field region are dominated by pressure gradient force, bottom pressure forcing, and horizontal advection, which are obviously affected by river mouth bar. The mid-field momentum balance indicates seasonal differences, while the Coriolis force, pressure gradient force, and horizontal advection have great contribution to momentums in flood season, and in the dry season, momentum is balanced by the Coriolis force, pressure gradient force, and bottom pressure forcing. The momentum balance in the far-field region is determined by the Coriolis force, pressure gradient force, and surface pressure forcing. The internal hydraulic jump can be detected around the mouth bar when the hydrodynamic condition transitions from supercritical to subcritical, which has a close relationship with the local topographic structures. Internal estuarine waves may be further generated with interaction of tide and stratified flows around the river mouth bar. [ABSTRACT FROM AUTHOR]

Mouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings. [ABSTRACT FROM AUTHOR]

Modern and ancient analogues are often consulted by geologists to help understand subsurface systems. While modern analogues provide information on the areal relationship between facies, ancient systems provide detailed data on the vertical facies variations, typically along a two‐dimensional outcrop. Combining data from modern and ancient systems effectively requires translating areal morphology, which is often still evolving, to the related sediments preserved in three dimensions. Process‐based models simulate both depositional processes while preserving stratigraphy. These models can be employed to unravel the relationship between sediment supply and preserved deposits in natural systems and to help integrate field data. Four synthetic deltas were modelled using different sediment supply compositions, from coarse to very fine sand systems. The resultant sedimentary deposits are classified into architectural elements, and the grain size composition of each architectural element is studied over time. Facies that are extensive in their horizontal dimensions are often less abundant in three‐dimensional preserved deposits. Between deltas, grain size compositions of a specific architectural element type (e.g. mouth bars) are more similar than their corresponding sediment supply compositions. This is due to selective deposition of grain size classes across each architectural element type. This selective deposition causes overrepresentation of the same range of grain sizes, even for systems with different sediment supply compositions. When a particular supply composition does not contain enough of the overrepresented grain size class for a particular architectural element, that element will be under‐supplied and constitute a smaller proportion of the overall delta deposits. It is imperative to account for over‐representation of grain size classes in particular architectural elements when estimating palaeo‐sediment supply, delta architecture and morphology from field data. Even when data availability/accessibility does not allow the inclusion of distal deposits in field studies, process‐based simulations can contribute valuable information on sediment sorting patterns in three dimensions. [ABSTRACT FROM AUTHOR]

Abstract Integration of the geological context, core analysis, and petrographic investigation, together with data from wireline logs, resulted in the recognition of petrofacies types and the representation of facies models characterizing the X–XII sand groups of the K2 qn 3 Formation in the Daqingzijing area of the Songliao Basin, China. The results show that the lithology of the reservoir’s X–XII sand groups includes shale calcium-bearing siltstone and sandstone, calcareous siltstone and silty sandstone. The petrofacies consist mainly of quartz, feldspar and rock fragments cemented by clay, and some samples include calcite. The studied interval was deposited onto a delta front. Four types of petrofacies were recognized: subaqueous distributary channel, mouth bar, distal bar and subaqueous interdistributary bay. According to background investigation, the study area’s X–XII sand groups have experienced a large-scale decline in lake level. There are many subaqueous distributary channels in layers 36–40, while other layers were mainly deposited in a subaqueous interdistributary bay.

Copyright of Special Oil & Gas Reservoirs is the property of Special Oil & Gas Reservoirs Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Tidal asymmetry (i.e., unequal ebb and flood intensities and durations) is a dominant factor in the dynamic equilibrium of current-related sediment transport in estuaries. The evolution of estuarine tides and sediment transport is of great importance to the development and utilization of channels in estuaries. Based on field hydrological and sedimentological data collected over multiple years, the hydrodynamic characteristics, suspended sediment concentration (SSC) and grain size, and median grain size of seabed sediments were analyzed to investigate the effects of the construction of a water–sediment regulation scheme (WSRS) in the Sheyang Estuary in China. Our results showed that small grain sizes (fine sand, silt, and clay) dominated and that suspension was the dominant transport mechanism in the area where tidal asymmetry was greatest. Tidal distortion occurred due to the construction of the WSRS. In this flood-dominant system (i.e., before and after the construction of phase I of the WSRS), the flood current velocity was significantly greater than the ebb current velocity, while it also had a shorter duration that caused higher SSCs during the flood current. This likely induced net sediment import to the estuary, which was the main cause of estuary infilling. Furthermore, the net transport of sediment into the estuary caused by the high flood current velocities resulted in the gradual deposition of sediments in the shipping channel of Sheyang Port. Ebb-dominant conditions (i.e., after the construction of phase II of the WSRS) induced net sediment export from the estuary, and sedimentation was significantly reduced. Since the ebb–flood current velocity ratio (R v) and ebb–flood mean SSC ratio (R s) could reflect tidal asymmetry and the direction of residual sediment transport with and without the WSRSs, they were used as important and sensitive indices to investigate hydraulic and sedimentological conditions. Results from this study can be used to improve the monitoring and management of navigation channels by providing insights into new methods of preventing or reducing sediment deposition in estuarine channels (i.e., by employing R v and R s). Highlights • A water–sediment regulation scheme (WSRS) in the Sheyang Estuary was evaluated. • Tidal asymmetry and channel infilling worsened with phase I of WSRS construction. • Overtopping flow and backflow near jetties caused the enhanced asymmetry. • Lengthening and raising of the jetties (phase II) resolved channel infilling. • WSRSs are effective for controlling sediment deposition in shipping channels. [ABSTRACT FROM AUTHOR]

