劉彥,張建軍,張巖?,阿彥,阿妮克孜·肉孜,楊松

(1.北京林業(yè)大學水土保持國家林業(yè)局重點實驗室,100083,北京;2.中國環(huán)境科學研究院,100012,北京)

三江源區(qū)近數(shù)十年河流輸沙及水沙關(guān)系變化

劉彥1,張建軍1,張巖1?,阿彥2,阿妮克孜·肉孜1,楊松1

(1.北京林業(yè)大學水土保持國家林業(yè)局重點實驗室,100083,北京;2.中國環(huán)境科學研究院,100012,北京)

河川徑流及泥沙在保障水資源、塑造河道形態(tài)、維持區(qū)域環(huán)境及生態(tài)系統(tǒng)等方面起著重要作用。為探討三江源區(qū)河流輸沙及水沙關(guān)系,基于三江源區(qū)9個水文站徑流泥沙觀測資料,采用Mann-Kendall趨勢檢驗、Mann-Kendall突變檢驗方法分析輸沙量、含沙量的變化趨勢及突變特征,利用評級曲線法,分析水沙關(guān)系。結(jié)果表明:1)從輸沙量來看,僅長江源區(qū)的新寨輸沙量呈顯著減少趨勢,并在1998年發(fā)生突變;2)長江源區(qū)新寨含沙量顯著減少,黃河源區(qū)的黃河沿、同仁及唐乃亥含沙量顯著增加,其他水文站含沙量沒有顯著變化趨勢,新寨和同仁含沙量分別在1999和1989年存在突變特征;3)直門達以上的長江源區(qū)及瀾滄江源區(qū)水沙關(guān)系未發(fā)生明顯變化,長江源區(qū)的新寨水文站控制區(qū)及黃河源區(qū)水沙關(guān)系發(fā)生變化;4)水流挾沙能力的變化表現(xiàn)出了明顯的空間差異性,主要分為減弱、增強及穩(wěn)定3種類型。河流輸沙及水沙關(guān)系發(fā)生的變化,可能與氣候變化和人類活動等有關(guān),研究成果可為三江源區(qū)流域規(guī)劃和生態(tài)保護,以及下游水庫泥沙淤積研究等提供參考。

三江源;輸沙量;水沙關(guān)系;趨勢分析;突變分析

河流系統(tǒng)是地球上重要且非?；钴S的自然系統(tǒng),而水沙變化則是河流系統(tǒng)對氣候變化與人類活動的直接響應[1]。隨著全球溫室效應和人類活動影響的不斷加劇,很多河流的徑流量、輸沙量均發(fā)生顯著的變化,直接影響流域水資源的合理配置、開發(fā)與利用,以及河流生態(tài)系統(tǒng)的物理、化學和生物過程[2]。河流水沙關(guān)系可以反映徑流量與輸沙量的匹配關(guān)系,研究河流水沙關(guān)系,對于揭示河流泥沙的來源與時空變化規(guī)律,分析河流泥沙沉積特征與河道整治措施均有重要作用[3]。河流輸沙的響應過程,也是近年來河流地貌學研究的熱點問題[4 5]。

