| The Poyang Lake which is a regulate lake is on the main stream of the middle and lower reache of the Yangtze river. It located in the north of Jiangxi province, and is currently the largest freshwater lake in China.In recent years, there are more and more researchers who study of Poyang Lake about the water and sedimenttransport. But they mainly concentrated in statistical analysis of water and sediment data at five hydrologic stations on the Ganjiang River,Fuhe River, Xinjiang River, Raohe River, XiushuiRiver. The data was from 1956 to2005 and the missing data was not interpolated in those researches.This article took the variation characteristics of runoff and sediment transport of the Poyang Lake as a whole to study. Studies of water and sediment transport characteristics provide evidence for researching the change in the morphology, and could give reasonable guidance in explotation and utilization of soil and water resources in the Poyang Lake.Firstly, This article explores the variation characteristics of natural runoff into the Poyang Lake, using the natural annual runoff time series data from seven gauging stations which are located at the main rivers of five rivers(Ganjiang River,Fuhe River, Xinjiang River, Raohe River, Xiushui River) into Poyang Lake.Especially runoff of Lijiadu station and Zhelin station was reduced, because it was evidently influenced by human activities. Then used two methods to interpolate the lack of measurement data about Poyang Lake from 1956 to 2011. Secondly, the variation characteristics of runoff and sediment transport at important hydrometric stations of the Poyang Lake were analyzed by many methods. Thirdly this article studied of the causes about the variation characteristics of runoff and sediment transport in recent decade years.The variation characteristics of the variation characteristics of runoff and sediment transport into the Poyang Lake were analyzed by the methods of thevariation coefficient method, the runoff anomaly percentage, Mann-Kendall trend analysis, rescaled range analysis and wavelet analysis, according to the data from1953 to 2011. The results show as follow:(1) The natural annual runoff of Lijiadu station is increased roughly by 25%compared with the previous results, and it increases more significantly during the dry year. But evolution of natural runoff has consistency in all stations of Fuhe river.In the Poyang Lake Basin, the annual variation and distribution of runoff at the main five rivers have similarity.(2) The annual distribution of runoff and sediment load into the lake are mainly concentrated in 4 ~ 6 months.and is non-uniformity.(3) Trend analysis on the annual runoff series emerged an obvious increase trend from 1953 to 2000 at eight gauging stations, but since entering the 21 th century, it displayed decreasing trend. Using rescaled range analysis to calculate the Hurst exponents of eight stations, the Hurst exponents of the Waizhou station and Meigang station indicate that the time series of runoff will have strong randomicity. However,the annual runoff time series data of others stations will show a persistence, so it will consistent with the trend of the past years.(4) Sediment load in Meigang and Zhelin stations appeared a mutation point around 1998 and 1974, respectively. Runoff into the Poyang lake did not occurr a mutation point.(5) Due to the upstream and the improvement of soil and water loss, construction of water conservancy and hydropower engineering lead to great changes have taken place in all the rivers into the lake sediment. The maximum average sediment discharge stations appear in the 60 s and 70 s last century, the minimum appeared in the 00 s.This article took the variation characteristics of runoff and sediment transport of the Poyang Lake as a whole to study. the variation characteristics of runoff and sediment transport at important hydrometric stations of the Poyang Lake were analyzed by the methods of mathematical statistics, double accumulative curve ofannual runoff and sediment and Mann-Kendall,according to the data from 1956 to2011. Then this article studied of the causes about the variation characteristics of runoff and sediment transport in recent decade years. The results showed that:(1) The annual distribution of runoff into the lake was consistent with sediment load, however, the phenomenon of the Yangtze river water and sediment flow backward influenced the annual distribution of runoff and sediment transport out the lake.(2) The trend of the annual variation of the suspension sediment load into the Poyang lake began to intensify decline from the 90 s, but the suspension sediment load out the Poyang lake presented whole descending from 1956 to 2000, the data also demonstrated that the suspension sediment load out the Poyang lake is on the increase from 2001 to 2011.(3) Runoff into and out the Poyang lake did not appear a mutation point. But variation of runoff exhibits a 35 yr first dominant cycle which is basically identical with variation of the precipitation. Sediment load into the Poyang lake appeared a mutation point around 1998.(4) Change of runoff transport tended to a relatively stable state in 56 years, but in recent decade years, it has close relation with the influence of the precipitation in the Poyang Lake basin. Then change of sediment transport of Poyang Lake is relatively complicated. Sediment load into the lake was significantly reduced, but sediment load out the lake increased obviously. The reasons caused sediment load into the lake reduce that:1) There were many reservoirs in five rivers of Poyang Lake,which had function of water storage and sediment retaining, such as Wanan reservoir.2) The government strengthened soil and water conservation in the Poyang lake basin so that this measures can obviously decrease sediment load. 3) The downstream of five rivers were infected by the sand-excavation on the river channel.That led to sediment load into the lake reduce. However, there were many reasons whichinduced sediment load out the lake increase, as follows: ① The depth of river bed was decreased in Hukou. ② Influenced by the Three-Gorges Project,gradient ration about the Poyang Lake and Yangtze River was increased. ③ Sand mining could cause the disturbance of the river bed so that the river velocity became faster. |
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