Abstract Mouth bars are important morphological units in deltaic and estuarine systems, which have encountered with significant topography variations driven by anthropogenic interferences and natural forcings. On the basis of seven selected maritime charts covering from 1960s to 2016, we focus on the morphological evolution of mouth bar with bifurcating channels in the Modaomen Estuary, the main fluvially-dominated estuary of the Pearl River Delta. The bar area is relatively in equilibrium with barely aggregation and degradation before 1990 while overall erosion was found thereafter. Sediment volume of the mouth bar between the −2 m and −7 m isobaths drastically decreased after 1990s. Correspondingly, the area of −4 m isobaths of the bar stepwise decreased from about 18 × 106 m2 to 2 × 106 m2, indicating the body of mouth bar above −4 m almost disappeared. The two side channels also suffered significantly morphological evolution. The West Channel (WC) was subjected to uninterrupted erosion. Especially during 2000–2005, the WC below the −2 m isobath experienced remarkable erosion with the increment of water volume reaching 6.7 × 106 m3. The East Channel (EC) had the potential to expand seaward between 2000 and 2011 yet encountered with accumulation after 2011. Meanwhile, the thalweg of the EC seemed hard to distinguish and the WC displayed more meandering thalweg. Furthermore, Empirical Orthogonal Function was applied to quantify the bathymetric changes with independent modes. The temporal variations of fluvial sediment input displayed significant decreasing trend at MK from 1960 to 2014, which presented a statistically significant relationship with the third mode. However, it only accounts for 13.4% of the overall evolution patterns. Although the remarkable reduction of sediment input generally associates with the degradation in bar area, the sediment load is probably not the primary mechanisms driving morphological changes in the Modaomen Estuary. Anthropogenic interferences including large-scale reclamation and intensive sand excavation should be responsible for the morphological changes. Highlights • Three major evolution patterns of mouth bar are distinguished by Empirical Orthogonal Function analysis. • The phase difference of flow between two distributaries relates with the erosion in the West Channel. • Morphological changes should be more attributed to anthropogenic disturbances rather than fluvial sediment source. [ABSTRACT FROM AUTHOR]

Integration of the geological context, core analysis, and petrographic investigation, together with data from wireline logs, resulted in the recognition of petrofacies types and the representation of facies models characterizing the X-XII sand groups of the K2qn3 Formation in the Daqingzijing area of the Songliao Basin, China. The results show that the lithology of the reservoir’s X-XII sand groups includes shale calcium-bearing siltstone and sandstone, calcareous siltstone and silty sandstone. The petrofacies consist mainly of quartz, feldspar and rock fragments cemented by clay, and some samples include calcite. The studied interval was deposited onto a delta front. Four types of petrofacies were recognized: subaqueous distributary channel, mouth bar, distal bar and subaqueous interdistributary bay. According to background investigation, the study area’s X-XII sand groups have experienced a large-scale decline in lake level. There are many subaqueous distributary channels in layers 36-40, while other layers were mainly deposited in a subaqueous interdistributary bay. [ABSTRACT FROM AUTHOR]

ABSTRACT Shim, W.J. and Kim, C.W., 2018. The necessity of coastal management in Busan Considering human and natural conditions: The case of barrier islands in Nakdong-estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp.1501–1505. Coconut Creek (Florida), ISSN 0749-0208. The Busan coasts have complex natural and human conditions including dynamic coastal, river processes and human activities. These complex natural and human factors have had direct and indirect impacts on the coastal areas of Busan, so a spatially integrated approach for management is required. Especially, the barrier islands located in the Nakdong River estuary are proper examples that show the effect of the sediment budget as natural and human conditions. This research aims to identify the effects of natural and human conditions on the barrier islands. The area of the barrier islands, sediment budget from the watershed, the amount of dredging at Nakdong-Estuarine-Dam and land use coverage were compared using correlation analysis. The more sediment eroded from watershed and the less sediment was dredged at Nakdong-Estuarine-Dam, the larger area of the barrier islands. This indicates that boundary conditions such as the supply of sediment from the rivers are related to the barrier islands; thus river and watershed management are important. Regarding land use, used and barren areas are positively correlated with the barrier islands, but water, forests and agricultural lands are negatively correlated. Internal factors within Busan, such as coastal modifications and urban growth, are affecting coastal dynamics, which change the sediment budget. These results show that the barrier islands sensitively respond to boundary conditions from the river and watershed and to internal conditions such as shoreline management and development. Therefore, for the effective management of Busan's coasts, it is necessary to consider how natural and human conditions interact spatially. [ABSTRACT FROM AUTHOR]

