三江源区近数十年河流输沙及水沙关系变化

刘彦,张建军,张岩†,阿彦,阿妮克孜·肉孜,杨松

(1.北京林业大学水土保持国家林业局重点实验室,100083,北京;2.中国环境科学研究院,100012,北京)

三江源区近数十年河流输沙及水沙关系变化

刘彦1,张建军1,张岩1†,阿彦2,阿妮克孜·肉孜1,杨松1

(1.北京林业大学水土保持国家林业局重点实验室,100083,北京;2.中国环境科学研究院,100012,北京)

河川径流及泥沙在保障水资源、塑造河道形态、维持区域环境及生态系统等方面起着重要作用。为探讨三江源区河流输沙及水沙关系,基于三江源区9个水文站径流泥沙观测资料,采用Mann-Kendall趋势检验、Mann-Kendall突变检验方法分析输沙量、含沙量的变化趋势及突变特征,利用评级曲线法,分析水沙关系。结果表明:1)从输沙量来看,仅长江源区的新寨输沙量呈显著减少趋势,并在1998年发生突变;2)长江源区新寨含沙量显著减少,黄河源区的黄河沿、同仁及唐乃亥含沙量显著增加,其他水文站含沙量没有显著变化趋势,新寨和同仁含沙量分别在1999和1989年存在突变特征;3)直门达以上的长江源区及澜沧江源区水沙关系未发生明显变化,长江源区的新寨水文站控制区及黄河源区水沙关系发生变化;4)水流挟沙能力的变化表现出了明显的空间差异性,主要分为减弱、增强及稳定3种类型。河流输沙及水沙关系发生的变化,可能与气候变化和人类活动等有关,研究成果可为三江源区流域规划和生态保护,以及下游水库泥沙淤积研究等提供参考。

三江源;输沙量;水沙关系;趋势分析;突变分析

河流系统是地球上重要且非常活跃的自然系统,而水沙变化则是河流系统对气候变化与人类活动的直接响应[1]。随着全球温室效应和人类活动影响的不断加剧,很多河流的径流量、输沙量均发生显著的变化,直接影响流域水资源的合理配置、开发与利用,以及河流生态系统的物理、化学和生物过程[2]。河流水沙关系可以反映径流量与输沙量的匹配关系,研究河流水沙关系,对于揭示河流泥沙的来源与时空变化规律,分析河流泥沙沉积特征与河道整治措施均有重要作用[3]。河流输沙的响应过程,也是近年来河流地貌学研究的热点问题[4 5]。

三江源是长江、黄河和澜沧江3大河流重要的水源涵养区,素有“中华水塔”之称。黄河流域河川径流量近35%以上来自唐乃亥以上的黄河源区[67],长江源区年径流量仅为黄河源区的60%[8],澜沧江总水量的15%来自三江源地区。三江源区黄河源区输沙量最大,长江源区次之,澜沧江最小[9]。1955—1998年间,黄河源头输沙模数呈自东向西递减的分布规律,而水沙量变化基本是稳定的[10]。赵玉等[11]指出,1950—2011年,唐乃亥站径流量和输沙量均无长期变化趋势;但孙永寿等[12]研究结果表明,2005—2012年期间,直门达以上的长江源区河流含沙量和输沙量有明显减小的趋势,其主要与长江源区来水量增加、径流集中期的推后、枯季径流比例的提高以及下垫面生态植被覆盖条件好转有关。国内外水沙关系研究已有很多[3,1320],但是三江源区研究相对较少,对长江源区直门达站1957—1999年,实测年输沙量与年径流量的相关分析表明,二者相关关系显著[21];对黄河源区唐乃亥站水沙关系分析表明,水沙量变化同步,相关关系显著[2223]。上述研究只是针对长江或黄河源区某一水文站点进行相关分析,研究方法单一,并且未分析水沙关系是否发生变化;因此,本文选取三江源区为研究对象,基于径流泥沙观测资料,对三江源区输沙及含沙量进行趋势和突变分析,以期了解是否存在同步变化特征,并采用评级曲线法,分析水沙关系的时空变化,为下游水库泥沙淤积研究和水资源的开发利用等提供参考。

