Sedimentation processes and sedimentary characteristics of tidal bores along the north bank of the Qiantang Estuary  

作　　者：FAN DaiDux CAI GuoFu SHANG Shuai WU YiJing ZHANG YanWei GAO Lei 

机构地区：[1]State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China [2]Key Laboratory of Marine Sedimentology&Environmental Geology,State Oceanic Administration,Qingdao 266061,China [3]State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai 200062,China

出　　处：《Chinese Science Bulletin》2012年第13期1578-1589,共12页

基　　金：supported by the National Natural Science Foundation of China (40876021 and 41076016);the State Key Lab of Marine Geology(MG200907);SOA Key Lab of Marine Sedimentology & Environmental Geology (MASEG200802);the Specialized Research Fund for the Doctoral Program of Higher Education (20090072110004);the Fundamental Research Funds for the Central University

摘　　要：A tidal bore is a unique Earth surface process, characterized by its highly destructive energy, predictable periodicities and magni-tudes, and the production of characteristic sedimentary features. Tidal bores and associated rapid flood flows are highly turbulent flows of the upper-flow regime with a velocity over several meters per second. Reynolds (Re) and Froude (Fr) numbers, respectively, are larger than 104 and 1.0, making them significantly different from regular tidal flows but analogous to turbidity currents. Until now, understanding of tidal-bore depositional processes and products has been limited because of the difficulty and hazards involved with gauging tidal bores directly. The Qiantang bore is known as the largest breaking bore in the world. Field surveys were carried out in May 2010, along the north bank of the Qiantang Estuary to observe the occurrence of peak bores, including regular observations of current, water level and turbidity at the main channel. Several short cores were sampled on the intertidal flats to study the characteristic sedimentary features of tidal bores. Hydrodynamic and sedimentological studies show that the processes of sediment resuspension, transport and deposition are controlled primarily by the tidal bores, and the subsequent abruptly accelerated and decelerated flood flows, which only account for one tenth of each semidiurnal tidal cycle in the estuary. Tidal-bore deposits are generally poorly sorted because of rapid sedimentation after highly mixed suspension by intense turbulence. This behavior is characteristic of the absence of tractive-current depositional components in a C-M diagram. It also goes along with well-developed massive bedding, graded bedding, basal erosion structures, convolute bedding and dewatering structures. Together, these sedimentary features can constitute fingerprinting of turbidites, widely distributed in the deep-water environment. However, a tidal bore is triggered by intensely deformed tidal waves propagating into a shallow-water environmeA tidal bore is a unique Earth surface process, characterized by its highly destructive energy, predictable periodicities and magnitudes, and the production of characteristic sedimentary features. Tidal bores and associated rapid flood flows are highly turbulent flows of the uppeflow regime with a velocity over several meters per second. Reynolds （Re） and Froude （Fr） numbers, respectively, are larger than 104 and 1.0, making them significantly different from regular tidal flows but analogous to turbidity currents. Until now, understanding of tidal-bore depositional processes and products has been limited because of the difficulty and hazards involved with gauging tidal bores directly. The Qiantang bore is known as the largest breaking bore in the world. Field surveys were carried out in May 2010, along the north bank of the Qiantang Estuary to observe the occurrence of peak bores, including regular observations of current, water level and turbidity at the main channel. Several short cores were sampled on the intertidal fiats to study the characteristic sedimentary features of tidal bores. Hydrodynamic and sedimentological studies show that the processes of sediment resuspension, transport and deposition are controlled primarily by the tidal bores, and the subsequent ab- ruptly accelerated and decelerated flood flows, which only account for one tenth of each semidiurnal tidal cycle in the estuary. Tidal-bore deposits are generally poorly sorted because of rapid sedimentation after highly mixed suspension by intense turbulence. This behavior is characteristic of the absence of tractive-current depositional components in a C-M diagram. It also goes along with well-developed massive bedding, graded bedding, basal erosion structures, convolute bedding and dewatering structares. Together, these sedimentary features can constitute fingerprinting of turbidites, widely distributed in the deep-water environment. However, a tidal bore is triggered by intensely deformed tidal waves propagating into a shallow-water en

关 键 词：钱塘江河口 沉积特征 沉积过程 战区导弹防御系统 沉积物再悬浮 平均晶粒尺寸 洪水流量 床上用品 

分 类 号：P736.21[天文地球—海洋地质]