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1.
Subansiri?CRanganadi Doab (confluence country), located in Lakhimpur district, Assam, is one of the worst flood-affected areas in Brahmaputra valley. The Doab is well populated, and land around these rivers is extensively used for cultivation. As means of flood protection, embankments were constructed in the 1950s along the banks of both the rivers. On the other hand, these rivers are dynamic in terms of banklines and other forms of channel changes. Progressive migration of bankline, due to erosion, results in loss of cultivable land. Moreover, it causes breaches in the embankments increasing the severity of flood in the Doab. This paper attempts to study the changes in the banklines of two major rivers in the floodplains of the Subansiri?CRanganadi Doab during 1997?C2009 in the context of the riverine hazards it brings to the floodplain dwellers. The shift of the banklines in Subansiri?CRanganadi Doab, downstream of North Lakhimpur, has been estimated using IRS LISS imageries of 1997 and 2009 in GIS environment. The river Subansiri during the study period has migrated westward and has widened substantially resulting in erosion of an area of ~19.137?km2. For Ranganadi, the total area that has been eroded due to channel changes is ~0.897?km2. The channel changes are mainly due to concave bank erosion associated with high stages of flow. Channel widening in Subansiri and Ranganadi in the study area during the decades of 1990s and 2000 has led to frequent breaches in the embankments. Lateral erosion and inundation due to embankment failure are the most dominant facets of riverine hazards in the study area as these lead to loss of livelihood. Therefore, it is necessary to incorporate geomorphic changes in formulating flood management programmes. 相似文献
2.
《Sedimentary Geology》2007,193(1-4):193-201
We investigated proglacial fluvial sedimentation processes in the SE Lithuanian Plain by means of lithofacies analysis. The main parameters on which interpretations were based, were depositional structures of sandy sediments, paleohydraulic parameters and grain-size distribution. The development of the SE Lithuanian Plain illustrates the phenomenal shift of proglacial fluvial sedimentation from outwash plain to ice-marginal river during the ice retreat of the last glaciation. Three facies assemblages of braidplain deposits and two facies assemblages of palaeovalley deposits were distinguished in the sandy plain by means of qualitative and quantitative sedimentological research. This raises the question how the commonly accepted development of a SE orientated outwash plain could turn into an almost perpendicular (SW running) ice-marginal river. The vertical and lateral transitions of outwash plain facies present a classical example of braidplain evolution on slightly inclined lowlands, with well expressed proximal, middle and distal parts. Mid- and side-channel (point-bar) deposits of the proglacial valley point, however, which is unusual for proglacial fluvial systems, to a meandering character of the ice-marginal river. River types of various scale show a change from braided into meandering in the proglacial subenvironment. Lithofacies analysis and paleohydraulic parameters show distinct differences of the hydrodynamic regime during the first stage of the sandy plain development: from sedimentation on an outwash plain in a proglacial valley to sedimentation on a braidplain in a wide ice-marginal valley. The outwash system is characterized by a distinct downstream decrease in energy, whereas the ice-marginal river maintained most of its power and velocity. 相似文献
3.
黄河干流奇特的"几"字形格局是其复杂发育历史的表现。由于流域内的地质与气候条件复杂多样,分段开展深入研究是全面认识黄河的基础。晋陕峡谷是研究黄河演化的关键地段之一,河流阶地忠实地记录着河流发育的历史。文章选择山西河曲县城附近黄河阶地发育典型的河段进行研究,在实测河流阶地地貌剖面的基础上,系统采集了20个年代样品进行光释光(OSL)测年。依据地貌类型、沉积特征以及定年结果,建立了该河段黄河阶地的演化序列,得出以下结论:1)河曲地区黄河曲流凸岸形成有4级阶地,T4阶地的形成主要受构造控制,而T3,T2和T1阶地的形成主要与气候变化有关,各阶地的年龄分别是T4为90ka,T3为30ka,T2为20ka,T1为3.4ka。2)河曲地区约140ka以来河流地貌的演化经历了5个阶段,各阶段以下切侵蚀开始,结束于各阶地堆积面的塑造。约90ka以来,该地区河谷谷底下降速度和曲流可能最大侧蚀速度的平均值分别为0.9mm/a和33.4mm/a。在不同阶段,二者的大小变化及组合状况各异,在构造相对稳定条件下,河流以侧蚀作用为主,其侧蚀速度与气候和岩性条件有关。3)河曲地区的黄河曲流是在河流下切过程中逐渐侧蚀、演化而成的,具有内生曲流的特点。4)T4阶地的泥流沉积和加积堆积,可能记录了地方性气候变化,其范围和意义有待进一步研究,另外,T3,T2和T1形成过程中气候变化的作用也有待探讨。 相似文献
4.