The geomorphology of the Yangtze Estuary in the Changjiang River Delta in Eastern China has been the subject of extensive research. This study extends previous work to examine the influence of wind-waves on the mouth-bar, where about half of the river-borne material settles to the bed. The site is located just outside of Changjiang River mouth, which is meso-tidal and subject to seasonally varying river flows and wind-wave conditions. Modeling was performed with a coupled wave-current hydrodynamic model using TELEMAC and TOMAWAC and validated against observed data. Bottom Shear Stress (BSS) from river, tide and waves based on the numerical model output was used to infer the respective contribution to the evolution of the subaqueous delta. Our examination did not however extend to modeling the sediment transport or the morphological bed changes. The results suggest that (i) the dominance of river discharge is limited to an area inside the mouth, while outside, the mouth-bar is tide-wave dominant; (ii) considering just the tide, the currents on the shallow shoals are flood dominant and deep channels are ebb dominant, which induces continued accretion over the shallows and erodes the deeper parts of the mouth-bar until the tidal currents become too weak to transport sediment; (iii) whereas waves are very efficient at reshaping the shallow shoals, with the effect being subtly dependent on the depth distribution over the mouth-bar; (iv) the stability of shallow shoal morphology is highly dependent on the presence of seasonal wind-waves and characterized as “summer storing and winter erosion”, while deep channels perform like corridors of water and sediment, exporting sediment all year round. The nature of the mouth-bar response has important implications for coastal management, such as the ongoing deep water channel maintenance, reclamations and coastal defense measures. [ABSTRACT FROM AUTHOR]

Abstract: Island formation and distributary channel branching are important processes in prograding river deltas. We develop and test a new theory predicting the distance to islands and channel bifurcations based on fluid mass conservation and radially symmetric transport conditions. We analyze channelization and island formation using nine new and five existing delta experiments as well as four field deltas. The new experiments were designed to produce islands from initial deposition of a mouth bar. Before island formation, each bar evolved into a radially symmetric deposit with unchannelized flow over its top previously described as a topographic flow expansion. This morphology was stable to topographic perturbations, and its distal limit prograded basinward while maintaining a characteristic flow depth. Island formation and channel branching occurred on top of this deposit. We hypothesize that this distance (Ψ) is set by the location where boundary shear stress applied by expanding, radially averaged flow falls below the threshold of sediment motion. The model predicts that the distance to the first island scales with water discharge, scales inversely with flow depth, and scales with the inverse square root of median grain diameter. From experiment to field scales, distances to island locations are predicted within a factor of two. [ABSTRACT FROM AUTHOR]

This study evaluates the evolution of a small-scale growth fault within a deltaic parasequence of the Ferron Sandstone, Utah. Analysis is based on 4 stratigraphic logs, and a panorama covering 100 m of lateral exposure. Five growth-fault blocks are displayed in strike and dip views. The listric faults dip basinward, and sole out into bedding parallel decollement surfaces associated with deformed prodelta shales, which also form diapirs. Throw on individual faults averages 4 m and heave increases with depth from ∼2.5 to ∼5 m. Strikes on fault planes average 160°, and fault dip decreases with depth from 50° to 0°, where they become parallel to bedding. Pre-growth facies comprise heterolithics with abundant graded beds, current-ripples, wave-ripples, small-scale soft sediment deformation, and a low bioturbation index. This indicates deposition in a river-dominated, storm-influenced delta that was supplied primarily by storm-triggered flood events and prograded rapidly. Growth strata are primarily planar and quasi-planar fine sandstones deposited as upstream and downstream accreting mouth bars. Faulting initiates with the building of a “critical load” reflecting a low-angle delta front foreset, probably linked to deposition in a mouth bar. Mobile prodelta muds form diapirs that breached the sediment-water interface, providing accommodation for the fault blocks. Termination of faulting occurred when sandy growth strata contacted and locked into higher strength pre-growth heterolithics deeper in the section. Minor deformation of growth strata is demonstrated by synthetic microfaulting in growth sands. This study emphasizes a localized stress field (i.e., point sourced) associated with sandy mouth bar deposits, which acted as fault initiation points. This contrasts with the distributed stress regimes commonly associated with regional-scale growth faults along continental margins. This can lead to expanded, but localized, reservoir compartments within river-dominated deltaic systems, especially those in epeiric seas or other shallow-water sedimentary basins, such as Prudhoe Bay Field, Alaska. [ABSTRACT FROM AUTHOR]

