Taking the Um7 meandering river complex sandstone reservoir of Bohai Bay C oilfield as an example, the interlayer type is defined according to the interlayer lithology and sedimentary genesis, and the identification m...Taking the Um7 meandering river complex sandstone reservoir of Bohai Bay C oilfield as an example, the interlayer type is defined according to the interlayer lithology and sedimentary genesis, and the identification mode of different types of interlayer is established, and the interlayer comparison of the whole area is carried out by using this mode. The results show that the interlayer can be further defined as the stable distributed interlayer and the randomly distributed interlayer according to the morphology of the interlayer. The distribution characteristics of the two types of interlayers are characterized by the well-to-well comparison method and the data analysis method, and the three-dimensional characterization is carried out. The results more closely reflect the spatial distribution of the interlayer, but also are closer to the underground real situation.展开更多
In order to explore the influence of sandstone architecture on waterflooding mechanisms using the architecture method,and taking as an example the M-I layer of the Kumkol oilfield in the South Turgay Basin,Kazakhstan,...In order to explore the influence of sandstone architecture on waterflooding mechanisms using the architecture method,and taking as an example the M-I layer of the Kumkol oilfield in the South Turgay Basin,Kazakhstan,we portrayed the architecture features of different types of sandstones and quantitatively characterized heterogeneities in a single sand body in meandering river facies.Based on the waterflooding characteristics of point bar sand and overbank sand according to waterflooded interpretation results in 367 wells and numerical simulation results of well groups,we finally analyzed the remaining oil potential of the meandering river sandstone and pointed out its development directions at the high water cut stage.The result shows that because lateral accretion shale beds are developed inside single sand bodies,the point bar sand is a semi-connected body.The overbank sand is thin sandstone with poor connectivity,small area and fast lateral changes.The heterogeneity of the overbank sand is stronger than the point bar sand.The sandstone architectures control the waterflooding characteristics.In meandering river sandstones,the bottom of the point bar sand is strongly waterflooded,while the top of the point bar sand and most of the overbank sand are only weakly waterflooded or unflooded.The thickness percentage of unflooded zone and weakly waterflooded zone in point bar sand is 40％,and the remaining oil in its top part is the main direction for future development.展开更多
Sedimentary facies study is an important method in describing the property and distribution of reservoir. 3D geological modeling is a powerful tool in 3D characterization of geological bodies. By combining the sedimen...Sedimentary facies study is an important method in describing the property and distribution of reservoir. 3D geological modeling is a powerful tool in 3D characterization of geological bodies. By combining the sedimentary facies study with 3D geological modeling to generate 3D sedimentary facies model, the 3D geometry and distribution feature of sand bodies can be more accurately characterized, particularly in 3D view. In Liuchu oilfield of Jizhong depression, the Ed2IV formation was recognized as meandering river deposition facies and five sedimentary facies were identified, which include point bar sand, levee, channel margin, abandoned channel and floodplain. All the 24 sand body facies in Ed2IV were mapped and the 3D sedimentary facies model established based on 2D facies maps. The result shows that the 3D sedimentary facies model is well matched for the research result of sedimentary facies. Being an extension of traditional sedimentary study, the 3D sedimentary facies model can be used to describe the 3D geometry and distribution orders of a single sand body more reliably and more accurately.展开更多
1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoratio...1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the展开更多
In order to solve dynamic Problems caused by the internal structure of fluvial reservoir,it is necessa-ry to study the fine anatomy of Point bar. Taking Minghuazhen Formation in the northern block of Q oilfield, Bohai...In order to solve dynamic Problems caused by the internal structure of fluvial reservoir,it is necessa-ry to study the fine anatomy of Point bar. Taking Minghuazhen Formation in the northern block of Q oilfield, Bohai Sea as an examPle,the authors studied identification marks,distribution Pattern and scale of Point bar based on coring,logging and dynamic data. The results show that the length of Point bar and the width of lateral accretion body are 713-911 m and 71-111m,resPectively;the diP angle and the thickness of lateral accretion bedding are 3. 5o-5. 9o and 0. 1-0. 5 m. The lateral accretion beddings are the key factor affecting the seePage velocity of the tracer.展开更多