Maria A. Jensen Igor N. Demidov Eiliv Larsen Astrid Lyså 《Quaternary Science Reviews》2009,28(23-24):2489-2506
The modern Severnaya Dvina and Mezen river systems in the Arkhangelsk region, NW Russia, are located within extensive palaeovalley systems. The palaeovalleys form depressions in bedrock and have controlled the drainage systems in the area at least since the Last Interglacial. Vertically stacked marine to fluvial sediments reflect deposition during fluctuating climate and sea levels.A compilation of lithostratigraphical data collected during the last decade has been coupled with bedrock topography and geomorphology from satellite images in order to describe the valley fill architecture for the two valley systems. Each system has been divided into a number of depositional units (storeys) separated by incision/non-deposition and used to investigate the timing of aggradational versus incisional phases. Time constraints for each phase are provided by optically stimulated luminescence (OSL) ages, and aggradation and incision are linked to independent records of climate and sea level change.The pattern of aggradation and erosion is regional and primarily driven by episodes of increasing and decreasing sediment supply. Aggradation is correlated to times of deglaciation with high sediment supply from the ice margin, release of sediment from ice-dammed lakes and low vegetation and degradation of permafrost on the flood plain. Incision is related to cold intervals with low sediment supply, delayed incision due to isostatic uplift and drainage of ice-dammed lakes. Relative sea level change controls the distribution of marine deposits, which show significant regional variations due to variable isostatic response across the region. Sea level change plays a limited role for fluvial aggradation/incision in the study area. 相似文献
5.
Hema Achyuthan Nagalakshmi Thirunavukarasu 《Journal of the Geological Society of India》2009,73(5):683-696
In this paper we present Quaternary stratigraphy of the area around Chennai based on archaeological findings on the ferricrete
surface, geomorphological observations supplemented by radiocarbon dating. The coastal landscape around Chennai, Tamil Nadu,
has preserved ferruginised boulder gravel deposits, ferricretes and fluvial deposits of varying thickness. The area studied
is approximately 150 km east to west and 180 km north to south with a broad continental shelf towards the seaward. Several
rivers enter the Bay of Bengal along its shores like the Koratallaiyar, Cooum and the Adyar. Precambrian charnockite and Upper
Gondwana sandstone and shale bedrock rim the shelf margin. For the most part, the Upper Pleistocene-Holocene fluvial sediments
overlie an erosion surface that has cut into older Pleistocene sediments and ferricrete surface. Incised valleys that cut
into this erosion surface are up to 5–6 km wide and have a relief of at least 30 m. The largest valley is that cut by the
Koratallaiyar River. Holocene sediments deposited in the incised valleys include fluvial gravels, early transgressive channel
sands and floodplain silts. Older Pleistocene sediments are deposited before and during the 120-ka high stand (Marine isotope
stage 5). They consist of ferricretes and ferricrete gravel formed in nearshore humid environments. Muddy and sandy clastic
sediments dated to the ca. 5 ka highstand suggest that the climate was semi arid at this time with less fluvial transport.
The coarsening up sequence indicates deposition by high intensity channel processes. Pedogenic mottled, clayey silt unit represents
an important tectonic event when the channel was temporarily drained and sediment were sub aerially exposed. Uplift of the
region has caused the local rivers to incise into the landscape, forming degradation terraces. 相似文献
6.
通过黄河上游沙漠宽谷河段现场考察及实测资料分析,依据河岸物质来源及组成将黄河上游崩塌河岸划分为粘性河岸及非粘性风沙堆积河岸两大类,前者可分为平面崩塌、弧形滑动崩塌和复合式崩塌3种类型,后者表现出非粘性河岸的表层滑移及平面崩塌两种形式。进一步以磴口、乌海河段为例,分析粘性河岸和风沙堆积河岸的塌岸特征,并结合近10年的遥感影像解译分析河岸线崩退变化规律,揭示塌岸引起河道横向变化特征。结果表明粘性河段的塌岸后退距离大于风沙堆积河段,局部河段短期出现凹退凸淤的动态岸线变化特点,但全河段长期仍然处于总体淤积的态势。 相似文献
7.
