Morphology of riffle–pool sequences in the River Severn,England     

Paul A. Carling  Harriet G. Orr 《地球表面变化过程与地形》2000,25(4):369-384

Despite the occurrence of riffle–pool sequences in many rivers there are few data concerning riffle–pool unit morphology. Of many criteria proposed to identify riffle–pool units, only three methods can be regarded as objective and robust. These are the ‘zero‐crossing’, the ‘spectral analysis’ and the ‘control‐point’ methods. In this paper statistics are developed using the first two of these methods to describe the streamwise morphology of 275 riffles and 285 pools which form a continuous 32·1 km reach of the bed of the River Severn in Shropshire, England. Yalin's theoretical relationship between the average riffle:pool unit length ( λ _p) and channel width ( W ), λ _p = 3 W , applies to the River Severn. Reach‐average riffle height ( H ) is a constant proportion of bankfull depth ( h ); typically H ≅ 0·16 h . Riffle height is a positive function of riffle length. Pool depth is a positive function of pool length. However, both riffle length and pool length increase more rapidly than the bed‐level amplitude, such that long riffles or pools are relatively ‘flat’. As channel gradient reduces, bedforms flatten and become more asymmetric as riffle stoss sides and the proximal slope of pools lengthen at the expense of riffle lee sides and pool distal slopes. The statistical relationships between riffle steepness (H/L) and water depth are similar to those for equilibrium subaqueous dunes. The Severn data are consistent with Yalin's theoretical analysis relating riffle bedform length (L _r) to water depth, i.e. L _r = α2π h, wherein α ≅ 1 for steep near‐equilibrium bedforms but α ≅ 2 to 3 as the relative depth decreases and riffles become long, low features. Theoretical consideration and turbulence data indicate that the frequency of coherent turbulent‐flow structures associated with the riffle–pool mixing length in the Severn should be of the order of 50 to 100 s. The morphological similarity of the steepest River Severn riffles with dunes raises intriguing questions with respect to self‐similar, convergent organization of periodic alluvial bedforms and to bedform dynamic classification particularly. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

德州市浅层地温能资源潜力评价          下载免费PDF全文

李志恒  卢建荣  杜风林  刘欢  李东亮  万鑫 《山东国土资源》2017,33(5)

随着我国社会经济的快速发展,对能源的需求大幅增加,供需矛盾越来越突出,煤炭、石油、天然气等常规能源的大量消耗对环境造成的压力也越来越大。浅层地温能是一种可再生的新型环保能源,逐步受到各级政府及社会各界的重视。通过对德州城区浅层地温能赋存条件的分析,利用试验测试数据对浅层地温能热容量进行了计算,并在适宜性分区在基础上,进行了浅层地温能资源潜力评价。结果表明,德州城区120 m深度内浅层地热容量为8.525×10~(13)k J/℃,相当于291万t标准煤。整个德州城区为地下水换热系统不适宜区,而适宜地埋管换热系统。在地埋管换热系统适宜区内,120 m深度范围内考虑土地利用系数,计算得出夏季换热功率为339.18万k W,冬季换热功率为343.22万k W。夏季可制冷面积4.845×10~7m~2,冬季可供暖面积6.240×10~7m~2。  相似文献   

