Sediment transport in high‐speed flows over a fixed bed: 2. Particle impacts and abrasion prediction          下载免费PDF全文

Christian Auel  Ismail Albayrak  Tetsuya Sumi  Robert M. Boes 《地球表面变化过程与地形》2017,42(9):1384-1396

Single bed load particle impacts were experimentally investigated in supercritical open channel flow over a fixed planar bed of low relative roughness height simulating high‐gradient non‐alluvial mountain streams as well as hydraulic structures. Particle impact characteristics (impact velocity, impact angle, Stokes number, restitution and dynamic friction coefficients) were determined for a wide range of hydraulic parameters and particle properties. Particle impact velocity scaled with the particle velocity, and the vertical particle impact velocity increased with excess transport stage. Particle impact and rebound angles were low and decreased with transport stage. Analysis of the particle impacts with the bed revealed almost no viscous damping effects with high normal restitution coefficients exceeding unity. The normal and resultant Stokes numbers were high and above critical thresholds for viscous damping. These results are attributed to the coherent turbulent structures near the wall region, i.e. bursting motion with ejection and sweep events responsible for turbulence generation and particle transport. The tangential restitution coefficients were slightly below unity and the dynamic friction coefficients were lower than for alluvial bed data, revealing that only a small amount of horizontal energy was transferred to the bed. The abrasion prediction model formed by Sklar and Dietrich in 2004 was revised based on the new equations on vertical impact velocity and hop length covering various bed configurations. The abrasion coefficient k_v was found to be vary around k_v ~ 10⁵ for hard materials (tensile strength f_t > 1 MPa), one order of magnitude lower than the value assumed so far for Sklar and Dietrich's model. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Evaluating a process‐based model for use in streambank stabilization: insights on the Bank Stability and Toe Erosion Model (BSTEM)          下载免费PDF全文

Kate Klavon  Garey Fox  Lucie Guertault  Eddy Langendoen  Holly Enlow  Ron Miller  Anish Khanal 《地球表面变化过程与地形》2017,42(1):191-213

Streambank retreat is a complex cyclical process involving subaerial processes, fluvial erosion, seepage erosion, and geotechnical failures and is driven by several soil properties that themselves are temporally and spatially variable. Therefore, it can be extremely challenging to predict and model the erosion and consequent retreat of streambanks. However, modeling streambank retreat has many important applications, including the design and assessment of mitigation strategies for stream revitalization and stabilization. In order to highlight the current complexities of modeling streambank retreat and to suggest future research areas, this paper reviewed one of the most comprehensive streambank retreat models available, the Bank Stability and Toe Erosion Model (BSTEM), which has recently been integrated with several popular hydrodynamic and sediment transport models including the Hydrologic Engineering Center's River Analysis System (HEC‐RAS). The objectives of this paper were to: (i) comprehensively review studies that have utilized BSTEM and report their findings, (ii) address the limitations of the model so that it can be applied appropriately in its current form, and (iii) suggest directions of research that will help make the model a more useful tool in future applications. The paper includes an extensive overview of peer reviewed studies to guide future users of BSTEM. The review demonstrated that the model needs further testing and evaluation outside of the central United States. Also, further development is needed in terms of accounting for spatial and temporal variability in geotechnical and fluvial erodibility parameters, incorporating subaerial processes, and accounting for the influence of riparian vegetation on streambank pore‐water pressure dynamics, applied shear stress, and erodibility parameters. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Biotic drivers of river and floodplain geomorphology – New molecular methods for assessing present‐day and past biota          下载免费PDF全文

Annegret Larsen  Nadir Alvarez  Christoph Sperisen  Stuart N. Lane 《地球表面变化过程与地形》2018,43(1):333-338

