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1.
High-quality 3D seismic data are used in this paper to: a) investigate the geometry of Miocene–Holocene submarine channels in confluence regions, and b) to correlate the geometry of channel confluences with the styles of topographic confinement imposed by salt structures in the Espírito Santo Basin (SE Brazil). A new method is used to analyse geomorphic parameters of three channel intervals (Units 1–3) and a modern channel. 5348 Channel Points (CP) are recorded on a sinusoidal slope interrupted by salt structures. In the upper-slope region, diapir confinement directly controls the location of channel confluences. These are characterised by a sharp increase in channel width and height at their junctions. Scale relationships show an increase in channel width of the order of 1.19 < W < 1.22 in confluence regions. Ratios of channel height between confluence and pre-confluence regions are 1.09 < H < 1.40, with ratios of <1 observed in post-confluence regions. This work proves the existence of a direct relationship between topographic confinement, confluence location and relative channel distribution. The studied submarine confluences are located in regions with high confinement created by salt diapirs. The results of this work are significant, as they show clustered distribution patterns in channels, with higher channel densities being observed in pre-confluence regions. Thus, we propose a new classification for submarine confluences based on a combined analysis of channel geometry and seismic attribute data. Confluences may be symmetric or asymmetric based on the equality of the angles the tributaries bear to the post-confluence channel. Symmetric confluences can be left or right symmetric, based on whether the dominant flow path is in the left- or right-hand tributary. Asymmetric confluences are pure asymmetric or secondary asymmetric depending on whether the dominant flow takes place along the main tributary and the post-confluence channel alignement, or along the secondary tributary which is at an angle with the main alignement.  相似文献   

2.
The deep-water fold and thrust belt of the southern Niger Delta has prominent thrusts and folds oriented perpendicular to the regional slope that formed as a result of the thin-skinned gravitational collapse of the delta above overpressured shale. The thrust-related folds have grown in the last 12.8 Ma and many of the thrusts are still actively growing and influencing the pathways of modern seabed channels. We use 3D seismic reflection data to constrain and analyse the spatial and temporal variation in shortening of four thrusts and folds having seabed relief in a study area of 2600 km2 size in 2200–3800 m water depth. Using these shortening measurements, we have quantified the variation in strain rates through time for both fault-propagation and detachment folds in the area, and we relate this to submarine channel response. The total amount of shortening on the individual structures investigated ranges from 1 to 4 km, giving a time-averaged maximum shortening rate of between 90 ± 10 and 350 ± 50 m/Myr (0.1 and 0.4 mm/yr). Fold shortening varies both spatially and temporally: The maximum interval shortening rate occurred between 9.5 Ma and 3.7 Ma, and has reduced significantly in the last 3.7 Ma. We suggest that the reduction in the Pliocene-Recent fold shortening rate is a response to the slow-down in extension observed in the up-dip extensional domain of the Niger Delta gravitational system in the same time interval. In the area dominated by the fault-propagation folds, the channels are able to cross the structures, but the detachment fold is a more significant barrier and has caused a channel to divert for 25 km parallel to the fold axis. The two sets of structures have positive bathymetric expressions, with an associated present day uphill slope of between 1.5° and 2°. However, the shorter uphill slopes of the fault-propagation folds and increased sediment blanketing allow channels to cross these structures. Channels that develop coevally with structural growth and that cross structures, do so in positions of recent strain minima and at interval strain rates that are generally less than −0.02 Ma−1 (−1 × 10−16 s−1). However, the broad detachment fold has caused channel diversion at an even lower strain rate of c. −0.002 Ma−1 (−7 × 10−17 s−1).  相似文献   

3.
The existence of a slope equilibrium profile has been widely used to account for erosional and depositional processes on submarine slopes and turbidite systems. Profiles out-of-equilibrium are commonly observed in actively deforming areas where channels seem to be deflected or diverted by seafloor structures. In this study the concept of the submarine equilibrium profile is tested in an area of extensive surface faulting to examine whether channels adopt an equilibrium-type profile through time. The study area is on the slope of the Nile Delta, which is disrupted by a number of surface-rupturing normal faults. Prior to fault linkage, several submarine channels flowed down the slope and either utilised relay ramps or flowed through fault scarps of the fault array. Where a relay ramp had been utilised, post fault linkage, the channels of the area either avulsed or converged into one major channel in response to a change in the deformed slope profile to a more concave shape. The thalweg of the post fault linkage channel and two slope profiles either side of it are measured in the area of the fault array, to understand how the channel evolved in response to the active faulting. When fault displacement is relatively small the combination of channel erosion and aggradation results in a channel thalweg profile near-equilibrium with predictable modifications of channel dimensions (depth and width) even if sediment supply was infrequent and episodic. It is concluded that turbidite channels can conform to the concept of equilibrium and submarine base level if it is the most energy efficient route for submarine gravity flows downslope. The most energy efficient route will be one where flows bypass the slope without eroding or depositing and move in a direct downslope course towards base level.  相似文献   

