River Mouth Bar Research Articles

Simulation of Tsunami Runup in the Tone River Using Generalized Coordinate System and Influence of River Mouth Bar on Tsunami Water Level

ABSTRACT Nikaido, R.; Aoki, S.; Tamura, H., and Jinbo, M., 2016. Simulation of tsunami runup in the Tone River using generalized coordinate system and influence of river mouth bar on tsunami water level. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 28 - 32. Coconut Creek (Florida), ISSN 0749-0208. This study simulated the tsunami runup in the Tone River using generalized coordinate system and discussed influence of river mouth bar on tsunami water level. This simulation focused on the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami. Numerical simulation of the 2011 Tsunami runup in the Tone River and comparison of the results with the field data showed that the model using generalized coordinate system gave more accurate results than the model using the Cartesian coordinate system. This may be because the configuration of the curved riv...

Applicability of 3D Beach Evolution Model with Wave-current Interaction to River-mouth Bar Formation

ABSTRACT Kuroiwa, M.; Shibutani, Y.; Yasumoto,; Mase, H, and Matsubara, Y., 2016. Applicability of 3D beach evolution model with wave-current interaction to river-mouth bar formation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 73–77. Coconut Creek (Florida), ISSN 0749-0208. A coastal area model with wave-current interaction was presented, and then the performance and applicability of the numerical to morphodynamics around river mouths due to waves, wave-induced currents and river flows were investigated. First, model tests were carried out under a variety of wave and river discharge conditions to investigate their capability of predicting the formation of sand spit and terrace topographies. Second, model verification using a field site was conducted and the applicability was investigated. From the computed results, it was confirmed that the p...

A Re-evaluation of the Depositional Environments and Sedimentary Facies of Middle Miocene Paralic Deposits (Agbada Formation), Ewan and Oloye Fields, Northwestern Niger Delta

This study analyses depositional environments and facies of the middle Miocene (Agbada Formation), northwestern Niger delta, based on cores and well log data, and incorporating ichonological data, that has led to a revision and re-evaluation of the facies within the study area. Log motif analysis, calibrated by lithology descriptions based on core photos, was used to define log facies associations and to identify stacking patterns and key surfaces. Six main wireline log facies associations have been recognized using gamma ray log motifs calibrated with core. Within the cored interval two lithofacies associations have also been identified, based on composition, colour, sedimentary structures, and ichnofabric. They are: slope channel sand and shoreface sequences. The interpreted depositional facies model suggests an extensive development of marine dominated slope channel fill and shoreface deposits in the northwestern part of the delta. This suggests that in the studied area, the coastal barrier complex contains a large amount of sand that was originally deposited in river mouth bars, but was laterally removed by longshore current and re-deposited on the shoreline margin and basin ward through developed of canyons on the slope which serves as feeders and conducts for slope and basin fans. The descriptive framework for the ichnofabrics analysis is based on bioturbation index (degree of bioturbation), burrow size, burrow frequency and ichonological diversity. Six ichnofabrics are recognized within the core namely: Planolites-Teichnichnus, Planolites-Phoebichnus, Planolites, Planolites-Thalassinoides, Teichichnus-PhoebichnusPlanolites and Palaeophycus-Planolites ichnofabrics. Observed tiering patterns are both simple and complex, which may reflect gradual aggradation or degradation of the substrate leading to overprinting as a stable ichnofauna structure develops. This type of tiering arrangement indicates a stable environment. The ichnofabrics are named after the dominant trace observed. Sedimentological analyses indicated that the depositional environments range from inner shelf to offshore.

Siliciclastic–carbonate mixing modes in the river-mouth bar palaeogeography of the Upper Cretaceous Garudamangalam Sandstone (Ariyalur, India)

Mixed siliciclastic–carbonate rocks constitute the Upper Cretaceous Garuda-mangalam Sandstone Formation, Ariyalur (India), and offer an opportunity to look into the broad spectrum of mixing of compositionally and genetically different components. The palaeogeographic reconstruction indicates that deposition in the nearshore zone differed strongly in energy and active processes operatives due to the presence of a shore-parallel river-mouth bar. The western wing of the Mississippi bird-foot delta is considered to be a present-day analogon. Facies analysis in combination with petrography clearly shows the variability in palaeoenvironmental characteristics, both biogenic and non-biogenic. It also indicates diagenetic uptake of carbonate that filled empty spaces and actively replaced original components. Chemical staining followed by limited application of cathodoluminescence and energy dispersive X-ray analysis (EDAX) hint at intricacies in mixing arising from the compositional variations in the carbonate components. A model of siliciclastic–carbonate sediment mixing, including both the depositional and diagenetic developments, is presented; it is aimed at generating a better overview of, and a deeper insight into, the physical and chemical mechanisms involved.

