Fine‐grained meandering systems of the Lower Permian Clear Fork Formation of north‐central Texas,USA: Lateral and oblique accretion on an arid plain          下载免费PDF全文

Sharane S.T. Simon  Martin R. Gibling 《Sedimentology》2017,64(3):714-746

Facies models that adequately represent the diverse range of fine‐grained fluvial systems are currently lacking from the literature. In this paper, the spectrum of these systems on the arid plains of western equatorial Pangea is explored, as well as the source and nature of the fine‐grained sediments. Eight fluvial elements in the Early Permian Clear Fork Formation of north‐central Texas represent channel systems up to 7 m deep with coarse basal deposits, three types of lateral‐accretion deposits and sandstone sheets, with laminated, disrupted and massive mudstones laid down in abandoned channels and on floodplains. The three fine‐grained fluvial styles represent a continuum between two end‐members: sustained lateral accretion of bedload composed of quartzose sediments and mud aggregates on point bars, and oblique accretion of suspended sediment on steep accretionary benches and banks with limited lateral migration. This spectrum is controlled, in part, by grain size and the proportion of suspended to bedload sediments. The presence of rarely documented swept ripples on exhumed accretion surfaces is attributed to rapid decline in water levels and downstream re‐entry of overbank floodwaters into the channel. Rill casts, roots and disrupted mudstones low down in channel bodies indicate periods of near‐dryness. Laterally extensive sheet sandstones were formed by episodic flows in broad, sandbed channels. The fluvial sediments were primarily intrabasinally sourced with extrabasinal sediments brought in during major floods from upland source areas or reworked from local storage in the basin, representing a supply limited system. The upward change in cement composition from mainly calcite and ankerite to dolomite and gypsum with minor celestine implies increasingly saline groundwater and progressive aridification, supporting Late Palaeozoic palaeoclimatic models. By integrating petrographic data with sedimentology, a plethora of information about ancient landscapes and climate is provided, allowing a fuller comparison between the Clear Fork Formation and modern dryland alluvial plains.  相似文献   

南洞地下河岩溶管道展布及结构特征的示踪试验解析   总被引：7，自引：6，他引：1  

赵一  李衍青  覃星铭  洪涛  程瑞瑞  蓝芙宁 《中国岩溶》2017,36(2):226-233

运用高精度的示踪试验研究了南洞地下河流域部分岩溶管道的展布状况,并对暗河管道的结构特征进行了分析。试验结果表明:一号暗河有一独立的含水系统,补给区为瓦白白一带,二号暗河主管道总体通往永宁和石洞方向,三号暗河通往城红寨方向,二号暗河和三号暗河在南洞口附近有连通,枯季时二号暗河补给三号暗河。此外,一号暗河和二号暗河分别呈老年期和壮年期地下河形态,较为畅通;三号暗河则发育较晚,出口处有较多的裂隙。最后,结合现有的资料及流域内的水文地质条件,对流域内岩溶管道的大体分布位置进行了推断,绘制了岩溶管道的展布图,以期为南洞地下河流域的岩溶水文地质调查、物探、钻探及地下水开发利用等提供理论依据。   相似文献   

网状河流多重河道形成过程的实验模拟   总被引：2，自引：1，他引：1  

王随继  薄俊丽 《地理科学进展》2004,23(3):34-42,i004

网状河流是受到人们关注的新型冲积河流,其水文特征、地貌特征和沉积特征已经不同程度地被揭示。然而,网状河流的水槽实验迄今仍是空白,而水槽模拟实验是在时间和空间都大大缩小之后的自然界河流演变过程的再现。本文报道的是在实验水槽中通过原河道决口后网状河流的发生和演变过程。实验初始条件为:水槽辅助区的待决口河道,目标区为轴部略微下凹的长方形泛滥平原(4.5 m×16.5 m),其上下层分别为1.5 cm厚、中值粒径为0.0132 mm的高岭土层和0.5 m厚、中值粒径为0.188mm的天然细砂层,从5.5 m-17 m区段的平均纵比降为0.0058,17m-22m区段的平均纵比降为0.0077。采用的定常流量为3 L/s,悬移质输沙量在前3小时为4.5g/min,其后为1.2 g/s。实验总历时50小时。实验初期,目标区的上游段以垂向加积作用为主,中游以随机侵蚀为主,下游以溯源侵蚀为主,在13.5小时左右,相互连通的多重河道的网状河流体系的雏形基本展现。此后至25.5小时,网状河道的演变以下蚀为主演变为以适度的侧蚀,但河岸的后退幅度很小,标志网状河道逐步过渡到成熟期。从25.5小时至50小时,个别河道的局部废弃和决口是该成熟期网状河道演变的新特点。实验成功地模拟了天然网状河流的形成、发展和演变过程,同时也证明了它是不同于分汉河流的河型。这不  相似文献   

