【作者】 李娜；

【导师】 王腊春；

【作者基本信息】 南京大学 ， 自然地理学， 2016， 博士

【摘要】 河流作为承载物质从陆地到海洋输送一个重要通道,其中水沙是最基本的物质元素。人类活动对入海水沙的影响一直是国际研究关注的热点,对入海水沙的改变会直接或者间接地影响着河口三角洲的水资源水环境、地质、航道和生物多样性的变化。本文的研究区域是长江河口区,结合地理学、水文学、泥沙动力学等学科,利用小波周期分析、趋势检验分析、跳跃分析等统计分析和数学模型的方法,研究长江流域干流以及入河口区水沙通量的特征,定量地计算气候变化和人类活动对长江入河口区输沙量变化的贡献率,然后建立长江河口区水沙模型,讨论枯季时长江河口区的沿岸调引水工程对河口区水动力环境的影响,最后研究预测长江河口区水沙输移对未来人类活动的响应,并得到如下的主要研究结论。基于近60年长江干流三个水文站年均径流量和输沙量以及大通站月均径流量和输沙量数据,识别长江干流和入河口区的水沙通量时间序列特征。1950-2013年长江干流宜昌、汉口和大通站的年径流量和年输沙量主周期有一定的相关性,但多水时段与多沙时段呈现不同步的变化特征。相比三峡大坝前期,在三峡大坝后期(2003-2013年)长江干流的1-3月份月均径流量增加,其余月份的月均径流量减少,但12个月的月均输沙量均减少。气候变化是影响长江干流径流量周期变化的主要因素,但径流量和输沙量的变化趋势是由于人类活动造成的,其中三峡工程的削峰补枯作用导致了长江干流枯季径流变化,同时增加了输沙量减少的程度,但这一影响在下游区域随距离三峡工程越远而逐渐变弱。长江入河口区的年径流量和年输沙量具有明显的年际变化,并且其平水年多次连续出现,而枯水年基本上以两年连续的形式出现;径流量和输沙量的年内分配不均,多年(1950-2013)平均月径流量和月输沙量最大值和最小值分别相差4.5倍和31倍;泥沙主要以细颗粒悬沙为主,其D50值随着时间变化在逐渐地变细,并且在一年内一般出现两次峰值。1950-2013年大通站年均径流量与洪季径流量在2003年之后处于少水期,但枯季径流量处于丰水期;在20年时间尺度上,大通站年均和洪季的输沙量处于少沙期,但枯季输沙量没有明显的主周期,并在短周期内没有变化。1950-2013年,大通站的枯季径流量呈现显著上升趋势(P<0.05),突变点是2003年,随之呈现显著上升趋势;但年均和洪季输沙量呈现显著下降趋势(P<0.001),其中,年均输沙量的突变点是1996年,随之呈现显著性下降趋势。人类活动是引起大通站径流量和输沙量趋势变化的主要原因,其中,三峡工程对长江入河口区水沙通量的变化具有直接和间接性的影响作用,并且本文定量地分析人类活动对长江入河口区输沙量变化的贡献率。1954-2013年,降水、产流能力和产沙能力对大通站年输沙量下降的贡献率分别3.95%、-0.11%和96.16%,并且不同时间阶段影响输沙量下降的主要因子是产沙能力,降水和产流能力对其下降的贡献可以忽略不计。人类活动是影响长江流域的产沙能力主要因素,其中流域水库建设对大通站输沙量减少的贡献率达到85%左右。长江流域入河口区的输沙量锐减的主要是人类活动对其产沙能力影响造成的,其中水库大坝是最主要的原因。然后,基于MIKE21_FM水动力和泥模型,建立了长江河口区二维水沙模型。在长江河口区沿岸调引水工程调查的基础上,设定枯季不同情景下大通径流和沿岸调引水的组合条件。在枯季,长江河口区调引水和外海潮汐条件不变的情况下,大通站的径流减少,长江河口区沿程的高低潮位变低和潮差增加。在枯季同一径流条件下,相比小潮期,调引水工程对大潮期的高低潮位和潮差影响更明显,使涨潮瞬时潮流界最远可上溯到南京段的上游。在全球气候变化的背景下人类活动对长江入河口区大通站流量、输沙量和含沙量的预测的基础上,研究未来人类活动对长江河口区潮流、水沙通量的影响。到2050年,未来人类活动对长江河口区汛期10月水沙输移的影响要强于枯季2月。在枯季,相比情景1,情景2人类活动影响下长江河口区沿程不同地区的高低潮位和潮差变化不一致,并且潮流界变化具有不确定性;长江入海水沙通量均减少,但增强了北支水沙倒灌南支;南港和北港的分流比较为均衡,但南港的分沙比占有优势,特别是大潮期。在汛期,相比情景1,情景2人类活动影响下长江河口区沿程潮差增加,潮流界向上游移动;长江入海水沙通量减少,并增强了北支水沙倒灌南支;大潮期和小潮期的南港分流、分沙比均占有优势。更多还原