4.
Submarine channel levee systems form important hydrocarbon reservoirs in many deep marine settings and are often deposited within a structurally active setting. This study focuses on recent submarine channels that developed within a deepwater fold and thrust belt setting from the Levant Basin, eastern Mediterranean Sea. Compressional deformation within the study area is driven by the up-dip collapse of the Nile cone above the ductile Messinian Evaporites. Structures such as folds and strike slip faults exert a strong control on channel location and development over time. From this study four end-member submarine channel–structure interactions can be defined: Confinement, diversion, deflection and blocking. Each of these channel–structure interactions results in a distinct submarine channel morphology and pattern of development compared to unconfined channel levee systems. Each interaction can also be used to assess timing relationships between submarine channel development and deformation.  相似文献   

5.
The Nile deep-sea fan (NDSF), turbiditic system reaching a size of about 90,000 km2, has been investigated since 1998 by several geophysical methods (multibeam bathymetry, backscatter imagery, seismic data, 3–5 kHz echo-sounding). The analysis of this important data set evidenced that the NDSF is the locus of numerous multi-scale slope instabilities. Three main types of instabilities have been defined, mainly on the basis of their size or origin. (1) First type of instabilities related to the generalized gravity spreading of the Plio-Quaternary deep-sea fan on Messinian salt layers. This global spreading is accommodated by numerous localized slides. (2) Second type of instabilities correspond to giant mass movements probably triggered either by earthquakes, fluids, or climate and eustatic oscillations. Finally, (3) third type of instabilities correspond either to localized levee liquefactions or to thin-skinned slides on the steep slopes of the Eratosthenes seamount. The deposits generated by these slope movements greatly participate in the building of the NDSF. The characterization of these different instabilities, in a petroleum province as the NDSF, has important implications in terms of risk assessments when considering drilling operations.  相似文献   

6.
We present a series of experiments that investigate the morphology of sediment deposits within sinuous submarine channels of different sinuosity (S = 1.14–1.94) and planform (symmetric and asymmetric bends), generated by bedload-dominated turbidity current flows. Flows were generated by releasing dense saline gravity currents over a mobile sediment bed through pre-formed sinuous channels. Flows had a basal-outwards helicity and produced a characteristic bed morphology with point bars downstream of the bend apex at the inside of bends and scour at the outside of bends. An increasing loss of fluid through overspill with increasing channel sinuosity results in a decreasing magnitude of cross-stream velocity downstream, a decreasing amount of erosion and deposition, and decreasing transverse slopes of in-channel deposits. Basal fluid from within the channel is transported over the outer-levee at bends, implying that proximal outer-bend levee deposits will have similar sediment composition to that within the channel. More deposition of coarse material might be expected on levees and in overbank regions close to higher amplitude bends. No simple relationship was observed between superelevation and sinuosity, probably due to changes in the relative influences of downstream velocity and bend curvature on centrifugal force and inertial run-up. In the channel with the tightest initial bend curvature, overspill fluid from Bend 1 re-entered the channel at Bend 2, dominating flow characteristics and disrupting the basal-outwards helicity observed in the other channels. Higher sinuosity channels and those with shallow regional and levee slopes are thus more likely to have a higher proportion of anomalous flow and sedimentation patterns due to the influence of overspill fluid re-entry into the channel. The results of this investigation are combined with published observations to enable the synthesis of a new model for sedimentation in sinuous submarine channels.  相似文献   