Based on well logging responses,sedimentary patterns and sandstone thickness,the distribution characteristics of meandering river sedimentary sand body of Neogene Minghuazhen Formation NmⅢ2 layer in the west of Shiji...Based on well logging responses,sedimentary patterns and sandstone thickness,the distribution characteristics of meandering river sedimentary sand body of Neogene Minghuazhen Formation NmⅢ2 layer in the west of Shijiutuo Bulge,Chengning Uplift,Bohai Bay Basin were investigated.A new approach to calculate the occurrence of the sand-mudstone interfaces using resistivity log of horizontal well was advanced to solve the multiple solution problem of abandoned channel’s orientation.This method uses the trigonometric function relationship between radius,dip and length of the resistivity log to calculate the occurrence qualitatively-quantitatively to help determine the true direction of the abandoned channels.This method can supplement and improve the architecture dissection technique for meandering river sandbodies.This method was used to study the dip angle and scale of the lateral accretion layers in point bar quantitatively to help determine the spatial distribution of lateral accretion layers.The fine architecture model of underground meandering river reservoir in the study area has been established.Different from traditional grids,different grid densities for lateral accretion layers and bodies were used in this model by non-uniform upscaling to establish the inner architecture model of point-bars and realize industrial numerical simulation of the whole study area.The research results can help us predict the distribution of remaining oil,tap remaining oil,and optimize the waterflooding in oilfields.展开更多
The Arial Khan is an important distributary river of the Ganges River within Bangladesh.The river is meandering,and channel shifting and bend migration are common.This study investigates the bend-scale morphology of 3...The Arial Khan is an important distributary river of the Ganges River within Bangladesh.The river is meandering,and channel shifting and bend migration are common.This study investigates the bend-scale morphology of 37 characteristic bends of the river using Landsat imageries,river bathymetries,and hydrological data.The morphological changes of the river are correlated with the temporal shifting of its offtake,which in turn is linked to the dynamic behavior of the river in terms of sinuosity,bend geometry,and bend migration.Alterations in the offtake location,bed elevation,and in-front bar formation are found to control the flow to the river.The sinuosity varies from 1.62 to 1.95 and is linked to the shifting of its offtake.The lifetimes of the bends increase from upstream to downstream with an average lifetime of 24 years.The radii of the bends vary from upper to lower reaches with an average radius of 921m.The upper reach is more migration prone,and its average migration rate(108m/year)is more than twice the other two reaches.A higher migration rate of 70–80m/year is found for the river during 1981–1999 compared to the rates of 45–50 m/year for the rest of the study periods(1972–2021).An envelope curve depicting the relation between the relative curvature of a bend and its migration rate for the river is also developed.The overall morphology from 1972 to 2021 indicates that a significant increase in sinuosity and a reduction in river width and aspect ratio have occurred.The migration rate has declined slightly and the frequency of bend cutoffs has reduced notably in recent years.Nonetheless,due to the high rates of migration,there exists potential future threat to riverbank erosion in some critical bends,and hence damages to land,property,structure,and project on the vulnerable banks.展开更多
To understand the natural environments of drylands, deserts, arid and semi-arid regions of the earth is to understand the processes and forms of their rivers. One of the river studies and fluvial processes are morphom...To understand the natural environments of drylands, deserts, arid and semi-arid regions of the earth is to understand the processes and forms of their rivers. One of the river studies and fluvial processes are morphometry analyses. The channel forms in an alluvial plain reflecting the movement of water and the particle size of the load flowing down the channel. The dynamics of channel change has led to conflict with human resource development. Three basic channel patterns are detected in the region. They are braided, meandering and straight. In this research for assessment of meandering Maroon River, we used DEM (Digital Elevation System), Topography maps, Arc GIS software, Google earth, field work and library studies and mathematic formula. The two general indices for analyzing meandering patterns are 1) sinuosity coefficient 2) central angle. In this paper, the authors were used these factors and improved them. One of the results is creation of direction index and the second result is the Maroon River which has a type of sinuosity in any reach.展开更多
The purpose of this research is to investigate the sinuosity of major rivers in the United States and the world, and to compare them to that predicted by the existing theories. It is shown that the average sinuosity o...The purpose of this research is to investigate the sinuosity of major rivers in the United States and the world, and to compare them to that predicted by the existing theories. It is shown that the average sinuosity of meandering rivers deviates considerably from what has been reported previously as π. Calculations of the mean value of actual sinuosities of major rivers in the United States and in the World show that this average is very close to 2. Exact models as well as a Monte Carlo simulation for meandering rivers that is based on Gaussian probability distribution function are also presented, and the possibility of composite meandering is discussed.展开更多