Shoal water deltaic sand bodies are widely deposited in lacustrine basins and serve as essential hydrocarbon reservoirs. The complex distribution patterns of such sand bodies present a challenge in the characterization and exploration of hydrocarbon reservoirs. Improving the understanding of jet plume deposits in ancient shoal water deltas could give new implication for reservoir characterization. Sedimentary facies of shoal water deltas were interpreted using high-resolution aerial photographs of the modern Ganjiang River delta and the ancient shoal water deltaic deposits in the Lower Cretaceous Quantou Formation, Songliao Basin. There are three jet plume-related sand bars between the multi-order distributary channel network in the Ganjiang River Delta. They are referred to as triangular-shaped bars, V-shaped bars, and diamond-shaped bars in this study. The V-shaped bar and diamond-shaped bar were also interpreted in the ancient deltaic deposits of the Songliao Basin. The jet plume related deposits experienced a river mouth stage under fully turbulent and expanding flow, followed by a fluvial-dominated stage during the progradation of the topset-dominated shoal-water deltas in geological history. The jet plume related sand bars in the lower delta plain were initially generated from the mouth bars in the delta front and were then incised by the fluvial processes during the delta progradation. Overall, knowledge of geometry and internal architecture of these jet plume related sand bars could provide new implication for characterization and prediction of ancient shoal-water deltaic reservoirs. • morphology of modern and ancient lacustrine shoal-water deltaic deposits. • ancient river mouth deposits influenced by jet plume. • deltaic sedimentary architecture controlled by jet plume and fluvial evolution. [ABSTRACT FROM AUTHOR]

After nearly 40 years exploration, the development of petroleum reservoir in Shangyi block of Shanghe oilfield, Huimin sag becomes much more difficult. In order to find the distribution of remaining oil, based on the abundant core and well logging data, the mouth bar reservoir in the third and the fourth sand groups of the second member of Shahejie Formation was analyzed for many aspects, including the grading system of architecture interfaces, the identification and characteristics of a single mouth bar and the vertical evolution law. The results show that the mouth bar reservoir can be classified into 5 grades architecture interfaces; the origin types of the fifth and fourth architecture interfaces are flood shale and argillaceous layers, respectively; the origin types of the third architecture interface are sedimentary with poor physical properties and diagenetic calcareous sandstone, and can be further subdivided into shale interlayer, calcareous interlayer and transitional interlayer; the shale interlayer has more lateral continuity than the calcareous and transitional interlayers in the third architecture interface, and can extend for 300-800 m; along the progradation direction of mouth bar, the dip angle of interface in the slope break belt can up to 8°, while the dip angle is less than 2°in the flat terrain; along the vertical provenance direction of sandbody, the dip angle of interface is generally below 1.5°; four identification marks recognizing lateral boundary of single mouth bar include that the top surface altitude difference of reservoir, the appearance of interval zone of mouth bar deposits, the fringe of two mouth bars overlapping each other and the existing difference from curves and deposition thickness of sandbody; the fluctuation of base level controls the superimposed relationship of sandbody, and determines the deposition thickness of mouth bar sandbody and the physical characteristics of reservoir. This results have an important significance in guiding prediction of the remaining oil’s distribution in Shanghe oilfield and other similar oilfields. [ABSTRACT FROM AUTHOR]

• The mouth bar's effect on salt intrusion in a partially mixed estuary is examined. • The mouth bar decreases the salt intrusion more in spring tide than in neap tide. • The mouth bar has greater effects on decreasing salt intrusion with wind and waves. • Hydraulic processes around the mouth bar enhances the tidal oscillatory transport. • The mouth bar has a greater effect under higher flow condition. The mouth bar is a common morphological unit in the river delta system. Its formation and evolution impose an impact on the material exchange between the estuary and ocean. Here we used an advanced wave-current coupled modeling system in an idealized estuary, with a prototype of the Modaomen estuary, China, to study the effects of the mouth bar on salt intrusion and the associated salt transport. The model results indicate that the mouth bar has a substantial effect on weakening the salt intrusion under the action of river discharge and tides, leading to a decrease in the salt intrusion length of 15～23%. When a down-estuary wind and a landward propagating offshore wave were included in the model, the mouth bar can decrease the salt intrusion length up to 21%. The hydraulic control at the mouth bar, in a state of partially blocked with lee jump, can enhance landward salt transport through tidal pumping. These findings indicate that the mouth bar has an important control on the salt transport, and provides implications for salt intrusion mitigation and sand resource management. [ABSTRACT FROM AUTHOR]

Lots of petroleum exploration for braided river delta reservoirs has entered high water cut stage in China, but the study on reservoir architecture of braided river delta is few, so that it affects the potential of digging residual oil for this kind of reservoir. Taking the thick sandbody in the second member of Shahejie Formation of Yong8 fault block, Shengli oilfield as a research object, according to the cores, well logging, seismic and development data, the main interval was divided into compound sedimentary body of delta front with the limitation of the fifth surface and single sedimentary body of delta front with the limitation of the fourth surface by interbed. The single sedimentary body of delta front includes architecture elements such as underwater distributary channel, overbank sandbody of channel periphery, main mouth bar, periphery of mouth bar and interdistributary bay, etc. The boundary of sandbody and superimposed relationship were divided according to the difference of well logging curve, lateral change of sandbody thickness, argillaceous sediment between sandbodies, and the number difference of interbeds; the architecture style of single sedimentary body of braided river delta front both in plane and profile was confirmed; the basic process of layer-by-layer progradation for each architecture unit of single sedimentary body was explained; the characteristics of braided river delta in this block were discussed, including the channel being narrow, thin and straight, and the mouth bar being wide, thick and lateral. The width of mouth bar for braided river delta in the second member of Shahejie Formation of the block is 2.23-8.95 times of that of distributary channel, and the thickness is 1.25-2.50 times of that of the distributary channel. [ABSTRACT FROM AUTHOR]