7.
In this contribution, the morphodynamics of open-sea tidal channels eroded into sandy seabed in regions of flow constriction is simulated by a one-dimensional model using the Bagnold formula for bedload transport rate, and accounting for the effect of bed slope. The results show that equilibrium conditions for such channels can be reached over a period of 102–103 years. Sediment eroded from the channel floor is transported in the direction of the dominant current, and deposited beyond the regions of flow constriction where the current looses competence due to spreading. In this way, the material remobilized from older strata in the channels is deposited in younger sand banks near the channel heads. Where several successive channels are incised along the current axis, they interact in their morphological evolution. The morphodynamic equilibrium of a tidal channel is reached once the combined interacting sedimentological and hydrodynamic factors, such as sediment particle diameter, tidal current velocity and flood/ebb dominance, are balanced. The model output shows that the equilibrium shape of the tidal channels appears to be related mainly to flow field characteristics and, to a lesser extent, to particle size. A positive correlation exists between the depth of the channels and their response times. The equilibrium water depths of the channels are more sensitive to current speed than to either particle size or the time–velocity asymmetry of the flow field. The response times for overall morphological equilibrium are sensitive to all of the above-mentioned parameters. In particular, sediment characteristics associated with critical current velocities have far-reaching effects on the morphodynamic behaviour of tidal channels.  相似文献   

8.
The megabenthic ecology of the cold water (<0 °C) area of the Faroe–Shetland Channel was investigated using an off-bottom towed camera platform WASP (wide angle seabed photography). A series of 10 photographic transects, approximately evenly spaced along the channel axis, were studied. Photographic transects allowed quantitative benthic diversity data to be obtained from this understudied yet commercially important area for oil and gas exploration. The sedimentary characteristics of the seabed changed dramatically from a region of ice-rafted boulders and gravel in the southwest to fine sediments more typical of the deep sea to the northeast. Despite the relatively low species richness of the megabenthos, variation in faunal composition with depth was apparent. Two distinct “communities” were identified, one in the south of the channel and the other in the north. Epibenthic megafaunal communities in the south were dominated by suspension and filter feeders and in the north by deposit feeders. Diversity and standing stock of megabenthos decreased to the northeast of the channel. Lebensspuren number and areal cover increased northwards in the Channel. The increase in bioturbation and deposit feeder abundance was concurrent with an increase in fine sediment quantity.  相似文献   

9.
Turbidity currents in sinuous submarine channels are an important mechanism for transporting terrestrial sediments to deep water, and their deposits are of increasing importance as hydrocarbon exploration targets. Despite this, the architecture and dynamics of submarine channel systems are not well understood. Analogies are often drawn with fluvial systems due to similarities between their planform shapes even though differences in channel evolution and hydrodynamics have been noted. A key question is the nature of deposition within submarine channel bends; in particular at inner bends where point bars form in alluvial meandering rivers. Recent experimental and numerical work has demonstrated that the fluid dynamics of submarine channel bend flow are markedly different from rivers. Notably, a reversal in the orientation of secondary (helical) flow at bend apices occurs in submarine channels. The potential influence of these differences in fluid dynamics on deposition within submarine channel bends is investigated herein. We report the results of a series of physical experiments in which solute-driven gravity currents were run through pre-formed sinuous channels containing mobile beds. These experiments reveal sedimentation patterns characterised by accumulation zones downstream of bend apices and erosion zones at outer bends. These patterns are broadly analogous to the point bars and outer-bank pools observed in meandering rivers, demonstrating that the longitudinal flow component dominates over the cross-stream component, as also occurs in rivers. However, the data suggest that the reversal in direction of the cross-stream flow component compared with subaerial flows is important in determining the position and morphology of ‘point bars’ relative to bend apices. From analogy with fluvial compound channels, and fluvial theory, this reversal in secondary flow cell orientation is also expected to influence the spatial variations of grain size in submarine channel ‘point-bar’ deposits.  相似文献   

10.
根据在亚洲快线海底光缆香港段(水深小于300m区域)开展的路由勘察中获取的浅地层剖面、侧扫声纳、柱状取样、多波束等数据,同时结合该区域的自然环境特征,对路由区的海底工程地质条件、自然环境条件等进行了详细的分析。通过分析发现,路由区海底地形无大的起伏,平均坡度小于0.3%;路由区跨越了淤泥/粘土质、砂质以及沙波区海底,其中发现的沙波最大波高达3~4m;路由区地震活动强度小,属于地壳稳定性较好的地区;路由区海底面存在沉船、抛弃物等海底障碍物。综合所有获取的数据和信息,在路由跨越大型沙波及距离障碍物太近的区域,对路由线路进行了适当调整,调整后的路由基本适合海底光缆的铺设,同时也提出了一些建议。  相似文献   