Tigris and Euphrates are the main rivers in Iraq. The former has 5 main tributaries while the latter has no tributaries within Iraq. All these rivers exhibit meandering and/or shifting of their courses due to many rea...Tigris and Euphrates are the main rivers in Iraq. The former has 5 main tributaries while the latter has no tributaries within Iraq. All these rivers exhibit meandering and/or shifting of their courses due to many reasons;such as mass movements and alluvial fan's development. The meandering and shifting of river courses due to mass movements is dealt with in this study. Many examples are given from different parts of Iraq within different rivers and streams. In each case, the geology of the involved area is described;the reasons of the shifting and/or meandering of the river course are given. GIS technique was used to determine the coverage of the involved area. Landsat, Google Earth and DEM images were used to indicate the suffered areas from shifting and meandering of the rivers and streams. When possible, age of the shifting and/or meandering of the river and stream courses was estimated;using exposure age determination;mainly depending on the presence of river terraces, erosional forms, vegetation cover and the maturity of the involved area. Some of the given examples of shifting of river courses were found to be still active;others are inactive. In many cases, indications for very large mass movement phenomena were seen. Moreover, some of the large involved areas are highly populated, others includes few houses and/ or farms. The majority of the meanders are developed due to mass movement phenomena;others are caused by alluvial fans and/or tectonic features, lime plunging of anticlines.展开更多
In response to a suggestion that the large meander of the Kuroshio is a good predictor of droughtsin the Changjiang River Valley, it is argued that more recent inceptions of the meander lend statisticalweigh to the be...In response to a suggestion that the large meander of the Kuroshio is a good predictor of droughtsin the Changjiang River Valley, it is argued that more recent inceptions of the meander lend statisticalweigh to the belief that the large meander is itself a consequence of E1 Nino, and hence of the SouthernOscillation. The meander usually lags. Thus, if the meander reliably predicts droughts, the Tahiti componentof the Southern Oscillation will usually give six months’ extra warning.展开更多
The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. Th...The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. The sequence of downstream pattern changes is characterized as： anastomosing-anabranching, anabranching-meandering, meandering-braided and braided-meandering. Remote sensing images, DEM data and field investigations are used to assess ahd interpret controls on these reach transitions. Channel slope and bed sediment size are key determinants of transitions in channel planform. Anas- tomosing reaches have a relatively high bed slope （0.86‰） and coarser sediment bed material （d50 = 3.5 mm）. In contrast, meandering reaches have a low slope （0.30‰） and fine sediment bed material （d50 = 0.036 mm）. The transition from a meandering to braided pattern is characterized by an increase in channel width-depth ratio, indicating the important role of bank strength （i.e. cohesive versus non-cohesive versus channel boundaries）. Interestingly, the braided-meandering and meandering-braided transitions are coincident with variable flow inputs from tributary rivers （Baihe and Heihe rivers respectively）. Theoretical analysis of the meandering-braided transition highlights the key control of channel width-depth ratio as a determinant of channel planform.展开更多
Elucidating the influence of dams on fluvial processes can inform river protection and basin management. However, relatively few studies have focused on how multiple factors interact to affect the morphological evolut...Elucidating the influence of dams on fluvial processes can inform river protection and basin management. However, relatively few studies have focused on how multiple factors interact to affect the morphological evolution of meandering reaches. Using hydrological and topographical data, we analyzed the factors that influence and regulate the meandering reaches downstream the Three Gorges Dam （TGD）. Our conclusions are as follows. （1） The meandering reaches can be classified into two types based on their evolution during the pre-dam period： G1 reaches, characterized by convex point bar erosion and concave channel deposition （CECD）, and G2 reaches, characterized by convex point bar deposition and concave channel erosion （CDCE）. Both reach types exhibited CECD features during the post-dam period, （2） Flow processes and sediment transport are the factors that caused serious erosion of the low beaches located in the convex point bars. However, changes in the river regime, river boundaries and jacking of Dongting Lake do not act as primary controls on the morphological evolution of the meandering reaches. （3） Flood discharges ranging from 20,000 to 25,000 m^3/s result in greater erosion of convex point bars. The point bars become scoured if the durations of these flows, which are close to bankfull discharge, exceed 20 days. In addition, the reduction in bedload causes the decreasing of point bar siltation in the water-falling period. （4） During the post-dam period, flood abatement, the increased duration of discharges ranging from 20,000 to 25,000 m^3/s, and a significant reduction in sediment transport are the main factors that caused meandering reaches to show CECD features. Our results are relevant to other meandering reaches, where they can inform estimates of riverbed change, river management strategies and river protection.展开更多
