Hydrological impacts of flow regulation associated with the Upper Nepean water supply scheme,NSW

The upper Nepean River has been progressively regulated for water supply to Sydney and Wollongong since 1886 by the Upper Nepean Water Supply Scheme which consists of four large dams, two small dams and two diversion weirs. Secular rainfall changes produced periods of high rainfall and large floods (flood‐dominated regimes) between 1857 and 1900 and 1947 and the present, and an intervening period (1901–46) of low rainfall and small floods (drought‐dominated regime). Upstream impoundment and flow regulation significantly reduced flood magnitudes for most return periods during both types of flood regimes. The probability distribution of mean daily flows was also changed significantly by flow regulation such that during the drought‐dominated regime, the high and low frequency flows were reduced substantially but the moderate frequency flows were increased due to dam releases; the change from a regulated drought‐dominated regime to a regulated flood‐ dominated regime resulted in a substantial increase in discharge for most durations; and increased water diversions to Wollongong during the current flood‐dominated regime produced a marked downward shift in the whole flow duration curve. Nepean Dam reduced downstream suspended sediment yields by two orders of magnitude because it traps in excess of 99 per cent of the inflowing suspended sediment load. Streamflow releases are urgently required from the two diversion weirs to improve downstream water quality and to ensure the viability of the resident ‘potentially threatened’ eastern Macquarie perch (Macquaria nov. sp.).     

Temporal variations in coda duration of local earthquakes in the Wellington region,New Zealand

Temporal variations of coda duration, relative to event magnitude, for local earthquakes near Wellington have been investigated. The region is one of plate convergence and subduction. The data consist of routinely made observations for events from 1978 through 1985 (1552 events), magnitude 1.6 to 5.2, depth 0.5 to 90.0 km. The observed average (over time) correspondence between duration (as measured from the origin time) and magnitude is reasonably well predicted by the single backscattering theory of coda formation for events of magnitude 4 or less; for larger events the observed durations are longer than predicted. This theory predicts that a temporal increase in scattering attenuation will reduce the coda duration relative to magnitude. Thus, any temporal changes in the duration-magnitude relation can be interpreted in terms of changes inQ. However, it is necessary to consider spatial biases since the observed durations are relatively long for shallow events and, for events of all depths, at stations situated in the south-eastern half of the region, usually believed part of the accretionary border. For both these situations other evidence would suggest that the scattering coefficient would be relatively high (lowQ). These observations may be due to a relatively high component of surface wave scattering and the importance of multiple scattering in the later part of the coda in regions of lowQ as suggested by finite element studies of coda formation. Despite the lack of any significant earthquakes during the 1978–1985 period there is nevertheless a significant temporal change in duration observed in the Wellington region: a change from relatively long to relatively short codas occurred in mid-1981. This change correlates well with changes in the rate of activity,b-value, radon emission, and ground tilt as derived from lake levels. It is not yet clear how all these parameters are related physically, but an episode of aseismic slip, or creep, along the plate interface below the region may have been the cause.     

The non‐stationary cross‐correlation coefficients in the seismic analysis of MDOF structural systems

A method concerning the evaluation, in a very compact form, of the non‐stationary modal cross‐correlation coefficients of MDOF structural systems subjected to seismic excitations is presented. It is available both in the case when the excitation is considered as a white‐noise process and when it is considered as a filtered process. The evaluation of these coefficients is required when a transient seismic analysis is performed by the use of the modal response spectrum approach. This is necessary when the strong‐motion phase of the earthquake is significantly short with respect to the fundamental period of the structure. Copyright © 2003 John Wiley & Sons, Ltd.     

Cyclic‐demand spectrum

The seismic response spectrum defines the amplitude of the load, but it does not specify the number of cycles for which the load must be resisted by the structure. The amplitude by itself is not sufficient to evaluate the seismic resistance of a structure, because the structure's strength, stiffness and energy‐dissipation capacity reduce with an increase in the number of load cycles. This paper presents a cyclic‐demand spectrum, which, in conjunction with the amplitude spectrum, provides a more complete definition of the seismic load, hence a way to consider the degradation in strength, stiffness and energy‐dissipation capacity in a rational manner. Similarly to three amplitude parameters (peak ground acceleration, peak ground velocity, and peak ground displacement), three cyclic‐demand parameters are introduced for stiff, moderately stiff, and flexible systems. A design example is presented to illustrate the use of the cyclic‐demand spectrum. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthetic regional flow duration curve for southern Taiwan

The primary purpose of this study is to develop the regional flow duration curves for southern Taiwan. To define homogeneous regions for developing regional flow duration curves, multivariate statistical analysis (principal component and cluster analysis) was applied to daily flow data from 34 stream-gauged stations in southern Taiwan. Two kinds of clustering variables, the dimensionless flow duration curve and specific flow duration curve, were compared in this study. It was found that three homogeneous regions delineated by specific flow duration curves as clustering variables have more reasonable results. The three homogeneous regions not only have well-defined geographical boundaries, but also correspond to the rainfall and geology characteristics of the regions. It seems that the technique of cluster analysis can reasonably define the homogeneous regions. In each homogeneous region, the synthetic regional flow duration curves were developed by a family of parametric duration curves. This approach has the advantage of being simple and needing only the basin area as an index. The performance of the regional flow duration curve was verified by the comparison of areas under the actual and synthetic flow duration curves; the latter were generated from the regional flow duration curve. Almost all the 34 stream-gauged stations had less than 25% absolute error.     

