Abandoned channel fill sequences in the tidal estuary of a small mountainous,dry‐summer river          下载免费PDF全文

Andrew B. Gray  Gregory B. Pasternack  Elizabeth B. Watson  Miguel A. Goñi 《Sedimentology》2016,63(1):176-206

This study proposes a modification of the current model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. Evidence supporting this concept came from a study of two consecutive channel abandonment sequences in Ropers Slough of the lower Eel River Estuary in northern California. Aerial photographs showed that Ropers Slough was abandoned around 1943, reoccupied after the 1964 flood, and abandoned again in 1974 with fill continuing to the present. Planform geomorphic characteristics derived from these images were used in conjunction with sub‐centimetre resolution stratigraphic analyses to describe depositional processes and their resultant sedimentary deposits. Both abandonment sequences recorded quasi‐annual scale fluvial/tidal deposition couplets. In both cases, tidal deposits contained very little sand, were higher in organic and inorganic carbon content than the sandier, fluvially dominated deposits, and possessed millimetre‐scale horizontal laminations. The two abandonment fills differed significantly in terms of the temporal progression of channel narrowing and fluvial sediment deposition characteristics. Aerial photographic analysis showed that the first abandonment sequence led to a more rapid narrowing of Ropers Slough and produced deposits with a positive relationship between grain size/deposit thickness and discharge. The second abandonment resulted in a much slower narrowing of Ropers Slough and generally thinner fluvial deposits with no clear relationship between grain size/deposit thickness and discharge. The δ¹³C values and organic nitrogen to organic carbon ratios of deposits from the first phase overlapped with Eel River suspended sediment characteristics found for low flows (one to five times mean discharge), while those of the second phase were consistent with suspended sediment from higher flows (seven to ten times mean discharge). When considered together, the results indicate that the early fill sequence recorded a reach experiencing regular fluvial deposition through flow conditions during the wet season, while the latter fill sequence records a reach more disconnected from the main stem in terms of flow and sediment. The major factor affecting the difference in sedimentation between the two fill periods appears to have been the morphology of the upstream river bend in relation to the position of the bifurcation node. During the first fill period, the upstream entrance to Ropers Slough seems to have remained open, in part due to the placement of its entrance on the outside of the mainstem river bend, and despite stronger tidal effects caused by a larger tidal prism and closer proximity to the tidal inlet. By the second fill sequence, the upstream bend morphology had altered, placing the entrance to Ropers Slough on the inner bank of the mainstem bend, which resulted in more rapid plug bar formation. The role of tidal effects in the geomorphic trajectory of the two abandonment sequences is unclear, but appears to have been less important than local bifurcation geometry.  相似文献   

A model of submarine channel-levee evolution based on channel trajectories: Implications for stratigraphic architecture   总被引：3，自引：0，他引：3  

Zoltán SylvesterAlessandro Cantelli 《Marine and Petroleum Geology》2011,28(3):716-727

Channel-levee systems are frequently interpreted as having a long history of cut-and-fill by channel-shaped features of different scales. Results from a simple geometric model based on a centerline migration algorithm combined with a vertical channel trajectory show that an incising-to-aggrading trajectory of a single channel can produce realistic morphologies similar to systems observed on the seafloor and subsurface, including features such as a basal erosional surface, coeval inner and outer levees, internal erosional boundaries, and terraces draped by inner levee deposits. Channel migration results in composite erosional surfaces that are distinct from topographic surfaces, and their formation does not require larger than usual erosional flows. Many submarine channels interpreted as underfit were probably carved by flows similar to the ones that eroded and deposited the entire channel system. We suggest that the features of most submarine channel-levee systems do not require large temporal variations in flow magnitude but can be explained by a simpler model whereby incision, migration and aggradation of a single channel form over time results in an apparently complex system.  相似文献   

Experimental analysis of cross‐sectional flow motion in a large amplitude meandering bend     