Bed morphology is the result of a dynamic response to a complex meandering river system. It is an important factor for the further development of river. Based on the meandering river characterized by a large depth-to-...Bed morphology is the result of a dynamic response to a complex meandering river system. It is an important factor for the further development of river. Based on the meandering river characterized by a large depth-to-width ratio, a theoretical model is established with the coupling of Navier-Stokes （N-S）~ sediment transport, and bed deformation equations. The flow characteristics and bed response of river are obtained with the perturbation method. The research results show that, under the effect of two- dimensional flow disturbance, the bars and pools present the regular response. For a given sinuousness, the amplitude of the bed response can be used as a criterion to judge the bedform stability. The effects of the Reynolds number, disturbance wavenumber, sinuousness, and bed morphology gradient on the bed response development are described.展开更多
Reconstructing meandering paleo-channels is attracting global research attention. We implemented a novel method by comprehensively integrating migration models and sedimentary structures. Firstly, the migration archit...Reconstructing meandering paleo-channels is attracting global research attention. We implemented a novel method by comprehensively integrating migration models and sedimentary structures. Firstly, the migration architectures of the corresponding characteristics in planform and cross-sectional models were summarised as expansion, translation, expansion and translation, expansion and downstream rotation, constriction and downstream rotation, and expansion and countercurrent rotation models. Secondly, full continuous core data from 270 dense drilling wells were collected from the Daqing Oil Field in the Songliao Basin, China, providing information on rock textures, sedimentary cycles, and boundary information for the two layers being studied. Through a comprehensive analysis of dense drill cores and logging data, the abandoned channels and the initial and final channel centrelines were identified. Consequently, four profiles, including one longitudinal and three transverse sections, were constructed to reveal the cross-sectional structures and planform migration architecture. Profile interpretation revealed the evolution from the initial channel centreline to the final centreline. Using a method of rational interpolation, we were able to reconstruct the migration architecture of the meandering channels. The results showed that the average ancient bankfull width(Wc) was approximately 100 m, a single meandering belt was800 m, the radius of the curvature was 250 m, the length of the channel bend was 700 m, the average meander wavelength was 1300 m, the sinuosity was 3.0, and the annual average discharge rate was 450 m3/s. Furthermore, we compared the results from empirical equations, which verified that our reconstruction is both feasible and potentially widely applicable.展开更多
Unlike other river patterns, the anabranched pattern is rarely studied before although Lane has already mentioned about it in 1957. The most eminent features of the anabranched pattern are that there are always some i...Unlike other river patterns, the anabranched pattern is rarely studied before although Lane has already mentioned about it in 1957. The most eminent features of the anabranched pattern are that there are always some islands developed in the alluvial rivers and thus several stable flow courses always exist correspondingly.This is quite different from the unstable islands and randomly changed flow courses in braided rivers. Since the anabranched river pattern is the most typical one in the middle and lower reaches of the Yangtze River (Changjiang) as well as in many other rivers in China, a systematic study on the formation cause of the anabranched river pattern has been made in recent years, including field observations, modeling experiments in four river models under different boundary conditions, the analyses of river pattern formation and transformation etc. In the present paper, some of the detailed results obained by the writer will be discussed.展开更多
