Trend detection in river flow series: 1. Annual maximum flow / Détection de tendance dans des séries de débit fluvial: 1. Débit maximum annuel     

《水文科学杂志》2013,58(5)

Abstract

Results of a study on change detection in hydrological time series of annual maximum river flow are presented. Out of more than a thousand long time series made available by the Global Runoff Data Centre (GRDC) in Koblenz, Germany, a worldwide data set consisting of 195 long series of daily mean flow records was selected, based on such criteria as length of series, currency, lack of gaps and missing values, adequate geographical distribution, and priority to smaller catchments. The analysis of annual maximum flows does not support the hypothesis of ubiquitous growth of high flows. Although 27 cases of strong, statistically significant increase were identified by the Mann-Kendall test, there are 31 decreases as well, and most (137) time series do not show any significant changes (at the 10% level). Caution is advised in interpreting these results as flooding is a complex phenomenon, caused by a number of factors that can be associated with local, regional, and hemispheric climatic processes. Moreover, river flow has strong natural variability and exhibits long-term persistence which can confound the results of trend and significance tests.  相似文献   

Curve‐Number/Green–Ampt mixed procedure for streamflow predictions in ungauged basins: Parameter sensitivity analysis     

S. Grimaldi  A. Petroselli  N. Romano 《水文研究》2013,27(8):1265-1275

A procedure combining the Soil Conservation Service‐Curve Number (SCS‐CN) method and the Green–Ampt (GA) infiltration equation was recently developed to overcome some of the drawbacks of the classic SCS‐CN approach when estimating the volume of surface runoff at a sub‐daily time resolution. The rationale of this mixed procedure, named Curve Number for Green–Ampt (CN4GA), is to use the GA infiltration model to distribute the total volume of the net hyetograph (rainfall excess) provided by the SCS‐CN method over time. The initial abstraction and the total volume of rainfall given by the SCS‐CN method are used to identify the ponding time and to quantify the hydraulic conductivity parameter of the GA equation. In this paper, a sensitivity analysis of the mixed CN4GA parameters is presented with the aim to identify conditions where the mixed procedure can be effectively used within the Prediction in Ungauged Basin perspective. The effects exerted by changes in selected input parameters on the outputs are evaluated using rectangular and triangular synthetic hyetographs as well as 100 maximum annual storms selected from synthetic rainfall time series. When applied to extreme precipitation events, which are characterized by predominant peaks of rainfall, the CN4GA appears to be rather insensitive to the input hydraulic parameters of the soil, which is an interesting feature of the CN4GA approach and makes it an ideal candidate for the rainfall excess estimation at sub‐daily temporal resolution at ungauged sites. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Abrupt behaviours of streamflow and sediment load variations of the Yangtze River basin,China     

Qiang Zhang  Vijay P. Singh  Chong‐Yu Xu  Xiaohong Chen 《水文研究》2013,27(3):444-452

Monthly sediment load and streamflow series spanning 1963–2004 from four hydrological stations situation in the main stem of the Yangtze River, China, are analysed using scanning t‐test and the simple two‐phase linear regression scheme. Results indicate significant changes in the sediment load and streamflow from the upper reach to the lower reach of the Yangtze River. Relatively consistent positive coherency relations can be detected between streamflow and sediment load in the upper reach and negative coherency in the middle and lower reaches. Interestingly, negative coherency is found mainly for larger time scales. Changes in sediment load are the result mainly of human influence; specifically, the construction of water reservoirs may be the major cause of negative coherency. Accentuating the human influence from the upper to the lower reach results in inconsistent correlations between sediment load and streamflow. Decreasing sediment load being observed in recent years has the potential to alter the topographical properties of the river channel and the consequent development and recession of the Yangtze Delta. Results of this study are of practical significance for river channel management and evaluation of the influence of human activities on the hydrological regimes of large rivers. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Dynamics of unsaturated poroelastic solids at finite strain     

Ryosuke Uzuoka  Ronaldo I. Borja 《国际地质力学数值与分析法杂志》2012,36(13):1535-1573

We derive the governing equations for the dynamic response of unsaturated poroelastic solids at finite strain. We obtain simplified governing equations from the complete coupled formulation by neglecting the material time derivative of the relative velocities and the advection terms of the pore fluids relative to the solid skeleton, leading to a so‐called u^s ? p^w ? p^a formulation. We impose the weak forms of the momentum and mass balance equations at the current configuration and implement the framework numerically using a mixed finite element formulation. We verify the proposed method through comparison with analytical solutions and experiments of quasi‐static processes. We use a neo‐Hookean hyperelastic constitutive model for the solid matrix and demonstrate, through numerical examples, the impact of large deformation on the dynamic response of unsaturated poroelastic solids under a variety of loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Quadrature-based approach for the efficient evaluation of surge hazard   总被引：3，自引：0，他引：3  

