近60年湘江流域水沙特性及其对人类活动的响应

湘江流域人类活动对湘江水沙变化具有显著影响。利用M-K次序法、Pettitt非参数检验法和双累积曲线法分析湘江干支流1953-2014年的年径流量、汛期径流量和非汛期径流量与输沙量的关系,并分析水土保持和水库建设等人类活动与水沙演变的关系。结果表明:1)湘江干支流水文站的年径流量、汛期径流量与输沙量的相关性强,且1990年后湘潭站径流量-输沙量的相关系数为0.83,而非汛期相关性较弱。1990年前,干流站点径流量和输沙量处于波动状态,1990年后干流站点径流量总体呈增加趋势,但输沙量呈减小趋势,且老埠头站的输沙量发生微幅突变。除个别站点之外,支流站点的径流量和输沙量发生突变的年份与变化规律均一致。2)水土保持以及水库建设对湘江流域的拦沙作用是输沙量减少的主要原因。相比支流,水土保持对湘江干流流域的输沙量减少影响更显著,水库建设与湘江干支流输沙量减少均密切相关。3)根据湘江流域输沙量突变点可划分A(1960-1987年)、B(1988-1996年)、C(1997-2013年)3个时期,在不考虑温度变化的影响下,以A时期1960-1987年为基准期,利用累积量斜率变化率比较法可知,相比基准期A时期,B、C时期水土保持和水库拦沙等人类活动对输沙量的减少的贡献率为88.58%和94.01%,人类活动为输沙量减小的主要因素。

Variability characteristics of runoff-sediment discharge and their response to human activities in Xiang River basin in recent 60 years

River water and sediment characteristics are the main index reflecting the surface hydrological cycle process and soil erosion, and is of great significance to water resources and water ecological environment in the basin. In recent years, influenced by human activities and natural conditions, soil erosion in many watersheds is serious. With the population and economic development, demands for resources and influence on environment by human activities are increasing, and the impact of water and sediment disasters on social and economic development is increasingly prominent and their consequences are closely related to people''s quality of lives. Human activities in Xiang River Basin have a significant impact on the change of runoff and sediment discharge in Xiang River. Through applying the Mann-Kendall test, Pettitt test, and double cumulative curve, we analyzed the relationships between human activities (e.g. water-soil conservations, reservoir constructions, etc.) and annual runoff, flood season runoff as well as non-flood season runoff and sediment transport of the mainstream and tributaries of Xiang River from 1953 to 2014. Among them, the main control stations of the main stream include the Laobutou station in the upper stream, Hengyang station in the middle stream and Xiangtan station in the lower stream. The main representative control stations of the tributaries include Ouyanghai station in Chongling River, Shenshantou station in Zheng River, Ganxi station in Mi River and Daxitan station in Lu River. Results indicated that annual runoff and flood season runoff at main-stream and tributaries stations showed a strong correlation (R2=0.83 in Xiangtan station) with sediment loads, while the correlations were weak in non-flood seasons after 1990. Before 1990, the runoff and sediment loads at main stream stations were basically fluctuating. After 1990, the runoff at main stream stations showed an increasing trend, while the sediment discharge showed a decreasing trend at those stations, and particularly mutated slightly at Laobutou station. Except for several stations, the mutation years and the variations of the runoff and sediment discharge at tributary stations were consistent overall. Water-soil conservations and reservoir construction were verified to be main factors leading to the decrease in sediment discharge in Xiang River basin. Compared to tributary basin, the water-soil conservations had a more significant impact on the reduction of sediment discharge in the main stream of Xiang River. Moreover a strong correlation between reservoir constructions and sediment discharge reduction was found at the main streams as well as tributaries. According to the abrupt change point of sediment transport in Xiang River Basin in 1987 and 1997, the long series of data were divided into three periods: Period A ( 1960-1987 ), Period B (1988-1996) and Period C (1997-2013). Without considering the influence of temperature change, the contribution rate of rainfall and human activities to the reduction of sediment discharge can be calculated by the cumulative slope change rates. Compared with period A, the contribution rate of human activities such as soil and water conservation and reservoir sediment interception to the reduction of sediment transport in periods B and C was 88.58% and 94.01%. That was, human activities were the main factors for the reduction of sediment transport.