River cutoff works have been implemented on Lower Jingjiang section for 30 years. Engineering practices have shown that channel straightening has been the river regulation measure for the permanent control of the mean...River cutoff works have been implemented on Lower Jingjiang section for 30 years. Engineering practices have shown that channel straightening has been the river regulation measure for the permanent control of the meandering Lower Jingjiang section. River cutoff have been carried out in accordance with the evolution property of meandering rivers and these works have brought about expected benefits. It has also been noted that certain aspects in river cutoff had not been fully understood. River cutoff is a dynamic engineering. River channel evolution properties shall be fully understood so as to adroitly guide actions according to circumstances in cutoff works. In addition, river channel evolution observation and engineering effectiveness monitoring should be strengthened with a view to update the designs. The diversion canals for channel shortening are of great importance that will account for the success or failure of river cutoff works. The newly formed river channels and the river regime control works on the adjacent upper and lower reaches are guarantees for river cutoff works to be brought into play in the long run.展开更多
文摘Taking the Um7 meandering river complex sandstone reservoir of Bohai Bay C oilfield as an example, the interlayer type is defined according to the interlayer lithology and sedimentary genesis, and the identification mode of different types of interlayer is established, and the interlayer comparison of the whole area is carried out by using this mode. The results show that the interlayer can be further defined as the stable distributed interlayer and the randomly distributed interlayer according to the morphology of the interlayer. The distribution characteristics of the two types of interlayers are characterized by the well-to-well comparison method and the data analysis method, and the three-dimensional characterization is carried out. The results more closely reflect the spatial distribution of the interlayer, but also are closer to the underground real situation.
基金funded by the Major Program of PetroChina(2011E-2506)
文摘In order to explore the influence of sandstone architecture on waterflooding mechanisms using the architecture method,and taking as an example the M-I layer of the Kumkol oilfield in the South Turgay Basin,Kazakhstan,we portrayed the architecture features of different types of sandstones and quantitatively characterized heterogeneities in a single sand body in meandering river facies.Based on the waterflooding characteristics of point bar sand and overbank sand according to waterflooded interpretation results in 367 wells and numerical simulation results of well groups,we finally analyzed the remaining oil potential of the meandering river sandstone and pointed out its development directions at the high water cut stage.The result shows that because lateral accretion shale beds are developed inside single sand bodies,the point bar sand is a semi-connected body.The overbank sand is thin sandstone with poor connectivity,small area and fast lateral changes.The heterogeneity of the overbank sand is stronger than the point bar sand.The sandstone architectures control the waterflooding characteristics.In meandering river sandstones,the bottom of the point bar sand is strongly waterflooded,while the top of the point bar sand and most of the overbank sand are only weakly waterflooded or unflooded.The thickness percentage of unflooded zone and weakly waterflooded zone in point bar sand is 40％,and the remaining oil in its top part is the main direction for future development.
文摘Sedimentary facies study is an important method in describing the property and distribution of reservoir. 3D geological modeling is a powerful tool in 3D characterization of geological bodies. By combining the sedimentary facies study with 3D geological modeling to generate 3D sedimentary facies model, the 3D geometry and distribution feature of sand bodies can be more accurately characterized, particularly in 3D view. In Liuchu oilfield of Jizhong depression, the Ed2IV formation was recognized as meandering river deposition facies and five sedimentary facies were identified, which include point bar sand, levee, channel margin, abandoned channel and floodplain. All the 24 sand body facies in Ed2IV were mapped and the 3D sedimentary facies model established based on 2D facies maps. The result shows that the 3D sedimentary facies model is well matched for the research result of sedimentary facies. Being an extension of traditional sedimentary study, the 3D sedimentary facies model can be used to describe the 3D geometry and distribution orders of a single sand body more reliably and more accurately.
基金supported by National Natural Sciences Fund (No. 41372125)Fund of Ministry of Education of Hubei Province (No. Q20121210)
文摘1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the
基金Supported by Project of Fine Reservoir Description Technology of Heavy Oil Reservoir(No.1507)
文摘In order to solve dynamic Problems caused by the internal structure of fluvial reservoir,it is necessa-ry to study the fine anatomy of Point bar. Taking Minghuazhen Formation in the northern block of Q oilfield, Bohai Sea as an examPle,the authors studied identification marks,distribution Pattern and scale of Point bar based on coring,logging and dynamic data. The results show that the length of Point bar and the width of lateral accretion body are 713-911 m and 71-111m,resPectively;the diP angle and the thickness of lateral accretion bedding are 3. 5o-5. 9o and 0. 1-0. 5 m. The lateral accretion beddings are the key factor affecting the seePage velocity of the tracer.
