Peak and trough distributions of nonlinear waves

The exact and approximate probability density functions of wave peaks and troughs are derived for nonlinear, narrow-band waves. A comparison of these quantities with those of linear waves is given. It is shown that nonlinearity has significant effect on these quantities.     

Identification and stochastic generation of representative rainfall temporal patterns in Hong Kong territory

In hydrosystem engineering design and analysis, temporal pattern for rainfall events of interest is often required. In this paper, statistical cluster analysis of dimensionless rainfall pattern is applied to identify representative temporal rainfall patterns typically occurred in Hong Kong Territory. For purpose of selecting an appropriate rainfall pattern in engineering applications, factors affecting the occurrence of different rainfall patterns are examined by statistical contingency tables analysis through which the inter-dependence of the occurrence frequency of rainfall patterns with respect to geographical location, rainfall duration and depth, and seasonality is investigated. Furthermore, due to inherent variability of rainfall mass curves or hyetographs within each classified rainfall pattern, a practical procedure to probabilistically generate plausible rainfall patterns is described. The procedure preserves the inherent stochastic features of random dimensionless rainfall hyetograph ordinates, which in general are correlated non-normal multivariate compositional variables.     

Modelling climate‐change impacts on stream temperature of Formosan landlocked salmon habitat

A physics‐based model is provided for predicting the impact of climate change on stream temperature and, in turn, on Formosan landlocked salmon (Oncorhynchus masou formosanus) habitat. Because upstream watersheds on Taiwan Island are surrounded with high and steep mountains, the influence of mountain shading on solar radiation and longwave radiation is taken into account by using a digital elevation model. Projections using CGCM2 and HADCM3 models and CCCM and GISS models provided information on future climatic conditions. The results indicate that annual average stream temperatures may rise by 0·5 °C (HADCM3 short term) to 2·9 °C (CGCM2 long term) due to climate change. The simulation results also indicate that the average suitable habitat for the Formosan landlocked salmon may decline by 333 m (HADCM3 short term) to 1633 m (CGCM2 long term) and 166 m (HADCM3 short term) to 1833 m (CGCM2 long term) depending on which thermal criterion (17 °C and 18 °C respectively) is applied. The results of this study draw attention to the tasks of Formosan landlocked salmon conservation agencies, not only with regard to restoration plans of the local environment, but also to the mitigation strategies to global climate change that are necessary and require further research. Copyright © 2005 John Wiley & Sons, Ltd.     

Incorporating daily rainfalls to derive rainfall DDF relationships at ungauged sites in Hong Kong and quantifying their uncertainty

Rainfall depth-duration-frequency (DDF) relationships are essential inputs for the design and management of various hydrosystem infrastructures (e.g., urban drainages, dams, dykes, etc.). In many cases, rainfall DDF relationships are required at a location where there is no gauge. However, due to the presence of intrinsic randomness of the precipitation process, limited rainfall record, and spatial interpolation, the derived DDF relationships at ungauged sites are subject to uncertainty. This is especially true in Hong Kong with regard to record length. To enhance the utilization of available rainfall data, a daily precipitation-based DDF generation framework for conventional rain gauges in Hong Kong has been developed by the authors utilizing a scaling model. In this article, the methodological framework is extended to derive rainfall DDF relationships at ungauged sites. Owing to the nonlinearity and complexity of the modeling process, exact statistical features of derived DDF relationships are difficult to obtain. In this study, Harr’s probabilistic point estimation method, known for its computational simplicity and accuracy, is applied to quantify the uncertainty features of rainfall DDF relationships derived for ungauged sites in Hong Kong. For illustration, four locations in different geographical locations in Hong Kong are considered. The results show that the uncertainty associated with the estimated statistical moments of annual maximum daily rainfall is significant in contributing to the overall uncertainty of derived rainfall DDF relationships.     