G.R. Toro  A.W. Niedoroda  D. Divoky 《Ocean Engineering》2010,37(1):114-124

The Joint Probability Method (JPM) has been used for hurricane surge frequency analysis for over three decades, and remains the method of choice owing to the limitations of more direct historical methods. However, use of the JPM approach in conjunction with the modern generation of complex high-resolution numerical models (used to describe winds, waves, and surge) has become highly inefficient, owing to the large number of costly storm simulations that are typically required. This paper describes a new approach to the selection of the storm simulation set that permits reduction of the JPM computational effort by about an order of magnitude (compared to a more conventional approach) while maintaining good accuracy. The method uses an integration scheme called Bayesian or Gaussian-process quadrature (together with conventional integration methods) to evaluate the multi-dimensional joint probability integral over the space of storm parameters (pressure, radius, speed, heading, and any others found to be important) as a weighted summation over a relatively small set of optimally selected nodes (synthetic storms). Examples of an application of the method are shown, drawn from the recent post-Katrina study of coastal Mississippi.  相似文献   

Discrete wavelet‐based trend identification in hydrologic time series     

Yan‐Fang Sang  Zhonggen Wang  Changming Liu 《水文研究》2013,27(14):2021-2031

Trend identification is a substantial issue in hydrologic series analysis, but it is also a difficult task in practice due to the confusing concept of trend and disadvantages of methods. In this article, an improved definition of trend was given as follows: ‘a trend is the deterministic component in the analysed data and corresponds to the biggest temporal scale on the condition of giving the concerned temporal scale’. It emphasizes the intrinsic and deterministic properties of trend, can clearly distinguish trend from periodicities and points out the prerequisite of the concerned temporal scale only by giving which the trend has its specific meaning. Correspondingly, the discrete wavelet‐based method for trend identification was improved. Differing from those methods used presently, the improved method is to identify trend by comparing the energy difference between hydrologic data and noise, and it can simultaneously separate periodicities and noise. Furthermore, the improved method can quantitatively estimate the statistical significance of the identified trend by using proper confidence interval. Analyses of both synthetic and observed series indicated the identical power of the improved method as the Mann–Kendall test in assessing the statistical significance of the trend in hydrologic data, and by using the former, the identified trend can adaptively reflect the nonlinear and nonstationary variability of hydrologic data. Besides, the results also showed the influences of three key factors (wavelet choice, decomposition level choice and noise content) on discrete wavelet‐based trend identification; hence, they should be carefully considered in practice. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Finite element modeling of heating phenomena of cracks excited by high-intensity ultrasonic pulses     

陈赵江  郑江  张淑仪  米小兵  郑凯 《海洋学报(英文版)》2010,29(11)

A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.  相似文献   

Re‐establishment of soil water repellency after destruction by intense burning in a Mediterranean heathland (SW Spain)     

Antonio Jordán  Félix A. González  Lorena M. Zavala 《水文研究》2010,24(6):736-748

Soil water repellency has been conventionally considered as a fire‐induced effect, but an increasing number of studies have suggested that natural background repellency occurs in many soil types, and many of them have suggested that water repellency can be re‐established over time after being destroyed. An experimental fire was conducted to study changes of the soil surface during the first 18 months following intense burning. The main objectives of this paper are as follows: (1) to investigate in situ water repellency changes at three soil depths (0, 2 and 4 cm) immediately after burning; (2) to evaluate the medium‐term evolution of water repellency under field conditions; and (3) to outline the main hydrological consequences of these changes. Also, different water repellency tests (water drop penetration time, ethanol percentage test (EPT) and contact angle (CA) between water drops and the soil surface) were carried out for comparison purposes. Field experiments showed that soil water repellency was partly destroyed after intense burning. Changes were relatively strong at the soil surface, but diminished progressively with depth. Levels of water repellency were practically re‐established 18 months after burning. This suggests that water repellency in the studied area is not necessarily a consequence of fire, but can instead be a natural attribute. Finally, although limited in time, destruction of soil water repellency has important consequences for runoff flow generation and soil loss rates, and, indirectly, for water quality. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Analytic element modelling for strip aquifers     

José Anderson N. Batista  Edson Wendland  Harry E. Schulz 《水文研究》2012,26(8):1254-1262

The Analytic Element Method (AEM) provides a convenient tool for groundwater flow analysis in unbounded continuous domains. The AEM is based on the superposition of analytic functions, known as elements, useful at both regional and local scales. In this study, analytic elements for strip aquifers are presented. Such aquifers occur in riverine or coastal deposits and in outcrop zones of confined aquifers. Local flow field is modelled indirectly, using a reference plane related to the aquifer domain through the Schwarz‐Christoffel transform. The regional flow is obtained as a solution of the one‐dimensional flow equation. The proposed methodology was tested by modelling two hypothetical situations, which were compared to exact solutions. It is shown that regional boundaries can be reproduced exactly while local fields are adequately reproduced with analytic elements. The developed elements are applied to simulate a real flow field in northeastern Brazil showing good agreement with measured water levels. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

浅淡奇石及其文化渊源     

艾宪森  柏鉴清 《山东国土资源》2000,(1)

介绍了我国奇石观赏的起源和发展进程 ,对我国石文化传统和各发展阶段的石文化特点进行了探讨  相似文献