The evolution of an asymmetric deltaic lobe (Sf. Gheorghe, Danube) in association with cyclic development of the river-mouth bar: Long-term pattern and present adaptations to human-induced sediment depletion

The asymmetric Sf. Gheorghe lobe is the only active lobe in the Danube delta associated with a river-mouth bar (and related barrier islands and spits) that has continuously displayed cyclic development during the last 1500years. During the early cycles, the Sf. Gheorghe distributary experienced a significant increase in sediment load (by an order of magnitude) as a result of the successive avulsions occurred 1.5–1.2ka, which redistributed more water and sediment captured from the neighboring branches of Împuţita (southern distributary of the Sulina arm) and Dunavăţ. Morphological and sedimentological analyses together with a newly obtained chronology throw light on the multiple ridgeset (10) structure of Sf. Gheorghe lobe, each of them (excepting the first one) following a common evolutionary pattern reflected by the cyclic succession of the recurring stages: i) subaqueous mouth bar building, ii) barrier island emergence, and iii) transformation into a barrier spit with several secondary spits. The spits become encased into the muddy deltaic plain as narrow sandy ridges building out on the downdrift side of the lobe as a barrier-marsh plain, whereas the updrift side constantly accreted fed by longshore currents, forming a classic beach ridge plain. The size of each ridgeset increased exponentially with every new cycle due to the constant lengthening of the coastline as the downdrift side of the lobe advanced seaward through a series of progressively larger similar quadrilaterals, yielding a corresponding geometric progression of the delta front size. Even though each newly formed ridgeset (cycle) had a longer lifespan (the latest cycles lasting 4–5 times longer than the first ones: 200–440years versus 50–80years), the evolutionary model remained unchanged as long as the balance between wave- and river-borne sediments, defined by the sedimentary index (Si), remained constantly low (Si≤0.1), whereas the mean advance rates of the river mouth remained constant at c.10m/year. Abrupt changes occurred within the last cycle (since the beginning of the 20th century) as a consequence of human-induced depletion of sediment supplied by the Danube flow, and is mainly expressed by the complete cessation of the updrift coastal progradation and the prevalence of erosion in front of the river mouth. These changes, which engendered a threefold increase of the Si (0.37 at present), are reflected by the recent (1930s–present) river mouth dynamics, characterized by cessation of its long-term seaward expansion in favor of downdrift migration. This is indicative of the transition of the Sf. Gheorghe mouth from an asymmetric to a deflected wave-influenced delta morphology whose current developments mark a significant change in the multicentennial cyclic evolutionary pattern. The asymmetric to deflected transition reflects the net increase in the influence of wave-driven sediment circulation on river mouth morphology, corresponding to a critical Si threshold of ca. 0.2 (≤0.2: asymmetric; >0.2: deflected).

Tidal modulated flow and sediment flux through Wax Lake Delta distributary channels: Implications for delta development

Abstract. In this study, a Delft3D model of the Wax Lake Delta was developed to simulate flow and sediment flux through delta distributary channels. The model was calibrated for tidal constituents as well as velocity and sediment concentration across channel transects. The calibrated model was then used to simulate full spring–neap tidal cycles under constant low flow upstream boundary conditions, with grain size variation in suspended load represented using two sediment fractions. Flow and sediment flux results through distributary channel cross-sections were examined for spatial and temporal variability with the goal of characterizing the role of tides in sediment reworking and delta development. The Wax Lake Delta has prograded through channel extension, river mouth bar deposition, and channel bifurcation. Here we show that tidal modulation of currents influences suspended sand transport, and spatial acceleration through distributary channels at low tides is sufficient to suspend sand in distal reaches during lower flows. The basinward-increasing transport capacity in distributary channels indicates that erosive channel extension could be an important process, even during non-flood events.

Shoreline Devastation of Hota Coast by Man-made Causes

The impact of the removal of a river mouth bar as a measure against river mouth closure to the surrounding coasts was investigated, taking the Hota coast as an example. Also, on this coast, landfilling was extensively carried out to build a coastal road along the coastline, resulting in the narrowing of the natural sandy beach. These anthropogenic factors affected the overall shoreline on a pocket beach, devastating the natural coastal environment. We investigated the effects of these impacts using aerial photographs and field observations.