Donatella Termini  Mafalda Piraino 《地球表面变化过程与地形》2011,36(2):244-256

Flow in meandering bends is characterized by the formation of a large cross‐sectional central‐region circulation cell. The width‐to‐depth ratio is one of the most important parameters affecting the entity of the cross‐circulation motion. In steep outside bends, beside the central‐region cell, a counter‐rotating circulation cell often forms in the upper part of the outer‐bank. In spite of its practical importance, the evolving mechanisms of both the circulation cells and their role on boundary shear stress distribution in bends are not yet fully understood. The aim of the present paper is to gain some insight into how cross‐sectional flow motion evolves along meandering bends. Experiments have been carried out in a laboratory meandering channel of large amplitude, over a deformed‐rigid bed, for two values of the width‐to‐depth ratio. The three‐dimensional flow velocity field has been measured in detail at five cross‐sections, almost equally spaced along the channel reach between two consecutive apex sections. The measurements have been carried out on a fine grid by an acoustic Doppler velocity profiler. The distributions of the cross‐sectional flow (e.g. cross‐sectional flow velocity, net transversal flux) and turbulent kinetic energy are analyzed in each investigated section. Measurements show that the counter‐rotating circulation cell is evident only in the case of ‘small’ width‐to‐depth ratio. Such circulation cell begins at the bend entrance and it is fully developed at the bend apex; then it decays. At the bend apex, the core of maximum velocity is found near the bed at about the separation between the central and the outer‐bank circulation cells. Moreover, the presence of the counter‐rotating circulation cell allows the bank shear stress to maintain low values in the outer‐side of the bend. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Hydraulic modelling of fish habitat in urban rivers during high flows     

D. J. Booker 《水文研究》2003,17(3):577-599

In urban rivers, flow regime and channel morphology are the drivers of physical habitat quality for aquatic species. Peak discharges are increased at high flows as a result of impermeable catchments and channel engineering for flood protection schemes. Hazardous conditions and flashy hydrographs mean that measurement of velocities at high flows is a difficult task. This research uses a three‐dimensional computational fluid dynamics (3D‐CFD) model to simulate hydraulic patterns in two urban river channels. A 3D‐CFD code, called SSIIM, was used to simulate hydraulic conditions in two engineered river reaches of the River Tame, Birmingham, UK. These two sites represent channels with different levels of engineering. Models were calibrated and tested using field measurements. Results show that modelled water surface levels and velocity profiles are well simulated. Calibrated roughness heights are compared with those derived from field measurement of sediment size. Numerical experiments are used to assess the relationship between grid resolution in the vertical dimension and the form of the modelled velocity profiles. Biologists have used laboratory experiments to determine maximum sustainable swimming speeds (MSSS) of fish, often in order to assess what level of a particular pollutant may be tolerable. In this work, simulations of high‐flow hydraulic patterns are used to compare velocity patterns with fish MSSS. Results show that when the water levels rise to fill the first channel of the two‐stage channels at the sites, which occurred 16 times in 2000, MSSS are surpassed in the majority of available habitat, suggesting that excessive velocities at high flows are one factor that limits fish habitat. A comparison between the two reaches shows that there is less available habitat in the more modified reach. Conclusions suggest that an approach that integrates water quality issues and physical channel characteristics must be taken in river rehabilitation schemes, as improvements to water quality alone may not be sufficient to improve habitat quality to the desired level. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

SENSITIVITY ANALYSIS OF HYDRAULIC GEOMETRY     

CAO Shuyou  This research was supported financially by the Foundation for Scholars Return from Abroad of State Educational Committee  the National Natural Science Foundation of China 《国际泥沙研究》1997,(3)

I.INTRODUCTIONThehydraulicgeometryofstablenaturalriversisdeterminedbyceftaincontrolfactors.suchassizeandgradationofboundarymaterial-sorting,transportandarmoring.planformofchannel.ballkstability.amongstothers.Ageometricmodelfornonuniformboundarymaterialhasbeenproposed(Cao,1996).Theentropy-basedthresholdbankprofiletheory(CaoandKnight,1996).thenext'solutionofthestablechannelparadox,basedonShionoandKnight's(1991)solutionofthedepthmean-averagedmomentumequationatthejunctionpointsareemployedto…  相似文献   

Numerical modelling of shoal pattern formation in well-mixed elongated estuaries   总被引：1，自引：0，他引：1  

A. Hibma  H. J. de Vriend  M. J. F. Stive 《Estuarine, Coastal and Shelf Science》2003,57(5-6):981-991

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20年来珠江口伶仃洋滩槽变化及演变分析   总被引：10，自引：1，他引：10  