天山天池水体季节性分层特征   总被引：4，自引：1，他引：3  

王斌  马健  王银亚  尹湘江 《湖泊科学》2015,27(6):1197-1204

于2014年6-10月,对高山深水湖泊天山天池水温、电导率、溶解氧、p H值、叶绿素a浓度和蓝绿藻细胞密度进行垂直剖面的连续监测,通过对其季节动态和垂直分层结构的分析,探讨天池水体季节性分层特征.天池出现明显水温分层的时间短(6-9月),夏季温跃层变化范围为2~18 m,而秋季温跃层不断下移,10月在18 m水深以下;受水温分层影响,天池水体溶解氧浓度、电导率、p H值、叶绿素a浓度和蓝绿藻细胞密度在垂直剖面表现出明显的季节性分层,尤其是夏季水温分层影响溶解氧浓度、叶绿素a浓度和蓝绿藻细胞密度在水体中的分布,对天池水质变化产生重要影响.天池浅水层(水深小于10 m)溶解氧浓度较高(大于8 mg/L),而深水层(水深超过18 m)溶解氧浓度9月接近4 mg/L,季节性缺氧导致底泥营养盐向上扩散,对水体水质产生不利影响.所以,应在夏、秋季节加强水质监测,以防止天池水华发生;天池叶绿素a浓度与蓝绿藻细胞密度的垂直剖面变化趋势相似,均随水深增加呈先增加后减小的趋势,但叶绿素a浓度在2~12 m水深处较高,蓝绿藻细胞密度在5~15 m水深处较高,表明5~15 m深度适合藻类生长,同时,电导率、p H值的垂直变化也说明藻类的生长情况,这为监测天池水体富营养化取样和分析提供依据.  相似文献   

太湖波浪数值模拟   总被引：8，自引：7，他引：1  

李一平  逄勇  刘兴平  罗潋葱  徐秋霞 《湖泊科学》2008,20(1):117-122

在太湖实际波浪观测的基础上,采用率定验证后的第三代动谱平衡方程,考虑实际水底地形、波浪折射、浅化、反射、破碎、湖流等条件下,对太湖波浪进行数值模拟,研究太湖波浪的主要影响因素.结果表明:SWAN模型可以较好地模拟风作用下太湖风浪的生成和传播过程,模型在太湖应用是合适的;波高、波长、波周期等波浪参数在太湖的分布与风速、风向、水深等因素密切相关;在相同风向、不同风速情况下,太湖波浪发展至稳定状态的时间不一样;在不同风向,相同风速持续作用下,有效波高达到稳定的时间差不多,变化趋势也比较相同.说明波浪的发展不光取决于风速的大小,还同风的持续吹的时间和风区长度有关.  相似文献   

数字地震台电源远程监控系统     

张秀萍  王曰风  郑毅  王志敏  张广莉  韩和平 《地震地磁观测与研究》2017,38(4):218-221

以STC89C52单片机为核心,开发基于"十五"网络的地震台站电源远程监控系统,实时的监控台站仪器设备的状态并收取状态参数,实现设备复位操作及故障报警,可以提高地震台网中心仪器运行效率。  相似文献   

河北省及邻区数字电扰动干扰分析   总被引：1，自引：1，他引：0  

乔子云  罗娜  贾立峰  寇海川  牛淑瑜  茅远哲 《地震地磁观测与研究》2017,38(4):158-164

通过对河北省及邻区数字电扰动观测资料进行分析和环境调查,发现主要干扰因素为供电或漏电干扰。如:昌黎地震台地电阻率整点测量受到供电干扰,三河地震台受到恒远自动化仪表厂工作时段供电干扰,高碑店地震台受到商场大型设备供电干扰,广平地震台受到UPS交流电源漏电干扰,昌平地震台受到地铁运行漏电干扰等。电扰动干扰形态相似,均为超过本底值几倍、数十倍乃至上百倍的高值脉冲变化。  相似文献   

汶川地震强余震场地非线性反应     

姚鑫鑫  任叶飞  温瑞智 《地震地磁观测与研究》2017,38(2):104-111

采用汶川地震强余震26个强震动台站记录,基于H/V谱比法,计算台站场地的强、弱震作用下场地卓越频率之比R_(fp)和体现强、弱震作用下场地H/V谱比曲线差异程度的DNL,进而识别并分析场地非线性反应特征。结果显示,R_(fp)、DNL与PGA之间存在显著相关性;其中10个台站出现明显的场地非线性反应特征;大部分台站发生场地非线性反应的PGA阈值为100 cm/s~2,部分为50 cm/s~2;实例证明,因某些台站不易通过H/V谱比法识别场地卓越频率,因此采用R_(fp)识别场地非线性反应具有一定局限性。  相似文献   

