【作者】 应铭；

【导师】 李九发；

【作者基本信息】 华东师范大学 ， 自然地理学， 2007， 博士

【摘要】 自1976年黄河入海尾间由刁口河改道清水沟流路后,因泥沙供给严重匮乏致使黄河三角洲北部岸滩进入快速的侵蚀与后退状态。该区域分布的大量油田亦为此而造成重大的经济损失,海岸防护工程受到破坏,相应的土地盐碱化等问题也日趋严峻。本文以多年重复测量的海岸剖面、2004年4月研究区大潮期间实测水文、悬沙和表层沉积物以及30m深柱状样资料为基础,利用机制分解法、EOF以及BP神经网络等技术手段,分别从动力作用、沉积物抗冲性以及剖面形态方面探讨黄河三角洲北部岸滩的强烈侵蚀和剖面塑造机理,同时针对不同冲淤状态的剖面变化趋势进行预测。主要结论包括:(1)黄河三角洲北部海域的波、流动力特征为:(a)由海向陆摩阻流速逐渐减小,在横向上呈线性分布,其中在研究水深范围内最大潮流摩阻流速为1.3-2.7cm/s,潮平均摩阻流速仅在0.8-1.8 cm/s,潮流的分布与摩阻流速相似;(b)波浪摩阻流速横向分布从深水向浅水逐渐增大,进入波浪破波带摩阻流速陡增;当波高小于0.5m摩阻流速不超过2.5cm/s,而波高大于4m的来波可导致摩阻流速峰值超过20cm/s;(c)地形因素对波浪传播衰减过程作用明显,坡度越缓,消耗波浪能量愈多。因此,相同来波条件下波浪摩阻流速研究区东侧大西侧小;相同剖面1976年后波浪摩阻流速逐渐变小。(2)含沙量变化与流速相关,高含沙量出现时刻滞后于高流速出现时刻约1小时。研究区水域高含沙量特征主要来源于本地局部泥沙再悬浮,悬沙以高含沙量水团形式从床底向上扩散,5m水深左右出现高能再悬浮环境。海区沉积物的分布特征主要是:实测表层沉积物以粉砂为主,整体上从岸向海,粒径逐渐变小,分选性变差直至10m水深转为变好趋势。海床表层沉积物可以分为3个区,近岸无潮沟岸段沉积物颗粒组成较粗,目前具有一定的抗冲能力;有潮沟岸段,沉积物组成粗细混合,以粉砂质粘土为主,分选较差,目前抗冲能力较弱;大于10m水深的深水区,沉积物组成相对较细。(3)海岸剖面变化特征:行水期淤积中心分布在入海尾间外,致使1976年后近岸强侵蚀区与淤积区对应,侵蚀强度东强西弱,剖面经历了快速侵蚀、波动调整和二次侵蚀期3个阶段。据此提出可反映剖面淤蚀和形态变化特征的形态参数A和F。当剖面变化越剧烈,形态参数变化越明显。依据参数A和F变化和剖面塑造等特征,可将研究区剖面分为三类,一是动态平衡型:建设期参数A变化率为1.20-1.26,参数F为1.19-1.38,剖面整体淤涨,形态上经三角洲浅水缓坡后呈上凹形直接向平坦海床过渡,缺少前缘斜坡段;1976年后主要是浅水区蚀退,整体变化微小;二是强淤弱蚀型:剖面由浅水缓坡、前缘斜坡和平坦海床构成,建设期参数A和F变化率分别为1.39～1.46和1.59～1.80;1976年黄河改道后,该剖面参数A和F变化率分别为0.84～0.87和0.66～0.71,剖面形态由“S”型向直线型转变,剖面在浅水区表现为侵蚀状态;三是弱淤强蚀型:以1976年为节点,在1976年前剖面形态参数A和F的变化率分别介于1.07-1.29和1.16～1.46范围,剖面亦由浅水缓坡、前缘斜坡和平坦海床构成,但三角洲前缘段分布较广;1976年后,参数A和F的变化率分别为0.56～0.67和0.45～0.67,剖面除在三角洲前缘斜坡与平坦海床过渡段略有淤积外,剖面蚀退集中在三角洲前缘斜坡段。(4)强侵蚀型剖面蚀退塑造机理:海区沉积物和动力因素的变化对剖面蚀退起决定作用。首先,三角洲废弃初期的高含水率、结构松散的沉积物抗冲性极差,加上波状地形易被夷平,废弃初期仅在潮流作用下岸滩就能发生快速蚀退;其次,松散沉积物消耗殆尽后,波流共同作用成为岸滩演变的动力,波浪主要起掀沙作用,潮流主要输运扩散泥沙作用。这主要体现在沉积物因筛选、以及埋深沉积物受到压实作用而抗冲性增强,波流共同作用的底部摩阻流速从废弃伊始逐渐减小,故剖面蚀退速度发生下降。最后,黄河入海尾闾的频繁摆动,导致河口坝和河口坝侧海湾出现不同沉积环境下的沉积体,其抗冲性不同,造成蚀退期间不同时期内(1985～1989年)蚀退速度迥异。(5)剖面变化的短期预测:EOF时空分解前2个特征函数可以较好的概括剖面变化特征,其中两个特征函数分别表征浅水区和深水区的变化。CS1-CS5剖面的第一特征函数主要表征深水区变化,第二特征函数主要表征浅水区变化;CS6-CS8剖面则相反。表征深水区变化的特征函数表征潮流作用,而表征浅水区变化的特征函数表征波浪作用。从研究区西侧到东侧,潮流作用占优势逐渐转变为波浪作用为主导。利用对EOF时空分解的时间函数的预测,可达到剖面的短期预测。此外,利用BP神经网络对剖面空间相和时间相分别进行预测,其中对于逐年变化存在趋势变化的剖面预测有较好的效果。(6)不同水文学方法技术的利用:传统水文学方法和国家规范方法在分析近海潮流数据时,垂线平均特征值误差在8%以下,计算潮周期单宽通量时,误差可忽略不计;究其物理意义,传统水文学方法处理数据结果适用讨论水动力和沉积物相互作用,国家规范方法在分析潮流、悬沙净通量时,其数值和角度更加可信。更多还原

【Abstract】 Since terminal reach of the Yellow River shifted from Diaokouhe channel to the Qingshuigou channel in 1976, the northern Yellow River Delta had been rapidly eroded owing to the lack of the sediment supply. Thereafter, many oil wells of the Shengli Oil Field located in Yellow River Delta had been seriously destroyed for the coastline retreat, which was a result of directly great economic loss. Moreover, the coastal engineerings were also damaged, and the area of coastal wetland reduced constantly, soil salinizaion aggravated and the ecological function of the littoral zone is weakened. Thus, the data including the repeatly measured coastal profiles lasted several decades, hydrology, suspended sediment, surficial sediments and a core sample of 30 m depth were obtained form the study area in the April 2004. Subsequently, from the view point of dynamics, the sediment resistance and the changes of the coastal profiles, respectively, these data were analyzed by using the mechanism analyses, empirical orthogonal function （EOF） and BP artificial neural network to discusse the mechanism of the intense erosion and profiles shaping processes of the northern Yellow River Delta. In addition, the