三江源是長江、黃河和瀾滄江3大河流重要的水源涵養(yǎng)區(qū),素有“中華水塔”之稱。黃河流域河川徑流量近35%以上來自唐乃亥以上的黃河源區(qū)[67],長江源區(qū)年徑流量僅為黃河源區(qū)的60%[8],瀾滄江總水量的15%來自三江源地區(qū)。三江源區(qū)黃河源區(qū)輸沙量最大,長江源區(qū)次之,瀾滄江最小[9]。1955—1998年間,黃河源頭輸沙模數(shù)呈自東向西遞減的分布規(guī)律,而水沙量變化基本是穩(wěn)定的[10]。趙玉等[11]指出,1950—2011年,唐乃亥站徑流量和輸沙量均無長期變化趨勢;但孫永壽等[12]研究結(jié)果表明,2005—2012年期間,直門達以上的長江源區(qū)河流含沙量和輸沙量有明顯減小的趨勢,其主要與長江源區(qū)來水量增加、徑流集中期的推后、枯季徑流比例的提高以及下墊面生態(tài)植被覆蓋條件好轉(zhuǎn)有關(guān)。國內(nèi)外水沙關(guān)系研究已有很多[3,1320],但是三江源區(qū)研究相對較少,對長江源區(qū)直門達站1957—1999年,實測年輸沙量與年徑流量的相關(guān)分析表明,二者相關(guān)關(guān)系顯著[21];對黃河源區(qū)唐乃亥站水沙關(guān)系分析表明,水沙量變化同步,相關(guān)關(guān)系顯著[2223]。上述研究只是針對長江或黃河源區(qū)某一水文站點進行相關(guān)分析,研究方法單一,并且未分析水沙關(guān)系是否發(fā)生變化;因此,本文選取三江源區(qū)為研究對象,基于徑流泥沙觀測資料,對三江源區(qū)輸沙及含沙量進行趨勢和突變分析,以期了解是否存在同步變化特征,并采用評級曲線法,分析水沙關(guān)系的時空變化,為下游水庫泥沙淤積研究和水資源的開發(fā)利用等提供參考。

1 研究區(qū)概況

三江源區(qū)位于我國西部,青藏高原腹地,青海省南部(E 89°24′～102°23′,N31°39′～36°16′),研究區(qū)地理位置為E 90°35′11″～103°23′15″,N 32°13′31″～35°30′39″,主要包括直門達水文站控制的長江源區(qū)、唐乃亥水文站控制的黃河干流、同仁水文站控制的黃河支流隆務河以及香達水文站控制的瀾滄江源區(qū),總面積為28.30萬km2(圖1)。長江和瀾滄江源區(qū)主要為冰川冰緣地貌和高山地貌,而黃河源區(qū)則呈現(xiàn)中心地貌和高原低山丘陵地貌等[24]。三江源區(qū)屬于青藏高原氣候系統(tǒng),是典型的高原大陸性氣候,年溫差小,日溫差大,年平均氣溫-5.4～4.1℃,年平均降水量262.2～772.8 mm,年蒸發(fā)量730～1 700 mm。

圖1 三江源區(qū)水文站點分布圖Fig.1 Distribution of hydrological station in the source region of 3 rivers

2 材料與方法

2.1 數(shù)據(jù)來源

選取長江源區(qū)的直門達、新寨和沱沱河,黃河源區(qū)的大米灘、黃河沿、唐乃亥、同仁和上村以及瀾滄江源區(qū)的香達,共9個水文站點的逐月徑流及泥沙數(shù)據(jù),進行三江源區(qū)泥沙特征及水沙關(guān)系分析。徑流及泥沙資料由青海省水土保持局、青海省生態(tài)環(huán)境遙感監(jiān)測中心提供,水文站點分布見圖1,資料基本情況見表1。

表1 三江源區(qū)水文站點基本信息Tab.1 Basic information of hydrological stations in the source region of 3 rivers

2.2 研究方法

采用Mann-Kendall趨勢檢驗[2526],對三江源各水文站控制區(qū)的年輸沙量和年含沙量有序數(shù)據(jù),進行變化趨勢分析。采用Mann-Kendall突變分析法[27]來檢驗年輸沙和含沙序列的突變情況,若正反兩個序列出現(xiàn)交點,且交點在臨界線之間,那么交點對應的時刻便是突變開始的時間。

采用評級曲線[2829],研究徑流和輸沙之間的關(guān)系。該評級曲線為冪函數(shù)