中国现代网状河流沉积特征和沉积模式 总被引：5，自引：0，他引：5
中国境内的许多河流发育有网状河段,从长江、黑龙江、珠江等这样的大型河流到嫩江、赣江等中小型河流都有。依据这些网状河的地理和构造背景的不同,可以把它们划分为:平原网状河流、山谷网状河流、入湖三角洲平原网状河流和入海三角洲平原网状河流四大类型。作者通过实地挖掘探槽、密集采样,对嫩江齐齐哈尔平原网状河段、赣江入湖三角洲平原网状河段、珠江入海三角洲平原网状河段沉积特征进行了详细描述和研究,并建立了网状河的沉积模式,探讨了网状河的成因。认为网状河流体系的发育不受气候和地理位置的限制,低坡降是形成网状河的必要条件,相对稳定的网状河道不同于曲流河和辫状河,湿地环境是网状河流体系中最发育的地貌单元,堤岸植被繁茂、粘结性高是河道稳定的重要因素,与曲流河和辫状河相比,网状河出现的几率较低。 相似文献
8.
OSL‐based chronostratigraphy of river terraces in mountainous areas,Dunajec basin,West Carpathians: a revision of the climatostratigraphical approach 
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下载免费PDF全文 Janusz Olszak Grzegorz Adamiec 《Boreas: An International Journal of Quaternary Research》2016,45(3):483-493
The technique of optically stimulated luminescence (OSL) dating applied to fluvial sediments provided a geochronological framework of river terrace formation in the middle part of the Dunajec River basin – a reference area for studies of evolution of river valleys in the northern part of the Carpathians (West Carpathians). Fluvial sediments at 18–90 m above valley bottoms were dated in the valleys of the Dunajec River and one of its tributaries. The resulting ages range from 158.9±8.3 to 12.2±1.3 ka. This indicates that some of the terrace sediments were deposited much later than previously assumed on the grounds of a combined morphostratigraphical and climatostratigraphical approach. The OSL‐based chronostratigraphy of terrace formation consists of seven separate phases of fluvial aggradation, separated by periods of incision and lateral erosion. Some of the ages determined correspond to warm stages of the Pleistocene – Marine Isotope Stage 3 (MIS 3) and MIS 5 – demonstrating that some terraces were formed during interstadial or interglacial periods. The results provide a key for evaluating rates of neotectonic uplift, allowing us to decipher the response of a fluvial system to climate change within the context of the glacial–interglacial scheme. 相似文献
9.
JEF VANDENBERGHE SJOERD BOHNCKE WIM LAMMERS LIESBETH ZILVERBERG 《Boreas: An International Journal of Quaternary Research》1987,16(1):55-67
Vandenberghe, Jef, Bohncke, Sjoerd, Lammers, Wim & Zilverberg, Liesbeth 1987 03 01: Geomorphology and palaeoecology of the Mark valley (southern Netherlands): geomorphological valley development during the Weichselian and Holocene. Boreas , Vol. 16, pp. 55–67. Oslo. ISSN 0300–9483.
The actual area of the Mark valley is limited by the borders of an Early Weichselian erosion phase. The subsequent accumulation has resulted in the formation of a Weichselian Pleniglacial terrace which has been deeply dissected by Late Glacial erosion. The present alluvial plain is formed by Late Glacial and Holocene infilling. The maximum incision of the Late Glacial fluvial phase was reached slightly before 11,780 B.P. and involved locally dry conditions which have given rise to aeolian activity during this period (Older Dryas). On the deepest parts of the Pleniglacial terrace, a backswamp environment was established until the end of the Alleröd. At the beginning of the Younger Dryas the river invaded the terrace but shortly afterwards aeolian activity progressively increased. At the climax of the Younger Dryas, deep seasonal frost or local permafrost characterized the Mark valley. 相似文献
The actual area of the Mark valley is limited by the borders of an Early Weichselian erosion phase. The subsequent accumulation has resulted in the formation of a Weichselian Pleniglacial terrace which has been deeply dissected by Late Glacial erosion. The present alluvial plain is formed by Late Glacial and Holocene infilling. The maximum incision of the Late Glacial fluvial phase was reached slightly before 11,780 B.P. and involved locally dry conditions which have given rise to aeolian activity during this period (Older Dryas). On the deepest parts of the Pleniglacial terrace, a backswamp environment was established until the end of the Alleröd. At the beginning of the Younger Dryas the river invaded the terrace but shortly afterwards aeolian activity progressively increased. At the climax of the Younger Dryas, deep seasonal frost or local permafrost characterized the Mark valley. 相似文献
10.