In Yangtze Estuary, the ETM is always accompanied by a board shallow area (basically around 6 m water depth) in the mouth zone, called mouth bars. After more than 40 years study, North Passage was selected as the deep-draft navigation channel and the regulation works started in 1998. Extensive engineering works, consisting two long training dikes and 19 groins, are implemented to achieve deeper water depth with the help of dredging activities in the North Passage of the Yangtze Estuary. After Yangtze Estuary deepwater channel improvement project in 1998, in north passage mouth bar terrain disappear, but turbidity maximum zone is still persisting. At the same time, since the completion of the engineering works, high siltation appears in the middle segment of the North Passage. To fulfil the needs of navigation, the maintenance dredging amount is unexpectedly large which is inefficient economically. Studies through field data analysis before and after the project reveal the evolution models of North Passage on the Yangtze Estuary, as well as the impact to the deep water channel siltation. Three-dimensional models using Delft3D are developed and validated including density gradients and fine sediment transport to investigate the respective role of several processes on the turbidity maximum behavior in the Yangtze estuary. The main goal of this work is to reproduce the turbidity maximum in the model and to compare sensitivity of the turbidity maximum to different model parameters. The stydy also aim to explore consequences for morphodynamic development and to reveal the reasons of high siltation in the North Passage by the simulation of ETM of numerical modeling. [ABSTRACT FROM AUTHOR]

The historic Late Triassic outcrops at Fuchsberg and Langenberg near Seinstedt (Lower Saxony, Germany) are constrained to the Norian/Rhaetian boundary interval by means of conchostracan and palynomorph biostratigraphy. A comprehensive revision revealed a fluvial-dominated delta plain that formed in response to the successive transgression of the 'Rhaetian Sea' and received siliciclastics from southern source areas. At Fuchsberg and Langenberg, the distal lower delta plain is exposed and brackish subaqueous delta plain wetlands, mouthbar/distributary channel complexes and interdistributary bay subenvironments are reconstructed. Delta formation was controlled by bifurcation of distributary channels and avulsion of delta lobes. A diverse ecosystem is documented: a rich invertebrate fauna of limulids (1 taxon), insects (at least 20 taxa of 9 orders), malacostracans and conchostracans (several taxa) and a vertebrate fauna of amphibians (at least 1 taxon), sharks (9 taxa) and osteichthyan fishes (at least 6 taxa). In particular, fossiliferous interdistributary bay lithologies detail trophic systems of autochthonous subaqueous and parautochthonous riparian habitats. Abundant remnants of cycadophytes, ferns, horsetails and large vertebrates from Fuchsberg and adjacent outcrops of the Seinstedt area enable the reconstruction of vegetated upstream environments at the upper delta plain and floodplain. [ABSTRACT FROM AUTHOR]

Tătui, F., Vespremeanu-Stroe, A. and Preoteasa, L., 2013. The correlated behavior of sandbars and foredunes on a nontidal coast (Danube Delta, Romania) Coastal foredunes, shoreline and nearshore sandbars compose one large-scale interactive morphological system. Although the variability of these coastal features and their connection to environmental factors have been the focus of many analyses, the direct interactions between them are yet poorly identified, especially for natural nontidal coasts. This paper presents the preliminary results regarding the correlated behavior of the foredunes, shoreline and sandbars in a multi-bar, low-lying deltaic coastal zone, based on six years of seasonal bathymetric and topographic surveys. The analysis shows that, at the multiannual scale, there is a good correlation between the morphometric parameters (volumes and widths) and behaviour (spatial and temporal) of sandbars and foredunes, especially along the accumulative and stable sectors of the study area. Good correlation of these sectors is expressed by the fact that the two entities are interdependent and they present similar variability. The weak correlation identified along the erosive sector is probably due to the significantly lower variability of the foredunes when compared to that of the sandbars. This could reflect the strong influence of the Sf. Gheorghe mouth bar and the pattern of sediment availability, wave climate and longshore sediment transport characteristics along the three sectors of the study area with different shoreline dynamics. [ABSTRACT FROM AUTHOR]

The mouth bar in the Yangtze estuarine waterways has a significant influence on navigational transport within the estuary, flood discharge and construction of the Shanghai Port. In this paper the morphological evolution and mechanisms of mouth bar formation of the Yangtze estuarine waterways are studied by analyzing hundreds of years of historical data and the latest profile maps of some or the main mouth bar channels in the Yangtze Estuary. The results are shown as follows: The mouth bars in the North Branch have moved gradually from outside the mouth to the inside and formed a huge sand bar. In the North Channel, the head of the mouth bar has migrated about 30 kilometers downstream, and a channel bar has been developing since 2001. Two mouth bar tops, which always existed in the North Passage, disappeared in 2010. The head of the mouth bar in the South Passage has migrated downstream about 14 km and the number of tops increased at first but is reduced to only one now. According to the results, we can conclude that the evolution of the mouth bars differs depending on their location. In the North Branch it is directly related to large-scale reclamation in Chongming Island, but in the North Passage it has a close relationship with regulation of the Yangtze Estuary Deepwater Channel. However, the evolution of mouth bars in the North Channel and South Passage is not only connected with the Yangtze Estuary Deepwater Channel Regulation Project, but also with the reclamation in the East Hengsha Shoal and the closure of the Qingcaosha Reservoir. [ABSTRACT FROM AUTHOR]