changes of the different profile types were also predicted. The conclusions were shown as follows:（1） The characteristics of the flow and wave located at the nearshore zone of the northern Yellow River Delta: （a） the friction velocity of tidal flow gradually decreases landward and the curve of the friction velocity of tidal flow vs spatial distance was appeared as a linear distribution with a maxmum value range of 1.3～2.7cm/s and the average value range of 0.8～1.8 cm/s. In addition, the characteristic of the tidal flow is similar to that of the friction velocity; （b） the friction velocity of wave increases landward with sharply strengthened trends in the wave broken zone. The value of the wave friction velocity with a wave height below 0.5m could not exceed 2.5cm/s, and the maximum wave friction velocity with a wave height over 4 m could exceed 20cm/s; （c） the process of wave propagation is strongly influenced by the topographical factors.（2） Closely correlation between the sediment concentration and flow velocity: the lagged phase for the high sediment concentration to the high flow velocity is about 1 hour owing to the sediment resuspended. The spreaded models for the suspended sediment is that the water body with high sediment concentration is upwards from the bottom.,and the high energy resuspending environment located at about the area of 5m depth. Moreover, Most of the surficial sediments consist of silt.The trend of the medium grain size (D₅₀) is diminished, and sorting coefficient is poor from the bank to seaeard area of below 10 m isobaths. The values of the sorting coefficient become well at area of over 10 m isobath. The deposition in the present sdudy area could be divided into 3 zones: The composition of the sediment grain size is rather coarse in the nearshore without tidal creeks and fine in the nearshore with tidal creeks; and the characristic of the sorting is worse and the composition of the grain-size is fine in the study area of over 10 m water depth.（3） Deposition centre located at outside of river mouth before1976, and the strong erosion areaoccurred in the same area after 1976. The degree of the erosion is strong in the eastern and weak in the western. Since the northern Yellow River delta was abandoned. The changes of the coastal profiles experienced three periods which could be termed as ’rapid erosion - slow eroding modulate - fluctuate triggering change’. The shape parameter A and F may be suggested to reflect the shape change of the profiles. The changes of the profiles were rather obvious when the the value of the shape parameter had a distinct changed trends. Based on the profile shape parameter and developing characteristics, the profiles could be divided into 3 types as follows: （a） the dynamic equilibrium type: change rate of the parameter A is 1.20～1.26 and parameter F is 1.19-1.38. The siltup was occurred around the profile with a concave appeareance located at the seawards of shallow water where the delta front slope was un-developed; In addition, although minor erosion was happed in the shallow water, the appeareance of the profile was stable after 1976; （b） the strong silting and weak erosion type: The profile consist of delta platform, delta front slope and pro-delta shelf. The change rates of parameter A and F are 1.39～1.46 and 1.59-1.80 respectively before 1976. After terminal reach shifted