广东流溪河水库湖沼学变量的时空动态特征   总被引：16，自引：7，他引：9  

林国恩  望甜  林秋奇  韩博平 《湖泊科学》2009,21(3):387-394

流溪河水库县位于北回归线上的大型山谷型水库,是一座典型的热带-亚热带过渡区水体.为了解该水库的特点,于2006年对水库的水文、营养盐状况及相关理化因子进行了逐月监测,对其主要的湖沼学变量的季节动态和空间分布进行了分析,探讨了湖沼学特征和生态过程的主要驱动因子.流溪河水库全年表层水温在14.9-31.6℃之间,水柱热分层开始于3月初,一直持续到12月,呈单循环混合模式.水库的水动力学主要受降水和水库用水的影响,2006年全年降雨量为2960mm,平均水力滞留时间长170d;降雨量集中在丰水期(4-9月),导致丰水期水力滞留时间短(65d),丰水期与枯水期水文水动力季节性差别显著,水文水动力学变化剧烈.2006年全年湖泊区的TN、TP、Chl.a、SD的平均值分别为0.66mg/L,0.016mg/L,2.2mg/m3,3.1m,指示该水库为贫中营养型水体.N/P的质量比为41:1,DIN/DIP的质量比为78:1,说明该水库浮游植物生长在强烈的磷限制性水体中,较高的N/P比是由流域中热带-亚热带红壤中营养盐组成特点所决定.营养盐、透明度和叶绿素a等变量的分布具有明显的时空异质性,丰水期初期(4-5月)营养盐浓度显著地高于其它月份,说明地表径流是输送营养盐入库的主要途径;沿入库河流至水库大坝方向,营养盐和Chl.a具有递减规律,即:河流区>过渡区>湖泊区.受季风的影响,丰水期的降水集中加上水库的本身形态是导致流溪河水库湖沼学特征呈显著的季节性和空间梯度的关键因素.  相似文献   

Travel time computations using a compact eikonal equation for vertical transverse isotropic media          下载免费PDF全文

Peyman Moghaddam  Reza Khajavi  Henk Keers 《Geophysical Prospecting》2018,66(8):1475-1484

Eikonal solvers often have stability problems if the velocity model is mildly heterogeneous. We derive a stable and compact form of the eikonal equation for P‐wave propagation in vertical transverse isotropic media. The obtained formulation is more compact than other formulations and therefore computationally attractive. We implemented ray shooting for this new equation through a Hamiltonian formalism. Ray tracing based on this new equation is tested on both simple as well as more realistic mildly heterogeneous velocity models. We show through examples that the new equation gives travel times that coincide with the travel time picks from wave equation modelling for anisotropic wave propagation.  相似文献   

Using the applied element method for modelling calcium silicate brick masonry subjected to in‐plane cyclic loading          下载免费PDF全文

Daniele Malomo  Rui Pinho  Andrea Penna 《地震工程与结构动力学》2018,47(7):1610-1630

The response of calcium silicate unreinforced masonry construction to horizontal cyclic loading has recently become the focus of experimental and numerical research, given its extensive use in some areas of the world that are now exposed to induced earthquakes (eg, north of the Netherlands). To assess the seismic behaviour of such construction, a relatively wide range of modelling methodologies are available, amongst which the discrete elements approach, which takes into account the intrinsic heterogeneity of a brick‐mortar assembly, can probably be deemed as the most appropriate computational procedure. On the other hand, however, since discrete elements numerical methods are based on a discontinuum domain, often they are not able to model every stage of the structural response adequately, and because of the high computational burden required, the analysis scale should be chosen carefully. The applied element method is a relatively recent addition to the discrete elements family, with a high potential for overcoming the aforementioned limitations or difficulties. Initially conceived to model blast events and concrete structures, its use in the earthquake engineering field is, of late, increasing noticeably. In this paper, the use of the applied element method to model the in‐plane cyclic response of calcium silicate masonry walls is discussed and scrutinised, also through the comparison with experimental results of in‐plane cyclic shear‐compression tests on unreinforced masonry walls.  相似文献   

Morphodynamic assessment of side channel systems using a simple one‐dimensional bifurcation model and a comparison with aerial images          下载免费PDF全文

