The manage-flood is very important for flood control safety and economic effectiveness of reservoir engineering. There are two approaches which can be used to calculate the manage-flood at present, i.e., one is based on Copula functions, and the other is based on the principle of total probability. The latter can be divided into direct method and indirect method. The direct method based on the principle of total probability is explored in this article. The flood data for calculation of manage-flood have been divided into three condition:Sufficient data condition, relatively sufficient data condition and insufficient data condition. For sufficient data conditions, the length of flood data series in main flood season is greater than 30 years and the length of flood data series in pre-main flood season and post-main flood season is no less than 20 years, respectively; For relatively sufficient data condition, the length of flood data series in main flood season is greater than 30 years and the length of flood data series in non-main flood season is no less than 20 years; For insufficient data condition, the length of flood data series in main flood season is greater than 30 years and the length of flood data series in non-main flood season is less than 20 years. The calculating methods of manage-flood for three flood data conditions have been presented based on the principle of total probability in this paper. For sufficient data condition, the mathematical expect formula of total probability has been adopted with frequency analysis; for relatively sufficient data condition, the mathematical expect formula of total probability with combined data in non-main flood season was applied; for insufficient data condition, the back calculation approach was presented, and the formula of manage-flood based on the principle of total probability has been suggested. The case studies for calculating of manage-flood in different flood data conditions have been given for different basins. The comparison of the suggested method to the method of Copula function has been discussed. The results have showed that the suggested method is better than the method of Copula function, and the designed value of manage-flood is reasonable.

Floods encountered by a reservoir project during operation and management period are mainly determined by the volume of rainstorm and the previous flood volume of the river. For small watersheds, the latter plays a minor role which can be ignored. For large and medium watersheds, the latter has a greater impact and thus should be paid attention to. Based on the total probability formula the concept of quantificational characterizing this influence of flood frequency distribution of the annual maximum time period flood volume whose condition is previous flood volume is proposed, and the calculation formula is given. Two calculation methods for the manage-flood based on previous flood volume are established, i.e., the direct method and the indirect method. The paper divides the previous flood volume of the river into two states: less water and more water. The direct method is based on the measured flood data, and the conditional distribution of less water and more water is deduced by the principle of single variable frequency calculation principle. The direct method is simple and practical, but it requires more data. In the indirect method, the Copula function is first used to describe the two dimensional joint distribution of the maximum period flood volume of annual (such as annual maximum seven days flood volume) and the previous flood volume of the river. The key of this method is the choice of Copula function. By analyzing the correlation charts of the maximum period flood volume of annual and the previous flood volume of the river, the Clayton–Copula function is selected to deduce the conditional distribution. The indirect method can be used in lack of data, but the shortcoming is that the appropriate Copula function should be selected, and the calculation is more complicated. Finally, the proposed direct method and indirect method were applied to the calculation of channel flood in Zagunao River. The results showed that the overall benefit of the reservoir was higher than that of the original operation that fixed the limits water level of reservoir in flood period.

The lack of flood measurement data due to complex and changeable landform brings about many incon-veniences to hydro-project construction in southwest China. According to data of design flood peak discharge (Qp) and collecting area(F) at 66 hydrologic stations in 11 basins in the southwest region of China,the relationship be-tween Qpand F is researched by statistical analysis. Results show the Qp-F relationships in the Jialing River basin, Tuojiang River basin, Fujiang River basin, Minjiang River basin and Lancang River basin follow linear relation-ship;while in the Dadu River basin,Qingyi River basin and Yalong River basin,the Qp-F relationships match well with exponential relationship;and in the Jinsha River basin,Nujiang River basin and Yarlung Zangpo River basin the relationships conform well to power function. The research results offer reference for obtaining the Qp-F relation-ships in ungauged river basins.

Engineering potential destruction risk caused by flood can be presented by the frequency of annual highest stages in front of engineering (Hm).A quantificational relational expression among annual highest stages,flood peak discharge (x) and flood volume (y) is established based on the condition that flood hydrograph was generalized into a triangle.And then,based on the stochastic simulation method,the annual highest stages (Hm) N are calculated according to the flood prevention standard.Therewith,the combinations of flood peak discharge and flood volume are analyzed by satisfying the standard.Results have shown that calculation was above the flood prevention standard on the condition of the combination that flood peak discharge and flood volume have the same frequency.In addition,the variation of engineering's characters of flood prevention have impact on Hm.

