Fluvial incision and channel downcutting as a response to Late‐glacial and Early Holocene climate change: the lower reach of the River Meuse (Maas), The Netherlands     

L. A. Tebbens  A. Veldkamp  W. Westerhoff  S. B. Kroonenberg 《第四纪科学杂志》1999,14(1):59-75

Detailed fieldwork and new extensive ¹⁴C dating of residual channel infillings provide data for the reconstruction of the Late‐glacial channel downcutting and incision history of the Venlo–Boxmeer lower reach of the River Meuse (= Maas) in the southern Netherlands. Within a period of 500–1300 yr after Late‐glacial climatic amelioration, the Meuse responded to increased discharges and decreased sediment supply by adjusting the width/depth ratio of its channels. Two main phases of channel downcutting are followed by two main phases of floodplain lowering and narrowing, indicating net floodplain degradation by the fluvial system as a non‐linear response to Late‐glacial and Early Holocene climate change. Some 1300 yr after initial late‐glacial warming, channels downcut rapidly during the Early Bølling (13.3–12.5 kyr BP) and adopted a high‐sinuosity meandering style. Channel downcutting paused around 11.9 kyr BP, possibly in response to rising groundwater levels and/or the Older Dryas cooling event. Between 11.9 and 11.3 kyr BP a new floodplain was formed. Then, lateral erosion took place and initiated a first phase of 2.6 m floodplain lowering during the Late Allerød. Gradual climate deterioration during the Allerød progressively broke up soils and vegetation cover, from 11.3 to 10.9 kyr BP. The Meuse gradually adjusted to an increased ratio of sediment supply over transport capacity through higher width/depth ratios. Main channels became shallower and adopted a low‐sinuosity pattern, finally culminating in a braided river system during the Younger Dryas. The final Holocene warming resulted, within 500 yr, in renewed rapid channel downcutting by a single low‐sinuosity channel during the Early Preboreal, followed by a second phase of 1.8–2.8 m floodplain lowering. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

A coarse-grained basin floor turbidite system – the Jurassic Los Molles Formation,Neuquen Basin,Argentina     

Gabriel Giacomone  Cornel Olariu  Ron Steel  Moonsoo Shin 《Sedimentology》2020,67(7):3809-3843

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LOCAL SCOUR ESTIMATION AT CHECK DAMS IN TORRENTIAL STREAMS IN SOUTH EAST SPAIN     

BY C. CONESA-GARCÍA  R. GARCÍA-LORENZO 《Geografiska Annaler: Series A, Physical Geography》2009,91(3):159-177

For several decades, the check dam building has been one of the most commonly used structural measures in the Forestry Hydrological Restoration Programs and Plans in the torrential basins of south east Spain. Two examples are the catchments studied here, drained by the Cárcavo and Torrecilla torrential streams belonging to the Segura Basin. Obtaining a more stable bed and a less powerful flow requires transitory hydro-morphological stages such as check dam filling upstream or local erosion downstream. The main aims of this paper are to estimate local scouring induced by check dams downstream, and to find evolution stages of scouring depth, the response time of the local erosion point and the local maximum depth to reach a stable bed situation. To do this, the results obtained by different methods were compared with measured scour depths for various hydraulic radii. From this comparison, performed in non-uniform sediment size beds and in clear-water conditions, the Fahlbusch's formula gives a better fit, while the Jaeger's and Bormann and Julien's methods tend to underestimate the results. These may be used to calculate local instantaneous scouring in flows less than bankfull, but give a worse estimate for maximum equilibrium scouring. Under active bed conditions, the temporal response of the cross-sections experiencing local scour processes below these structures reflects the variations in hydraulic regime during flooding. In general, a rapid evolution phase is followed by a slow stage, which in the most torrential sectors has still not reached the equilibrium threshold.  相似文献   

穿透岩层地下电流场通信信道分析   总被引：1，自引：0，他引：1  

向新  罗奕  易克初  张仲礼  田红心  王继矿 《煤田地质与勘探》2005,33(4):77-79

考虑到传统的有线及无线地下通信方式的弱点,提出了利用电流场实现穿透地层的地下通信方式,并根据甚低频电磁波在地层中的传播特点,提出了利用恒流场模型作为电流场通信的电磁波传播模型,同时对电流场地下通信方式的性能进行了分析,并得到一些重要结论。   相似文献   

Bed morphology and generation of step–pool channels     

Roman B. Weichert  Gian Reto Bezzola  Hans‐Erwin Minor 《地球表面变化过程与地形》2008,33(11):1678-1692

Flume experiments have been carried out to study the formation processes and the bed morphology of step–pool channels. From the experiments different step types and step configurations could be distinguished depending on the stream power. These step types can be seen as an image of the generation mechanisms of step–pool systems. These results suggest that the bed roughness geometry develops towards a condition that provides the maximum possible bed stability for a given grain size distribution. In contrast to a variety of other studies, antidunes did not contribute to the generation of the step structures. However, the data of the presented study fits well into the region of antidune formation proposed by Kennedy for sand‐bed rivers. This observation points out that step–pool field‐data located in the Kennedy region do not inevitably prove that antidunes played a role in step development. It is rather proposed that in Kennedy's region of antidune formation there exist hydraulic conditions where the flow resistance is maximized. It is suggested that such maximum flow resistance is associated with an optimal distance between the bedforms and their height, independently of whether these are antidunes in sand‐ and gravel‐bed rivers or step–pool units in boulder‐bed streams. The considerations of the Kennedy region of antidune formation and the analysis of planform step types depending on stream power both suggest that steep channels have a potential for self‐stabilization by modifying the step–pool structure towards a geometry that provides maximum flow resistance and maximum bed stability. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Dynamics of intertidal drainage channels on a multi‐barred macrotidal beach     