【Abstract】 River systems play a significant role in the transport of water and sediment from land to the ocean,which must be seen as a key pathway for material transfer on the Earth.In the world,the influence of the human activities on the flow and sediment fluxes into the sea has always been attached great foeus in the intemation research,which directly and indirectly influenced the water resources and environment,geological,and waterway.The research,of which the study area is the Yangtze River Estuarine area,combines with geography,hydrology,sediment dynamics,etc.,uses the statistical analysis,such as trend,jumping and wavelet cycle analysis,and mathematical model to detect the trends of runoff and sediment in the mainstream and transporting into the estruary of the Yangtze River,and quantitatively analyze the contribution rate of climate change and human activities on the sediment discharge at the Datong hydrological station.And then,the hydrological and sediment model of the Yangtze River estuary was established to discuss the influence of water diversion project on the hydrodynamic conditions in the dry season,and predict the future of human activities impact on the water and sediment transport of the study area.On the basis of about sixty years annual runoff and sediment load at three hydrological stations in the mainstream,the study indentified the characteristics of runoff and sediment load.From 1950-2013,the main cycle of the annual runoff and seiment load at the three stations had good consistency,but the wet season period had not good correlation with the sandy period.Compared with the pre-TGD period,the dry season runoff increased and the monthly sediment load decreased at the mainstream of the Yangtze river in the pos-TGD period(2003-2013).The climate changes was the main reason for the interannual variations of the runoff,and the trend changes of the runoff and sediment load were attributed to human activities,especially the Three Gorge Dam(TGD),which was the main reason for the increasing of dry season runoff,but the effect weakened with the distance along the downstream direction from TGD.The runoff and sediment load at Datong station,from which the stream flow and sediment flux into Yangtze River Estuary,had obvious interannual variation.From 1950-2013,the maximum values of the monthly runoff and sediment load were 4.5 times and 31 times of the minmum values,respectively.The sediment at Datong station was mainly composed by suspend fine-sediment.The median endothelial cushion grain-size(Dso)became gradually smaller.In the period analysis,after 2003,the annual and flood season runoff at Datong station were in dry period,and in 20 years time scale,the annual and flood season sediment load was in less sand period.From 1950-2013,the dry season runoff was in significantly increasing(P<0.05),of which the abrupt change point was 2003,and annual and flood season sediment load was in significantly decreasing trend(P<0.05),with the abrupt change points of the annual sediment load were 1996.The change trends of water and sediment flux into the estuary were attributed to the human activities,and the study quantitively analyzed the contribution rate of human activities on change trend of sediment flux into the estuary.From 1954 to 2013,the contribution rates of precipition,water yield capacity and sediment concentration were 3.95%,-0.11%and 96.16%respectively,and indifferent periods,the sediment concentration was the main factor resulting in the decrearing of the sediment load at Datong station.The sediment concentration was influenced by human activities in Yangtze River Basin,and the contration rate of the reservoir construction resulting in the decreasing of sediment load at Datong station was about 85%.The human activities influced the sediment concentration in the Yangtze River resulting into the decreasing of the sediment load,and reservoir construction was the main reason.And then,based on MIKE 21 hydrodynamic and mud model,we constructed the 2-dimensional(2-D)hydrodynamic and mud model of the study area.On the basis of the investigation of the water diversion projects in the study area,we set different scenarios with combination between the discharge of Datong with the water diversion in the dry season.In the dry season,under the premise of constant tidal condition from the sea,as the discharge of Datong station decreased,the tidal level dropped and tidal range increased.In the same flow condition at Datong station,the instantaneous tidal current limit could be traced as far as the upper reach of the estuary during neaping tide.On the basis of the future climate change and human activities influences on stream flow and sediment flux into the estuary,we researched the impact of future human activities on flow and sediment transport in the study area.In 2050,the influence of human activities on flow and sediment transport in wet season(Octorber)was more than that in the dry season(February).In the dry season,compared with scenoria l,the human activities in scenoria 2 had no consistent influence on the tidal level and tidal range in different area along the estuary,resulting in the uncertainty change of the tidal current limit,the flux of stream flow and suspended sediment into sea would decrease,but the ratio of the flow of South and North Branch would be balanced and the ratio of the sediment of South would have an advantage,especially in the spring tide.In the wet season,in scenoria 2,the tidal level dropped and tidal range increased,resulting in the tidal current limit moving to the upstream,the flux of stream flow and suspended sediment into sea would decrease,and the diversion ratio of the flow discharge and sediment transport of the south branch would have an advantage.更多还原