【作者】 夏小明；

【导师】 金翔龙；

【作者基本信息】 浙江大学 ， 地质学， 2011， 博士

【摘要】 潮汐汊道是位于陆海相互作用区的主要海岸带子系统之一,其在港口航道、能源基地、临港工业、滩涂开发、生态保护等方面已愈来愈重要。与砂质海岸潮汐汊道相比,国内外对基岩海岸潮汐汉道的研究不够深入,没有形成比较完整的理论体系。本论文选择具有代表性的三门湾潮汐汊道系统,运用沉积学、地貌学和同位素年代学等多学科交叉方法,研究人类活动背景下的沉积地貌过程与发育演变机制,评价潮汐汉道的稳定性规律及其演化趋势,丰富了基岩海岸潮汐汊道理论研究内容。根据浅地层剖面探测记录与钻孔资料对比,三门湾浅部沉积地层明显分为四层,第一层以水平状层理为主,第二层以倾斜状、交错状层理为主,第三层底界面起伏不平,局部有古水道充填沉积。根据不整合面特征和沉积相标志,推断上部三层为全新世地层,厚度在20～35m之间,古水道充填沉积厚度可达42m。推算全新世平均沉积速率一般为0.2～0.5cm/a。对18个沉积物柱样进行岩性、结构分析和210Pb、137Cs年代测定,结果表明,三门湾潮滩为典型的潮汐沉积层理特征,现代沉积速率介于0.6～2.4cm/a；猫头水道浅水区以潮汐沉积为主,现代沉积速率介于1.9～2.6cm/a,深潭区以残留的风暴骤淤沉积为主,现代沉积速率介于3.9～8.6cm/a。三门湾沉积过程具有明显的时间尺度效应和区域空间差异特征。全新世平均沉积速率与现代沉积速率相差约一个量级,全新世平均沉积速率与水深之间是负相关关系,即水深愈大,沉积速率愈小。现代沉积速率与水深之间是正相关关系,即水深愈大,沉积速率愈大。利用不同历史时期海图和水下地形图资料对比分析,结果表明,1930年三门湾海岸、滩槽地貌格局已成型；1930～1964年,三门湾整体上处于稳定或缓慢淤积的自然状态；1964年以来,受围涂堵港工程的影响,三门湾海岸线外推明显,潮滩淤涨加快,汊道深槽普遍淤积。潮汐汊道系统的地貌发育与演变呈现出明显的阶段性、区域性特征。综合分析,认为地质构造与原始地形、潮流、悬浮泥沙是三门湾发育演变的主要因素,而近代人类活动(围涂堵港)通过改变原有的海岸边界、削弱落潮优势流,促进了潮滩淤涨和深槽淤积,已成为影响三门湾潮汐汊道系统发育演变的主要营力。对现有潮汐汊道P-A关系的统计分析方法进行剖析,认为不适用于单个潮汐汊道系统的稳定性评价。根据三门湾发育演变的区域性、阶段性和相似性的特点,从动力地貌学的角度出发,对三门湾复合型潮汐汊道系统进行分区、分级。基于1964年均衡状态下各分级、分区汊道系统的P和A实测数据的回归分析,推导出三门湾均衡态P-A关系式：A=2.49×10-4P0.940974,相关系数R达到0.999。运用均衡态P-A关系式,推算1994、2003、2007年各汊道口门达到均衡状态下的口门断面面积和口门断面平均水深,与实测值进行比较,评价三门湾潮汐汊道系统的稳定性变化。结果显示,人类开发活动影响下的三门湾潮汐汊道的各个子系统的发育演变与调整均趋向均衡态P-A关系曲线,并具有明显的区域性、阶段性特征。其中,沥洋港、青山港能够较快调整、达到均衡状态；蛇蟠水道受到晏站涂前沿舌状浅滩、纳潮区围涂工程的双重影响,处于周期性变化状态；猫头水道、三门湾口门受到沥洋港、青山港、蛇蟠水道演化的多重影响,调整过程复杂多变,具有明显的滞后特征。根据三门湾近期围垦规划,预测了各汊道系统发展趋势。其中,猫头水道在今后的二十年内将一直处于快速淤积调整状态,达到均衡状态下的口门断面平均水深为12.6m,比2003年实测口门断面平均水深小5m,估算猫头深潭最大水深将不足35m,可能影响到三门核电站取排水口的水深条件和温排水扩散能力。更多还原

