Runoff Prediction Of Middle Reaches Of The Yarlung Zangbo River For Choicing The Impoundment Date Of Zangmu Hydropower Plant

Yarlung Zangbo River(hereinafter referred to as Yajiang) is the largest river in Tibet, and also the highest river in the world. The total area of the basin is about 0.24 million km2. The potential hydropower is great. According to the fifth work in Tibet puts forward to building Tibet into a national important energy connecting base, and the development of hydropower resources in Yajiang will become the one of the key areas in hydropower engineering construction in China. At present, the middle reaches of Yarlung Zangbo River which located at the downstream of Yangcun hydrological stations was planning to construction seven hydropower stations that are Bayu, Dagu, Jiexu, Zangmu, Jiacha, Lengda and Zhongda. Among them, Zangmu Hydropower Station started construction in 2010, which is the first hydropower station in Yajiang, and the largest hydropower station in Tibet, with the total installed capacity of 510 MW. In order to achieve the aim of the first power unit starting power generation at the end of October 2014, the power station planned to impound water in October, under the design condition for the runoff is less than Q=839m3/s. Based on the choice of the impoundment date, the runoff simulation and prediction of the middle reaches of Yarlung Zangbo river is of great importance.Based on literature research and field data collection, MK method was used to test and analyze monthly runoff data of 1956-2003 at Yangcun Station. The results showed that there was increasing trend, failed the test statistics of alpha = 0.05 or alpha = 0.1 test. The change trend was not obvious. The MK mutation analysis result showed that UF value significantly decreased after 1969, and UF value begun to rise significantly after 1997. The great change occurred in the year of 1959, 1964, 1987 and 1997. The absolute value of 1997 is the biggest.For runoff prediction, three hydrological models which were Xinanjiang model, SIMHYD model and SMAR model were employed. The dam measured data from June 2009 to May 2014 was used, and the data of June 2010 ~ May 2011 was taken as the calibration data. Then SCE UA algorithm was used for parameters optimization of hydrological models. According to the evaluation of three kinds of model simulation precision, in terms of R2, XAJ model had the highest precision, followed by SIMHYD model, the simulation precision of SMAR model was the lowest. In terms of RE, XAJ model simulation results with the minimum error of the measured flow rate was the best, SMAR model precision was the second, and SIMHYD model simulation results was a bit poor. Then three hydrological models after calibration were used for runoff prediction. Three recommendation project of the suggestions on the impoundment date of Zangmu hydropower station were given based on the design flow in late October.Yarlung Zangbo River with high terrain and small population is very lack of hydrological data. Based on the limited measured data, mathematical methods and hydrological models, the analysis and prediction of Yajiang runoff is carried out in this paper. It will greatly improve the accumulation for the regional economic development and ecological protection.