Direct relationships of discharges to the mean and standard deviation of the intervals between their exceedences

Abstract

This article paves a way for assessing flood risk by the use of two-parameter distributions, for the intervals between threshold exceedences rather than by the traditional exponential distribution. In a case study, the apparent properties of intervals between exceedences of runoff events differ from those anticipated for exponentially distributed series. A procedure is proposed to relate two statistical parameters of the intervals to threshold discharges. It considers partial duration series (PDS) with thresholds equal to all high enough observed discharges. To avoid unnecessary assumptions on the behaviour of those parameters and effects of dependence between parameters for different PDS, a non-parametric trend-free pre-whitened scheme is applied. It leads to power-law relationships between a discharge and the mean and standard deviation of the intervals between its exceedences. Predicted mean inter-exceedence intervals, for the highest observed discharges at the stations, are closer to the observational periods than those predicted by GEV distributions fitted to AMS, and by GP distributions to fitted PDS. In the present case, the latter predictions are longer than the observational periods whereas some of the predicted mean inter-exceedences are shorter than the corresponding observational periods and some others are longer.

Citation Ben-Zvi, A. & Azmon, B. (2010) Direct relationships of discharges to the mean and standard deviation of the intervals between their exceedences. Hydrol. Sci J. 55(4), 565–577.     

Modelling streamflow trends for a watershed with limited data: case of the Litani basin,Lebanon

Abstract

Streamflow variability in the Upper and Lower Litani basin, Lebanon was modelled as there is a lack of long-term measured runoff data. To simulate runoff and streamflow, daily rainfall was derived using a stochastic rainfall generation model and monthly rainfall data. Two distinct synthetic rainfall models were developed based on a two-part probabilistic distribution approach. The rainfall occurrence was described by a Markov chain process, while the rainfall distribution on wet days was represented by two different distributions (i.e. gamma and mixed exponential distributions). Both distributions yielded similar results. The rainfall data were then processed using water balance and routing models to generate daily and monthly streamflow. Compared with measured data, the model results were generally reasonable (mean errors ranging from 0.1 to 0.8?m³/s at select locations). Finally, the simulated monthly streamflow data were used to investigate discharge trends in the Litani basin during the 20th century using the Mann-Kendall and Sen slope nonparametric trend detection methods. A significant drying trend of the basin was detected, reaching a streamflow reduction of 0.8 and 0.7 m³/s per decade in January for the Upper and Lower basin, respectively.

Editor D. Koutsoyiannis; Associate editor Sheng Yue

Citation Ramadan, H.H., Beighley, R.E., and Ramamurthy, A.S., 2012. Modelling streamflow trends for a watershed with limited data: case of the Litani basin, Lebanon. Hydrological Sciences Journal, 57 (8), 1516–1529.     

卡尔曼滤波在建筑沉降监测数据处理中的应用

卡尔曼滤波作为一种动态数据处理方法已广泛应用于变形监测数据处理中。本文结合合肥市某小区6号楼沉降监测数据,建立相应的卡尔曼滤波模型,通过MATLAB编程实现,成果显示该模型较好的模拟了建筑物沉降的变化规律。     

基于环境控制的深基坑工程管井回灌设计分析

为探讨管井回灌在深基坑工程中的设计及应用,分析了基于环境控制的深基坑工程管井回灌设计的特殊性,开展了悬挂式帷幕下不同回灌滤管类型的降水回灌渗流分析及对比,探讨了影响回灌管井平面布设以及管井滤管设计的关键因素,同时针对深基坑工程回灌的特殊性,提出了“双点位流态”控制设计原则、回扬控制措施的确定方法以及回灌水质应满足的3项原则。     

UUVs集群协同定位的分散式增广信息滤波方法

无人水下航行器集群协同作业能够扩展单体UUV的感知范围,实现单体UUV无法或难以完成的复杂任务。由于水下环境的复杂性及UUV各传感器存在观测限制、时延等问题,传统分散式Kalman滤波方法所需要的庞大实时通信在实际中难以实现,使得当前UUVs集群协同定位为不严密的解算。本文提出一种以增广信息滤波为核心的UUVs集群协同定位分散式滤波方法,在顾及算法严密性的基础上实现了UUVs分散式协同定位。每个UUV平台根据本地的传感器数据建立自己的状态链,同时广播自己的观测信息,各个平台协同完成信息矩阵的Cholesky修正。基于严密的数理理论证明了所提出的UUVs协同定位的分散式滤波与集中式滤波的一致性,并与传统方法进行对比分析。理论仿真分析表明,较之传统方法单体UUV的观测更新或两个UUV之间的相互观测都会导致UUVs集群全体状态更新,本文方法使得观测更新仅与观测直接涉及的UUV相关,有效地降低了通信载荷,实现观测信息的即插即用,扩展性良好。     