安徽省国家强震动台站场地响应及背景噪声分析     

龙剑锋  温瑞智  周冬瑞  赵希磊  刘泽民 《地震地磁观测与研究》2017,39(1):89-95

利用安徽省部分强震动台站记录的地脉动数据和历史地震数据,采用H/V谱比法和噪声功率谱密度函数法,对比分析台站的场地响应及背景噪声,结果表明：全椒、马鞍山地震台的场地卓越周期小且背景噪声低;沈巷地震台卓越周期大且背景噪声高;三山地震台无明显卓越周期;地震台站背景噪声与场地响应曲线之间不存在一一对应关系。  相似文献   

宝石CT评价冠脉支架的临床应用价值          下载免费PDF全文

荘高明  钟伟锋  陈显杰  李淑明  劳敏华 《CT理论与应用研究》2017,26(6):689-694

目的:探讨宝石CT对冠脉支架的临床应用价值。方法:收集45例冠脉支架置入术后患者的宝石CTA数据,测量支架内腔的实际直径,比较支架内腔CT值与邻近血管腔CT值的差异。结果:共60枚支架,均显示清晰、无术后狭窄。当支架实际内腔直径≥2 mm时,支架内腔CT值测量稳定性较好,支架内腔CT值与邻近血管腔CT值无明显统计学差异。支架内腔直径<2 mm时,支架内腔CT值测量稳定性差、测量不准确,但是仍能部分观察支架内腔情况。结论:宝石CT冠脉CTA成像,对冠脉支架内腔直径≥2 mm者诊断较理想,对支架内腔直径<2 mm者仍有一定诊断价值。   相似文献   

The influence of tectonic subsidence on volcaniclastic sedimentation: The Cretaceous upper Daeri Member,Wido Island,Korea          下载免费PDF全文

Yong Sik Gihm  Min‐Cheol Kim  Moon Son  In Gul Hwang 《Island Arc》2017,26(3)

The Daeri Member, a Cretaceous volcanic–sedimentary succession, can be divided into lower, middle, and upper parts based on vertical changes in its lithologic characters. The lower Daeri Member is composed of siliciclastic deposits formed in a semi‐arid floodplain environment, which is overlain by the middle Daeri Member consisting mainly of andesite lava flow. After the emplacement of the andesite, activities of intrabasinal normal faults created accommodation on hanging wall blocks together with the development of intrabasinal topographic relief. The upper Daeri Member occurs only in hanging wall blocks and is composed of rhyolitic volcaniclastic sediments formed during an explosive volcanic eruption. Following the eruption, owing to semi‐arid climatic conditions and the destruction of vegetation, the eruptive materials were easily remobilized and deposited by episodic sediment gravity flows, resulting in deposition of the resedimented volcaniclastic deposits with sheet‐like geometry. Away from the intrabasinal normal faults, the resedimented volcaniclastic deposits show a decrease in grain size together with changes in inferred depositional processes from debris flows to hyperconcentrated flows and supercritical sheetfloods. This suggests that the resedimented volcaniclastic deposits were stacked on alluvial fan environments induced by intrabasinal topographic relief associated with normal fault activities. In addition, episodic movement of the faults gave rise to periodic fluctuation of the accommodation and an increase in gradient of the alluvial fan surface, resulting in the development of coarsening‐upward trends in the resedimented volcaniclastic deposits. The development of the alluvial fan and the coarsening‐upward trends indicate that dynamic tectonic subsidence and concomitant changes in the intrabasinal physiographic relief influenced the depositional processes and sizes of the transported volcaniclastic sediments of the upper Daeri Member. Thus, it is necessary to carefully observe tectonic signatures in volcaniclastic successions, particularly the syneruptive lithofacies, in order to reconstruct the tectonic and volcanic histories of receiving basins.  相似文献