According to the study on flood hydrograph, the new concept of specific flood hydrograph and its connotation were pro-posed. Meanwhile, the external and essential implication of engineering flood prevention standard were expounded. And then the re-lationship that was the new concept of external frequency of flood hydrograph between specific flood hydrograph and flood preven-tion standard was drawn. The specific flood hydrograph of three types of transformation and its calculation method were elaborated. The advantages and disadvantages of the common multiple method and the common frequency method of specific flood hydrograph were pointed out. A brief introduction about the basic idea of new calculation method of specific flood hydrograph was given.

Bivariate return periods of floods,with peak flood discharge x and flood volume y as variables,are important to calculation and evaluation of flood control in hydraulic engineering.For a flood event,calculation of its return periods much depends on its components and how to match the demands.This paper discusses and calculates four types of return periods using the Copula function theories-univariate return period N1,OR-event return period N2,AND-event return period N3,and matching retum period N4 -focusing on the demonstration of N4.And the four return periods are compared in a case study of the Mabian hydrological station of the Mabian River,a branch of the Minjiang River.The results show that for a given set (x0,y0) of the bivariate variables,the values of these periods are quite different.When both x0 and y0 are large or small,they follow a decreasing order of N3＞ N4＞ N1＞ N2;when x0 is large and y0 is small or y0 large and x0 small,N4 could become possibly much larger than N3 or even smaller than N1.Thus,attention should be paid to the special properties of the Copula functions and we recommend the use of bivariate matching values N4 in flood control calculations.

The Tibetan Plateau is the source area of many major rivers in Asia. In order to realize the variation of hydrology and climate in the Tibetan Plateau, this paper investigated variation trends of annual temperature, annual precipitation and annual runoff since 1980s in six large river basins including the Yalung Zangbo River (Nuxia station), the Salween River (Jiayuqiao station), the Mekong River (Changdu station),the Tongtianhe River (Zhimenda station), the Yalongjiang River (Luning station) and the Yellow River ( Tangnaihai station) in Eastern Tibetan Plateau, and analyzed the response of runoff to the variation of climatic elements ( precipitation and temperature) . The results show that annual mean temperature and precipitation at all stations show obviously increasing trends, but the annual runoff affected by temperature and precipitation exhibits different trends:at Nuxia station, Jiayuqiao station and Luning sta-tion, the runoff shows slightly increasing trend, while shows decreasing trend at the other three stations. By analyzing the relationship between the trend of annual runoff and the area ratio of snow and ice, the change trend of annual runoff has a positive correlation with the area ratio of snow and ice:the area ratio of snow and ice is larger in the basins where the annual runoff has an upward trend, the change trend of runoff is greatly affected by the increase of precipitation and snowmelt, while the area ratio of snow and ice is smaller in the basins where the annual runoff has a downward trend, the impact of the runoff decreasing caused by the increase of evapotranspira-tion due to rising temperatures is large. These results will play an important role in flood control and drought relief, rational allocation of water resources and the sustainable utilization of regional water resources in the Tibetan Plateau.

The concepts of time-risk and annual-risk were respectively presented based on the annual multi-samples method and the annual maximum sample method aiming at the inconsistent of return periods about design rainstorm in the municipal and water conservancy systems.The risk of municipal system was caused by the annual biggest flood or the second flood or others, but the risk of water conservancy systems was caused by the annual biggest flood.Taking the storm data in Guangzhou city as an example, the relationship between the two kinds return period was deeply analyzed.Results show that the return period of municipal system is not more than water conservancy system.The key to change the two return periods into accordance is unifying the two risk concepts and adopting the annual maximum sample method.

论述以下几个关键问题:①涉水工程防洪安全设计零风险理念导致极限洪水新概念;②极限洪水的四大特性;③可能极限洪水的新见解;④极限洪水和万年一遇洪水既对立又统一,不能孤立地对待;⑤在敲定极限洪水采用值时合理性分析至关重要.