11.
Submarine channel-levee systems commonly develop in structurally active deepwater settings. Despite their widespread development in such settings, only recently have researchers begun to address the response of channel-levee system evolution to deformation. Key factors which govern channel evolution and morphological development are relative rates of deformation and channel deposition and erosion, and also the number and scale of deformational structures, relative to the scale of the submarine channel. Submarine channel-structure interactions can be split into four end-members: deflection, blocking, diversion and confinement. Where deformation is coeval with channel development, an increase in the relative rate of uplift versus deposition and erosion causes a transition from channel deflection to blocking. Diversion and confinement are linked by the number, scale and orientation of structures relative to the channel flow path. Increasing the number of structures and their scale typically results in channel confinement. Underlying all of these individual controls is the distribution of local accommodation, which is determined by specific structural style. This distribution of accommodation over relatively small (<10 km) length scales strongly affects local channel development in order to attain the equilibrium profile. Knowledge of these controls on submarine channel development can increase our understanding of how these deepwater sedimentary systems evolve and distribute sediment across deforming submarine slopes. Understanding the factors governing spatial variations in channel morphology may also be applied when exploring for hydrocarbon reservoirs in structurally active deepwater settings.  相似文献   

12.
卢惠泉  孙全 《台湾海峡》2009,28(1):96-101
根据路由勘察区水深测量、旁侧声纳、浅地层剖面探测等多项物理探测所获取的资料，结合其它自然环境及历史资料，对勘察区内海底工程地质条件进行了详尽的分析和研究．此外，还对近20a来勘察区海床稳定性进行初步分析，为选择一条最佳的路由通道提供依据．研究分析表明：可能影响该海缆安全运行的不良工程地质条件主要为海底灾害性地貌，如基岩、潮流冲刷槽等；勘察区不同区域内海底冲淤变化存在一定差异，潮汐通道底部受较强冲刷，冲刷速率为0．035～0．1m／a，20m以浅区域海底处于弱冲刷状态一冲淤动态平衡状态，冲刷速率为0．015m／a，海床较稳定；该路由勘察区工程环境较适合海缆的铺设，且其最佳路由区域是在勘察区南半部相对稳定的海底平滑区．  相似文献   

13.
Several laterally offset and aggradational sinuous submarine channels are contained within a 54 km long segment of the Benin-major Canyon. Axial channel deposits produce high amplitude reflections on three-dimensional (3-D) seismic profiles. Some seismic reflections have U- or V-shaped cross-sectional motifs that were correlated with confidence along linear to meandering paths for distances up to 70 km. They are referred to here as channel-forms (CFs), and are believed to be the axial parts of submarine channels preserved during overall channel floor aggradation. A total of 15 separate CFs were mapped allowing thalweg-gradients, dimensions, and morphology to be studied spatially and through time, providing insight into how submarine canyons fill. Their planform geometry evolved predominantly in a stepwise fashion through alternating periods of cut-and-fill, but more gradual channel migrations are also observed. The largest offsets in successive channel floor position occur after periods of significant vertical CF fill (‘thalweg plugging’—with deposits commonly consisting of lower amplitude, transparent to chaotic seismic reflections). The passage of erosive flows after such periods of fill caused abrupt shifts in channel position, particularly at meander bends, with increased potential for the formation of pseudo meander loop cut-offs. Significant spatial differences in the stacking architecture of CFs are attributed to local slope deformation and perhaps also to a recent channel avulsion just west of the study area. Abrupt channel straightening in the western study area coincides with a period of increased valley-gradient associated with amplification of an underlying anticlinal fold. The youngest CFs in this area show limited aggradation and are characterized by repeated episodes of headward erosion causing knickpoint migration as the recent channel floor tried, unsuccessfully, to establish a smooth graded depth profile. This is in stark contrast to the time-equivalent predominantly aggradational CFs in the eastern study area that show a progressive increase in sinuosity through time.  相似文献   

14.
由于海床起伏不平,斜坡的存在必然改变波浪对管线及海床的作用特性,进而影响管线三维冲刷。基于波浪港池实验,考虑规则波的作用,采用中值粒径为0.22mm的原型沙铺设与波浪传播方向成45°夹角的斜坡,研究斜向波作用下斜坡上海底管线的三维冲刷特性。通过测量管线下方冲刷坑宽度和深度的差异,分析管线三维冲刷的不均衡性。实验表明:管线的存在使斜坡上的波高有所降低;斜向波作用下管线三维冲刷的不均衡性表现为深度不均衡性和宽度不均衡性,宽度不均衡性主要是管后淤积泥沙的后移引起的,周期对三维冲刷不均衡性的影响比波高对其的影响程度大;管线自深海向近岸延展时,随水深的减小,冲刷深度分为缓慢发展阶段和快速发展阶段。  相似文献   