Geomorphology has increasingly considered the role of biotic factors as controls upon geomorphic processes across a wide range of spatial and temporal scales. Where timescales are long (centennial and longer), it has been possible to quantify relationships between geomorphic processes and vegetation using, for example, the pollen record. However, where the biotic agents are fauna, longer term reconstruction of the impacts of biological activity upon geomorphic processes is more challenging. Here, we review the prospect of using environmental DNA as a molecular proxy to decipher the presence and nature of faunal influences on geomorphic processes in both present and ancient deposits. When used appropriately, this method has the potential to improve our understanding of biotic drivers of geomorphic processes, notably fauna, over long timescales and so to reconstruct how such drivers might explain the landscape as we see it today. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Hierarchically nested river landform sequences. Part 2: Bankfull channel morphodynamics governed by valley nesting structure          下载免费PDF全文

Gregory B. Pasternack  Dastagir Baig  Matthew D. Weber  Rocko A. Brown 《地球表面变化过程与地形》2018,43(12):2519-2532

River corridors exhibit landforms nested within landforms repeatedly down spatial scales. In Pasternack et al. ( 2018 ), a new, scale‐independent, hierarchical river classification was developed that uses five landform types to map the domains of a single fluvial process – flow convergence routing – at each of three–five spatial scales. Given those methods, this study investigated the details of how flow convergence routing organizes nested landform sequences. The method involved analyzing landform abundance, sequencing, and hierarchical nesting along the 35 km gravel/cobble lower Yuba River in California. Independent testing of flow convergence routing found that hydraulic patterns at every flow matched the essential predictions from classification, substantiating the process–morphology link. River width and bed elevation sequences exhibit large, nonrandom, and linked oscillations structured to preferentially yield wide bars and constricted pools at base flow and bankfull flow. At a flow of 8.44 times bankfull, there is still an abundance of wide bar and constricted pool landforms, but larger topographic drivers also yield an abundance of nozzle and oversized landforms. The nested structure of flow convergence routing landforms reveals that base flow and bankfull landforms are nested together within specific floodprone valley landform types, and these landform types control channel morphodynamics during moderate to large floods. As a result, this study calls into question the prevailing theory that the bankfull channel of a gravel/cobble river is controlled by in‐channel, bankfull, and/or small flood flows. Such flows may initiate sediment transport, but they are too small to control landform organization in a gravel/cobble river with topographic complexity. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Wolf‐triggered trophic cascades and stream channel dynamics in Olympic National Park: a comment on East et al. (2017)          下载免费PDF全文

Robert L. Beschta  William J. Ripple 《地球表面变化过程与地形》2018,43(4):930-935

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Reservoir architecture and heterogeneity distribution in floodplain sandstones: Key features in outcrop,core and wireline logs     

Luis Miguel Yeste  Augusto N. Varela  César Viseras  Neil D. Mcdougall  Fernando García-García 《Sedimentology》2020,67(7):3355-3388

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Fluvial response to Weichselian climate changes in the Niederlausitz (Germany)     

JOANNE MOL 《第四纪科学杂志》1997,12(1):43-60

The last glacial shows large variations in climate, which are reflected in the fluvial record in the Niederlausitz, eastern Germany. The entire sequence resembles the fluvial development in other river basins in northwestern Europe, which show contemporaneous changes in depositional style at the onset of a climatic change. During the Middle and the Late Pleniglacial, permafrost conditions resulted in an episodic river discharge. The presence or absence of vegetation, in combination with such ephemeral stream conditions, determined the type of river during each period. A relatively well-developed vegetation cover on the flood plains during the Middle Pleniglacial resulted in a low sediment yield. In combination with the intermittent discharge, this caused the development of an ephemeral anastomosing river system, a river with stable channels and extensive sandy overbank areas. The decline in vegetation cover at ca. 28 ka BP caused an increase in sediment yield and peak discharges, which resulted in the development of a sandy braided river in adjustment to these new conditions. Following the coldest period at around 20 ka, precipitation was so low that fluvial activity was limited and aeolian deposition took place in the valley. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Badland Morphology and Evolution: Interpretation Using a Simulation Model     