1 研究区概况

三江源区位于我国西部,青藏高原腹地,青海省南部(E 89°24′～102°23′,N31°39′～36°16′),研究区地理位置为E 90°35′11″～103°23′15″,N 32°13′31″～35°30′39″,主要包括直门达水文站控制的长江源区、唐乃亥水文站控制的黄河干流、同仁水文站控制的黄河支流隆务河以及香达水文站控制的澜沧江源区,总面积为28.30万km2(图1)。长江和澜沧江源区主要为冰川冰缘地貌和高山地貌,而黄河源区则呈现中心地貌和高原低山丘陵地貌等[24]。三江源区属于青藏高原气候系统,是典型的高原大陆性气候,年温差小,日温差大,年平均气温-5.4～4.1℃,年平均降水量262.2～772.8 mm,年蒸发量730～1 700 mm。

图1 三江源区水文站点分布图Fig.1 Distribution of hydrological station in the source region of 3 rivers

2 材料与方法

2.1 数据来源

选取长江源区的直门达、新寨和沱沱河,黄河源区的大米滩、黄河沿、唐乃亥、同仁和上村以及澜沧江源区的香达,共9个水文站点的逐月径流及泥沙数据,进行三江源区泥沙特征及水沙关系分析。径流及泥沙资料由青海省水土保持局、青海省生态环境遥感监测中心提供,水文站点分布见图1,资料基本情况见表1。

表1 三江源区水文站点基本信息Tab.1 Basic information of hydrological stations in the source region of 3 rivers

2.2 研究方法

采用Mann-Kendall趋势检验[2526],对三江源各水文站控制区的年输沙量和年含沙量有序数据,进行变化趋势分析。采用Mann-Kendall突变分析法[27]来检验年输沙和含沙序列的突变情况,若正反两个序列出现交点,且交点在临界线之间,那么交点对应的时刻便是突变开始的时间。

采用评级曲线[2829],研究径流和输沙之间的关系。该评级曲线为幂函数

或对两边同时取对数,则表示为

式中:Qs为输沙率,即单位时间内的泥沙通量,kg/s;Cs为含沙量(泥沙质量浓度),kg/m3;Q为流量,m3/ s;a为系数,b为指数。该关系式反映大部分河道的输沙特性,系数a和指数b反映河流水沙变化指标。高a值代表流域中可侵蚀搬运的沉积物较多,很容易被侵蚀,并被河流运输,则泥沙供给量也就越大[13]。对于一个特定流域而言,系数a随时间变化,与人为扰动过程有关。指数b(或b+ 1)是双对数水沙关系直线的斜率,用来表示该河流的侵蚀驱动,主要反映水流挟沙能力的强弱[30],在河流界广泛应用的张瑞瑾[31]公式表明,b值越高,水流的挟沙能力越强。

3 结果与分析

3.1 三江源区泥沙特征分析

3.1.1 输沙趋势及突变分析 利用Mann-Kendall趋势分析法,对三江源区9个水文站输沙量变化趋势进行检验(图2)。结果表明:长江源区的沱沱河和直门达水文站、黄河源区5个水文站及澜沧江源区的香达水文站,输沙量均没有显著变化趋势,只有长江源区的巴塘河新寨输沙量呈显著减少趋势,通过置信度90%的显著性检验,其变化趋势率为-0.19万t/a。突变分析结果表明,自1998年以后呈下降趋势。

3.1.2 含沙量趋势及突变分析 对三江源区含沙量进行变化趋势检验(表2)发现,长江源区沱沱河和直门达水文站含沙量无显著变化趋势,而新寨水文站含沙量呈显著减少趋势,达到95%的置信度水平,变化率为-0.002 5 kg/(m3·a)。黄河源区大米滩和上村水文站含沙量无显著变化趋势,而同仁、唐乃亥及黄河沿水文站含沙量呈显著增加趋势,均达到了90%的置信度水平,其变化率分别为0.002 6、0.007 4和0.004 4 kg/(m3·a)。澜沧江源区香达水文站含沙量无显著变化趋势。