The evolution of Sf. Gheorghe (Danube) asymmetric deltaic lobe

The wave asymmetric Sf. Gheorghe lobe is the only active in the Danube delta where river mouth bar (and the associated barrier islands and spits) continuously deployed a cyclic development for almost two millennia. During first stage, the Sf. Gheorghe distributary had a small discharge (with an order of magnitude lower than present) which after that experienced a rapid increase in consequence of the successive avulsions of Impuţita (southern distributary of Sulina arm) and Dunavaţ distributaries. Our morphological analyses together with the newly obtained chronology, revealed the multiple ridgesets structure of Sf. Gheorghe deltaic lobe. In fact, all ridgesets (10) follow a common morphodynamic pattern characterized by the cyclic succession of three stages: i) subaqueous mouth bar development, ii) barrier island emergence, iii) barrier spit phase with several secondary spits derived from an updrift trunk ridge. The size of each ridgeset increased exponentially with every new cycle due to the constant lengthening of the coastline as the downdrift side of the lobe advances seaward through a series of progressively larger similar quadrilaterals, yielding to a constant enlargment of the delta front size.

NUMERICAL SIMULATIONS OF CHANNEL INFILLING ASSOCIATED WITH DEFORMATION OF RIVER MOUTH BAR

Masuda port is located in both sides of the mouth of Takatsu River, the access channel of which passes behind a river-mouth bar. This study intends to develop a tool for examination of countermeasures against channel infilling which is very linked with deformation of river-mouth bar. First, the relation between the sand bar deformation and channel infilling has been examined for the river mouth area of Takatsu River through analysis of aerial photos, current and wave data, bathymetric survey data, and so on. As the results, two dominant processes of flushing sand bar due to flood and reformation of sand bar by waves are confirmed. Also, numerical simulations for the two dominant processes have been conducted and the reproducibility of the model has been examined.

Anatomy of falling‐stage deltas in the Turonian Ferron Sandstone of the western Henry Mountains Syncline, Utah: Growth faults, slope failures and mass transport complexes

AbstractFalling‐stage deltas are predicted by sequence stratigraphic models, yet few reliable criteria are available to diagnose falling‐stage deltaic systems in surface exposures. Recent work on the Upper Cretaceous (Turonian) Ferron Sandstone in the western Henry Mountains Syncline of south‐central Utah has established its environment of deposition as a series of modest‐sized (5 to 20 km wide), probably asymmetrical, mixed‐influence deltas (‘Ferron Notom Delta’) that dispersed sediment eastwards from the rising Sevier orogenic hinterland into the Western Cordilleran Foreland Basin. Analysis of sandstone body stacking patterns in a 67 km long, depositional strike‐parallel (north–south) transect indicates that the growth of successive deltas was strongly forced by synsedimentary growth of a long wavelength (ca 100 km), 50 m amplitude fold structure. Herein, two discrete areas within this transect, superbly exposed in three dimensions, are documented in order to determine the details of stratal stacking patterns in the depositional dip direction, and thereby to assess the stratigraphic context of the Ferron Notom Delta. In the two study areas, dip transects expose facies representing river mouth bar to distal delta front environments over distances of 2 to 4 km. Key stratal packages are clinothems that offlap, downlap, and describe descending regressive trajectories with respective to basal and top datums; they are interpreted as the product of relative sea‐level fall. The vertical extent of clinoforms suggests that deltas prograded into <30 m of water. Furthermore, these deltaic successions preserve abundant evidence of delta front slope failure, growth faulting, and incision and filling of deep (<15 m) slope gullies. Gully fills are composed of chaotic intraformational breccia and/or massive sandstone, and constitute linear, ‘shoestring’ sandbodies in the distal portions of individual palaeodelta systems. They are interpreted to have been cut and filled during the late falling‐stage and lowstand of relative sea‐level cycles. The north–south distribution of the stratal style described above seems to be focused on the flanks of the growth anticline, and so the numerous falling‐stage systems tracts preserved within the Ferron Notom Delta probably owe their origin to synsedimentary structural growth, and the unstable fluid pressure regime that this growth imposed on the sea floor and shallow subsurface.

Near-bed sediment transport in a heavily modified coastal plain estuary

Numerous estuaries of the world have been strongly modified by human activities. These interferences can make great adjustments of not only sediment transport processes, but also the collective behavior of the estuary. This paper provides a typical case of a heavily modified coastal plain estuary of Sheyang on the China coast, where a sluice barrage was built in 1956 to stop the intrusions of storm surges and saline water. Four sets of instrumented tripods were simultaneously deployed along a cross-shore transect to continuously observe near-bed flow currents and sediment transport. The in-situ surveys lasted over a spring and neap tide cycle when a strong wind event occurred in the neap tide. Comparisons of flows and sediment transport between tide-dominated and wind-dominated conditions demonstrated the important role of episodic wind events in flows and sediment transport. The wind-induced currents, bottom stresses, and sediment transport rates were significantly greater when wind was present than corresponding quantities induced by the tides. The long-shore sediment transport induced by winds exceeds the cross-shore component, especially near the river mouth bar. These results indicate the noticeable importance of wave-dominated coastal processes in shaping topographic features. A regime shift of estuarine evolution under highly intense human forcing occurs from fluvial to marine processes. This finding suggests that the management strategy of the estuarine system should focus on the restoration of estuarine processes, rather than the present focus on inhibition of marine dynamics.

