Runoff Distribution And Lowflow Features And Mechanism Of The Bailongjiang Basin

Influenced by global climate change and increased human activity, river runoff has undergone significant changes in recent decades. River runoff within 6 main basins endures different degrees of reduction. Changes of temporal and spatial distribution of river runoff have a substantial impact on natural and ecological environment and activities of human society. In arid land of northwest China, water resource is restriction to social and economic development and to influence ecological security, making an important distribution to future sustainable development of economy and society. In pace with the effective promotion of the "Western Development Strategy" and construction of the "Silk Road Economic Belt", northwest China has been the focal point of attentions all over the country and society. Concern about security of water resource in northwest China has been rising.The research chooses upstream of Bikou hydrologic station of mainstream of the Bailongjiang River as the study-area. Based on the monthly runoff data of Baiyun, Mayasi, Zhouqu, Wudu and Bikou hydrologic stations on the main stream of the Bailongjiang River for the past 50 years range from 1960～2009, distribution and transformation features of runoff within years, annual transformation features of runoff, runoff mutability, tendency of runoff transformation, distribution features of lowflow runoff within years, parameters of 8 typical probability distribution functions fit for lowflow runoff of the Bailongjiang River, probability distribution functions which describe lowflow runoff of the Bailongjiang River, characteristic values of different probability of lowflow runoff in the main stream of the Bailongjiang River, lowflow runoff mutability and tendency of lowflow runoff transformation of the Bailongjiang River are analyzed taking advantage of non-uniformity coefficient, fully accommodation coefficient, concentration ratio and concentration period, Mann-Kendall mutability test, Mann-Kendall trend test, R/S analysis, L-moments method and probability plot correlation coefficient(PPCC) method. The research indicates:1. Annual runoff distribution of the Bailongjiang River is very uneven and with strong seasonality. From upstream to downstream, mal-distribution within years showing an increase-reduce law and the runoff concentration period gradually shifts to early times.2. Runoff concentration ratio of the Bailongj iang River has a trend of reduction, and the distribution of runoff within years tends to be uniformed. The runoff concentration period tends to advance in time.3. Annual runoff series of stations on the mainstream of the Bailongjiang River have mutation point and the mutability is significant. Transformation features and tendency experience difference around the mutation points.4. The trend of reduction of runoff of the Bailongjiang River is significant. The Bailongjiang River basin paces into a relatively dry period from a relatively wet period in the past 50 years.5. The time when the minimum monthly-averaged runoff occurs is relatively concentrated. The time when the minimum monthly-averaged runoff occurs matches well through upstream to downstream. The most probable time when the minimum monthly-averaged runoff occurs is February in all the stations. The frequency of February is more than 50%. December to March of the next year is the dry season of the Bailongjiang River.6. Generalized Pareto distribution, generalized extreme-value distribution, generalized logistic distribution, lognormal distribution and Pearson type III distribution are capable of lowflow runoff analysis of the mainstream of the Bailongjiang River. Among above, generalized logistic distribution presents the best in relativity and robustness.7. Except Zhouqu station, minimum monthly-averaged runoff series of the other hydrological stations have mutation points. Times of mutations show relatively strong relationship between annual runoff and the lowflow runoff series.8. Minimum monthly-averaged runoff of Baiyun, Mayasi, Wudu and Bikou stations have a trend of reduction. Among them, the trend of reduction of Mayasi, Wudu and Bikou stations is significant. Reduction of minimum monthly-averaged runoff of Baiyun, Wudu and Bikou stations shows constancy, while reduction of minimum monthly-averaged runoff of Mayasi and Zhouqu stations shows anti-constancy.