图2 三江源区新寨年输沙量Mann-Kendall突变检验曲线Fig.2 Mann-Kendall change-point test curve of sediment discharge at Xinzhai station in the source region of 3 rivers

对三江源区含沙量进行突变检验(表2)发现,按照9个水文站控制区来计算,大部分区域不存在突变年份,即不存在突变特征。只有长江源区新寨以及黄河源区同仁水文站,含沙量存在突变年份,分别为1999和1989年。从图3可知,新寨含沙量自1999年以后呈下降趋势,并且在2005—2012年间,达到了0.05的显著性水平;同仁含沙量自1989年以后,开始逐渐呈上升趋势,但并未达到0.05的显著性水平。

3.2 三江源水沙关系分析

通过观察三江源区9个水文站控制区的年径流量和输沙量双累积曲线,分析其斜率的变化,寻找曲线发生明显转折的点,确定其年限,从而据此确定时段划分,绘制径流输沙评级曲线(图4)。根据三江源区径流和输沙评级曲线图及评级参数(表3)可知,长江源区新寨和黄河源区的同仁、唐乃亥和上村,以及大米滩水文站控制区的水沙关系发生了变化。新寨水文站1995—2012年输沙关系点据位于1985—1997年点据的下方,说明在同等径流条件下,输沙率明显减少,而同仁及唐乃亥水文站输沙率则分别在1989—2012年、1981—2000年有所增加。新寨水文站的ln(a)值由-6.49变化为-4.64,相比增加28.5%,说明巴塘河流域1997年以后,可侵蚀搬运的沉积物增多,泥沙供给量变大;而b值则从1.41变化为0.60,降低57.4%,表明巴塘河水流挟沙能力减弱。通过判定系数R2可知,1997年以后,该流域水沙相关性减弱。同仁水文站的ln(a)值由

-1.18变化为-1.08,相比增加8.5%,表明隆务河流域泥沙供给量变大;b值由0.42变化为0.57,增加35.7%,表明隆务河水流挟沙能力增强,判定系数变化,说明其水沙相关性自1988年以后有所增强。唐乃亥水文站的ln(a)由-7.20变化为-8.29,相比减少15.1%,表明唐乃亥水文站控制区泥沙供给量变小;而b值则由1.05变化为1.18,增加12.4%,表明该区水流挟沙能力增强,其水沙相关性也有所增强。上村水文站的ln(a)值由-3.76变化为-1.54,增加59.0%,表明1988年以后,大河坝河区泥沙供给量明显增加;而b值则由1.92变化为0.94,下降51.0%,表明大河坝河水流挟沙能力明显减弱,其水沙相关性也减弱。大米滩水文站1959—1990年间,泥沙供给量较小,而1991—2001和2002—2010年的泥沙供给量,相对1990年以前均有所增大,但曲什安河水流挟沙能力自1990年以后减弱,在1991—2001年间,水沙相关性很弱,2002年以后明显增强,但不及1959—1990年间。黄河沿水文站控制区情况比较特殊,多数年份输沙率很低。1976—1999年间,ln(a)值为-2.58,b值为0.07,表明该区水流挟沙能力很弱, R2为0.63,水沙相关性较好;但2000年径流量急剧减少,输沙率却没有明显减少,这可能与扎陵湖、鄂陵湖两湖的调节作用有关[10]。

表2 三江源区9个水文站含沙量Mann-Kendall趋势分析及突变分析Tab.2 Mann-Kendall trend analysis and change-point analysis of sediment concentration at 9 stations in the source region of 3 rivers

图3 三江源区9个水文站年均含沙量Mann-Kendall突变检验曲线Fig.3 Mann-Kendall change-point test curve of sediment concentration at 9 stations in the source region of 3 rivers

