Formation and erosion of sediment cover in an experimental bedrock‐alluvial channel          下载免费PDF全文

Rebecca Hodge  Trevor Hoey  Georgios Maniatis  Emilie Leprêtre 《地球表面变化过程与地形》2016,41(10):1409-1420

Sediment grains in a bedrock‐alluvial river will be deposited within or adjacent to a sediment patch, or as isolated grains on the bedrock surface. Previous analysis of grain geometry has demonstrated that these arrangements produce significant differences in grain entrainment shear stress. However, this analysis neglected potential interactions between the sediment patches, local hydraulics and grain entrainment. We present a series of flume experiments that measure the influence of sediment patches on grain entrainment. The flume had a planar bed with roughness that was much smaller than the diameters of the mobile grains. In each experiment sediment was added either as individual grains or as a single sediment pulse. Flow was then increased until the sediment was entrained. Analysis of the experiments demonstrates that: (1) for individual grains, coarse grains are entrained at a higher discharge than fine grains; (2) once sediment patches are present, the different in entrainment discharge between coarse and fine grains is greatly reduced; (3) the sheltering effect of patches also increases the entrainment discharge of isolated grains; (4) entire sediment patches break‐up and are eroded quickly, rather than through progressive grain‐by‐grain erosion; (5) as discharge increases there is some tendency for patches to become more elongate and flow‐aligned, and more randomly distributed across the bed. One implication of this research is that the critical shear stress in bedrock‐alluvial channels will be a function of the extent of the sediment cover. Another is that the influence of sediment patches equalizes critical shear stresses between different grain sizes and grain locations, meaning that these factors may not need to be accounted for. Further research is needed to quantify interactions between sediment patches, grain entrainment and local hydraulics on rougher bedrock surfaces, and under different types of sediment supply. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Holocene flood histories in south‐western USA     

Tessa Harden  Mark G. Macklin  Victor R. Baker 《地球表面变化过程与地形》2010,35(6):707-716

River basins in south‐western USA are some of the most extensively studied arid land fluvial systems in the world. Since the early 1960s their hydro‐climatic histories have been reconstructed from the analysis of alluvial cut‐and‐fill cycles, while from the late 1970s there have been investigations of slackwater deposits and palaeostage indicators for large floods in stable‐boundary bedrock reaches. However, no studies have regionally integrated Holocene fluvial histories from these two different types of fluvial environments. The current study combines the alluvial archive with flood records from bedrock reaches to generate a probability‐based 12,000 year record of flooding in south‐western USA. Using more than 700 ¹⁴C‐dated fluvial units, the analysis produces a high resolution (centennial) flood record. Seven episodes of increased flooding occurred at 11,250–10,400, 8800–8350, 8230–7600, 6700–5700, 5600–4820, 4550–3320 and 2000–0 cal. BP. Bedrock reaches are found to record more frequent floods during the middle to late Holocene, while in alluvial rivers more flood units are dated to the early and middle Holocene. These differences are primarily the result of selective preservation with alluvial reaches tending to erode during periods characterised by very large floods. Episodes of major Holocene flooding recorded in slackwater deposits within bedrock systems correspond with periods of increased precipitation in the region and lower temperatures. In contrast, within alluvial rivers above‐average flooding probabilities, as well as regionally extensive channel entrenchment episodes, match with reduced annual precipitation and lower temperatures. The results of this study clearly demonstrate the value of the Holocene fluvial archive for reconstructing regional, short‐term hydro‐climatic change in south‐western USA. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Application of a coil‐type TDR probe for measuring the volumetric water content in weathered granitic bedrock     

Shin'ya Katsura  Ken'ichirou Kosugi  Takahisa Mizuyama 《水文研究》2008,22(6):750-763

As a first step toward describing water flow processes in bedrock, a coil‐type time domain reflectometry (TDR) probe capable of measuring volumetric water content, θ, in weathered bedrock at three depths was prepared. Because the coil‐type TDR probe is large in diameter (19 mm), it can be installed even in highly weathered bedrock more easily and appropriately than conventional TDR probes that consists of two or three rods of small diameter (5‐8 mm). The probe calibrations suggest that the values measured by the probe are very sensitive to changes in θ. Using the calibrated probe together with commercially available profile soil moisture sensors, the θ profile was monitored for 1 year. Even rainfall events with relatively small cumulative rainfall of 15 mm increased the bedrock θ, and the increments were comparable to those in the soil. After the end of the rainfall events, the bedrock θ displayed a more rapid drop than the soil, and varied little during the period of no rainfall. The water storage showed similar tendencies. These observations suggest that the bedrock θ is controlled by clearly distinguishable macropores and micropores within the bedrock. It is concluded that the coil‐type TDR probe is very effective in determining θ in weathered bedrock, and that bedrock, conventionally defined by conducting cone penetration tests and treated as impermeable, does conduct and hold substantial amounts of water, and therefore contribute greatly to hydrological processes in headwater catchments. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