Navin juyal Yaspal Sundriyal Naresh rana Shipra chaudhary Ashok k. Singhvi 《第四纪科学杂志》2010,25(8):1293-1304
The present study aims to explain the spatial and temporal variability in phases of aggradation/incision in response to changes in climate and seismicity during the late Quaternary in the Alaknanda River valley (a major tributary of the river Ganges or Ganga). Geomorphology, stratigraphy and optical dating of the fluvial sediment reveal that the oldest fluvial landforms preserved in the south of the Main Central Thrust are debris flow terraces developed during the early part of pluvial Marine Isotopic Stage 3. Following this, a period of accelerated incision/erosion owing to an increase in uplift rate and more intense rainfall occurred. In the Lesser Himalaya, three phases of valley fill aggradation around 26 ± 3 ka, 18 ± 2 ka and 15 ± 1 ka and 8 ± 1 ka occurred in response to changes in monsoon intensity and sediment flux. The last phase was regionally extensive and corresponds to a strengthening of the early Holocene Indian Summer Monsoon. A gradual decline in the monsoon strength after 8 ± 1 ka resulted in reduced fluvial discharge and lower sediment transport capacity of the Alaknanda River, leading to valley fill incision and the development of terraces. The study suggests that fluvial dynamics in the Alaknanda valley were modulated by monsoon variability and the role of tectonics was subordinate, limited to providing accommodation space and post‐deposition modification of the fluvial landforms. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
11.
黄河的形成与演化对于认识我国宏观地貌格局的形成、青藏高原及黄土高原的区域构造活动历史、华北平原及黄渤海陆架的形成和演化等问题具有重要意义。目前对黄河演化历史的研究主要集中在龙羊峡以下的河段,对于黄河源段的关注较少。文章基于黄河源地区河谷地貌的实地考察,并利用SRTM1-DEM数据,分析了黄河源段干流及支流河谷橫剖面的地貌特征,并与该区典型的冰川谷和兰州附近黄河的河谷横剖面进行了对比。结果表明:黄河源地区的河谷规模巨大,并呈现出谷底开阔、河床窄小、阶地不明显、谷坡陡立、河谷横剖面左右对称的U型谷特征。这些特征与该区冰蚀谷的特征相似,但与兰州段黄河成型河谷的特征相差甚远,且其河谷规模更大。我们推断,黄河源地区的河谷可能主要为冰期时的冰蚀作用所塑造,而非单纯的流水侵蚀形成。由于冰蚀作用的存在,该区早期的河流阶地可能被随后冰期的冰蚀作用所破坏,当前基于黄河源地区现存河流阶地年代的研究很可能低估了该区水系的发育历史。此外,反复的冰川进退也可能导致黄河源水系自上而下贯通,而非溯源侵蚀形成。 相似文献
12.
辫状河流属于冲积河流的主要类型,对流水地貌景观、水生栖息地和河流开发与生态保护具有重要科学意义。根据辫状河流演变过程与机理的国内外研究进展,对定义与形态特征进行综合描述,并给出常用的形态表征方法与参数。总结辫状河流的4种野外地形观测方法以及水槽试验和数值模型的应用,比较它们的适合范围;描述辫状河流的不同形态单元的组成,列举沙洲形成、汊道调整与横向迁移、岸滩侵蚀、河漫滩淤积等基本演变规律;对比分析水流功率、床沙粒径、泥沙补给、滨河植被、河谷宽度等影响辫状河流形态动力学过程的主要控制因素;指出青藏高原不同空间尺度辫状河流的形成原因、形态特征和演变规律是河流动力学的重要研究方向。 相似文献
13.