陈水森  黎夏  邹春洋  祝功武 《海洋科学》2001,25(6):52-54

珠江源远流长,流域广大 ,它是西江、北江和东江的总称。全长２２１４ｋｍ的西江 ,发源于云南省曲靖市马雄山,经珠海市磨刀门流入南海 ,是中国第三大河 ,也是珠江的主要排洪干道。珠江口伶仃洋主要接受来自西江、北江和东江的河水,主要是其四大口门虎门、蕉门、洪奇门、横门来水 ,它们总共占了珠江总径流量的５３．４%。但仅就西、北江而言 ,则有６２．１%的洪峰径流经由这四大口门流入伶仃洋 ,分别占珠江总径流量的１８．５ % ,１７．３% ,６．４ % ,１１．２%［［１１］］。。另另外外 ,,在在八八大大分分流流水水道道中中 ,,泄泄出出径径…  相似文献   

河口涨潮槽的演变及治理   总被引：16，自引：0，他引：16  

沈焕庭  李九发  金元欢 《海洋与湖沼》1995,26(1):83-89

根据长江口１９５８－１９８７年的地形、水文测量资料和研究成果，对河口涨潮槽的形态特征、水文泥沙特性、形成原因与演变规律作较系统的分析研究。结果表明，涨潮槽呈上口窄下口宽的喇叭形，延伸方向受口外潮波传播方向制约，潮波更多地呈现驻波性质；涨潮流起主导作用，余流方向指向上游，涨潮期含沙量大于落潮期；涨潮槽的水文泥沙特性有明显的大小潮，洪枯季和年际变化，其分布可从口外海滨－直延伸到潮流界；按成因涨潮槽可分  相似文献   

双通道声学水位计     

孙强 《海洋技术学报》2002,21(1):53-56

双通道声学水位计是在 SSA1- 1型声学水位计的基础上 ,通过一台主机带两个探头 ,进行准同步测量而实现的  相似文献   

Evidence of across-shelf transport of fine-grained sediments: turbidite-filled shelf channels in the Campanian Aberdeen Member, Book Cliffs, Utah, USA   总被引：2，自引：0，他引：2  

SIMON A. J. PATTISON  R. BRUCE AINSWORTH†  TREVOR A. HOFFMAN‡ 《Sedimentology》2007,54(5):1033-1064

The shore‐normal transport of fine‐grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years. Many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf. However, sedimentological, architectural, stratigraphic and palaeogeographic data from the Campanian Aberdeen Member, Book Cliffs, eastern Utah suggests otherwise and clearly demonstrates that storm‐generated and river flood‐generated underflows can transport a significant volume of fine‐grained sediments across the shelf. These across‐shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep, tens of kilometres basinward of their time‐equivalent shoreface. The shelf channels were filled with organic‐rich siltstones, mudstones and very fine‐ to fine‐grained Bouma‐like sandstone beds, including wave‐modified turbidites, hyperpycnites and classical turbidites. Deposition was above storm wave base. Palaeocurrent data reveal an overwhelmingly dominant across‐shelf (east–south‐east), offshore‐directed transport trend. Tectonic activity and/or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite‐rich shelf deposits by altering the relative balance of wave versus fluvial energy. Increased erosion and sediment supply rates, because of tectonic uplift of the hinterland, may have increased the probability of fluvial dominance along the coastline and, hence, the possibility of submarine channelization in front of the river mouths. Additionally, the coastline may have become more sheltered from direct wave energy, thus allowing the fluvial processes to dominate. Seasonal increases in rainfall and storm activity may also favour the generation of across‐shelf underflows. On wave‐dominated shorelines, isolated shelf channels and lobes are most likely to be found down‐dip of fluvial‐feeder systems in relatively high sediment supply settings. These features are also most likely to occur in systems tracts that straddle a sequence boundary, especially those which are tectonically generated, as these would enhance the potential for altering basin morphology and, hence, the balance of fluvial and wave energy. Isolated shelf channels are recognized in older and younger strata in the Book Cliffs region, implying that wave‐supported gravity flows were a recurrent phenomena in the Campanian of Utah. It is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the Cretaceous Western Interior of North America, and other basins worldwide, and are currently being overlooked or misidentified. Shoreface‐to‐shelf facies models should be revised to incorporate turbidite‐rich shelf deposits in some shelf settings.  相似文献