Abstract: Climate change and intensive human activities are threatening water resource systems throughout the world. The water system in Poyang Lake Basin is especially vulnerable to these impacts due to the human influences, climate changes and interaction between Yangtze River and Poyang Lake. In recent decades, more and more studies have focused on the extreme hydro-meteorological events. By use of observed records of Poyang Lake Basin for nearly 50 years, the occurrence, frequency and changing trends of extreme streamflow indices (including annual maximum flow, peak-over-threshold flow indices and low flows) are analyzed for ten hydrological stations. Results indicate that most annual maximum flows occurred from April to June, highly attributed to the Southeast Asian summer monsoons, whereas the annual minimum flow concentrated between January and February. As for the low flow indices, (Annual minimum flow, Annual minimum 7-day flow, and Annual minimum 30-day flow) a significant increasing trend was detected in most parts of the Poyang Lake Basin. The trends illustrate the potential effects of climate change and human activities on the hydrological cycle over Poyang Lake Basin.
Abstract: The hydrologic process influenced by the multi-action of climate, geography, vegetation and human activities becomes more and more complex, which is the important characteristic of hydrologic system. The different complexity distributions of precipitation process of Chien River Basin (sub-basin of MinChiang Basin) in two periods(one is from 1952 to 1980 and the other is from 1981 to 2009) are illustrated respectively in this paper in which the fractal based on Continuous Wavelet Transform (CWT) is used. The results are indicated as follows: first, in basin scale the precipitation process in the latter period is more complex than that in the former period; second, the maximum value of the complexity distribution moved from the east to the middle and last, through analyzing the time-information and space-information concealed in this complexity change, the precipitation characteristics in changing environment are illuminated in study Basin. This study would provide reference for the research of disaster pre-warning in the changing environment and for the integrated water resources management in the local basin.
Abstract: The traditional operation rule of Three Gorges reservoir has mainly focused on water for flood control, power generation, navigation, water supply and recreation and given less attention to the negative impacts of reservoir operation on river ecosystem. In order to reduce the negative influence of reservoir operation, ecological operation of the reservoir should be studied to maintain healthy river ecosystem. The study considered the ecological operation targets, including maintaining river environmental flow and protecting the spawning and reproduction of Chinese sturgeon and four major Chinese carps. Based on the flow data from 1900 to 2006 of Yichang gauge as the control station of the Yangtze River, the minimal and optimal river environmental flows were analyzed, and eco-hydrological targets of Chinese sturgeon and four major Chinese carps in the Yangtze River were calculated. The paper proposed a reservoir ecological operation model of comprehensively considering flood control, power generation, navigation and ecological environment. Three typical periods including wet, normal and dry year were selected and particle swarm optimization was applied to analyze the model. The results show that there are different influences of ecological operation rules on economic benefit of hydropower station and reservoir ecological operation model can simulate the flood pulse for requirement of spawning of Chinese sturgeon and four major Chinese carps. Finally, ecological operation measures of Three Gorges reservoir were proposed. According to the results, by adopting a suitable re-operation scheme, the hydropower benefit of the reservoir will not decrease dramatically while the ecological demand can be met. The results provide the reference for making the reasonable operation schemes for Three Gorges reservoir.
Abstract: Material fluxes (e.g. nutrients) from coast to offshore play an important role in controlling the water quality in the concerned adjacent sea not only by the increase of nutrient concentration but by the change of nutrient structure. In the present work, naturally occurring isotopes (226Ra and 228Ra) had been measured by alpha spectrometry in Wenjiao/Wenchang and Wanquan river estuaries and adjacent sea water of the east coast of Hainan Island. The excess dissolved 226Ra and 228Ra activities were observed in comparison with the values expected from the conservative mixing of freshwater and seawater end-members in both estuaries. Using 1-Dimensional Diffusion model, the estimated horizontal eddy diffusion coefficients (Kh) derived from 228Ra activities away from its sources was 3.16?105 cm2 s-1. Furthermore, the corresponding nutrient fluxes into the coastal area were assessed. The results can provide useful information for the processes of mixing and exchange of coastal water as well as the transportation of dissoluble pollutants in this sea area.
