Applied Mechanics and Materials Vols. 212-213

Abstract: the layout and the characteristics of the cascade reservoirs and hydropower stations in the upper reaches of the Yellow River, determine that cascade hydropower stations scheduling must be operated based on the joint operation between Longyangxia and Liujiaxia cascade hydropower stations, especially on flood control operation. This paper deeply analyzes design flood storage area of the Liujiaxia composition and Longyangxia-Liujiaxia joint flood regulating principle on the basis of analyzing and calculating each ten-day design flood of the Tangnaihai above main stream and the intervals. Therefore, the reasonable combination of interval flood and the process of Longyangxia reservoir flood discharge is confirmed, and thereby, studying Liujiaxia reservoir inflowing design flood under a controlling operation of flood limited water level for a period of ten-day to ensure the safety of Liujiaxia reservoir flood control.

Abstract: In view of the disadvantages of drought evaluation methods in irrigation district, the variable fuzzy sets theory has been adopted in this paper to establish the variable fuzzy sets drought evaluation method in irrigation district. At the same time, the improved entropy method has been employed to determine the objective weights and the minimum discrimination information principle has been used to combine the subjective weights with the objective weights, which have eliminated the one-sidedness of the application of a single weighting preferred program.

Abstract: Agricultural droughts occur frequently and cause severe losses in Liaoning province, especially in northwestern region where drought could happen 9 times during 10 years averagely. Drought characteristics are studied and drought situation is analyzed in northwestern Liaoning. Risk analysis method and research route of index frame are put forward so as to supply scientific evidences for drought relief and drought evaluation as well as take some measures to prevent drought.

Abstract: Experiments are conducted to study the change of Manning coefficient of reed population along the channel in gradually varied flow. Water depth and velocity are investigated under various reed densities, corresponding to a set of discharge values. The corresponding Manning coefficients along the channel and the functional relationships with vegetation density are studied. The results show that the Manning coefficient is more volatile in vegetation zone and the average Manning coefficient exhibits a linear relationship with the vegetation density. The conclusions can provide some guidance and reference for cofferdam design in natural and constructed wetland and the research on vegetated channel erosion.

Abstract: During rainy seasons, flood damage occurs easily to the riverside highway subgrade in mountainous areas, threatening the driving safety. Therefore, to master the environmental characteristics and the disaster-causing patterns is of great significance for the radical treatment of flood damage. On the basis of theoretical analysis and field survey, this work, taking Qinling-Bashan (hereinafter referred to as Qin-Ba) Mountainous Area in Southern Shaanxi Province for example, mainly deals with the types and the causes of the flood damage of riverside highway subgrade and hence the corresponding prevention measures against it, which may provide a basis for the design of riverside highway and also the prevention of flood damage in rainy season.

Abstract: Recent years, there were many piers constructed in tail reach of Yongjiang River. This made river channel in estuarial reach shrank gradually, which in turn influenced the shipping ability of estuarial area. Taking Qingshuipu pier that would be constructed in the left bank of Yongjiang river estuarial reach as an example, a numerical simulation have been done, and resistance parameter had been proved reasonably by author. The flow pattern, backwater height and channel scour-fill intensity near the pier trestle have been studied in different kinds of flood and tidal stencils. In engineering project, the trestle prevents flood from diffusing by dipping into the river. Meanwhile, backwater and deposition occur in the bank, which have impact on flow capacity. If the siltation in the area accumulates, then, point bar could not be scoured adequately in great flood period, which will force mainstream to move towards right bank. Based on the backwater and local scouring and silting situation near the pier trestle, the author puts forward a revised proposal and gains a preferable result. So, reasonable pier arrangement is the important condition for keeping steady and healthy to the tail reach of tidal river.

Abstract: Very large volume of mined ore materials are processed annually to obtain the various types of minerals that are essential to industrial processes, the upstream tailings dam is usually constructed to store these wastes. But with the increasing of dam quantities, the tailings dam collapsing in flood which are among the most dangerous hazards that affect mountainous and rural areas in a wide range of environments become more and more. Therefore it’s necessary to analyze the collapse mode of upstream tailings dam in flood situation. This paper using the physical model experiment and numerical simulation methods to research on the displacement, saturation line, stress and the broken processes, and the collapse mode of upstream tailings dam in flood water encountered in 100 years are explored. The results have very important significance and scientific support to understand the mechanism of collapse and broken mode deeply, and which have any new exploration for the prevention and control in flood hazard.

Abstract: Monthly precipitation data of 76 meteorology stations over the middle and lower reaches of Yangtze river for 1961–2010 were analyzed by using the standardized precipitation index (SPI) and aridity index (I) for the rainy season (April–September) and winter (December– February). Trends of the number of wet and dry months were tested with Mann-Kendall technique. The results showed that: (1) The middle and lower reaches of the Yangtze River as a whole has become wetter during the rainy season and winter. (2) Major parts of the study area are characterized by increasing frequencies of severe and moderate wet months in the rainy season. (3) The study tries to explore the spatial and temporal changes in the wet and dry conditions across the middle and lower reaches of the Yangtze River by using SPI and I, and get the complete picture of the change of wet and dry.

Abstract: Jingping II hydropower project is a diversion type hydropower station with low dam, long tunnel and large capacity. Cofferdams are set to retain water flow which will be diverted through a single tunnel during dry seasons, yet be designed to allow controlled flooding during flood seasons. A physical model is built to study the hydraulic features during flooding process. Then the velocity distribution at critical positions over the overtopped earth-rock cofferdams is tested under design flux and other working conditions, as well as other hydraulic parameters such as press distribution over cofferdam slopes. Moreover, the flow regime over cofferdams is observed, and then the section forms of cofferdams are optimized to ensure the safely passing of flood during construction.

Abstract: To solve the risk model for dam overtopping and instability of dam slope in the embankment systematic risk, the structural reliability theory is used in this paper. By using the single risk which has been calculated, the risk rate of embankment dam overtopping flood system can be approached. During the research of systematic risk rate, the problems which exist in the method of only using Bayesian networks solving systematic risk model are analyzed, then the methods of combining the structural reliability theory and Bayesian networks to solve the systematic risk model are put forward, which are also made use of to solve the systematic risk model of simplified embankment dam.