The paper presents a 3D sedimentological characterization of a delta plain reservoir. The analysis started with detailed core description studies focusing on the genetic interpretations of the sedimentary structures and multivariate statistical analyses (including Q-mode cluster and R-mode factor analysis), of the sporadic grain-size distributions. These results made the depositional processes of channels, bar-crests and crevasse splays probable. By calibration of the well log responses to the cores with total core recovery, we were able to identify two types of vertical facies transitions: (1) mouth-bars and channels; (2) crevasse splays, crevasse channels and minor mouth bars. In addition, a vertical sequence of a relative thick distributary mouth bar was also recognized. Lateral extension was determined by contouring the sand content on surfaces parallel to the upper time horizon. On these surfaces, the sand content and porosity grid systems facilitated the use of an unconventional 3D geo-cellular modelling approach for both well-log porosities and sand contents. Since vertical depositional facies were extended into the 3D, rock bodies of the most characteristic channel and mouth bar environments could be cut out from the porosity and sand content models. In this way not only their general geometry and internal characteristics, but also the basic geostatistical features (ratio of anisotropy, the direction of major and minor continuity) of their sand content and porosity were identified. [ABSTRACT FROM AUTHOR]

The paper presents the Danube delta evolution during the Holocene with an emphasis on the last three centuries. Detailed descriptions of the physiographic evolution and depositional characteristics of the delta are given on the basis of detailed sedimentological and geomorphological studies. For the recent period (last three centuries) the physiographical changes are highlighted using the most interesting cartographic documents stored in different archives and libraries of European countries and the USA. The main documents used are: the maps of 1771 and 1778, the maps of 1856-1857 made by the Danube European Commission (HMSV Medina under the direction of Captain Spratt), the Austrian map of 1918, the Royal Navy Chart of 1926/1936, the German map of 1944, the Soviet map of 1983, the Romanian map of 1985, the British Sea Chart of 1999 and the most recent satellite images offered by Google (2004, 2006). Some conclusions on the delta development and on the hydrodynamic and sedimentological laws governing the processes in the delta area, especially at the distributary mouth zones and on the coastal area are given [ABSTRACT FROM AUTHOR]

Deposystems are complex and governed by discrete depo events with variable intervals of stasis or erosion in between. Since shoreface sediments indicate sea level, depo events of shoreline facies are discrete samples of sea level. Only if these samples are sufficiently regular and frequent will the shoreline trajectory in the space domain accurately reflect the sea-level curve in the time domain. This study presents a method to convert shoreline trajectory in the space domain to sea-level curve in the time domain from artificial miniature deltas. One obtains the depo sequence as function of time and uses it to: convert depo sequence from time-to space domain, correlate depo sequence to shoreline trajectory in the space domain, and convert shoreline trajectory from space-to time domain. For natural deltas one would extract the depo set in the frequency domain, i.e. the probability density function of stasis intervals between depo events from the experimental depo sequence and use it to: convert shoreline trajectory from space-to time domain, and infer a range of possible sea-level curves. This method therewith explicitly includes the uncertainty of the inferred sea-level curve. [ABSTRACT FROM AUTHOR]

Based on mass bathymetric data and remote sensing data in the Modaomen Estuary, this study explored the long-term evolutionary characteristics of the mouth bar in the Modaomen Estuary of the Pearl River from 1964 to 2019. In the past 55 years, due to the impact of human activities, such as shoal reclamation and estuarine regulation in the Modaomen Estuary, the river mouth moved out of the shallow sea covered by several islands and faced the South China Sea directly. Therefore, the mouth bay became a siltation center in the estuarine region and expanded outwards, gradually evolving a geomorphic pattern with three shallow shoals and two distributary branches; a west branch as the main branch accompanied by a small east branch. Over the past decade, high-intensity sand dredging activities in the mouth bar have led to a considerable deepening of the water depth and a significant refinement of bed sediments, forming a discharge pattern of a wide and shallow channel flowing into the sea. Therefore, the evolutionary characteristics of the mouth bar have become abnormal in recent years, so additional field bathymetric data and hydrological data are required for further research regarding the subsequent evolution of the mouth bar, against the background of a significant reduction of sediment discharge and high-intensity human activities. [ABSTRACT FROM AUTHOR]

