渤海湾西北湾顶泥沙运动特征及模拟
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摘要
渤海湾西北湾顶处于粉沙质到淤泥质海岸过渡地带,泥沙运动复杂.根据三角架定点观测和水文测验资料,分析了不同水文条件下的含沙量变化特征,探讨了风浪掀沙模拟的关键处理方法.研究表明,研究海域泥沙运动与风浪关系密切,在小风天气下含沙量很小,六七级风以上天气条件下,且持续作用时,含沙量持续增大,较小风天气增幅达3～6倍左右;含沙量明显变化的临界波高约为0.5 m.从研究海域观测的底部边界层水流结构、剪切力等角度进行了波浪掀沙的水动力机制分析.基于泥沙扩散方程,提出了风浪条件下泥沙模拟的处理方法,包括含沙量层化效应、制约沉速、动床阻力、参考浓度等.与实测资料比较表明,提出的计算方法基本可模拟风浪过程引起的含沙量变化.该研究不仅为类似海域提供基本数据,而且给出了模拟计算关键问题的处理方法,具有重要的理论和实践意义.
The evolution and utilization of estuarine and coastal regions are largely restricted by sediment issues. Waves and currents are the main dynamic driving forces of sediment transport in estuary and coastal areas. The study of wave-current movement and sediment transport is of great significance in both academic research and engineering practice, which has received much attention from many scholars and engineers. The northwestern head of Bohai Bay belongs to a transitional area from silty coast to muddy coast, where the sediment movement is complex. Firstly, based on the field observation data measured with a tripod system and the hydrological data in the northwestern head of Bohai Bay, the characteristics of tidal currents, waves, and suspended sediment concentration(SSC) changes under different hydrological conditions were analyzed. Sediment density distribution was detected by a γ-ray densitometer. Results show that the SSC is mainly influenced by wave-induced sediment suspension: Under light wind conditions the SSC was very low, with the peak value generally less than 0.1 kg/m~3; the SSC increased continuously under the gales over 6-7 in Beaufort scale, with sustained wind action. The measured peak SSC at 0.4 m above the seabed was 0.15-0.32 kg/m~3, with the average value of0.08-0.18 kg/m~3, which is about 3-6 times the value under light wind conditions. The density at the bed bottom was about1.4-1.6 g/cm~3, and decreased to 1.02-1.03 g/cm3 at 0.1-0.2 m above the bed; there was rarely little fluid mud in the study area.Secondly, the mechanism of wave-induced SSC was studied from the view of flow structure, shear stress in the bottom boundary layer. The friction velocity was calculated by fitting the datasets of the measured logarithmic velocity profile.Comparison shows that the wave shear stresses(calculated from the bottom velocity profile) is higher than the current shear stress(calculated from the upper velocity profile). Following the Reynolds' decomposition method, expressions of waveinduced and current-induced shear stress were derived by splitting the variables into a fluctuating component, an averaged component and an oscillatory component. Compared with uniform flow, an additional item of wave streaming leads to a higher wave-induced shear stress.Finally, by analytically solving the sediment diffusion equation, a numerical procedure was proposed for sediment concentration under combined action of waves and currents. Some key approaches for fine sediment simulation were presented, including stratification effects, hindered settling, moving bed roughness, reference concentration and critical shear stress. Under combined wave-current conditions, the combined sediment diffusivity is given by the square sum of the wave-related and current-related diffusivities, and a toe-type distribution of wave-related eddy viscosity was employed.The stratification effects are considered by introducing the turbulence damping coefficient. The approaches of hindered settling for silt were employed. The enhanced roughness due to mobile bed effects was included. Comparison shows that,these approaches can properly simulate the measured wave-induced sediment concentration. This study provides basic data for coastal protection and utilization as well as for scientific study of silty-muddy coast, which is of great significance in practice and theory.