或?qū)蛇呁瑫r取對數(shù),則表示為

式中:Qs為輸沙率,即單位時間內(nèi)的泥沙通量,kg/s;Cs為含沙量(泥沙質(zhì)量濃度),kg/m3;Q為流量,m3/ s;a為系數(shù),b為指數(shù)。該關(guān)系式反映大部分河道的輸沙特性,系數(shù)a和指數(shù)b反映河流水沙變化指標。高a值代表流域中可侵蝕搬運的沉積物較多,很容易被侵蝕,并被河流運輸,則泥沙供給量也就越大[13]。對于一個特定流域而言,系數(shù)a隨時間變化,與人為擾動過程有關(guān)。指數(shù)b(或b+ 1)是雙對數(shù)水沙關(guān)系直線的斜率,用來表示該河流的侵蝕驅(qū)動,主要反映水流挾沙能力的強弱[30],在河流界廣泛應用的張瑞瑾[31]公式表明,b值越高,水流的挾沙能力越強。

3 結(jié)果與分析

3.1 三江源區(qū)泥沙特征分析

3.1.1 輸沙趨勢及突變分析 利用Mann-Kendall趨勢分析法,對三江源區(qū)9個水文站輸沙量變化趨勢進行檢驗(圖2)。結(jié)果表明:長江源區(qū)的沱沱河和直門達水文站、黃河源區(qū)5個水文站及瀾滄江源區(qū)的香達水文站,輸沙量均沒有顯著變化趨勢,只有長江源區(qū)的巴塘河新寨輸沙量呈顯著減少趨勢,通過置信度90%的顯著性檢驗,其變化趨勢率為-0.19萬t/a。突變分析結(jié)果表明,自1998年以后呈下降趨勢。

3.1.2 含沙量趨勢及突變分析 對三江源區(qū)含沙量進行變化趨勢檢驗(表2)發(fā)現(xiàn),長江源區(qū)沱沱河和直門達水文站含沙量無顯著變化趨勢,而新寨水文站含沙量呈顯著減少趨勢,達到95%的置信度水平,變化率為-0.002 5 kg/(m3·a)。黃河源區(qū)大米灘和上村水文站含沙量無顯著變化趨勢,而同仁、唐乃亥及黃河沿水文站含沙量呈顯著增加趨勢,均達到了90%的置信度水平,其變化率分別為0.002 6、0.007 4和0.004 4 kg/(m3·a)。瀾滄江源區(qū)香達水文站含沙量無顯著變化趨勢。

圖2 三江源區(qū)新寨年輸沙量Mann-Kendall突變檢驗曲線Fig.2 Mann-Kendall change-point test curve of sediment discharge at Xinzhai station in the source region of 3 rivers

對三江源區(qū)含沙量進行突變檢驗(表2)發(fā)現(xiàn),按照9個水文站控制區(qū)來計算,大部分區(qū)域不存在突變年份,即不存在突變特征。只有長江源區(qū)新寨以及黃河源區(qū)同仁水文站,含沙量存在突變年份,分別為1999和1989年。從圖3可知,新寨含沙量自1999年以后呈下降趨勢,并且在2005—2012年間,達到了0.05的顯著性水平;同仁含沙量自1989年以后,開始逐漸呈上升趨勢,但并未達到0.05的顯著性水平。

3.2 三江源水沙關(guān)系分析

通過觀察三江源區(qū)9個水文站控制區(qū)的年徑流量和輸沙量雙累積曲線,分析其斜率的變化,尋找曲線發(fā)生明顯轉(zhuǎn)折的點,確定其年限,從而據(jù)此確定時段劃分,繪制徑流輸沙評級曲線(圖4)。根據(jù)三江源區(qū)徑流和輸沙評級曲線圖及評級參數(shù)(表3)可知,長江源區(qū)新寨和黃河源區(qū)的同仁、唐乃亥和上村,以及大米灘水文站控制區(qū)的水沙關(guān)系發(fā)生了變化。新寨水文站1995—2012年輸沙關(guān)系點據(jù)位于1985—1997年點據(jù)的下方,說明在同等徑流條件下,輸沙率明顯減少,而同仁及唐乃亥水文站輸沙率則分別在1989—2012年、1981—2000年有所增加。新寨水文站的ln(a)值由-6.49變化為-4.64,相比增加28.5%,說明巴塘河流域1997年以后,可侵蝕搬運的沉積物增多,泥沙供給量變大;而b值則從1.41變化為0.60,降低57.4%,表明巴塘河水流挾沙能力減弱。通過判定系數(shù)R2可知,1997年以后,該流域水沙相關(guān)性減弱。同仁水文站的ln(a)值由