Nuclear-magnetic resonance (NMR) measurements provide petrophysicists with porosity distributions that are lithology-independent. Forward modeling allows analyzing NMR, taking into account all data available. Based on the study of distributary bar system, we found that: (1) mouth bar facies studied are characterized by unimodal distribution of T2, "free-fluid" maximum at 20.0-40.0 ms and a "tail" associated with the chlorite coating and partially dissolved feldspar microporosity at 0.5-3.0 ms; (2) Delta front facies have bimodal distribution with maximums at ≈2.0 and ≈30.0 ms, a 4.8 ms and ≈65 ms cut-off values were established to define clay-bound and free-fluid volumes; and (3) Distal bar sands with calcite cementation have cut-offs of 12.0 ms and 90+ ms. To characterize delta front facies, an additional case has been modeled to illustrate the dependence of clay-bound water cut-off point upon mineralogy: (a) chlorite - mixed layer grain coating have ≈5.0 ms cut-off, and (b) kaolinte pore filling has a cut-off value of ≈20 ms. [ABSTRACT FROM AUTHOR]

By analysis of published papers on the Yangtze estuary and hydrological and sediments data in Yangshan Harbor area, many similarities are found between Yangshan Harbor area and the Yangtze estuary. These similarities include the phenomenon of stagnating flow areas, the distributive characteristics of the highest suspended sediment concentration areas, superficial sediments and shoal bars. The stagnating flow area is the major similarity which causes other similarities. These similarities indicate that: 1) Turbidity Maximum and mouth bars in estuaries are mainly caused by the hydraulic balance of stagnating flow areas of estuaries; 2) The stagnating sand area of sands caused by stagnating flow area often locates on the narrower side of the stagnating flow area; 3) The location (or shape) of fine sediments area caused by stagnating flow area reflects the location (or shape) of the stagnating flow area. Both Yangshan Harbor area and the Yangtze estuary are the important developmental areas in the future (man-made similarity). In-depth studies on these similarities between Yangshan Harbor area and the Yangtze estuary will have momentous theoretical and practical significance. [ABSTRACT FROM AUTHOR]

In situ data show that fluid mud of the Changjiang Estuary consists of fine sediment ranging from 8 to 11.5 μm (median grain-size) including 28.8%-36.4% of clay. The composition of the clay is illite, chlorite, kaolinite and montmoillonite. The FM is a layer of high sediment concentration near the bed and results from flocculation under the environment of salt and fresh water mixing. Three kinds of FM have been identified under typical dynamic conditions: the first one is formed at slack water of ebb tide during the flood season, with the characteristics of extended area and low thickness; the second one is formed following a storm, characterized by large area and larger thickness; the third one is formed around the front of the saltwater wedge, characterized by small area but large thickness. In the dredged channel, the FM can be accumulated up to 1 m thick. In general, FM will change with the alternation from spring to neap tides, flood and dry seasons. Drastic change can happen during storms. At the same time, the change of FM is closely related to the erosion and growth of the mouth bar. [ABSTRACT FROM AUTHOR]

We conducted, for the first time, a study of the long-term evolution of an inner mouth bar in a microtidal environment that complements field observations with detailed numerical modelling of the same morphodynamics. Images collected by a video-monitoring station, from 2016 to 2019, were processed to study the evolution of a persistent inner mouth bar formed inside the highly engineered Misa River estuary (Senigallia, Italy) after years of reduced precipitation and discharges. We developed a semi-automatic procedure to detect the emerged area of this deposit. We seek to quantify the relationship between the long-term evolution of the bar and the forcing from the river, waves and tides. The observed high peaks in river discharge caused a strong downriver bar migration (i.e. almost twice the river width). Conversely, the observed sea storms produced an upriver bar migration smaller than one river width. A much slower and weaker (less than half the river width) upriver migration was also observed during periods of large area accretion and due to mild wave climate. Moreover, results showed that the sea water level variation did not directly impact the morphodynamics of the estuary, affecting the emerged portion of the bar only. Numerical simulations, run with Delft3D, were used to complete the information coming from field observations. After some checks on the proper use of the solver for the scenarios and environments of interest, some parametric simulations were run to highlight the role of the different forcing on the bed evolution. Simulations showed, as expected, erosion of the riverbed and significant downriver migrations (four river widths) during peaks of river discharge comparable to the 1-year return period discharges. Numerical results also showed upriver sediment transport when the wave forcing was dominant, with 10-years return period waves inducing an upriver bar migration in the order of one river width. Then, one real-life event was simulated to inspect the interaction of the various forcing and to compare their effects with the observations. Our analysis provides new insight into the complex morphodynamics in a microtidal estuary when weak river discharge is opposed by sea waves driving upriver sediment transport. A more thorough understanding of the morphodynamics is needed for future forecasting of the formation and evolution of sediment deposits inside estuarine channels that can inhibit both navigation and the flux of sediment from the river to the estuary. • Detection of an inner bar at the mouth of a microtidal river from images acquired by a video-monitoring station. • Correlation of the bar area evolution and centre of mass migration with the estuarine forcings. • Field observations show the effect of different combinations of river flows and waves on the evolution of the bar. • Parametric simulations show that, at a given return period, the river discharge caused a larger bar migration than sea waves. • A real-life numerical simulation displays evolution behaviours in agreement with field observations. [ABSTRACT FROM AUTHOR]