The evolution and utilization of estuarine and coastal regions are largely restricted by sediment issues. Waves and currents are the main dynamic driving forces of sediment transport in estuary and coastal areas. The study of wave-current movement and sediment transport is of great significance in both academic research and engineering practice, which has received much attention from many scholars and engineers. The northwestern head of Bohai Bay belongs to a transitional area from silty coast to muddy coast, where the sediment movement is complex. Firstly, based on the field observation data measured with a tripod system and the hydrological data in the northwestern head of Bohai Bay, the characteristics of tidal currents, waves, and suspended sediment concentration(SSC) changes under different hydrological conditions were analyzed. Sediment density distribution was detected by a γ-ray densitometer. Results show that the SSC is mainly influenced by wave-induced sediment suspension: Under light wind conditions the SSC was very low, with the peak value generally less than 0.1 kg/m~3; the SSC increased continuously under the gales over 6-7 in Beaufort scale, with sustained wind action. The measured peak SSC at 0.4 m above the seabed was 0.15-0.32 kg/m~3, with the average value of0.08-0.18 kg/m~3, which is about 3-6 times the value under light wind conditions. The density at the bed bottom was about1.4-1.6 g/cm~3, and decreased to 1.02-1.03 g/cm3 at 0.1-0.2 m above the bed; there was rarely little fluid mud in the study area.Secondly, the mechanism of wave-induced SSC was studied from the view of flow structure, shear stress in the bottom boundary layer. The friction velocity was calculated by fitting the datasets of the measured logarithmic velocity profile.Comparison shows that the wave shear stresses(calculated from the bottom velocity profile) is higher than the current shear stress(calculated from the upper velocity profile). Following the Reynolds' decomposition method, expressions of waveinduced and current-induced shear stress were derived by splitting the variables into a fluctuating component, an averaged component and an oscillatory component. Compared with uniform flow, an additional item of wave streaming leads to a higher wave-induced shear stress.Finally, by analytically solving the sediment diffusion equation, a numerical procedure was proposed for sediment concentration under combined action of waves and currents. Some key approaches for fine sediment simulation were presented, including stratification effects, hindered settling, moving bed roughness, reference concentration and critical shear stress. Under combined wave-current conditions, the combined sediment diffusivity is given by the square sum of the wave-related and current-related diffusivities, and a toe-type distribution of wave-related eddy viscosity was employed.The stratification effects are considered by introducing the turbulence damping coefficient. The approaches of hindered settling for silt were employed. The enhanced roughness due to mobile bed effects was included. Comparison shows that,these approaches can properly simulate the measured wave-induced sediment concentration. This study provides basic data for coastal protection and utilization as well as for scientific study of silty-muddy coast, which is of great significance in practice and theory.
引文
1 Lu Y J,Li S Q,Zuo L Q,et al.Advances in sediment transport under combined action of waves and currents.Int J Sediment Res,2015,30:351-360
2 Xu J J,He Q,Wang Y Y.Application of instrumented tetrapod in bottom boundary layer for water-sediment measurement(in Chinese).Ocean Eng,2009,27:55-61[徐俊杰,何青,王元叶.底边界层水沙观测系统和应用.海洋工程,2009,27:55-61]
3 Yuan Y.Observation of suspended sediment dynamics in Chinese coastal seas by acoustic instruments(in Chinese).Doctor Dissertation.Qingdao:China Ocean University,2009[原野.基于声学方法的中国近海沉积物和悬浮颗粒物动力过程观测研究.博士学位论文.青岛:中国海洋大学,2009]