Buried channels provide keys to infer Quaternary stratigraphic and paleo-environmental changes:A case study from the west coast of India     

K.M.Dubey  A.K.Chaubey  V.P.Mahale  S.M.Karisiddaiah 《地学前缘(英文版)》2019,10(4):1577-1595

High resolution shallow seismic data was acquired from inner continental shelf of Goa,west coast of India to map underlying stratigraphic and buried geomorphic features of shelf strata.Seismic data revealed characteristic channel incisions beneath 4-15 m thick sediment layer and corresponds to multi cycle incisions.Stratigraphic analysis of these incision signatures reveals three prominent subaerial unconformities S6,S7 and S9.These unconformities were exposed during the last glacial,penultimate glacial(MIS-6)and prior to penultimate glacial(MIS-8)periods.On the basis of interpreted age of subaerial unconformities and differences in their morphological features,observed channel incisions have been divided grossly into three phases of incision.Phase-1 incisions are older than ～330 kyr BP,whereas,incisions of Phase-2 and Phase-3 correspond to ～320-125 kyr BP and ～115-10 kyr BP respectively.Plan form of these incisions varied from a straight channel type to ingrown meander and then to anastomosing channel types.These channels meet at the confluence of present-day Mandovi and Zuari rivers.The confluence point has varied in due course of time because of cyclic incision and burial with repeated sea level fluctuations.The preserved main channel width varies from ～100 m to 1000 m.and maximum channel depth reaches up to ～35 m.Comparison of quantitative and qualitative morphologic results of different phases of incisions suggest that Phase-2 channels had ～33% more mean bank full discharge than that of the Phase-3 channels.Phase-2 incisions had been carved in higher hydraulic energy condition as compared to Phase-3 incisions implying that the Indian summer monsoon was better during formative stages of Phase-2 incisions.  相似文献   

Urban stream channel hazards   总被引：4，自引：0，他引：4  

Ken J Gregory  & Anne Chin 《Area》2002,34(3):312-321

In managing urban stream channels there are pressures to use soft engineering techniques to restore channels wherever possible, to undertake management within a drainage basin context, to produce sustainable solutions and to consider community views. However, specific methods for characterizing the channel network in terms of possible management options have not been developed explicitly for urban areas. A method of characterizing the entire drainage network of urban areas, based upon segmentation of the stream channel network according to the incidence of road crossings and stormwater outfalls, is proposed together with consideration of ways in which the segments can be characterized, including stream channel hazards as a means of providing one basis for urban channel management.  相似文献   

Test of scale modelling of sediment transport in steady unidirectional flow     

John B. Southard  Lawrence A. Boguchwal  Richard D. Romea 《地球表面变化过程与地形》1980,5(1):17-23

In two steady uniform flows at different physical scales in a small open channel, with variables characterizing flow, sediment, and fluid adjusted for dynamic similitude by means of four dimensionless modelling parameters (a Reynolds number, a Froude number, a density ratio, and a length ratio), measured frequency distributions of height, spacing, and migration rate of current ripples were almost identical when scaled, thus verifying that exact Reynolds-Froude modelling of loose-sediment transport is valid and workable. Modelling should be valid as well for a wide range of other transport conditions in the same kind of flow, because no additional kinds of forces or effects would be present in transport of loose grains in modes other than as ripples. In scaled-down modelling, a scale ratio of 2.5 is attainable without recourse to exotic fluids by use of water at 85°C to model natural flows at 10°C.  相似文献   

Semi-determinate hydraulic geometry of river channels,South Island,New Zealand     

M. Paul Mosley 《地球表面变化过程与地形》1981,6(2):127-137

Data to describe the morphologic, hydrologic and sedimentologic characteristics of 72 South Island, New Zealand, rivers were collected and analysed. Nearly 70 per cent of variation in channel morphology is accounted for by differences in cross-sectional area, slope, and cross-section shape; only 53 per cent of the morphologic variability could be statistically ‘explained’ by the hydrologic and sediment variables used. The level of explanation varied for different morphologic variables; nearly 90 per cent of the variability in cross-sectional area could be explained, but aspect ratio (maximum depth divided by hydraulic radius) was completely independent. Apart from the inadequacy of the measured variables as indices of the true underlying controlling factors, and the imperfect measurement and sampling procedures, the low level of explanation is probably due to the influence of factors such as floodplain vegetation, high quasi-random variability in bark sediment character, boundary effects imposed by bedrock bluffs, and the precise sequence of flood events, none of which are easily quantified. In addition, observations indicate that there is a large random variation in channel form which cannot be related to any factor. An attempt to relate channel morphology to flow variability, using simple indices of the latter, was unsuccessful.  相似文献   