15.
This study integrates newly acquired stratigraphic data, geologic mapping, and paleocurrent data to constrain the stratigraphic evolution of the oldest channel-lobe complex in the Upper Cretaceous Cerro Toro Formation in the Silla Syncline area of the Magallanes Basin, termed the Pehoe member. The Pehoe member ranges in thickness from 60 m in the north to at least 410 m farther down system and comprises three separate divisions (A, B, and C). A lower conglomerate unit and an upper one, termed Pehoe A and C divisions respectively, represent the fill of major incised submarine channels or channel complexes. These are separated by stratified sandstone of the Pehoe B division, representing a weakly confined lobe complex, either transient or terminal.The integration of new data with observations from previous studies reveal that the three main coarse-grained conglomerate and sandstone members in the Cerro Toro Formation in the Silla Syncline include at least seven distinct submarine channels or channel complexes and two major lobe complexes. The thinning and disappearance of these units along the eastern limb of the syncline reflect confinement of the flows to a narrow trough or mini-basin bounded to the east by a topographic high. This confinement resulted in unidirectional paleocurrents to the south and southeast in all deposits. Changes in depositional geometries are interpreted as reflecting changes in sediment supply and relative confinement. Submarine channels were from 700 m to 3.5 km wide and occupied a fairway that was 4-5 km wide. Flows moving south and southeast in this mini-basin probably crossed the eastern topographic high south of the present exposures and joined those moving southward along the axis of the foreland basin at least 16 km to the east.  相似文献   

16.
Over 25,300 seabed pockmarks were mapped from the Rosetta Channel region of the Western Nile Deep Sea Fan (NDSF) using concurrent High Resolution 2D, Chirp profiler and multibeam bathymetry data which spans the Holocene–Pleistocene period. Within the region, a pockmark field containing >13,800 pockmarks was analysed using spatial statistics to determine the distribution of pockmarks within the field. Pockmarks within the field are small (∼16 m diameter), shallow (∼0.5 m deep) circular depressions which formed within the last ∼ 6500 years. The fluid source for the field is identified as an accumulation/generation of gas beneath a hemipelagic seal c. 20–40 ms beneath the seabed. The position of the pockmarks is shown to be unrelated to the depth to the fluid source and an irregular high amplitude acoustic anomaly which is tentatively interpreted as a possible carbonate precipitate of biogenic microbial activity. Statistical spatial analysis of the field confirms the distribution of pockmarks is not random. An exclusion zone surrounding each individual pockmark is identified. The exclusion zone is a unique minimum radius around each pockmark which is not penetrated by any other pockmark. The exclusion zone works in unison with Self-Organised Criticality (SOC) in determining the spatial distribution of pockmarks within the field. The exclusion zone is interpreted as a pockmark “drainage cell”. A conceptual model for a pockmark drainage cell is proposed whereby pockmark formation dissipates a radius/area of fluid and overpressure, thereby preventing the formation of another pockmark within that cell. Consequently, pockmarks are observed to separate or produce anti-clustering tendencies within the field.  相似文献   

17.
利用在南海东沙群岛北部至西北海域为工程目的所采集的海底地形测量、底质取样、海底底流测量资料,以及以往的区域地质、地球物理资料,采用沉积学、构造学和海洋水动力学综合研究方法,对该区海底沙波形成及稳定性进行了综合分析。认为该区海底沙波是在目前水动力环境下所形成,为今生,海底表层沉积物为晚更新世地层受到冲刷改造的再沉积。沙波形成主要受潮流底流的水动力作用控制,并与构造抬升有关。沙波具有一定的活动性,主要由SE向NW方向移动,且活动性逐渐减弱。北区段海底沙波稳定,中区段海底沙波较稳定,它们对海底工程建设不会造成影响;而南区段海底沙波较为活动,当沙波发生较大规模移动时,对海底工程建设会造成一定影响。  相似文献   