4 Sternberg R W.Friction factors in tidal channels with differing bed roughness.Mar Geol,1968,6:243-260
5 Cacchione D A,Sternberg R W,Ogston A S.Bottom instrumented tripods:History,applications,and impacts.Cont Shelf Res,2006,26:2319-2334
6 Salehi M,Strom K.Measurement of critical shear stress for mud mixtures in the San Jacinto estuary under different wave and current combinations.Cont Shelf Res,2012,47:78-92
7 Liu M,Wu H L,Wang Y Y,et al.Integrated observation study on wave-current-sediment in the Sheyang Estuary under strong winds(in Chinese).JSediment Res,2010,(2):15-21[刘猛,吴华林,王元叶,等.射阳河口大风天波流沙综合观测研究.泥沙研究,2010,(2):15-21]
8 Liu H,Yin X L,Wu C Y,et al.Turbulence feature research within bottom boundary layer induced by tide in the Pearl River Estuary(in Chinese).Chin J Hydrodyn,2009,24:133-140[刘欢,尹小玲,吴超羽,等.珠江河口潮流底边界层的湍流特征量研究.水动力学研究与进展A辑,2009,24:133-140]
9 Li Z H,Gao S,Chen S L.Characteristics of tide-induced bottom boundary layers over the Dafeng intertidal flats,Jiangsu Province,China(in Chinese).Ocean Eng,2007,25:53-60[李占海,高抒,陈沈良.江苏大丰潮滩潮流边界层特征研究.海洋工程,2007,25:53-60]
10 Wang Y Y.The observation and models of bottom boundary layer for fine sediment(in Chinese).Doctor Dissertation.Shanghai:East China Normal University,2007[王元叶.细颗粒泥沙近底边界层观测和模型研究.博士学位论文.上海:华东师范大学,2007]
11 Wang A J,Wang Y P,Ke X K,et al.Calibration and observation by using a water level,current speed,and turbidity monitoring system in coastal areas(in Chinese).Mar Sci Bull,2003,22:61-68[王爱军,汪亚平,柯贤坤,等.潮间带水沙多层位同步测量系统应用的初步研究.海洋通报,2003,22:61-68]
12 Pang Q X,Xin H X.Study on the factors affecting suspension sediment concentration during large wind wave in the muddy coast(in Chinese).Chin J Hydrodyn,2011,26:413-421[庞启秀,辛海霞.大风浪期间淤泥质海岸实测含沙量影响因素研究.水动力学研究与进展A辑,2011,26:413-421]
13 Zuo L Q,Lu Y J,Wang Y P,et al.Field observation and analysis of wave-current-sediment movement in Caofeidian sea area in the Bohai Bay,China.China Ocean Eng,2014,28:331-348
14 Wang Y P,Gao J H,Pan S M.Measurement of bottom boundary layer parameters of the Yangtze River Estuary(in Chinese).Mar Geol Lett,2006,22:16-20[汪亚平,高建华,潘少明.长江河口区边界层参数的观测与分析.海洋地质动态,2006,22:16-20]
15 Gao J H,Wang Y P,Wang A J,et al.Suspended sediment behavior and transport in Changjiang River Estuary(in Chinese).Geogr Res,2004,23:455-462[高建华,汪亚平,王爱军,等.ADCP在长江口悬沙输运观测中的应用.地理研究,2004,23:455-462]
16 Ji R Y.Morphodynamic processes and engineering reaction of tidal channels--Taking Caofedian nearshore area in Bohai Bay for example(in Chinese).Doctor Dissertation.Nanjing:Nanjing Hydraulic Research Institute,2008[季荣耀.潮汐深槽动力地貌过程及工程效应研究--以渤海湾曹妃甸近岸海区为例.博士学位论文.南京:南京水利科学研究院,2008]
17 Lu Y J,Ji R Y,Zuo L Q.Morphodynamic responses to the deep water harbor development in the Caofeidian sea area,China’s Bohai Bay.Coast Eng,2009,56:831-843
18 Lu Y J,Zuo L Q,Ji R Y,et al.Effect of development of Caofeidian harbor area in Bohai bay on hydrodynamic sediment environment(in Chinese).Adv Water Sci,2007,18:793-800[陆永军,左利钦,季荣耀,等.渤海湾曹妃甸港区开发对水动力泥沙环境的影响.水科学进展,2007,18:793-800]
19 Zuo L Q,Lu Y J,Ji R Y,et al.Field observation and analysis on fluid mud and sediment concentration during windy days in Fengnan port,Tangshan(in Chinese).Technical Report,Nanjing Hydraulic Research Institute,2012[左利钦,陆永军,季荣耀,等.唐山丰南港区底质采样、浮泥与大风天含沙量现场观测及分析.技术报告,南京水利科学研究院,2012]
20 Ji R Y,Lu Y J,Zuo L Q.Coastal geomorphology and stability analysis in Fengnan coast,Tangshan(in Chinese).Technical Report,Nanjing Hydraulic Research Institute,2011[季荣耀,陆永军,左利钦.唐山丰南段岸线海岸动力地貌及岸滩稳定性分析.技术报告,南京水利科学研究院,2011]
21 Tang C B.Averaged velocity for sediment incipient motion(in Chinese).J Hydraul Eng,1963,(4):1-12[唐存本.泥沙起动规律.水利学报,1963,(4):1-12]
22 Nielsen P.Coastal Bottom Boundary Layers and Sediment Transport.Singapore:World Scientific,1992
23 van Rijn L C.Principles of Sediment Transport in Rivers,Estuaries and Coastal Seas.The Netherlands:Aqua publications Amsterdam,1993
24 Wang Y P,Gao S,Jia J J.Flow structure in the marine boundary layer and bedload transport:A review(in Chinese).Mar Geol Quatern Geol,2000,20:101-106[汪亚平,高抒,贾建军.海底边界层水流结构及底移质搬运研究进展.海洋地质与第四纪地质,2000,20:101-106]