R. Pepijn van Denderen  Ralph M. J. Schielen  Astrid Blom  Suzanne J. M. H. Hulscher  Maarten G. Kleinhans 《地球表面变化过程与地形》2018,43(6):1169-1182

Side channel construction is a common intervention applied to increase a river's conveyance capacity and to increase its ecological value. Past modelling efforts suggest two mechanisms affecting the morphodynamic change of a side channel: (1) a difference in channel slope between the side channel and the main channel and (2) bend flow just upstream of the bifurcation. The objective of this paper was to assess the conditions under which side channels generally aggrade or degrade and to assess the characteristic timescales of the associated morphological change. We use a one‐dimensional bifurcation model to predict the development of side channel systems and the characteristic timescale for a wide range of conditions. We then compare these results to multitemporal aerial images of four side channel systems. We consider the following mechanisms at the bifurcation to be important for side channel development: sediment diversion due to the bifurcation angle, sediment diversion due to the transverse bed slope, partitioning of suspended load, mixed sediment processes such as sorting at the bifurcation, bank erosion, deposition due to vegetation, and floodplain sedimentation. There are limitations to using a one‐dimensional numerical model as it can only account for these mechanisms in a parametrized manner, but the model reproduces general behaviour of the natural side channels until floodplain‐forming processes become important. The main result is a set of stability diagrams with key model parameters that can be used to assess the development of a side channel system and the associated timescale, which will aid in the future design and maintenance of side channel systems. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Modelling soil moisture in a high‐latitude landscape using LiDAR and soil data          下载免费PDF全文

Julia Kemppinen  Pekka Niittynen  Henri Riihimäki  Miska Luoto 《地球表面变化过程与地形》2018,43(5):1019-1031

Soil moisture has a pronounced effect on earth surface processes. Global soil moisture is strongly driven by climate, whereas at finer scales, the role of non‐climatic drivers becomes more important. We provide insights into the significance of soil and land surface properties in landscape‐scale soil moisture variation by utilizing high‐resolution light detection and ranging (LiDAR) data and extensive field investigations. The data consist of 1200 study plots located in a high‐latitude landscape of mountain tundra in north‐western Finland. We measured the plots three times during growing season 2016 with a hand‐held time‐domain reflectometry sensor. To model soil moisture and its temporal variation, we used four statistical modelling methods: generalized linear models, generalized additive models, boosted regression trees, and random forests. The model fit of the soil moisture models were R² = 0.60 and root mean square error (RMSE) 8.04 VWC% on average, while the temporal variation models showed a lower fit of R² = 0.25 and RMSE 13.11 CV%. The predictive performances for the former were R² = 0.47 and RMSE 9.34 VWC%, and for the latter R² = 0.01 and RMSE 15.29 CV%. Results were similar across the modelling methods, demonstrating a consistent pattern. Soil moisture and its temporal variation showed strong heterogeneity over short distances; therefore, soil moisture modelling benefits from high‐resolution predictors, such as LiDAR based variables. In the soil moisture models, the strongest predictor was SAGA (System for Automated Geoscientific Analyses) wetness index (SWI), based on a 1 m² digital terrain model derived from LiDAR data, which outperformed soil predictors. Thus, our study supports the use of LiDAR based SWI in explaining fine‐scale soil moisture variation. In the temporal variation models, the strongest predictor was the field‐quantified organic layer depth variable. Our results show that spatial soil moisture predictions can be based on soil and land surface properties, yet the temporal models require further investigation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

On the importance of soil moisture in calibration of rainfall–runoff models: two case studies     

Mahshid Shahrban  Jeffrey P. Walker  Q. J. Wang  David E. Robertson 《水文科学杂志》2018,63(9):1292-1312

Streamflow modelling results from the GR4H and PDM hydrological models were evaluated in two Australian sub-catchments, using (1) calibration to streamflow and (2) joint-calibration to streamflow and soil moisture. Soil moisture storage in the models was evaluated against soil moisture observations from field measurements. The PDM had the best performance in terms of both streamflow and soil moisture estimations during the calibration period, but was outperformed by GR4H during validation. It was also shown that the soil moisture estimation was improved significantly by joint-calibration for the case where streamflow and soil moisture estimations were poor. In other cases, addition of the soil moisture constraint did not degrade the results. Consequently, it is recommended that GR4H be used, in preference to the PDM, in the foothills of the Murrumbidgee catchment or other Australian catchments with semi-arid to sub-humid climate, and that soil moisture data be used in the calibration process.  相似文献   