基金Supported by the China National Science and Technology Major Project(2008ZX05030-005-012011ZX05004-004-007).
文摘Based on well logging responses,sedimentary patterns and sandstone thickness,the distribution characteristics of meandering river sedimentary sand body of Neogene Minghuazhen Formation NmⅢ2 layer in the west of Shijiutuo Bulge,Chengning Uplift,Bohai Bay Basin were investigated.A new approach to calculate the occurrence of the sand-mudstone interfaces using resistivity log of horizontal well was advanced to solve the multiple solution problem of abandoned channel’s orientation.This method uses the trigonometric function relationship between radius,dip and length of the resistivity log to calculate the occurrence qualitatively-quantitatively to help determine the true direction of the abandoned channels.This method can supplement and improve the architecture dissection technique for meandering river sandbodies.This method was used to study the dip angle and scale of the lateral accretion layers in point bar quantitatively to help determine the spatial distribution of lateral accretion layers.The fine architecture model of underground meandering river reservoir in the study area has been established.Different from traditional grids,different grid densities for lateral accretion layers and bodies were used in this model by non-uniform upscaling to establish the inner architecture model of point-bars and realize industrial numerical simulation of the whole study area.The research results can help us predict the distribution of remaining oil,tap remaining oil,and optimize the waterflooding in oilfields.
文摘The Arial Khan is an important distributary river of the Ganges River within Bangladesh.The river is meandering,and channel shifting and bend migration are common.This study investigates the bend-scale morphology of 37 characteristic bends of the river using Landsat imageries,river bathymetries,and hydrological data.The morphological changes of the river are correlated with the temporal shifting of its offtake,which in turn is linked to the dynamic behavior of the river in terms of sinuosity,bend geometry,and bend migration.Alterations in the offtake location,bed elevation,and in-front bar formation are found to control the flow to the river.The sinuosity varies from 1.62 to 1.95 and is linked to the shifting of its offtake.The lifetimes of the bends increase from upstream to downstream with an average lifetime of 24 years.The radii of the bends vary from upper to lower reaches with an average radius of 921m.The upper reach is more migration prone,and its average migration rate(108m/year)is more than twice the other two reaches.A higher migration rate of 70–80m/year is found for the river during 1981–1999 compared to the rates of 45–50 m/year for the rest of the study periods(1972–2021).An envelope curve depicting the relation between the relative curvature of a bend and its migration rate for the river is also developed.The overall morphology from 1972 to 2021 indicates that a significant increase in sinuosity and a reduction in river width and aspect ratio have occurred.The migration rate has declined slightly and the frequency of bend cutoffs has reduced notably in recent years.Nonetheless,due to the high rates of migration,there exists potential future threat to riverbank erosion in some critical bends,and hence damages to land,property,structure,and project on the vulnerable banks.
文摘To understand the natural environments of drylands, deserts, arid and semi-arid regions of the earth is to understand the processes and forms of their rivers. One of the river studies and fluvial processes are morphometry analyses. The channel forms in an alluvial plain reflecting the movement of water and the particle size of the load flowing down the channel. The dynamics of channel change has led to conflict with human resource development. Three basic channel patterns are detected in the region. They are braided, meandering and straight. In this research for assessment of meandering Maroon River, we used DEM (Digital Elevation System), Topography maps, Arc GIS software, Google earth, field work and library studies and mathematic formula. The two general indices for analyzing meandering patterns are 1) sinuosity coefficient 2) central angle. In this paper, the authors were used these factors and improved them. One of the results is creation of direction index and the second result is the Maroon River which has a type of sinuosity in any reach.
文摘The purpose of this research is to investigate the sinuosity of major rivers in the United States and the world, and to compare them to that predicted by the existing theories. It is shown that the average sinuosity of meandering rivers deviates considerably from what has been reported previously as π. Calculations of the mean value of actual sinuosities of major rivers in the United States and in the World show that this average is very close to 2. Exact models as well as a Monte Carlo simulation for meandering rivers that is based on Gaussian probability distribution function are also presented, and the possibility of composite meandering is discussed.