图4 三江源区9个水文站径流量与输沙率评级曲线Fig.4 Rating curves of water discharge and sediment transport rate at 9 stations in the source region of 3 rivers

长江源区直门达以上控制区及澜沧江源区香达水文站控制区,其水沙关系没有发生变化,并且水沙相关性均较好。直门达及香达水文站控制区泥沙供给量均较少,而水流挟沙能力则较强。沱沱河水文站控制区泥沙供给量较大,但水流挟沙能力较弱。

4 讨论

本文选取三江源区为研究对象,对长江、黄河和澜沧江3条河流源区的输沙量及含沙量,进行变化趋势及突变特征分析,并且采用评级曲线,进行水沙关系分析,不仅能反映水沙相关性,还更好的揭示水流挟沙能力的空间差异。从1956—2012年的长期变化趋势来看,直门达输沙量和含沙量均无显著变化趋势;但已有研究表明,在2005—2012年期间,直门达以上的长江源区含沙量和输沙量有明显减少趋势[12]。结论不同,可能是由于分析方法和使用数据年限不同导致。有研究表明,1958—2005年长江源区的直门达站径流变化趋势不显著[32],而1956—2009年黄河源区大部分径流变化呈显著减少趋势[33],可知径流变化对输沙有一定的影响,但水沙变化并不完全一致。根据第1次全国水利普查青海省水土保持情况普查成果,三江源区玉树县有点状小型蓄水保土工程13个,而巴塘河位于玉树县内,该控制区输沙量显著减少,说明人类活动对输沙量有影响。景可等[34]指出,影响流域侵蚀量的主要因素是降雨、植被、土壤、地形和人为等因素,影响输沙量的主要因素除流域侵蚀产沙量外,也与径流量和水文特性、流域的形态及河床纵比降有关,可知流域侵蚀和输沙没有必然联系。有研究表明,气候变化和人类活动是对河流输沙产生变化的2个最重要因素[35],水沙关系发生变化可能与实施水土保持措施或土地利用、覆盖发生变化有关。

由于数据资料有限,笔者仅以三江源区9个水文站控制区作为研究对象,日后应该全面搜集三江源区流域各水文站的水文气象资料,使数据时间尺度更长,更好的反映整个三江源区流域输沙及水沙关系变化。此外,对于泥沙分析并未涉及泥沙级配和流态等,水沙关系也只研究径流量和输沙量的关系,没有进行输沙量对降雨量响应的空间差异分析,在以后应对泥沙问题,尤其是汛期高洪水泥沙特征及水沙关系有待进一步研究。水土保持措施和土地利用等因素,对输沙及水沙关系的影响也有待深入研究。

表3 三江源区9个水文站泥沙评级参数(ln(a)和b)及判定系数(R2)Tab.3 Sediment rating parameters(ln(a)and b)and coefficient of determination(R2)at 9 stations in the source region of 3 rivers

5 结论

通过对三江源区9个水文站控制区,其输沙量及含沙量进行趋势和突变分析,并对水沙关系开展研究,得出以下结论:

1)从输沙量来看,除长江源区的巴塘河新寨呈显著减少趋势,且在1998年发生突变,此后呈下降趋势外,其他水文站输沙量既不存在显著变化趋势,也不存在突变特征。

2)长江源区新寨水文站含沙量显著减少,黄河源区的黄河沿、同仁及唐乃亥水文站含沙量显著增加,其他水文站含沙量没有显著变化趋势。长江源区新寨和黄河源区同仁水文站的输沙量分别在1999和1989年发生突变,且分别在1999和1989年以后,呈下降趋势和上升趋势。