Béatrice Reichmüth  Edward J. Anthony 《地球表面变化过程与地形》2008,33(1):142-151

The intertidal drainage channels on a macrotidal bar–trough (ridge‐and‐runnel) beach were monitored during a 17‐day survey. Type 1 channels were persistent, dominantly longshore systems essentially limited to the wide intertidal zone between mean high and low water neap tidal levels. The cumulative length of this channel type fluctuated as a function of topographically controlled through‐flow or flow impedance in troughs, and showed no correlation with the semi‐lunar tidal cycle. Smaller, ephemeral type 2 channels appeared as dominantly cross‐shore systems incising bars on the narrower upper and lower beach zones during spring tides. They disappeared during neap tides through infill by waves and aeolian activity. The only significant phase of type 1 channel mobility occurred during a brief moderate‐energy storm at the start of the survey. The effect of this mobility on beach morphology was inextricably linked to that of waves and currents. Meander bend migration, forced by wave‐ and longshore‐current‐induced migration of a bar during the storm, resulted in important but highly localized morphological change that was only a minor part of an irregular saw‐tooth pattern of change that affected the entire beach profile, and that was largely controlled by wave processes and longshore currents. The flow velocities in channels on this beach are too weak to generate the formation and longshore migration of high‐energy bedforms. Channel mobility and impact on beach morphology are expected to increase under storm conditions. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Blind deconvolution methodology for site-response evaluation exclusively from ground-surface seismic recordings     

A. Zerva  A. P. Petropulu  P. -Y. Bard 《Soil Dynamics and Earthquake Engineering》1999,18(1):805

A novel blind deconvolution methodology for identification of the local site characteristics based on two seismograms recorded on the free surface of a sediment site is presented. The approach does not require recordings at depth nor at a nearby rock outcrop, and eliminates the need for any prior parameterization of source and site characteristics. It considers that the surface recordings are the result of the convolution of the ‘input motion at depth' with transfer functions (channels) representing the characteristics of the transmission path of the waves from the input location to each recording station. The input motion at depth is considered to be the common component in the seismograms (same input in a statistical sense). The channel characteristics are considered to be the part in the seismograms that is non-common, since the travel path of the waves from the input motion location at depth to each recording station is different, due to spatially variable site effects. By means of blind deconvolution, the algorithm eliminates what is common in the seismograms, namely the input motion at depth, and retains what is different, namely the transfer functions of the site from the input location to each recording station. It estimates the site response in both frequency and time domains, and identifies the duration of the site's transfer functions. The methodology is applied herein to synthetic data at realistic sites for performance validation. The blindly estimated results are in almost perfect agreement with the actual site characteristics, indicating that the approach is a promising new tool for seismic site-response identification from recorded data.  相似文献   

舟山群岛峡道潮滩动力沉积特性   总被引：14，自引：3，他引：11  

蒋国俊  陈吉余  姚炎明 《海洋学报》1998,20(2):139-147

潮滩研究是现代河口海岸学研究中一直受到重视的重要方面,自德国学者Hantzschel[1].  相似文献   

长江葛洲坝水库溪口滩的演变及其对航道的影响     

林承坤  高锡珍 《湖泊科学》1995,7(2):119-126

葛洲坝水库位于长江三峡,库容15.8×10~8m~3,水库长度188.1km,其中变动回水段占66％。溪口潍主要由粒径大于20mm的卵石推移质组成。葛洲坝库区的卵石推移质有65％来源于灰岩为主补给区,该补给区卵石推移质数量大,颗粒粗,易成滩,所以库区溪口滩有92％分布在以灰岩为主的补给区。葛洲坝库区溪口滩可分洪水急流滩、洪中水急流滩、中水急流滩、中枯水急流滩与枯水急流潍等5种类型,建库后库区回水变动段占总数50％的溪口滩得到改善。但是占总数50％的位于库尾段的溪口滩与变动回水段洪水急流滩溪口滩,未能得到改善。随着这些溪口滩得到卵石推移质补给,航道将会恶化。在三峡水库建成前应加强对溪口滩的观测、研究与整治。  相似文献   

洞庭湖城陵矶水道水力几何形态的研究   总被引：1，自引：1，他引：0  

黎明 《湖泊科学》1997,9(2):112-116

根据１９５１－１９８８年洞庭湖城陵矶站的水文测验资料,运用Ｌ．Ｂ．Ｌｅｏｐｏｌｄ河床力几何形态原理,建立洞庭湖出口－城陵矶水道河相关系式,研究该水道水力几何形态的特点及变化。研究表明,与河流水道相比,洞庭湖出口水道河宽指数ｂ随流量的变化较小,而水深指数ｆ及流速指数ｍ随流量的变化较大,河床横面具有窄深的特点。  相似文献