Extreme value distribution of earthquake magnitude

Probability distribution of maximum earthquake magnitude is first derived for an unspecified probability distribution of earthquake magnitude. A model for energy release of large earthquakes, similar to that of Adler-Lomnitz and Lomnitz, is introduced from which the probability distribution of earthquake magnitude is obtained. An extensive set of world data for shallow earthquakes, covering the period from 1904 to 1980, is used to determine the parameters of the probability distribution of maximum earthquake magnitude. Because of the special form of probability distribution of earthquake magnitude, a simple iterative scheme is devised to facilitate the estimation of these parameters by the method of least-squares. The agreement between the empirical and derived probability distributions of maximum earthquake magnitude is excellent.     

Energy dissipation in rocking bridge piers under free vibration tests

This research aims to investigate the dynamic characteristic of rocking bridge columns subjected to quick release loads. Precast columns anchored by unbonded steel bars at the centre of each column can rock on the foundation surface without inducing any residual deformation after earthquakes. The restoring force of columns relies on gravity load from the superstructure and tensile strength in anchor bars. Radiation damping is evaluated through each impact of column rocking. To validate the theoretical damping proposed by previous researchers, four columns were constructed. Research parameters included steel or plastic materials used as rocking interfaces, area of anchor bars, aspect ratio and size effect of columns. Test results revealed that stocky columns slid apparently in the first impact then rocked, but taller columns rocked with minor slips in the entire motion. And freestanding columns slid significantly in the first impact that led to a higher damping. Radiation damping due to impact in the entire motion for all tests was within 5%. Copyright © 2006 John Wiley & Sons, Ltd.     

Modification of the Natural Slake Test and Assessment of Slaking Behavior of a Shale from Malaysia Under Rainfall

Geotechnical and Geological Engineering - The durability of clay-bearing rocks has been a concern to the construction industry. Extensive research have been conducted to determine the durability of...     

Lacustrine sedimentological and geochemical records for the last 170 years of climate and environmental changes in southeastern China

Reconstruction of modern climate and environmental changes in east Asia using inland natural climate archives can provide valuable insights on decadal–multidecadal climate and environmental patterns that are probably related to both natural and anthropogenic forcing. Here we investigated an 89‐cm‐long sediment core (TH1) from Tian Lake, southeastern China, for sedimentological, physical and geochemical parameters in order to understand climate and environmental changes for the latest two centuries. ¹³⁷Cs‐ and ²¹⁰Pb‐based age models show that the fine sand–coarse silt‐dominated core contains ~170 years (c. AD 1842–2011) of continuous sedimentation. Sediments with fine sands, low MS values, high water content, high TOC content and a high C:N ratio from c. AD 1842 to 1897 suggest intense hydrological conditions and strong runoff in the catchment, probably because of a humid climate. From AD 1897 to 1990, sediments with very fine sand and coarse silt, high MS values, low water content and unchanged TOC and C:N ratios indicate normal hydrological conditions and in‐lake algae‐derived organic matter. During this interval, the chemical weathering indicators show stronger weathering conditions compared with sediments deposited during AD 1842–1897, supporting the dominance of weathered surface soil input in the earlier interval and physical erosion dominance in the later period, respectively. Since AD 1990, the continuous decrease of geochemical proxies suggests human‐interacted Earth surface processes in the catchment of Tian Lake. A PCA revealed four dominant geochemical controlling factors – detrital input, trophic status, grain size and early diagenesis –, accounting for 26, 20, 18 and 16% of total variance, respectively. This study for the first time provides lacustrine geochemical evidence for the most recent two centuries of climate and environmental changes in coastal southeastern China, a region that is currently undergoing an inversion of critical zone, i.e. an overturning of its soil profile, owing to swift modernization.     

On the nonlinear waves in a developing process

Based on the discrete form of the main governing equation derived, a single wave as the main motion of the instability analysis was found. This solution gives the whole process from the initial stage to the nonlinear equilibrium state. Next we examined the instability of the main motion above-mentioned in the initial stage and showed the instability properties of a developing process. Contribution No. 987 from the Institute of Oceanology, Academia Sinica.