Characterization of the spatial variability of channel morphology

The spatial variability of two fundamental morphological variables is investigated for rivers having a wide range of discharge (five orders of magnitude). The variables, water‐surface width and average depth, were measured at 58 to 888 equally spaced cross‐sections in channel links (river reaches between major tributaries). These measurements provide data to characterize the two‐dimensional structure of a channel link which is the fundamental unit of a channel network. The morphological variables have nearly log‐normal probability distributions. A general relation was determined which relates the means of the log‐transformed variables to the logarithm of discharge similar to previously published downstream hydraulic geometry relations. The spatial variability of the variables is described by two properties: (1) the coefficient of variation which was nearly constant (0·13–0·42) over a wide range of discharge; and (2) the integral length scale in the downstream direction which was approximately equal to one to two mean channel widths. The joint probability distribution of the morphological variables in the downstream direction was modelled as a first‐order, bivariate autoregressive process. This model accounted for up to 76 per cent of the total variance. The two‐dimensional morphological variables can be scaled such that the channel width–depth process is independent of discharge. The scaling properties will be valuable to modellers of both basin and channel dynamics. Published in 2002 John Wiley & Sons, Ltd.     

THE FORMING CONDITIONS OF ALLUVIAL RIVER CHANNEL PATTERNS

1 INTRODUCTION It is well known that the river channel patterns are determined by long-term water-sediment conditions. However, quantitative expressions for river channel patterns and their fluvial processes still remain not clear. Existing theories in this aspects, such as geomophological theory, theory of maximum energy consuming rate, stability theory, theory of probability, and statistic analysis, are developed based on certain simplified assumptions and can not be successfully used t…     

泥石流流域的形态特征

泥石流是特殊的流域侵蚀作用,同其他流域过程一样,密切联系着流域的形态特征.一般说来,泥石流都发生在小流域(102km2以下),而经典的流域形态研究所涉及的流域范围却达到107km2的尺度.我们想知道泥石流小流域是否具有特殊的数量特征.通过流域特征量的统计,我们看到,与一般流域相比,泥石流小流域的特征参数之间的关系形式上相同,而在数值上不同,这从一个方面肯定了流域演化存在着普遍规律(如自组织临界性),同时也证明泥石流是流域演化历史的"特殊一幕".     

Effects of Urbanisation on Channel Morphology: The Case of Ekulu River in Enugu, South Eastern Nigeria

This study focuses on the effects of urbanisation on the morphology and hydraulic geometry of the Ekulu River in Enugu, southeastern Nigeria. Measurements of channel properties were taken along a 25 km stretch at 45 sites grouped into three sections: section A, upstream of the town (15); section B, within the town (15); and section C, downstream of the town (15). Spatial interpolation techniques were used to predict channel morphometric properties within and downstream of Enugu on the basis of upstream relationships. The independent variable in the analysis was drainage area, used as a surrogate for discharge. In section A, channel parameters increased systematically downstream with basin area. Within the town, channel parameters exhibited sudden dimensional increases. Based on sectoral relationships, measured channel dimensions showed moderate increases above the expected values, with average enlargement ratio indices of 34 per cent, 91 per cent and 65 per cent in width, channel capacity and depth, respectively, between sections A and B. Between B and C the channel exhibited average reduction ratio indices of 21 per cent and 27 per cent in capacity and depth, respectively, and an average enlargement ratio index of 17 per cent in width relative to the expected value. The increase in channel dimension within the town is explained by: (1) the confluence with a third-order tributary; (2) the poorly structured, loose, incoherent and highly erodible channel bank materials; (3) high volumes of runoff generated from the impermeable urban surfaces; (4) urban hydrological routing due to urban drainage; (5) human traffic across the river banks; and (6) the huge volume of garbage and solid wastes dumped into the channel.     

Morphology and curvature of delta slopes in Swiss lakes: lessons for the interpretation of clinoforms in seismic data

Seismic surveys were conducted and bathymetric data obtained from four alpine lakes in Switzerland. The curvature of the delta slopes was analysed with mathematical equations. Linear or exponential profiles are observed, representing planar or concave morphologies respectively. Planar profiles are interpreted to represent sediment that rests at the angle-of-repose. The slope angle of these profiles shows a correlation with sediment calibre. Exponential profiles do not show a clear correlation between sediment calibre and slope angle; they do not rest at the angle-of-repose, and different kinds of sediment can rest at the same slope angle. At the transition from lower slope to toe- of-slope, the exponential equation fails to predict the present-day morphology. The toe-of-slope lies above the predicted trend. This is attributed to a drastic increase in turbidite deposition that provides additional sediment and raises the basin-floor profile above the predicted trend. The breaks between delta plain and slope are sharp, reflecting an abrupt change from transport by river flow and waves to gravity-driven transport. In these lakes, the base-level fluctuations relative to supply are small and insufficient to alter this sharp topographic break. The absence of sigmoidal profiles on the Swiss deltas is attributed to the high rate of progradation coupled with small fluctuations in base level.     

岩溶形态系统的分形特征及其机理探讨

运用分形理论，系统研究了构成岩溶形态系统的岩溶地貌、水文网和洞穴系统的分形特征，并计算了分维值，以鄂西岩溶区的地貌小区为例，建立了地表峰体的分维与控制岩溶系统发育的岩性，外源水等因素的联系，揭示了分维的岩溶学含义，进而从岩溶系统介质场结构及岩溶作用过程的非线性动力特征分析探讨了岩溶形态系统的分形机理。     

一些硫化物矿物的晶体形貌学研究

论述了辰砂、雄黄、雌黄、辉锑矿、辉铋矿、毒砂、车轮矿、钽锰矿８种矿物的晶体形貌。文中所提供的全部形态测量结果是按Ｖ．Ｇｏｌｄｓｃｈｍｉｄｔ方法严格测量的新资料。     

新疆某地红宝石和蓝宝石矿物学研究

本文系统地研究了新疆某地红宝石-蓝宝石矿床,基本查明了该矿床中红宝石和蓝宝石矿床的粒度、形态、双晶、裂纹、包裹体形态和成分,以及硬度、密度、多色性、吸收性、Ne和No值;晶胞参数、化学成分等特征,从而为该类矿床的开发利用提供了重要信息。并根据该矿红、蓝宝石的物理性质、光学性质和化学成分上的不同,进一步探讨了呈色机理。     

Effects of coarse woody debris on morphology and sediment storage of a mountain stream system in western Oregon

Effects of coarse woody debris (CWD) on channel morphology and sediment storage were investigated at five sites, representative of first-order to fifth-order streams. In the steep and bedrock-confined stream (first-second order), interaction between the channel and CWD was limited, except where breakage upon falling produced CWD pieces shorter than channel width. Channel widening, steepening and sediment storage associated with CWD were observed predominantly in third- to fifth-order streams. Variation in channel width and gradient was regulated by CWD. In the fifth-order stream, most of the CWD pieces derived from the riparian forest interacted directly with the channel without being suspended by sideslopes. In this system CWD promoted lateral channel migration, but sediment storage was temporary, with annual release and capture.