中国基岩海湾潮流地貌模式及其沉积动力特征     

边淑华  夏东兴  吕京福 《海洋科学进展》2003,21(3):298-307

对我国基岩海湾内的潮流沉积和地貌进行了系统研究。根据潮滩、潮流水道、潮流沙脊等地貌单元的组合特征，概括出3种潮流地貌模式：潮滩型、滩-槽型和滩槽-脊型。通过各模式海湾环境特征的对比分析，设定紊动射流系数Rbjet做为判别潮流水道形成发育程度的水动力参数，发现潮流水道较为发育的滩-槽型和滩-槽-脊型海湾往往开敞度较小，纵深较长，而平均潮差较大，Rbjet大于45。潮流沙脊是区分滩-槽型和滩-槽脊型潮流地貌模式的标志地貌，粗颗粒泥沙来源是其发育的必备条件：残留沉积、海岸侵蚀来沙丰富的海湾内潮流沙脊发育；河流来沙则可以改造形成小规模现代潮流脊；而靠近大河河口，细颗粒来源丰富的海湾则不利于潮流沙脊发育，湾内形成滩-槽型潮流沉积。  相似文献   

Some geological-morphological features of the formation of gold-bearing placers in the Amur region     

L. V. Eirish 《Russian Journal of Pacific Geology》2008,2(5):454-463

The intensity of placer formation is controlled by many factors, mainly by the erosion level of orebearing structures. Their deep erosion and long-term denudation resulted in the formation of numerous, often large placers with fine gold, which lost their relation with bedrocks and were derived mainly by rewashing of loose deposits from the depressions adjacent to the ore-bearing orogens. These placers are developed in many gold-bearing areas: Dambuki, Sutara, Erik, and others. Rich placers with coarse gold of high fineness were formed via erosion of gold mineralization that was previously metamorphosed by post-ore granitoids (Niman and Kerbi regions, Central Sikhote Alin).  相似文献   

浸矿开采对离子型稀土基岩力学特性的影响研究     

钟文  朱文韬  曾鹏  黄震  王晓军  郭钟群  胡凯建 《岩土力学》2022,43(6):1481-1492

为研究原地浸矿母液对离子型稀土矿收液底板的侵蚀影响,以离子型稀土矿基岩（半/弱风化花岗岩）为研究对象,开展了室内浸矿模拟试验。对比分析了不同浸矿时间岩样的应力−应变曲线、峰值应力、峰值应变和弹性模量,获取了不同浸矿历时岩样的孔隙度和细观形貌特征,并运用盒维法对岩样的非线性裂纹特征进行了定量化描述。结果表明：浸矿侵蚀作用对离子型稀土矿底板基岩力学性质的影响主要表现在前150 d,破坏形式由贯穿破坏转变为贯穿破坏与片状剥落并存;浸矿母液侵蚀作用下,基岩力学特性呈现先大幅减小后大幅回升,其后在小范围波动现象,浸矿约60 d对基岩力学特性的影响程度最大;浸矿母液侵蚀造成基岩内小孔隙增长,导致表面出现腐蚀及孔洞现象;浸矿时间不同将造成岩石不同的微观结构变化。  相似文献   

柴达木盆地东坪地区侏罗系分布及基岩岩性预测     

尹成明  张弘强  杨大兵  王占斌  吴鹏 《地质通报》2016,35(203):211-220

柴达木盆地东坪地区东坪1井天然气的发现揭开了柴达木盆地基岩天然气藏勘探的序幕。勘探和研究认为,东坪地区基岩气藏以侏罗系烃源岩为气源,纵向上通过断裂、裂缝系统迁移,横向上通过不整合面、优质砂体运移,在花岗岩和片麻岩基岩中聚集成藏。因此,侏罗系分布和基底岩性预测是该区基岩气藏勘探的关键问题。通过CEMP勘探结合重磁资料研究,明确了侏罗系的分布,预测了东坪—冷湖地区基岩分布及特征,与钻井吻合良好,对东坪—冷湖地区的基岩气藏勘探具有指导意义。  相似文献   

四川省南江县陈家湾滑坡稳定性分析及防治建议          下载免费PDF全文

张涛  石胜伟  谢忠胜  梁炯  熊德清 《探矿工程》2016,43(1):14-19

由于山体的特殊地质背景及人类工程活动,四川省南江县陈家湾滑坡在平面位置上以中间山梁为界分为Ⅰ号、Ⅱ号滑坡及潜在不稳定斜坡。通过地质灾害勘查,研究了滑坡特征及其地质成因机制,并进行了稳定性分析评价。结果表明：仅Ⅰ号滑坡在暴雨工况下处于欠稳定状态。根据滑坡地形特征、稳定性分析结果,结合保护对象,对Ⅰ号滑坡提出了“抗滑桩+截水沟”和“预应力锚索+抗滑短桩+截水沟”两种防治方案。通过对比分析,推荐“抗滑桩+截水沟”为实施方案。  相似文献   

水力压裂技术在豫西基岩地热井增产中的应用研究          下载免费PDF全文

申云飞  卢玮  陈莹  程存平 《探矿工程》2016,43(10):253-256

地热资源是清洁能源,其开发利用主要通过钻井工程来实现。地热资源量（水量）大小决定着开发利用的价值。实际中,因地层等条件的复杂和不确定性,导致地热井出水量和温度不能达到预期的目标。特别是在山区基岩缺水地区地热资源开发,由于水量和温度指标偏低,严重影响了清洁能源的开发利用。本文结合工程实例,首次在豫西基岩严重缺水地区通过压裂车和钻井泵分段水力压裂技术,使低产地热井出水量增加3倍,达到了预期的目的。为今后基岩地区地热和地下水资源开发利用增产提供了借鉴。  相似文献   

基岩测量在地球化学普查中的应用     

程培生 《物探与化探》2003,27(2):113-114

结合安徽石台-九华山地区1:5万地球化学普查成果,说明改进的基岩测量在地球化学普查中,不仅能够获得丰富的找矿信息,还能加速异常的筛选、评价,并取得良好的效果.  相似文献