Piotr Owczarek Adam Nawrot Krzysztof Migała Ireneusz Malik Bartosz Korabiewski 《Boreas: An International Journal of Quaternary Research》2014,43(2):384-402
Changes in the supply of water and sediment to high‐latitude rivers related to contemporary climate change and glacier fluctuations largely determine the activity of fluvial processes. This study reconstructs fluvial dynamics since the end of the Little Ice Age (LIA) in two small, partially glaciated basins in the southern part of Spitsbergen, Svalbard Archipelago. We use a combination of aerial photograph interpretation, field mapping and dendrochronological analysis. Sequences of abandoned channels and glacifluvial terraces are distinctly visible in middle and lower parts of the Brattegg and Arie basins in this area. The advance of glaciers during the LIA in the upper part of the basins led to the development of a braiding pattern and to channel aggradation corresponding to the highest glacifluvial levels. The decreasing activity of these braidplains occurred at the turn of the 19th and 20th centuries, immediately prior to a significant incision period. A second generation of braided channels developed during the first half of the 20th century. Ice‐marginal lake development, less input of fine‐grained sediment to the river channel, and fast incision began from the second half of the 20th century onward. During the last two decades, the main fluvial response to the climatic warming has been contraction of flow within a narrower channel and the abandonment of braidplains. The increased lateral erosion and rate of downcutting and the formation of the most downstream reaches of the modern valley bottom occurred in the 1980s and 1990s. This process was intensified under flood conditions generated by extreme rainfall events. These micro‐scale (small partially glaciated basins) observations concerning the changes of the activity of fluvial processes since the end of LIA may be helpful for the reconstruction of past fluvial changes over longer time scales. 相似文献
14.
15.
山区地下水对平原区的侧向径流补给量是一个长期争议且悬而未决的难题,这个量在西北内陆干旱盆地,被估算得或很小或很大。在总结前人研究的基础上,采用地质水文地质调查、物探、钻探、抽水试验、地下水动态观测、水化学测试、盆地地下水水位统测和综合研究等技术方法,查明了黑河中游盆地南部山盆交接带的地质构造接触关系、地层岩性接触关系及梨园河口白垩系风化壳含水层结构和水文地质参数。通过山区不同流域等级的地表水与地下水转化关系分析,将山区地下水对平原区侧向径流补给带划分为大中型河流河谷补给段和小微型河流或冲沟群流域构成的浅山带补给段。河谷补给段勘探资料较为丰富,多用达西断面流方法计算;针对浅山带补给段极为缺乏勘探资料的实际,以梨园河口断面径流量为参照,构建了浅山带岩性、汇水区面积、降水量等3 个变量的山区地下水对平原区侧向径流补给量的估算方法。估算出黑河中游盆地南部山区浅山带地下水对平原的侧向径流补给量为0.40×108 m3/a,河谷段基岩侧向补给量为0.07×108 m3/a;推算出河谷段第四系地下水补给量为0.30×108 m3/a;3 项补给量之和为0.77×108 m3/a,占盆地地下水资源量的3.0%。该研究为西北内陆干旱盆地山区地下水对平原区侧向径流补给量的估算提供了一个可供借鉴的实例。 相似文献
16.
Nowadays, in parts of Iran, rivers and flood plains are being used as sand and silt mines, and the removal of river bed materials is performed without studying its effects on hydraulic behavior. On the other hand, the flood plain lands are in danger of floods and bank erosion. Zaremrood River in Tajan watershed due to removal of river bed material, two planes of before and after removal with scale of 1:1,000, has been used as basic data. The field investigation was emphasized on the end part of Zaremrood with a length of 5 km and starts from Ghandikola village to Ahoodasht Bridge. Using total station and field observations, the characteristics of reaches and cross sections of right bank, left bank, and main bed of river are written separately. Using software of HEC-RAS, ArcView 3.2, and extension HEC-GeoRAS, the flood zoning with different return periods to investigate water velocity and its changes, geometrical simulation of the bed, sides and flood way of rivers, and then by entering the results of HEC-GeoRAS into hydraulic software HEC-RAS for two before and after planes have been performed, and flow velocity was analyzed for three return periods of 10, 50, and 100 years. The results of this research showed that the velocities due to removal for floods with different return periods have increased, whereas water height and level during removal period have decreased. 相似文献
17.