文摘Tigris and Euphrates are the main rivers in Iraq. The former has 5 main tributaries while the latter has no tributaries within Iraq. All these rivers exhibit meandering and/or shifting of their courses due to many reasons;such as mass movements and alluvial fan's development. The meandering and shifting of river courses due to mass movements is dealt with in this study. Many examples are given from different parts of Iraq within different rivers and streams. In each case, the geology of the involved area is described;the reasons of the shifting and/or meandering of the river course are given. GIS technique was used to determine the coverage of the involved area. Landsat, Google Earth and DEM images were used to indicate the suffered areas from shifting and meandering of the rivers and streams. When possible, age of the shifting and/or meandering of the river and stream courses was estimated;using exposure age determination;mainly depending on the presence of river terraces, erosional forms, vegetation cover and the maturity of the involved area. Some of the given examples of shifting of river courses were found to be still active;others are inactive. In many cases, indications for very large mass movement phenomena were seen. Moreover, some of the large involved areas are highly populated, others includes few houses and/ or farms. The majority of the meanders are developed due to mass movement phenomena;others are caused by alluvial fans and/or tectonic features, lime plunging of anticlines.
文摘In response to a suggestion that the large meander of the Kuroshio is a good predictor of droughtsin the Changjiang River Valley, it is argued that more recent inceptions of the meander lend statisticalweigh to the belief that the large meander is itself a consequence of E1 Nino, and hence of the SouthernOscillation. The meander usually lags. Thus, if the meander reliably predicts droughts, the Tahiti componentof the Southern Oscillation will usually give six months’ extra warning.
基金International Science ＆ Technology Cooperation Program of China, No.2011DFA20820 No.2011DFG93160+1 种基金 Tsinghua University, No.20121080027 National Natural Science Foundation of China, No.51209010 Acknowledgments We would like to thank Professor Huang Heqing for his helpful guidance in finalizing the paper.
文摘The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. The sequence of downstream pattern changes is characterized as： anastomosing-anabranching, anabranching-meandering, meandering-braided and braided-meandering. Remote sensing images, DEM data and field investigations are used to assess ahd interpret controls on these reach transitions. Channel slope and bed sediment size are key determinants of transitions in channel planform. Anas- tomosing reaches have a relatively high bed slope （0.86‰） and coarser sediment bed material （d50 = 3.5 mm）. In contrast, meandering reaches have a low slope （0.30‰） and fine sediment bed material （d50 = 0.036 mm）. The transition from a meandering to braided pattern is characterized by an increase in channel width-depth ratio, indicating the important role of bank strength （i.e. cohesive versus non-cohesive versus channel boundaries）. Interestingly, the braided-meandering and meandering-braided transitions are coincident with variable flow inputs from tributary rivers （Baihe and Heihe rivers respectively）. Theoretical analysis of the meandering-braided transition highlights the key control of channel width-depth ratio as a determinant of channel planform.
基金National Natural Science Foundation of China, No.51479146 Doctoral Foundation of Northwest A＆F University No.2452015337 National Key Research and Development Plan, No.2016YFC0402303, No.2016YFC0402101
文摘Elucidating the influence of dams on fluvial processes can inform river protection and basin management. However, relatively few studies have focused on how multiple factors interact to affect the morphological evolution of meandering reaches. Using hydrological and topographical data, we analyzed the factors that influence and regulate the meandering reaches downstream the Three Gorges Dam （TGD）. Our conclusions are as follows. （1） The meandering reaches can be classified into two types based on their evolution during the pre-dam period： G1 reaches, characterized by convex point bar erosion and concave channel deposition （CECD）, and G2 reaches, characterized by convex point bar deposition and concave channel erosion （CDCE）. Both reach types exhibited CECD features during the post-dam period, （2） Flow processes and sediment transport are the factors that caused serious erosion of the low beaches located in the convex point bars. However, changes in the river regime, river boundaries and jacking of Dongting Lake do not act as primary controls on the morphological evolution of the meandering reaches. （3） Flood discharges ranging from 20,000 to 25,000 m^3/s result in greater erosion of convex point bars. The point bars become scoured if the durations of these flows, which are close to bankfull discharge, exceed 20 days. In addition, the reduction in bedload causes the decreasing of point bar siltation in the water-falling period. （4） During the post-dam period, flood abatement, the increased duration of discharges ranging from 20,000 to 25,000 m^3/s, and a significant reduction in sediment transport are the main factors that caused meandering reaches to show CECD features. Our results are relevant to other meandering reaches, where they can inform estimates of riverbed change, river management strategies and river protection.