Importance of frictional effects and jet instability on the morphodynamics of river mouth bars and levees

In this work, extensive numerical simulations have been performed to assess the hydrodynamic and morphodynamic behavior of a river jet debouching in a large quiescent water body. A refined three‐dimensional grid has been used to capture the transition zone between a stable jet and an unstable meandering jet. The model results show that the stability number S, which is a function of friction and river mouth aspect ratio, and the mouth Reynolds number are the two parameters that describe the stable/unstable character of the jet. From a morphodynamic point of view, a stable jet always tends to form a mouth bar. However, a decrease of the stability number together with jet instability increase the delivery of sediments to the jet margins, favoring the formation of subaerial levees and elongated channels. Frictional effects play a major role to set the distance at which the mouth bar becomes stagnant. The importance of the stability number in setting depositional patterns at the river mouth is larger than other variables (i.e., momentum of the jet and potential vorticity) and therefore should be considered in the design of restoration schemes for deltaic land.

Initiation of the Changjiang (Yangtze) delta and its response to the mid-Holocene sea level change

The Changjiang (Yangtze) delta in eastern China is one of the largest tide-dominated deltas in the world. To obtain a more detailed information on its initiation, we drilled three sediment cores, PK01, HG01 and XJ03, from the uppermost region of the delta plain. On the basis of sedimentary facies and AMS 14C dating, we identified three depositional systems: (1) a fluvial system, (2) an estuarine system, and (3) a deltaic system including an initial delta (estuary–delta transition) and a typical delta. The maximum flooding surface separates the estuarine and deltaic systems and occurred at ca. 8.0calkyr BP, when brackish water intruded landward and reached the Nanjing area. The Changjiang delta was initiated at the area between Nanjing and Yizheng when the sea-level rise decelerated after the rapid rise in sea level during 9.0–8.2calkyr BP.The subsequent evolution of the Changjiang delta has been shown as a seaward development model of river-mouth bars with shoreline migration. The oldest river-mouth bar called Hongqiao sand body, which is located most landward, was dated at 6.0–5.5calkyr BP in this study, nearly one thousand years younger than the previous estimates. A tide-dominated, funnel-shaped estuary was formed at 8.0calkyr BP, and lasted until the Hongqiao sand bar became exposed. This stage is regarded as an aggradation-dominated initial stage of the Changjiang delta, followed by a progradation-dominated stage that is characterized by the formation of a series of seaward migrating river-mouth bars. A relative sea level highstand in the mid-Holocene may be associated with glacio-hydro-isostatic tilting.

Growth of river mouth bars in sheltered bays in the presence of frontal waves

AbstractOne of the key processes for the formation of deltas and their fluvial networks is the deposition of mouth bars in front of prograding distributaries. Waves influence mouth bar growth, but it is not clear how and to what extent. Toward this end, we conduct a modeling study on deltas forming in sheltered bays, where waves are locally generated and both longshore currents and surf zone are absent. We focus on the simplified case of a homopycnal river plume subject to frontal wave attack, and we begin by isolating the effects of waves on jet spreading. An analytical model for the hydrodynamic interaction between incoming waves and a turbulent expanding jet is developed and tested with the numerical model Delft3D coupled to the wave model SWAN. Both the analytical model and Delft3D predict that incoming surface gravity waves increase the spreading of the jet and the interaction between wave and current boundary layers causes an increase in bottom friction. To investigate how waves influence mouth bar morphodynamics, a set of numerical simulations is run with Delft3D‐SWAN utilizing a geometry and wave characteristics typical of sheltered bays. Our numerical results show that in the presence of waves, mouth bars form up to 35% closer to the river mouth and 40% faster when compared to cases without waves. The distance from the river mouth to the stagnated mouth bar decreases with increasing wave height and wave period. The timescale of bar formation is inversely proportional to wave height and directly proportional to wave period. Our modeling study suggests that wave influence on mouth bar growth is complex. Small waves, like the ones modeled here, promote mouth bar formation via increased jet spreading and faster formation time, which in turn should create deltas with more distributary channels. On the other hand, large waves suppress mouth bar formation, as seen in other studies, leading to fewer distributary channels.