in 1976, change rates of parameter A and F are 0.84～1.87 and 0.66～1.71, respectively. The changed trend of the profile configuration was from the symbol "S" to a linetype. However, it is strong erosion in the shallow water; （c） the weak silting and strong erosion type: Taking the year 1976 as the node, before 1976 change rates of parameter A and F are 1.07～1.29 and 1.16～1.46 respectively. It also has the three parts that were delta platform, delta front slope and pro-delta shelf, and the delta front slope is the broad. After 1976, Change rates of parameter A and F are 0.56～1.67 and 0.45～1.67 respectively. This types of the profile has minor accretion coccured in the transition between the the delta frnt slope and sea bed, and erosion focused on the delta front slope.（4） The developed mechanism of strong erosion type profile: The development characteristic of topographical is decided by hydrodynamic force and sediment factor. Firstly, during the initiative abandoned stage, the weak sediment resistance of newly incompact deposition and the fluctuant coast line are the main reasons for erosion and retreation of the profile with a high speed. Secondly, the main erosion action force was changed from tidal to co-action of tidal and wave after the newly incompact deposition disappeared. The wave plays a role of lifting the sand, and the flow transports sediment mainly. The frition velocity of co-action of wave and flow reduced gradually after 1976; Due to the effect of the sorting and compaction, the retreating speed of the profile was slow down. Finally, due to the frequently swing of terminal reach of the Yellow River, the sea region experienced the two sedimentary environments that are mouth bar type and side bay type of mouth bar, which has different sediment resistance and different erosion rate during the different periods （1985～1989）.（5） The prediction of profile change in the short-time period. The first and second eigenfunctions of EOF could explain the main change characteristic, one shows the changes of the shallow water zone and the another shows deep water zone. The first eigenfunction of profiles CS1-CS5 could reflect the changes in the deep water zone, the second eigenfunction reflect the changes of shallow water zone profiles CS6～CS8 are opposite. The eigenfunction thatshows the deep water zone represents the tidal action; the eigenfunction that shows shallow water zone represents the wave action. From profile CS1 to CS8, the change of the dominant actions is transferred from tidal flow to wave gradually. By EOF method, the development of profiles in the short term could be forcasted. Moreover, BP artificial neural network is used to predict the development of space phase and time phase seperately. The results show that the BP artificial neural network method can be applied to predict the changes of the profile while the changed trend of the profile is obvious.（6） The differences between analysis methods of hydrology. The vertical average characteristic value error between nation criterion and traditional hydrology method is below 8%; while calculating per wide flux of tide period, the error could be ignored. The traditional hydrology method is availiable to deal with interaction of water dynamic force and sediment, and the nation criterion method could be adapt to analyse the tidal flow and direction of net flux.更多还原