全球稀土贸易网络的动态演变与影响机制————基于产业链的视角

基于稀土产业链视角,通过依赖关系构建稀土初级加工品、中级加工品和制成品贸易网络,运用社会网络分析法和动态指数随机图模型对稀土贸易网络结构演变特征及其影响机制进行对比分析。结果表明：① 3个环节稀土贸易网络均呈现向复杂网络演变的趋势,且稀土中级加工品贸易网络的变化趋势依次领先于稀土制成品和初级加工品贸易网络;② 从主干结构看,3个环节稀土贸易网络依次由欧洲主导向欧美并立演变、由中国主导向欧亚并立演变、由欧美亚三足鼎立向亚洲主导演变;③ 中国在3个环节稀土贸易网络中均发展成为直接影响力前三甲国家（地区）,但其领先优势逐渐缩小,而间接影响力仅在初级加工品和制成品网络进入前三甲行列,且增幅较小;④ 互惠、三角形、星形辐射和星形扩张结构效应对3个环节稀土贸易网络动态演变具有显著的异质性影响。     

基于非线性滤波的风廓线雷达数据处理

针对实际工程中风廓线雷达风向、风速随高度分布取值的非线性特性以及非气象干扰因素,基于非线性化方法——扩展卡尔曼滤波法,对风廓线雷达探测数据进行滤波处理.先利用泰勒展开式的一次项对非线性方程作线性化处理,再结合经典的卡尔曼滤波进行滤波估计,将非线性滤波问题转化为一个近似的线性滤波问题.仿真实验结果表明,该方法可以有效去除风场数据中掺杂的噪声干扰,很好地发挥了其非线性特性,滤波效果优于传统的卡尔曼滤波,具有一定的工程应用前景.     

江苏省冬季气温、降水年代际异常及相关分析

利用NCEP/NCAR再分析资料和江苏省冬季气温、降水资料,运用带通滤波、经验正交分解(EOF)和相关分析等方法,分析了江苏省冬季气候年代际异常及同期气温与降水的相关特征.结果表明:江苏省冬季气候的年代际变化具有很好的空间一致性,表现为全省整体偏暖(偏冷)和偏涝(偏旱)的趋势;冬季气候存在明显的年代际突变,时间在1980s中期前后,平均气温从偏冷时期向偏暖时期转换,降水由偏少期向偏多时期转换.通过冬季同期降水和气温的相关分析发现,降水和气温具有一定的正相关性,而他们的年代际分量的正相关性更为显著,这与冬季大气环流场和海温场的年代际变化有密切的关系.     

基于图像处理的回声定位信号检测方法

鲸豚类海洋哺乳动物发出的回声定位信号是一种频率较高的短时脉冲信号,研究回声定位信号检测方法有助于快速、准确地检测海洋哺乳动物发声,进而更好地保护海洋哺乳动物.本文提出了一种基于图像处理的鲸豚类动物回声定位信号检测方法.该方法首先对收集到的数据进行分帧,计算每帧信号的时频图;使用Frangi滤波器对时频图进行滤波,以降低...     

Identification of non-linear and non-stationary soil properties during the 1995 Hyogoken-nanbu earthquake

An extended Kalman filter algorithm with local iteration is presented for the identification of non-linear and non-stationary soil properties. Borehole-array strong motions were recorded at a liquefied site during the 1995 Hyogoken-nanbu earthquake. In this study, a modified Kalman filtering method in which the extended Kalman filter is iteratively used at every local time-step to track rapid parameter changes is proposed. The method is then applied to the instrumented soil layer, which is modeled by an equivalent linear model. An identification of non-linear and non-stationary soil properties was conducted successfully; and non-linear restoring force–displacement relationships including progression with time were obtained.