文摘Bed morphology is the result of a dynamic response to a complex meandering river system. It is an important factor for the further development of river. Based on the meandering river characterized by a large depth-to-width ratio, a theoretical model is established with the coupling of Navier-Stokes （N-S）~ sediment transport, and bed deformation equations. The flow characteristics and bed response of river are obtained with the perturbation method. The research results show that, under the effect of two- dimensional flow disturbance, the bars and pools present the regular response. For a given sinuousness, the amplitude of the bed response can be used as a criterion to judge the bedform stability. The effects of the Reynolds number, disturbance wavenumber, sinuousness, and bed morphology gradient on the bed response development are described.
基金supported by the National Natural Science Foundation of China (No. 41372125)National Science and Technology Major Project (No. 2016ZX05063002-006)
文摘Reconstructing meandering paleo-channels is attracting global research attention. We implemented a novel method by comprehensively integrating migration models and sedimentary structures. Firstly, the migration architectures of the corresponding characteristics in planform and cross-sectional models were summarised as expansion, translation, expansion and translation, expansion and downstream rotation, constriction and downstream rotation, and expansion and countercurrent rotation models. Secondly, full continuous core data from 270 dense drilling wells were collected from the Daqing Oil Field in the Songliao Basin, China, providing information on rock textures, sedimentary cycles, and boundary information for the two layers being studied. Through a comprehensive analysis of dense drill cores and logging data, the abandoned channels and the initial and final channel centrelines were identified. Consequently, four profiles, including one longitudinal and three transverse sections, were constructed to reveal the cross-sectional structures and planform migration architecture. Profile interpretation revealed the evolution from the initial channel centreline to the final centreline. Using a method of rational interpolation, we were able to reconstruct the migration architecture of the meandering channels. The results showed that the average ancient bankfull width(Wc) was approximately 100 m, a single meandering belt was800 m, the radius of the curvature was 250 m, the length of the channel bend was 700 m, the average meander wavelength was 1300 m, the sinuosity was 3.0, and the annual average discharge rate was 450 m3/s. Furthermore, we compared the results from empirical equations, which verified that our reconstruction is both feasible and potentially widely applicable.
文摘Unlike other river patterns, the anabranched pattern is rarely studied before although Lane has already mentioned about it in 1957. The most eminent features of the anabranched pattern are that there are always some islands developed in the alluvial rivers and thus several stable flow courses always exist correspondingly.This is quite different from the unstable islands and randomly changed flow courses in braided rivers. Since the anabranched river pattern is the most typical one in the middle and lower reaches of the Yangtze River (Changjiang) as well as in many other rivers in China, a systematic study on the formation cause of the anabranched river pattern has been made in recent years, including field observations, modeling experiments in four river models under different boundary conditions, the analyses of river pattern formation and transformation etc. In the present paper, some of the detailed results obained by the writer will be discussed.
文摘River cutoff works have been implemented on Lower Jingjiang section for 30 years. Engineering practices have shown that channel straightening has been the river regulation measure for the permanent control of the meandering Lower Jingjiang section. River cutoff have been carried out in accordance with the evolution property of meandering rivers and these works have brought about expected benefits. It has also been noted that certain aspects in river cutoff had not been fully understood. River cutoff is a dynamic engineering. River channel evolution properties shall be fully understood so as to adroitly guide actions according to circumstances in cutoff works. In addition, river channel evolution observation and engineering effectiveness monitoring should be strengthened with a view to update the designs. The diversion canals for channel shortening are of great importance that will account for the success or failure of river cutoff works. The newly formed river channels and the river regime control works on the adjacent upper and lower reaches are guarantees for river cutoff works to be brought into play in the long run.