Towards estimation of extreme floods: examination of the roles of runoff process changes and floodplain flows   总被引：1，自引：0，他引：1  

Chatchai Jothityangkoon 《Journal of Hydrology》2003,281(3):206-229

This paper presents the development and application of a distributed rainfall-runoff model for extreme flood estimation, and its use to investigate potential changes in runoff processes, including changes to the ‘rating curve’ due to effects of over-bank flows, during the transition from ‘normal’ floods to ‘extreme’ floods. The model has two components: a hillslope runoff generation model based on a configuration of soil moisture stores in parallel and series, and a distributed flood routing model based on non-linear storage-discharge relationships for individual river reaches that includes the effects of floodplain geometries and roughnesses. The hillslope water balance model contains a number of parameters, which are measured or derived a priori from climate, soil and vegetation data or streamflow recession analyses. For reliable estimation of extreme discharges that may extend beyond recorded data, the parameters of the flood routing model are estimated from hydraulic properties, topographic data and vegetation cover of compound channels (main channel and floodplains). This includes the effects of the interactions between the main channel and floodplain sections, which tend to cause a change to the rating curve. The model is applied to the Collie River Basin, 2545 km², in Western Australia and used to estimate the probable maximum flood (PMF) from probable maximum precipitation estimates for this region. When moving from normal floods to the PMFs, application of the model demonstrates that the runoff generation process changes with a substantial increase of saturation excess overland flow through the expansion of saturated areas, and the dominant runoff process in the stream channel changes from in-bank to over-bank flows. The effects of floodplain inundation and floodplain vegetation can significantly reduce the magnitude of the estimated PMFs. This study has highlighted the need for the estimation of a number of critical parameters (e.g. cross-sectional geometry, floodplain vegetation, soil depths) through concerted field measurements or surveys, and targeted laboratory experiments.  相似文献   

The frictional resistance characteristics of a bedrock‐influenced river channel     

G. L. Heritage  B. P. Moon  L. J. Broadhurst  C. S. James 《地球表面变化过程与地形》2004,29(5):611-627

Much of the published literature relating to reach‐scale total ?ow resistance concentrates on alluvial rivers and little mention is made of the more extreme resistance found in bedrock‐in?uenced river systems. This paper presents the results of a detailed investigation of total ?ow resistance variation for ?ve channel types on the Sabie River, South Africa (cohesive mixed anastomosed, uncohesive mixed anastomosed, mixed pool–rapid, alluvial braided and alluvial single thread) over a range of discharges. Manning's ‘n’ and Darcy‐Weisbach f resistance coef?cients are calculated using Barnes' methodology (H. H. Barnes, US Geological Survey Water Supply Paper 1849, 1967). These data are analysed at the scales of channel type and morphologic unit and the resultant resistance values are compared with the literature. Generally the low‐?ow friction values estimated for the bedrock‐in?uenced channel types are higher than any reported. Flow resistance quanti?cation of the alluvial channel type study sites on the Sabie River produced values slightly higher than earlier studies of similar morphologies. In situations where signi?cant areas of irregular bedrock are exposed (cohesive mixed anastomosed and mixed pool–rapid channel types) the high ?ow resistance coef?cients at low discharges probably re?ect energy dissipation due to hydraulic jumps and internal distortions; however, these values fall as discharge increases to values comparable to those recorded for step–pool rivers. It is suggested that the slightly elevated resistance coef?cients recorded in the alluvial channel types are the result of the vegetation roughness component, operating when the macro‐channel bar features are inundated. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

复式河槽阻力系数及过流能力计算   总被引：1，自引：0，他引：1       下载免费PDF全文

杨克君  曹叔尤  刘兴年 《水科学进展》2005,16(1):23-27

水位流量关系在流域管理中占有十分重要的地位.而对于复式河槽,水位流量关系的推求是十分困难的.无论采用单一河槽法还是传统的断面分割法,都将带来很大的误差.将复式河槽分为滩地边坡区、滩地区、主槽边坡区和主槽区,并运用英国科学工程研究协会洪水水槽设施(SERC-FCF)的大量的系列水槽实验资料,分析了各区Darcy-Weisbach阻力系数之间的关系.SERC-FCF的实验资料表明主槽区的阻力系数与相对水深有关,滩地区和主槽区阻力系数之比随相对水深成指数关系,滩地边坡区、主槽边坡区阻力系数可用主槽区和滩地区阻力系数表示.利用这些阻力系数关系分别推求各区的流量及总流量.实验资料验证表明:计算流量与实测流量基本吻合.  相似文献