Alan D. Howard 《地球表面变化过程与地形》1997,22(3):211-227

A drainage basin simulation model is used to interpret the morphometry and historical evolution of Mancos Shale badlands in Utah. High relief slopes in these badlands feature narrow divides and linear profiles due to threshold mass-wasting. Threshold slopes become longer in proportion to erosion rate, implying lower drainage density and higher relief. By contrast, in slowly eroding areas of low relief, both model results and observations indicate that drainage density increases with relief, suggesting control by critical shear stress. Field relationships and simulation modelling indicate that the badlands have resulted from rapid downcutting of the master drainage below an Early Wisconsin terrace to the present river level, followed by base level stability. As a result, Early Wisconsin alluvial surfaces on the shale have been dissected up to 62 m into steep badlands, and a Holocene alluvial surface is gradually replacing the badland slopes which are erocing by parallel retreat. © 1997 by John Wiley & Sons, Ltd.  相似文献   

The Role of Fluvial and Glacial Erosion in Landscape Evolution: The Ben Ohau Range,New Zealand     

Martin Kirkbride  David Matthews 《地球表面变化过程与地形》1997,22(3):317-327

A morphometric comparison of valleys has been made for the Ben Ohau Range in the central Southern Alps of New Zealand. The range is undergoing rapid tectonic transport and uplift. The humid north of the range is a glacial trough-and-arête landscape, with a temperate glacial climate. The dry south has rounded divides and plateau remnants dissected by fluvial valleys. Assuming that space–time substitution allows today's spatial valley-form transition to represent evolutionary stages in valley development, the tectonic history allows time constraints to be placed on the rate of transition to an alpine glacial landscape. Morphometric change has been quantified using hypsometric curves, and distance–elevation plots of cirque and valley-floor altitudes. Ancestral fluvial valleys have less concave long profiles but are stepped at altitude owing to the presence of high-level cirques and remnant plateau surfaces, and possess a low proportion of land area at low elevation. Increasing glacial influence is manifest as smoother, more deeply concave long profiles and U-shaped cross-profiles associated with a higher proportion of the land area at lower elevation. The full morphological transition has involved up to 2.4 km of vertical denudation over the 4 Ma lifetime of the mountain range, of which 80 per cent would have occurred by preglacial fluvial erosion. Combining the trajectory of tectonic transport with reconstructed glaciation limits and climatic history, it is indicated that about 200 ka of temperate glacial erosion produces recognizable trough-and areête topography. Mean and modal relief increase where glacial activity is confined to cirques, but decrease when trough incision by ice becomes established as a dominant process in the landscape. © 1997 by John Wiley & Sons, Ltd.  相似文献   

云南小江流域典型泥石流沟中底栖动物群落特征及其对河流地貌的响应   总被引：2，自引：2，他引：0  

朱朋辉  潘保柱  李志威  蒋小明  赵娜  赵耿楠  何浩然 《湖泊科学》2019,31(3):869-880

云南小江流域为典型干热河谷区,该区域干热少雨,流域内泥石流沟众多,生态环境十分脆弱.2017年4月和9月对小江流域的吊嘎河、蒋家沟、蓝泥坪沟、清水沟、陶家小河5条泥石流沟及小江干流开展了系统调查,旨在摸清5条泥石流沟及小江干流河流地貌、水环境及底栖动物群落现状,分析不同河床结构发育程度的泥石流沟间的底栖动物群落差异,揭示底栖动物对反映河床结构发育程度的河流地貌特征参数凹凸度的响应关系.调查期间于5条泥石流沟及小江干流中共采集到底栖动物70种,隶属于4门6纲38科69属,其中环节动物6种,软体动物2种,节肢动物61种,扁形动物1种.从种类类群来看,5条泥石流沟及小江干流的底栖动物物种数、密度、生物量上均以节肢动物占绝对优势,分别占总量的78.0%~92.5%、98.7%~100%、65.0%~100%.从功能摄食类群上来看,5条泥石流沟及小江干流底栖动物密度上均以直接收集者为主,占总量的74.3%~96.3%.回归分析表明,5条泥石流沟中底栖动物物种数、密度及生物量均与河流地貌特征参数凹凸度呈正相关关系,由此可见,发育良好的河床结构在维持河流地貌稳定和改善河流生态方面起着举足轻重的作用.本研究结果可为小江流域山区河流泥石流沟河床结构重建及生态修复提供科学依据.  相似文献