Floodplains along the braided gravel-bed Waimakariri River are discontinuous although generally extensive landforms composed predominantly of gravel bars capped with vertically accreted fines. In order of importance, three mechanisms lead to floodplain formation. River bed abandonment by lateral migration of the braid-train initiates the formation of the largest floodpiains, which usually occur downstream of tributary fans and valley bedrock spurs. In the headwater reaches, localized river bed aggradation during high magnitude events leads to floodplain formation by producing a surface resistant to erosion by lesser events due to either the coarse nature of the deposit, or by its elevation over the river bed, or both. The least important mechanism initiating floodplain development is localized river or channel incision. A six stage model is proposed for the sequential development of floodplains on the Waimakariri River from: (i) active river bed; (ii) stabilizing bar; (iii) incipient floodplain; (iv) established floodplain; (v) mature floodplain; and to (vi) terrace. Two mechanisms, lateral migration by the braid-train and reactivation of abandoned channels within floodplains, operating separately or in combination, are responsible for floodplain reworking and their relatively young age (<250 years). Clearly, braided rivers can construct substantial areas of well developed floodplain. 相似文献
18.
《Journal of South American Earth Sciences》1999,12(3):333-341
Remnants of an old aggradational landscape, Cerro Cuadrado Proglacial, are preserved on top of the high mesetas Pampa Alta and La Meseta on both sides of the upper Santa Cruz river valley, South Patagonia.A first dissection of the mesetas, attributable to extended river erosion, predates the expansion of glacier lobes down the piedmontane area. The glacial advance is represented by the moraines of Pampa Alta Glaciation displayed on the top of Meseta Pampa Alta. Glacifluvial outlets contribute to the proglacial plain, Pampa Alta Proglacial, which is widespread to the southeast.Strong and persistent fluvial erosion followed the retreat of the ice masses leading to the formation of several terrace levels in the main upper valley, La Australasia Terraces and San Fernando Terraces, and a step, Cordón Alto, that truncates the Meseta Pampa Alta. These foreland features and the relief covered by the basalts at Cerro Fraile in the cordillera, are probably a consequence of a diastrophic phase that affected both areas during this stage.Late Pliocene basaltic lavas draining into the main and tributary valleys overran this landscape. The evidence indicates that during the eruption of the basalts the glaciation was active in the cordillera and that coeval fluvial and lacustrine aggradation took place in the extra-andean valleys.During the Middle Pleistocene subsequent lava flows covered the high pampas and partially occupied the fluvial valleys again. After this last volcanic episode the glaciers reached their maximum expansion to the east. 相似文献
19.
利用残存的地貌标志恢复原始地貌形态是地貌研究的难点之一。青藏高原东北缘循化－贵德地区晚新生代构造活动强烈,晚新生代黄河在本区发育,其后期演化记录了青藏高原隆升扩展的详细信息,同时黄河侵蚀下切过程本身也是值得深入研究的重要科学问题。由于黄河水系的发育,晚更新世以后循化－贵德盆地地区实现由盆地加积向退积的调整,盆地地区逐渐开始遭受黄河水系的侵蚀下切,并逐渐形成现今青藏高原东北缘的地貌形态。野外地质调查发现更新统的变形程度较弱,由于区域构造隆升与河流强烈下切的共同作用,现今保存的更新统已经成为盆地内部的分水岭,如龙羊峡地区。本研究正是选取循化－贵德盆地及其邻区更新统地层为古地貌重建的标志,基于数字高程模型(DEM)空间分析技术,构建了青藏高原东北缘循化－贵德盆地地区更新世古地貌形态,并进行了初步分析,主要认识有： 1)秦岭北缘断裂带构成其南西向北东方向地形快速降低的边界带; 2)在北西南东方向上,西秦岭、黄河、拉脊山、湟水河以及祁连山等总体上构成了向形－背形相间的地貌格局。同时以古地形为基础,定量计算了盆地区更新世以来的侵蚀分布图像,定量结果表明： 1)剥蚀量的分布形态与高原东北缘盆山地貌系统之间有一定相关耦合性,盆地地区的剥蚀量比较大,而相邻山脉地区的剥蚀量都比较小; 2)剥蚀量比较大的盆地地区剥蚀量与盆地内部河流形态之间也具有明显的关联特征,盆地内部剥蚀量最大的区域往往是盆地内部独立河流的中游地区。 相似文献