Universality of a higher-order closure model for turbulent rotating flows     

A. S. Hsieh 《地球物理与天体物理流体动力学》2018,112(2):156-164

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官厅水库水体营养状况分析   总被引：23，自引：4，他引：19  

杜桂森  王建厅  张为华  冯伶亲  刘静 《湖泊科学》2004,16(3):277-281

2001-2002年的调研结果显示,官厅水库为富营养型湖泊.初级生产力为浮游藻类与大型水生高等植物混合型.浮游藻类细胞密度为1126.54×104cells/L,其中蓝藻占53.4%,绿藻占32.1%.优势种为水华微囊藻(Microcystisflos-aquae)和铜绿微囊藻(M.aeruginosa).7-10月库区水体出现大面积的微囊藻水华.TN、TP分别为1.182mg/L和0.045mg/L,水体已达富营养.官厅水库TN和TP的质量浓度比大于7,Chla与TP存在显著的正相关.磷是水体中初级生产力增长的限制性营养盐.官厅水库的污染物主要来自点源,其次是面源和内源.应以点源为主进行综合防治,恢复其饮用水源地功能,以缓解北京市淡水资源的紧缺状态.  相似文献   

多方向不规则波传播变形数值模拟   总被引：2，自引：1，他引：1  

潘军宁左其华  王红川 《海洋工程》2004,22(3):14-19,29

在推广的缓坡方程数学模型基础上建立了多方向不规则波数学模型,综合考虑了波浪折射、绕射、反射、底摩擦和风能输入等因素。基于线性波浪理论,将波浪方向谱在频率和方向上按等能量分割法离散后,分别计算各组成波的传播变形,再计算合成波要素。缓坡方程数学模型采用改进的ADI法求解,计算效率高,稳定性好。采用椭圆形浅滩不规则波模型试验结果和单突堤不规则波绕射理论解对数学模型进行了验证,数值模拟结果和试验值及理论解符合良好。利用该模型进行了某港港内波浪折射、绕射和反射的联合数值模拟,给出了合理的港内波高分布。  相似文献   

答“评‘紫坪铺水库造成孔隙弹性耦合变化及其对2008年汶川地震触发作用’二维模拟的局限性”          下载免费PDF全文

陶玮  沈正康  张永 《地球物理学报》2015,58(4):1462-1465

程惠红等(2015)在"评‘紫坪铺水库造成孔隙弹性耦合变化及其对2008年汶川地震触发作用’二维模拟的局限性"一文中提出,陶玮等(2014)采用二维模型模拟紫坪铺水库造成孔隙弹性耦合变化是一个不足,夸大了汶川地震震源处库仑应力增长值.我们认为采用二维模型模拟水库造成汶川地震震源处库仑应力变化确实可能存在一定偏差,但不会如程惠红等认为的"与三维模型相比夸大三倍".这是因为在程惠红等引用的论证中,二维模型计算中选取了接近水库最大剖面宽度而不是水库平均剖面宽度作为加载量参数,造成计算得到震源处库仑应力明显夸大.此外,陶玮等(2014)提出论断的主要依据不是"震源处"库仑应力值的大小,而是紫坪铺水库蓄水"由浅入深影响到整条断层,尤其对浅层范围的加载作用明显,达上百千帕,为整个断层面的失稳提供了基础".初始破裂的发生既可能是由水库蓄水引起,也可能是并非水库蓄水造成的一次普通构造小震,但其发生引发断层面上部已被水库蓄水弱化部分的连锁失稳而发生大震.即汶川地震既可能为直接触发也可能为间接触发,而我们的研究结果认为地震的发生完全可能由间接触发产生.若仅纠结于"震源处"的库仑应力变化,则忽视了水库蓄水影响的主体.水库蓄水对地震触发作用是一个复杂问题,相对这一问题所涉及的一系列不确定性因素来说,二维模拟的局限性所造成的影响并不很大也不是最大的,也不妨碍我们据此得出紫坪铺水库蓄水促进汶川地震发生的结论.  相似文献