18.
Examining bathymetric and seismic reflection data collected from the deep-sea region between Taiwan and Luzon in 2006 and 2008, we identified a connection between a submarine canyon, a deep-sea channel, and an oceanic trench in the northern South China Sea. The seafloor of the South China Sea north of 21°N is characterized by two broad slopes: the South China Sea Slope to the west, and the Kaoping Slope to the east, intersected by the prominent Penghu Canyon. This negative relief axis parallels the strike of the Taiwan orogen, extends downslope in an approx. N–S direction, and eventually merges with the northern Manila Trench via a hitherto unidentified channel. The discovery of this channel is pivotal, because it allows connecting the Penghu Canyon to the Manila Trench. This channel is 80 km long and 20–30 km wide, with water depths of 3,500–4,000 m. The progressive morphological changes recorded in the aligned canyon, channel, and trench suggest that they represent three distinct segments of the same longitudinal sediment conduit from southern Taiwan to the northern Manila Trench. Major sediment input would be via the Kaoping Canyon and Kaoping Slope, with a smaller contribution from the South China Sea Slope. We determined the northern end of the Manila Trench to be located at about 20°15′N, 120°15′E, where sediment accumulation has produced a bathymetry shallower than 4,000 m, thereby abruptly terminating the trench morphology. Comparison with existing data reveals a similarity with, for example, the Papua New Guinea–Solomon Sea Plate convergent zone, another modern analog of a mountain source to oceanic sink longitudinal sediment transport system comprising canyon–channel–trench interconnections.  相似文献   

19.
The Dongsha Basin, circling Dongsha Island that is amid the northern margin of the South China Sea, is characterized by thin (∼0.5 km) Cenozoic sediments veneering on thick (up to 5 km) Mesozoic strata. Recently, several geophysical and geological surveys, including multiple channel reflection seismic, sub-bottom profiling and benthic dredging, have been conducted on the slope southwest to the Dongsha Island, where the water depth varies from 400 m to 2000 m. A novel discovery is numerous submarine mud volcanoes of various sizes over there, typically 50–200 m high and 0.5–5 km wide. Geophysical profiles document their unusual features, e.g., roughly undulating seafloor, high-amplitude seabed reflectivity, foggy hyperbolic diffractions up to 50 m in water column above seabed, and internal reflection chaos and wipe-out down to 2–3 km level or deeper below the seabed. Benthic dredging from the mud volcanoes gives abundant faunas of high diversity, e.g., scleractinian (stony coral), gorgonian, black coral, thiophil tubeworm, glass sponge, bryozoan etc., indicating booming chemosynthetic community, among which the Lophelia pertusa-like coral and the Euretidae-like glass sponges are the first reports in the South China Sea. Concomitantly with them, there are also abundant authigenic carbonate nodules and slabs, raw, brecciated and breccias with bio-clasts congregation. Besides, there coexist massive mudflows and allogenic coarse-grained quartz, feldspar and tourmaline most likely brought out by mud volcanism. Geochemical analysis of the bottom water samples give dissolved methane concentration up to 4 times higher than the background average. These results lend comprehensive evidences for the ongoing and historical mud volcanism. The escaping methane gas is inferred to source mainly from the Mesozoic strata. Occupying a large province of the deep water slope, ca. 1000 km2 or more, the mud volcanoes is prospective for gas hydrate and natural gas for the Dongsha Basin.  相似文献   

20.
Submarine channels are major morphological features of the sea floor and are important in the transport of sediment to the deep ocean. Although much is known concerning the large-scale distribution of sediment within and surrounding submarine channels, there is little understanding of the fluid dynamic processes that control this sedimentation. Direct measurement of flow velocities and concentrations has proved to be extremely difficult within submarine channels, with the resultant paucity of direct observations making physical laboratory modelling a critical technique for examining the processes that operate in, and control, submarine channel development.Recent experimental and numerical studies have proposed a new model of secondary circulation within submarine channel bends, characterised by a reversal in the orientation of the secondary circulation cell relative to that found in meandering rivers. This new paradigm for submarine channels thus predicts basal flow from the inside to the outside of the bend at a bend apex, with an upper return flow directed towards the inner bend. The reversal in orientation of the secondary flow cell has been linked to the vertical distribution of downstream velocity and associated changes in centrifugal and pressure gradient forces. However, previous work has additionally proposed that shearing of the within-channel flow by overbank flow may also generate secondary flow reversal.This study assesses the applicability of the proposed submarine bend flow model against a range of key channel parameters. We demonstrate that the sense of secondary circulation is the same for all experimental conditions, strongly supporting the new model of secondary flow in submarine channels. Furthermore, investigation of overbank shear induced secondary circulation confirms for the first time that this mechanism can occur, and identifies the channel styles most likely to exhibit this effect. Such shear-induced circulation is, however, shown to be a secondary mechanism, with the vertical distribution of downstream velocity the principal mechanism. In certain channel configurations, the two mechanisms may act to augment one another.  相似文献   

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