【Abstract】 Tidal inlets are common along littoral drift shores all over the world, and literatures on tidal inlets among barrier coastlines are numerous. In contrast, study on tidal inlets in rocky coast does not draw much attention. Located in the rocky coast of East China Sea, Sanmen Bay is a big tidal inlet system with great values in terms of port and navigation, nuclear station construction, tidal flat cultivation, and environment protection. Several aspects of the Sanmen inlet system are of scientific research significance. First, as a typical tidal inlet system on the rocky coast, Sanmen Bay is an excellent case for study of stability of tidal inlet. Moreover, the latest 50 years saw fast environmental changes happening in Sanmen Bay. Such changes deserve extensive research focusing on the interaction between human activities and coastal evolution.Based on the sub-bottom profile records and lithofacies of drill cores, the thickness of Holocene deposit is estimated as 20-35 m in average, with maximum of 42 m being found in buried ancient channel. The calculated sedimentation rate is about 0.2～0.5 cm/a.18 short cores were collected at different locations in Sanmen Bay. Their lithological character (such as wet and dry density, moisture content) and sedimentary structure were analyzed, and 210Pb、137Cs radioactivity were deteceted in laboratory. Using CIC dating model, the modern sedimentation rates are calculated as 0.6-2.4cm/a for tidal flat,1.9～2.6cm/a in the shallow area and 3.9～8.6cm/a in the deep area of Maotou Channel, respectively.The sedimentation process of inlet system is of typically temporal and spatial variation. Holocene depositional rate is negatively related to water depth, while recent depositional rate is positively related to water depth. Recent depositional rate is ten times larger than that of the Holocene.Derived from the analysis of sea charts and underwater topographic charts since 1930, the geomorphological process show regional and staged feature. In 1930, the recent geomorphology structure formed. From 1930 to 1964, the inlet system was on the stable or slowly accretion condition. Since 1964, the inlet system advance in the faster accumulation rate because of the reclamation of tidal flat. From comprehensive analysis, the geological structure and original topography, tidal current and suspended sediment are main factors influencing the formation and evolution of inlet system. Recently, human activities such as reclamation becomes the main factor and bring about a rapid accumulation by changing coastal boundary and weakening ebb current.The traditional P-A relationships are not fit for a single inlet system. According to the evolutional similarity, the inlet system in Sanmen Bay can be divided into several sub-inlet units, and each sub-inlet unit stands for different spacial scale. Based on sea chart data in 1964 when Sanmen Bay inlets is believed in balanced state, the P-A relationships of inlet systems in Sanmen Bay is calculated as A=2.49x10-4P0.940974, with corelation coefficient being 0.999.Using the above P-A relationship formula, the stability of inlet system in Sanmen bay is evaluated. The different scale of inlets in the Sanmen Bay evolved and readjusted to the above equilibrium P-A relationship under the influence of human activity. Liyang inlet and Qingshan inlet took shorter time to readjust to equilibrium state. Shepan inlet show periodic fluctuation around equilibrium state because upstream Yanzhan tidal flat stretch out and draw back periodically. Maotou inlet readjusted to the equilibrium state slowly than the upstream inlets.According to the future plan for reclamation in Sanmen Bay, the trendency of the inlets system are predicted. Maotou inlet will be in a rapid accumulation state in the next twenty years, and the mean water depth over entrance equilibrium section will be 12.6 m, much less than present water depth of 17.5 m. The estimated maxium water depth in Maotou Trench will be less than 35 m, which may influence the water intake and the diffuse of the warm drain water of nuclear station.更多还原