The source, distribution, and potential toxicity of sedimentary polycyclic aromatic hydrocarbons (PAHs) along the mouth bar of the Yangtze River Estuary were investigated. Total concentrations of 17 PAHs in the study area ranged from 34.94 to 580.26 ng/g (mean value 146.31 ng/g). Results of PMF model revealed that mixed vehicle emissions (38.43%), natural gas combustion (24.98%), biomass combustion (20.76%) and coal combustion (15.83%) were sources of these sedimentary PAHs. The ERL/ERM, TEL/PEL and TEC/PEC values showed that the potential toxicity of PAHs was at low to medium level, but the presence of benzo[ a ]pyrene (BaP) and benzo[ e ]pyrene (BeP) requires more attention and research. Sedimentary PAHs pollution level in the three shoals (East Nanhui Shoal, Jiuduansha Shoal and Hengsha Shoal) was higher than that of the two passages (South Passage and North Passage), which demonstrates the possibility of restoration of the adjacent shoals by dredged soils in terms of PAHs pollution. Unlabelled Image • Sedimentary PAHs from mouth bar of studied estuary ranged from 34.94 to 580.26 ng/g. • PAHs studied were from mixed vehicle emission, natural gas and biomass combustion. • Sedimentary PAHs studied was at low to medium pollution level. • Sedimentary PAHs pollution of three shoals was higher than that of two passages. • Dredged soils of two passages have possibility to use for restoration of shoals. [ABSTRACT FROM AUTHOR]

Floods and storms are common phenomena at river mouths with some degree of wave influence. They can have a considerable impact on river-mouth sedimentation and morphological change, although studies elucidating this relationship are relatively rare. The present paper analyzes annual bathymetric changes based on surveys at the mouth of the Sfântu Gheorghe branch of the Danube river delta between 2004 and 2018, and relates bed changes with measured river freshwater and solid discharges, and wave height data. We found a strong inter-annual variability of morphological volume change which ranged from 5.23 × 106 m3 deposited during the extreme flood of 2006 (maximum discharge of ~4000 m3/s), to −6.88 × 106 m3 removed during the stormy year of 2012 (wave heights >6 m). The sediment budget of the river-mouth area is modulated by the inter-annual variability of storms and floods, and can be estimated by the newly proposed Flood/Storm index based on river water or sediment discharge and wave height proxies (R2 = 0.84). A selection of discharge and wave thresholds were simulated with Mike 21/3 by DHI (Danish Hydraulic Institute), a coupled hydrodynamic and wave model to characterize circulation and the applied bed shear stresses at this complex river-mouth sedimentary system. The model simulates 3D jet and plume hydrodynamics during floods, and the longshore current and wave dissipation during storms. Finally, field data are integrated with the Mike 21/3 model results to derive a conceptual hydro-morphodynamic model of an asymmetric wave influenced river-mouth bar during the two antagonistic phases of flood-driven and storm-driven dynamics. During floods, the importance of current circulation and counter- plume currents in trapping sediments in a seaward-thinning depositional wedge is discussed. During storms, the sediment deposited during floods is removed by the high bed shear stresses generated by waves and currents. Unlabelled Image • A conceptual model of the role of floods and storms in driving morphological change at the river mouth is presented. • During floods, a seaward-thinning depositional wedge forms (m to cm-scale), related to plume transport and sediment settling. • During storms, high bed shear stresses generated by currents and waves remove the sediment deposited during floods. • The new FL/ST index based on flood and storm thresholds explains the sediment budget variability at the Sf. Gheorghe mouth. • A linear response in bathymetric change was found in relation to the relative influence of floods and storms. [ABSTRACT FROM AUTHOR]

The Pearl River Delta (PRD) is one of the most economically important and urbanized deltas in Asia. The Modaomen Estuary, being the most important passage of water and sediment through the PRD into the sea, was regulated by estuarine reclamation since the mid-1980s. After the completion of regulation projects in the 1990s, it was transformed from a shallow bay into a series of regulated channels. As a result, the evolution of the mouth bar of the Modaomen Estuary, a key morphological unit determining delta formation, has been altered. In this study, we examine morphological responses of the mouth bar of the Modaomen Estuary to human activities and natural factors (i.e., riverine flood) from 1994 to 2010. As an effect of the estuarine extension towards the sea caused by the regulation projects, the mouth bar has gradually moved towards the sea. From 1994 to 2010, for instance, the west and east branches extended more than 2.1 km further seawards. In addition, flood scouring played an important role in the bar extension and the formation of secondary branches at the mouth bar. Furthermore, the front of the mouth bar was eroded by wave dynamics because of reductions in the sediment load from the Pearl River. In general, the mouth bar deflected southwestward after 1994, indicating an evolution of the sediment sink at the Modaomen estuary in the same direction. Our studies contribute to better understanding of the evolution of large estuaries and provide scientific guidelines for the sustainable management of the PRD. • The evolution of mouth bar in the Modaomen estuary was examined since 1994. • The regulation projects resulted the rapid extension of the mouth bar. • Flood scouring played a key role in the formation and extension of the branch. • Sediment sinks in the Modaomen estuary have deflected towards the southwest. [ABSTRACT FROM AUTHOR]