Abstract: Free surface flows in macro- and intermediate roughness conditions have a high aeration potential in which the flow characteristics vary with slopes and discharges. The underlying phenomenon of two phase flow characteristics in the macro and intermediate roughness conditions were analyzed in a setup assembled at the PITLAB center of the University of Pisa, Italy. Crushed angular rocks and hemispherical boulders were used to intensify the roughness nature of the bed. Flow discharges per unit width ranging between 0.03 m2/s and 0.09 m2/s and slopes between 0.26 and 0.46 were tested over different arrangements of rough bed. Analyses were mainly concentrated in the inner flow region which constitutes both bubbly and intermediate flow region. The findings revealed that two phase flow properties over rough bed were very much affected by the different rough bed arrangement. Turbulence features of two phase flows over rough beds were compared with that of the stepped chute data under similar flow conditions. Overall the results highlighted the flow features in the inner layers of the two phase flow.
Abstract: The Velocity Dip phenomenon will appear in part or whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and Laser Doppler Velocimetry, the influence of the distance to side wall and the aspect ratio of the Velocity Dip is investigated. Through applying statistical methods to obtained results,, it is proposed that the flow field may be divided into two regions, the Relative Strong Side Wall Region and the Relative Weak Side Wall Region. In the Relative Strong Side Wall Region, the distance to the side wall greatly affects the location of maximum velocity, and in the Relative Weak Side Wall Region, both the distance to the side wall and the aspect ratio influence the location of maximum velocity.
Abstract: Bed structures which developed in many mountain rivers provide additional resistance to the flow. A field experiment was conducted on debris flow deposits in the valley of jiangjiagou ravine, a tributary of Yangtze river in southwestern China, to study the evolution and distribution of bed structures and their relationship with environmental conditions. Water and sediment from the jiangjiagou main stream were diverted into the experiment channel. Several hydrological schemes were adopted to scour the channel until equilibrium. And during this process the evolution of bed structures and channel configuration was investigated. The results indicated that stronger bed structures meant greater stream power consumption, larger resistance and steeper channel slope in a certain section when rivers are in dynamic equilibrium. Thus to some extent the channel longitudinal profiles could be determined by the distribution of bed structures. In natural cases, the strength and evolution of bed structures were under the influences of environmental conditions such as discharge and bedload transportation rate. That is, given the same conditions, the same bed structures distribution and longitudinal profile can be predicted.
Abstract: In order to understand the dominant factors of ice physical properties for ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were done, in the stages of fast ice growth and steady ice growth. These ice samples were used to observe ice crystals and gas bubbles in ice, and to measure ice density. Vertical profiles of the ice crystal type, ice crystal size, gas bubble shape and size, gas bubble content, as well as ice density were ontained. The results reveal that the upper part of the samples is granular ice and the lower part is columnar ice, the average grain size increases along ice depth and keeps steady within fast and steady ice growth stages; the shape of gas bubbles in ice upper layer is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content are active along with the ice growth stage; ice density decreases with the gas content increasing.
Abstract: There existed some limitations when analyzing the anti-sliding seismic stability of dam-foundation system by traditional pseudo-static method and response spectrum method. The dynamic strength reduction method was used to study on the deep anti-sliding stability of a high gravity dam considering complex dam foundation under strong earthquake-induced ground action. The static analysis was firstly carried out by reducing the shear strength parameters of the dam foundation’s rock mass with equal proportion. Then, the time-history seismic analysis was carried out based on the static analysis. It was proposed as one of dynamic instability criterions that the peak values of the dynamic displacements and plastic strain energy change suddenly with increasing strength reduction coefficient. The elasto-plastic behavior of the dam foundation was idealized using Drucker–Prager yield criterion based on associated flow rule assumption. Through the static, dynamic strength reduction analysis and dynamic linear elastic analysis of the overflow dam monolith of a high gravity dam, the results’ reliability of elastic-plastic time history analysis was confirmed. The results also showed that the rock mass strength of the high gravity dam foundation has higher strength reserve coefficient. The instability criterions of dynamic strength reduction method proposed were feasible. Although the static anti-slide analysis methods and standards of gravity dam based on the numerical methods are being discussed at present, the dynamic calculation method and instability criterions proposed in this paper would provide some meaningful suggestions for the dynamic analysis of the similar projects.
Abstract: Recently, the critical chain study has become the hot spot within the project management research field, so as the construction of it with multi-resource constraints become the new research subject. Referring to System Analysis Theory and Project Portfolio Theory, this paper discusses the creation of project portfolio based on project similarity, and definition of priority in multi-resource allocation based on quantitative analysis. Then according to the theory on critical chain construction, the author made relevant research and proposed the construction model with the multi-resource constraints, which to be applied to the critical chain construction of A-bid section in South-to-North Water Diversion Project. And necessary contrast analysis with the Comprehensive Treatment Construction Method and Aggressive Treatment Construction Method also has been made within this paper.
