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Morphological evolution of a well‐constrained,subaerial–subaqueous source to sink system: Wabush Lake 
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下载免费PDF全文 Since 1964, the Iron Ore Company of Canada has deposited iron tailings resulting from mining operations into Wabush Lake, Western Labrador, Canada. This activity has resulted in a continuous hyperpycnal flow flowing over the lake floor. Bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental Iron Ore Company of Canada plans to maintain safe disposal strategies of tailings into the lake. Here, this dataset is used to study the evolution of different channels present in Wabush Lake and their link with knickpoints found at the head of most of these channels. The channels show notable evolution from one survey to the next. Some knickpoints and channels may be followed throughout more than one survey; the evolution of these knickpoints is the process responsible for the creation of erosional channels. The context in which they appear, as well as the evolution of some of the subaqueous channels is analysed. Cyclic steps and sediment waves are also found in the lake. These rhythmic bedforms, also created by the passage of turbidity currents, are analysed. Sediment waves found in Wabush Lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment. 相似文献
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Flow energy and channel adjustments in rills developed in loamy sand and sandy loam soils 总被引：1，自引：0，他引：1
The storms usually associated with rill development in nature are seldom prolonged, so development is often interrupted by interstorm disturbances, e.g. weathering or tillage. In laboratory simulated rainfall experiments, active rill development can be prolonged, and under these conditions typically passes through a period of intense incision, channel extension and bifurcation before reaching quasi‐stable conditions in which little form change occurs. This paper presents laboratory experiments with coarse textured soils under simulated rainfall which show how channel adjustment processes contribute to the evolution of quasi‐stability. Newly incised rills were stabilized for detailed study of links between rill configuration and flow energy. On a loamy sand, adjustment towards equilibrium occurred due to channel widening and meandering, whereas on a sandy loam, mobile knickpoints and chutes, pulsations in flow width and flow depth and changes in stream power and sediment discharge occurred as the channel adjusted towards equilibrium. The tendency of rill systems towards quasi‐stability is shown by changes in stream power values which show short‐lived minima. Differences in energy dissipation in stabilized rills indicate that minimization of energy dissipation was reached locally between knickpoints and at the downstream ends of rills. In the absence of energy gradients in knickpoints and chutes, stabilized rill sections tended toward equilibrium by establishing uniform energy expenditure. The study confirmed that energy dissipation increased with flow aspect ratio. In stabilized rills, flow acceleration reduced energy dissipation on the loamy sand but not on the sandy loam. On both soils flow deceleration tended to increase energy dissipation. Understanding how rill systems evolve towards stability is essential in order to predict how interruptions between storms may affect long‐term rill dynamics. This is essential if event‐based physical models are to become effective in predicting sediment transport on rilled hillslopes under changing weather and climatic conditions. Copyright © 2008 John Wiley and Sons, Ltd. 相似文献
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Dimitri Lague 《地球表面变化过程与地形》2014,39(1):38-61
The stream power incision model (SPIM) is a cornerstone of quantitative geomorphology. It states that river incision rate is the product of drainage area and channel slope raised to the power exponents m and n, respectively. It is widely used to predict patterns of deformation from channel long profile inversion or to model knickpoint migration and landscape evolution. Numerous studies have attempted to test its applicability with mixed results prompting the question of its validity. This paper synthesizes these results, highlights the SPIM deficiencies, and offers new insights into the role of incision thresholds and channel width. By reviewing quantitative data on incising rivers, I first propose six sets of field evidence that any long‐term incision model should be able to predict. This analysis highlights several inconsistencies of the standard SPIM. Next, I discuss the methods used to construct physics‐based long‐term incision laws. I demonstrate that all published incising river datasets away from knickpoints or knickzones are in a regime dominated by threshold effects requiring an explicit upscaling of flood stochasticity neglected in the standard SPIM and other incision models. Using threshold‐stochastic simulations with dynamic width, I document the existence of composite transient dynamics where knickpoint propagation locally obeys a linear SPIM (n=1) while other part of the river obey a non‐linear SPIM (n>1). The threshold‐stochastic SPIM resolves some inconsistencies of the standard SPIM and matches steady‐state field evidence when width is not sensitive to incision rate. However it fails to predict the scaling of slope with incision rate for cases where width decreases with incision rate. Recent proposed models of dynamic width cannot resolve these deficiencies. An explicit upscaling of sediment flux and threshold‐stochastic effects combined with dynamic width should take us beyond the SPIM which is shown here to have a narrow range of validity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Estimation of the recession rate of waterfalls is a crucial issue in bedrock river erosion because waterfall recession can cause a major impact on bedrock incision, especially when waterfall recession rates are high. Areas of active volcanoes are often characterized by many waterfalls in the volcanic edifice. This study examines recession rates of waterfalls in welded Aso‐1 ignimbrite from the Aso volcano in southwestern Japan using an empirical equation, which comprises a force/resistance index composed of measurable geomorphic parameters. The estimated recession rates are on the order of 0·01–0·07 m a?1. The estimated rates are then validated by examining the duration and distance of their recession. The duration of waterfall recession is derived from eruptive ages of the Aso ignimbrites, giving waterfall recession distances of approximately 10 km. Although the original locations of the waterfalls suggested by the recession distances exceed the downstream limit of the present Aso‐1 ignimbrite remnants along valley floors, features of the surrounding topography are consistent with these localities being where the waterfalls formed. The use of an equation to estimate recession rates is therefore considered to be valid and practical. The contrast between the highly dissected landforms downstream of the present waterfalls and the gentle landscapes upstream of the waterfalls suggests that the rapid recession of the waterfalls is the major cause of post‐eruptive fluvial erosion into ignimbrites. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Morphotectonic characteristics of the Meenachil River and its major tributaries in Kerala, India, were evaluated to understand the effects of tectonic processes on stream characteristics. Parameters such as longitudinal profile, stream length-gradient index (SL index), SL anomaly index, and transverse topographic symmetry factor (T) were considered. Longitudinal profiles of all the rivers show convexity and knickpoints in the segments between the headwaters and middle reaches, and further follow smooth profiles. Anomalies in longitudinal profiles were confirmed by the relatively high SL indexes. The SL anomaly index categorizes stream segments based on the severity of anomalies. The T index indicates the differential effect of tectonic processes in the river basin and in channel characteristics by showing spatial variation in its magnitude and orientation. Variations in the SL index, SL anomaly index, and T index in rivers flowing through similar lithology confirm the influence of differential effects of tectonic processes over the stream and networks and the nonequilibrium condition of the Meenachil River basin as a single unit. 相似文献
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不同尺度DEM的河流裂点提取及其效应分析 总被引：1，自引：0，他引：1
以不同尺度DEM数据提取裂点及其效应存在较大差异。本文以1：1万DEM为基础数据,通过小波分析生成多尺度DEM数据。以庐山地区16条河流为例,实现了多尺度DEM数据的河流裂点提取,探讨了河流裂点的变化规律,并构建了裂点个数的尺度预测模型。实验结果表明：(1)采用河道纵剖面与点坡降相结合的方法可快速准确地判断裂点;(2)在庐山地区,1:1万DEM数据可准确判断高差不小于5 m的裂点,对于高差小于5 m的裂点由于DEM表达精度和数据误差,而无法准确判定;(3)DEM尺度对裂点提取影响显著,裂点个数随着DEM分辨率降低逐渐减少,符合幂函数递减规律;(4)通过与ASTER GDEM和SRTM DEM对比验证,本文所构建的裂点个数与DEM尺度的拟合模型具有一定的预测精度。 相似文献
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