-1.18變化為-1.08,相比增加8.5%,表明隆務河流域泥沙供給量變大;b值由0.42變化為0.57,增加35.7%,表明隆務河水流挾沙能力增強,判定系數(shù)變化,說明其水沙相關(guān)性自1988年以后有所增強。唐乃亥水文站的ln(a)由-7.20變化為-8.29,相比減少15.1%,表明唐乃亥水文站控制區(qū)泥沙供給量變小;而b值則由1.05變化為1.18,增加12.4%,表明該區(qū)水流挾沙能力增強,其水沙相關(guān)性也有所增強。上村水文站的ln(a)值由-3.76變化為-1.54,增加59.0%,表明1988年以后,大河壩河區(qū)泥沙供給量明顯增加;而b值則由1.92變化為0.94,下降51.0%,表明大河壩河水流挾沙能力明顯減弱,其水沙相關(guān)性也減弱。大米灘水文站1959—1990年間,泥沙供給量較小,而1991—2001和2002—2010年的泥沙供給量,相對1990年以前均有所增大,但曲什安河水流挾沙能力自1990年以后減弱,在1991—2001年間,水沙相關(guān)性很弱,2002年以后明顯增強,但不及1959—1990年間。黃河沿水文站控制區(qū)情況比較特殊,多數(shù)年份輸沙率很低。1976—1999年間,ln(a)值為-2.58,b值為0.07,表明該區(qū)水流挾沙能力很弱, R2為0.63,水沙相關(guān)性較好;但2000年徑流量急劇減少,輸沙率卻沒有明顯減少,這可能與扎陵湖、鄂陵湖兩湖的調(diào)節(jié)作用有關(guān)[10]。

表2 三江源區(qū)9個水文站含沙量Mann-Kendall趨勢分析及突變分析Tab.2 Mann-Kendall trend analysis and change-point analysis of sediment concentration at 9 stations in the source region of 3 rivers

圖3 三江源區(qū)9個水文站年均含沙量Mann-Kendall突變檢驗曲線Fig.3 Mann-Kendall change-point test curve of sediment concentration at 9 stations in the source region of 3 rivers

圖4 三江源區(qū)9個水文站徑流量與輸沙率評級曲線Fig.4 Rating curves of water discharge and sediment transport rate at 9 stations in the source region of 3 rivers

長江源區(qū)直門達以上控制區(qū)及瀾滄江源區(qū)香達水文站控制區(qū),其水沙關(guān)系沒有發(fā)生變化,并且水沙相關(guān)性均較好。直門達及香達水文站控制區(qū)泥沙供給量均較少,而水流挾沙能力則較強。沱沱河水文站控制區(qū)泥沙供給量較大,但水流挾沙能力較弱。

4 討論

本文選取三江源區(qū)為研究對象,對長江、黃河和瀾滄江3條河流源區(qū)的輸沙量及含沙量,進行變化趨勢及突變特征分析,并且采用評級曲線,進行水沙關(guān)系分析,不僅能反映水沙相關(guān)性,還更好的揭示水流挾沙能力的空間差異。從1956—2012年的長期變化趨勢來看,直門達輸沙量和含沙量均無顯著變化趨勢;但已有研究表明,在2005—2012年期間,直門達以上的長江源區(qū)含沙量和輸沙量有明顯減少趨勢[12]。結(jié)論不同,可能是由于分析方法和使用數(shù)據(jù)年限不同導致。有研究表明,1958—2005年長江源區(qū)的直門達站徑流變化趨勢不顯著[32],而1956—2009年黃河源區(qū)大部分徑流變化呈顯著減少趨勢[33],可知徑流變化對輸沙有一定的影響,但水沙變化并不完全一致。根據(jù)第1次全國水利普查青海省水土保持情況普查成果,三江源區(qū)玉樹縣有點狀小型蓄水保土工程13個,而巴塘河位于玉樹縣內(nèi),該控制區(qū)輸沙量顯著減少,說明人類活動對輸沙量有影響。景可等[34]指出,影響流域侵蝕量的主要因素是降雨、植被、土壤、地形和人為等因素,影響輸沙量的主要因素除流域侵蝕產(chǎn)沙量外,也與徑流量和水文特性、流域的形態(tài)及河床縱比降有關(guān),可知流域侵蝕和輸沙沒有必然聯(lián)系。有研究表明,氣候變化和人類活動是對河流輸沙產(chǎn)生變化的2個最重要因素[35],水沙關(guān)系發(fā)生變化可能與實施水土保持措施或土地利用、覆蓋發(fā)生變化有關(guān)。