3)直门达以上的长江源区及澜沧江源区,水沙关系未发生明显变化;而在长江源区的新寨水文站控制区及黄河源区,由于湖泊的调节,导致水沙关系急剧变化。水流挟沙能力表现出明显的空间差异性,主要分为减弱、增强及稳定3种类型。长江源区的新寨和黄河源区的上村水文站控制区域,水流挟能力有所减弱,而黄河源区的同仁、唐乃亥水文站控制区则有所增加,大米滩水文站控制区则是先减少后增加,直门达以上长江源区及澜沧江源区未发生变化。

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Variations of riverine sediment and the relationship between
runoff and sediment in the source region of three rivers

Liu Yan1,Zhang Jianjun1,Zhang Yan1,A Yan2,Anikezi·Rouzi,Yang Song

(1.Key Laboratory of State Forestry Administration on Soil and Water Conservation(Beijing Forestry University),100083, Beijing,China;2.Chinese Research Academy of Environmental Sciences,100012,Beijing,China)

[Background]Runoff and sediment play an important role in the supply of water resources, shaping the river morphology,maintaining the regional environmental and ecological system.[Methods]To explore the characteristics of river sediment and the relationship between runoff and sediment in the source region of 3 rivers(the Yangtze River,the Yellow River,and the Lancang River),based on observation data of runoff and sediment at 9 hydrologic stations in the source region of 3 rivers,the change trends and change-point of sediment discharge and sediment concentration were analyzed using the Mann-Kendall trend test,Mann-Kendall change-point test methods,and the relationship between runoff and sediment was analyzed using the rating curve method.[Results]1)There were no significant change trend and change-point of annual sediment discharge in Zhimenda hydrologic station in the source region of the Yangtze River,Tangnaihai and Tongren hydrologic stations in the source region of the Yellow River,and Xiangda hydrologic station in the source region of the Lancang River,while the trend of annual sediment discharge in Xinzhai hydrologic station(Batang River)in the source region of theYangtze River was reduced significantly and changed greatly in 1998.2)The annual sediment concentration,in Xinzhai hydrologic station,in the source region of the Yangtze River,reduced significantly,while it increased conspicuously in Huangheyan,Tongren and Tangnaihai hydrologic stations in the source region of the Yellow River,and the sediment concentration did not change apparently in other 5 hydrologic stations.A change-point of sediment concentration existed in Xinzhai hydrologic station of Batang River,in 1999,and in Tongren hydrologic station of Longwu River,in 1989.Exactly,sediment discharge in Xinzhai hydrologic station had presented a downward trend since 1999 and contrarily an upward trend in Tongren hydrologic station since 1989.3)Relationship between runoff and sediment did not change obviously in watershed in the source region of Yangtze River controlled by Zhimenda hydrologic station and in which,in source region of Lancang River,controlled by Xiangda hydrologic station.Adversely,the relationship varied obviously in Xinzhai control area in the source region of the Yangtze River and control areas in the source region of the Yellow River.Meanwhile, the relationship between runoff and sediment in Huangheyan hydrologic station control area changed stupendously due to adjustments stem from lakes.4)The change of the capacity of water-carrying sediment showed an obvious distribution of spatial heterogeneity,mainly divided into three types, including weakening,enhancing and stabilizing.[Conclusions]Heterogeneity of sediment transport and relationship between water and sediment were revealed in the source region of 3 rivers,which may be concerned with climate change and human activities.The above research achievements can be useful reference to plans and ecological conservations in this region and research concerning sediment concentration in reservoirs of its lower reaches.

the source region of 3 rivers;sediment discharge;runoff-sediment relationship;trend analysis;analysis of abrupt change

TV145.3

A

1672-3007(2016)06-0061-09

10.16843/j.sswc.2016.06.008

2016 01 28

2016 07 05

项目名称:中国工程院咨询研究项目“三江源区生态资产核算与生态文明制度设计”(2014XZ313)

刘彦(1990—),女,硕士研究生。主要研究方向:自然资源监测与管理。E-mail:1210257552@qq.com

†通信作者简介:张岩(1970—),女,教授,硕士生导师。主要研究方向:土壤侵蚀和水土保持。E-mail:zhangyan9@bjfu.edu. cn