Spatial-temporal variations in cold surge events in northern China during the period 1960–2016

Journal of Geographical Sciences - Among the most devastating extreme weather events, cold surge (CS) events frequently impact northern China. It has been reported that extreme weather events will...     

Hydrometeorological assessments and suspended sediment delivery from a central Himalayan glacier in the upper Ganga basin

Integrated hydrometeorological investigations are not frequently available at a regional scale over a longer time period, especially near the terminus of Indian Himalayan glaciers. An integrated approach to the collection of hydrological data has major advantages for understanding the runoff generation mechanisms at basin scale, particularly when coupled with meteorological observations. The current study involves time series analysis of hydrometeorological records collected near the terminus of the Chorabari Glacier, for four consecutive ablation seasons(June-Sept.) 2009-2012. The analysis shows that variation in rainfall was higher(c_v= 0.9) at the same elevation over proximal sites, while the intensity of extreme rainfall events was 121-160 mm/d. The diurnal temperature range(DTR) has a tendency to reduce over the ablation season because of the onset of the Indian Summer Monsoon(ISM) and then further increases during the ISM withdrawal indicating humid-temperate conditions. The peak discharge(Qpeak) was found to be higher during July and August. Snow and glacier melt contributed 76% of the total suspended sediment transport during peak ISM months(July and August) reflecting seasonal evolution of the hydrologic conduits. The results indicate that Karakoram and western Himalayan glaciers produce comparatively low sediment yield compared to central Himalayan glaciers. The hydrological variations are depicted through flow duration curves(FDC) for meltwater discharge and sediment load. The flow corresponding to Q_(50), Q_(75), and Q_(90)(where Qx is the discharge that is exceeded x percent of the time referred to as % dependability) are 4.2, 3.7, and 2.8 m~3/s; and the corresponding dependability for suspended sediment loads(SSLs) are 409.0, 266.0, and 157.2 t/d, respectively. The daily SSL and discharge(Q) from 2009 to 2012 were used to develop a sediment rating curve(SSL = 39.55 × Q~(1.588). R~2 = 0.8).Multiple regressions are used to determine the impacts of meteorological parameters on glacier melt.The meteorological conditions, hydrological characteristics, and suspended sediment delivery for the Chorabari Glacier provide insight on meltwater generation processes and sediment transport patterns during the ISM season.     

Information theory measures for the engineering validation of ground‐motion simulations

This short communication introduces a quantitative approach for the engineering validation of ground‐motion simulations based on information theory concepts and statistical hypothesis testing. Specifically, we use the Kullback‐Leibler divergence to measure the similarity of the probability distributions of recorded and simulated ground‐motion intensity measures (IMs). We demonstrate the application of the proposed validation approach to ground‐motion simulations computed by using a variety of methods, including Graves and Pitarka hybrid broadband, the deterministic composite source model, and a stochastic white noise finite‐fault model. Ground‐motion IMs, acting as proxies for the (nonlinear) seismic response of more complex engineered systems, are considered herein to validate the considered ground‐motion simulation methods. The list of considered IMs includes both spectral‐shape and duration‐related proxies, shown to be the optimal IMs in several probabilistic seismic demand models of different structural types, within the framework of performance‐based earthquake engineering. The proposed validation exercise (1) can highlight the similarities and differences between simulated and recorded ground motions for a given simulation method and/or (2) allow the ranking of the performance of alternative simulation methods. The similarities between records and simulations should provide confidence in using the simulation method for engineering applications, while the discrepancies should help in improving the tested method for the generation of synthetic records.     

Rocking amplification and strong‐motion duration

This paper characterizes the ability of natural ground motions to induce rocking demands on rigid structures. In particular, focusing on rocking blocks of different size and slenderness subjected to a large number of historic earthquake records, the study unveils the predominant importance of the strong‐motion duration to rocking amplification (ie, peak rocking response without overturning). It proposes original dimensionless intensity measures (IMs), which capture the total duration (or total impulse accordingly) of the time intervals during which the ground motion is capable of triggering rocking motion. The results show that the proposed duration‐based IMs outperform all other examined (intensity, frequency, duration, and/or energy‐based) scalar IMs in terms of both “efficiency” and “sufficiency.” Further, the pertinent probabilistic seismic demand models offer a prediction of the peak rocking demand, which is adequately “universal” and of satisfactory accuracy. Lastly, the analysis shows that an IM that “efficiently” captures rocking amplification is not necessarily an “efficient” IM for predicting rocking overturning, which is dominated by the velocity characteristics (eg, peak velocity) of the ground motion.     

云南地磁台地震前地磁谐波振幅比分析

采用云南永胜和通海地磁台2010年1月至2018年12月记录的地磁分钟值数据,计算谐波振幅比随时间的变化,分析发现:2014年8月3日鲁甸6.5级地震、2018年9月8日墨江5.9级地震前,谐波振幅比曲线有2次明显下降—转折—恢复异常,分别于第1次异常恢复上升过程和第2次异常转折过程中发震,异常持续时间分别为3年和2年多,持续时间越长,震级越高;距震中较近的地磁台站谐波振幅比曲线出现不同步现象,即YZHx(NS)向与YZHy(EW)向的不同步及长短周期不同步。