大規模洪水時の河口砂州と周辺河床の変動解析-平成23年阿賀野川洪水を対象として-

In the Agano River estuary flowing into Japan Sea, bars at the mouth are developed from both river banks. The bar causes the river discharge capacity to decrease and the water level to rise. Therefore, it is important to understand mechanism of river mouth bar flushing during a flood event. One of the authors has shown that flow and bed variation during a flood event may be explained by means of a suitable numerical analysis method using temporal changes in observed water surface profiles effected by various events in the river. The objective of this paper is to clarify flushing at river mouth bar during a large flood by temporal observed water surface profiles and the numerical analysis.

高津川河口の砂州変形と航路埋塞の数値シミュレーション

Masuda port is located in both sides of the mouth of Takatsu River, the access channel of which passes behind a river-mouth bar. This study intends to develop a tool for examination of countermeasures against channel infilling which is very linked with deformation of river-mouth bar. First, the relation between the sand bar deformation and channel infilling has been examined for the river mouth area of Takatsu River through analysis of aerial photos, current and wave data, bathymetric survey data, and so on. As the results, two dominant processes of flushing sand bar due to flood and reformation of sand bar by waves are confirmed. Also, numerical simulations for the two dominant processes have been conducted and the reproducibility of the model has been examined.

Deformation of Sandy Beach and Inundation on Iwama-Sanuka Coast in Fukushima Prefecture due to the 2011 Tohoku Earthquake Tsunami

The massive earthquake with a magnitude of 9.0 occurred at 14:46 on March 11, 2011, with an epicenter 130 km offshore from the Oshika Peninsula in Japan’s northeastern Miyagi Prefecture. After the earthquake, large tsunamis were generated owing to abrupt crustal subsidence and uplift, which inundated Japan’s eastern Pacific Ocean coastline. We carried out field observations to investigate the deformation of a previous river-mouth bar by comparing oblique photographs, and investigated the damage to seawalls and the tsunami inundation depth on the Iwama-Sanuka coast, located north of the Same River in southern Fukushima Prefecture. Here, the results of the field observations on the deformation of the sandy beach and the inundation of the Iwama-Sanuka coast are reported.

The effect of wind waves on the development of river mouth bars

River deltas are among the most important environments on earth, housing productive ecosystems and a large fraction of the human population. The key process for delta development is the deposition of mouth bars in front of delta distributaries. Predicting mouth bar formation on marine coastlines is complex because of the interactions between waves, tides, water and sediment discharge. Here we study the effects of waves on mouth bar growth with the coupled sediment transport and wave model Delft3D‐SWAN. Our results show that wave characteristics (height, period, and direction) play an important role in the formation of mouth bars. In our numerical experiments waves affect bar development in three ways: by modifying the direction of the river jet, by increasing bottom shear stresses at the river mouth, and by changing bottom friction and hence increasing jet spreading. We further show that high waves with long period prevent the formation of mouth bars; in particular, wave angles between 45° and 60° are the least favorable to bar formation, likely producing a deflected river mouth.

Delta Front Depositional System Study Based on Seismic Attributes and Well Logging Facies

Along with analysis of logging facies characteristics of drilled wells, isometric strata slicing technique for seismic attribute is applied to interpret the distribution of the depositional systems in the study area. It is understood that Nenjiang3 Formation in Xinbei area of Xinli field consists of water regressive and sand progressive delta front depositional system from bottom to top. Combined with analogue analysis of well logging facies and planar seismic attributes, it is learned that sediments generally came from the north area, and main sedimentary microfacies include underwater distributary channels, river mouth bars, sheet sands body and interdistributary bays of delta front. With isometric slicing for the extraction of seismic attributes and logging operation, the distribution rules for sedimentary systems could analyzed, thereby providing a feasible method that could be referenced by the study on sedimentary system distribution of other areas.

福島県鮫川河口を含む竜宮岬～勿来漁港間における津波後の海浜応答

On March 11, 2011, the Great Tsunami hit the northeast Japan's coasts, causing severe disaster along the coastline. The river mouth bar of the Same River flowing into a pocket beach with 6.5 km length bounded by Point Ryugu and Nakoso fishing port on the north and south ends, respectively, was eroded and disappeared by the return currents of tsunami. Simultaneously ground subsidence by 0.5 m occurred due to the earthquake in this area. In this study, the shoreline changes of this pocket beach after the tsunami and ground subsidence were investigated using aerial photographs and bathymetric survey data. It was found that the recovery of the river mouth bar caused beach erosion on the nearby coasts.