由于數(shù)據(jù)資料有限,筆者僅以三江源區(qū)9個水文站控制區(qū)作為研究對象,日后應該全面搜集三江源區(qū)流域各水文站的水文氣象資料,使數(shù)據(jù)時間尺度更長,更好的反映整個三江源區(qū)流域輸沙及水沙關(guān)系變化。此外,對于泥沙分析并未涉及泥沙級配和流態(tài)等,水沙關(guān)系也只研究徑流量和輸沙量的關(guān)系,沒有進行輸沙量對降雨量響應的空間差異分析,在以后應對泥沙問題,尤其是汛期高洪水泥沙特征及水沙關(guān)系有待進一步研究。水土保持措施和土地利用等因素,對輸沙及水沙關(guān)系的影響也有待深入研究。

表3 三江源區(qū)9個水文站泥沙評級參數(shù)(ln(a)和b)及判定系數(shù)(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 結(jié)論

通過對三江源區(qū)9個水文站控制區(qū),其輸沙量及含沙量進行趨勢和突變分析,并對水沙關(guān)系開展研究,得出以下結(jié)論:

1)從輸沙量來看,除長江源區(qū)的巴塘河新寨呈顯著減少趨勢,且在1998年發(fā)生突變,此后呈下降趨勢外,其他水文站輸沙量既不存在顯著變化趨勢,也不存在突變特征。

2)長江源區(qū)新寨水文站含沙量顯著減少,黃河源區(qū)的黃河沿、同仁及唐乃亥水文站含沙量顯著增加,其他水文站含沙量沒有顯著變化趨勢。長江源區(qū)新寨和黃河源區(qū)同仁水文站的輸沙量分別在1999和1989年發(fā)生突變,且分別在1999和1989年以后,呈下降趨勢和上升趨勢。

3)直門達以上的長江源區(qū)及瀾滄江源區(qū),水沙關(guān)系未發(fā)生明顯變化;而在長江源區(qū)的新寨水文站控制區(qū)及黃河源區(qū),由于湖泊的調(diào)節(jié),導致水沙關(guān)系急劇變化。水流挾沙能力表現(xiàn)出明顯的空間差異性,主要分為減弱、增強及穩(wěn)定3種類型。長江源區(qū)的新寨和黃河源區(qū)的上村水文站控制區(qū)域,水流挾能力有所減弱,而黃河源區(qū)的同仁、唐乃亥水文站控制區(qū)則有所增加,大米灘水文站控制區(qū)則是先減少后增加,直門達以上長江源區(qū)及瀾滄江源區(qū)未發(fā)生變化。

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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

項目名稱:中國工程院咨詢研究項目“三江源區(qū)生態(tài)資產(chǎn)核算與生態(tài)文明制度設計”(2014XZ313)

劉彥(1990—),女,碩士研究生。主要研究方向:自然資源監(jiān)測與管理。E-mail:1210257552@qq.com

?通信作者簡介:張巖(1970—),女,教授,碩士生導師。主要研究方向:土壤侵蝕和水土保持。E-mail:zhangyan9@bjfu.edu. cn