25 Sleath J F A.Velocities and shear stresses in wave-current flows.J Geophys Res,1991,96:15237-15244
26 van Rijn L C.Unified view of sediment transport by currents and waves.II:Suspended transport.J Hydraul Eng,2007,133:668-689
27 Zuo L Q.Modelling and analysis of fine sediment transport in wave-current bottom boundary layer.Doctor Dissertation.Delft:TU Delft and UNESCO-IHE,2018
28 Grant W D,Madsen O S.The continental-shelf bottom boundary layer.Annu Rev Fluid Mech,1986,18:265-305
29 Te Slaa S,van Maren D S,He Q,et al.Hindered settling of silt.J Hydraul Eng,2015,141:4015020
30 Camenen B,Larson M,Bayram A.Equivalent roughness height for plane bed under oscillatory flow.Estuar Coast Shelf Sci,2009,81:409-422
31 Yao P,Su M,Wang Z B,et al.Experiment inspired numerical modeling of sediment concentration over sand-silt mixtures.Coast Eng,2015,105:75-89
32 Zuo L Q,Roelvink D,Lu Y J,et al.On incipient motion of silt-sand under combined action of waves and currents.Appl Ocean Res,2017,69:116-125
2 Xu J J,He Q,Wang Y Y.Application of instrumented tetrapod in bottom boundary layer for water-sediment measurement(in Chinese).Ocean Eng,2009,27:55-61[徐俊杰,何青,王元叶.底边界层水沙观测系统和应用.海洋工程,2009,27:55-61]
3 Yuan Y.Observation of suspended sediment dynamics in Chinese coastal seas by acoustic instruments(in Chinese).Doctor Dissertation.Qingdao:China Ocean University,2009[原野.基于声学方法的中国近海沉积物和悬浮颗粒物动力过程观测研究.博士学位论文.青岛:中国海洋大学,2009]
4 Sternberg R W.Friction factors in tidal channels with differing bed roughness.Mar Geol,1968,6:243-260
5 Cacchione D A,Sternberg R W,Ogston A S.Bottom instrumented tripods:History,applications,and impacts.Cont Shelf Res,2006,26:2319-2334
6 Salehi M,Strom K.Measurement of critical shear stress for mud mixtures in the San Jacinto estuary under different wave and current combinations.Cont Shelf Res,2012,47:78-92
7 Liu M,Wu H L,Wang Y Y,et al.Integrated observation study on wave-current-sediment in the Sheyang Estuary under strong winds(in Chinese).JSediment Res,2010,(2):15-21[刘猛,吴华林,王元叶,等.射阳河口大风天波流沙综合观测研究.泥沙研究,2010,(2):15-21]
8 Liu H,Yin X L,Wu C Y,et al.Turbulence feature research within bottom boundary layer induced by tide in the Pearl River Estuary(in Chinese).Chin J Hydrodyn,2009,24:133-140[刘欢,尹小玲,吴超羽,等.珠江河口潮流底边界层的湍流特征量研究.水动力学研究与进展A辑,2009,24:133-140]
9 Li Z H,Gao S,Chen S L.Characteristics of tide-induced bottom boundary layers over the Dafeng intertidal flats,Jiangsu Province,China(in Chinese).Ocean Eng,2007,25:53-60[李占海,高抒,陈沈良.江苏大丰潮滩潮流边界层特征研究.海洋工程,2007,25:53-60]
10 Wang Y Y.The observation and models of bottom boundary layer for fine sediment(in Chinese).Doctor Dissertation.Shanghai:East China Normal University,2007[王元叶.细颗粒泥沙近底边界层观测和模型研究.博士学位论文.上海:华东师范大学,2007]
11 Wang A J,Wang Y P,Ke X K,et al.Calibration and observation by using a water level,current speed,and turbidity monitoring system in coastal areas(in Chinese).Mar Sci Bull,2003,22:61-68[王爱军,汪亚平,柯贤坤,等.潮间带水沙多层位同步测量系统应用的初步研究.海洋通报,2003,22:61-68]
12 Pang Q X,Xin H X.Study on the factors affecting suspension sediment concentration during large wind wave in the muddy coast(in Chinese).Chin J Hydrodyn,2011,26:413-421[庞启秀,辛海霞.大风浪期间淤泥质海岸实测含沙量影响因素研究.水动力学研究与进展A辑,2011,26:413-421]
13 Zuo L Q,Lu Y J,Wang Y P,et al.Field observation and analysis of wave-current-sediment movement in Caofeidian sea area in the Bohai Bay,China.China Ocean Eng,2014,28:331-348
14 Wang Y P,Gao J H,Pan S M.Measurement of bottom boundary layer parameters of the Yangtze River Estuary(in Chinese).Mar Geol Lett,2006,22:16-20[汪亚平,高建华,潘少明.长江河口区边界层参数的观测与分析.海洋地质动态,2006,22:16-20]
15 Gao J H,Wang Y P,Wang A J,et al.Suspended sediment behavior and transport in Changjiang River Estuary(in Chinese).Geogr Res,2004,23:455-462[高建华,汪亚平,王爱军,等.ADCP在长江口悬沙输运观测中的应用.地理研究,2004,23:455-462]
16 Ji R Y.Morphodynamic processes and engineering reaction of tidal channels--Taking Caofedian nearshore area in Bohai Bay for example(in Chinese).Doctor Dissertation.Nanjing:Nanjing Hydraulic Research Institute,2008[季荣耀.潮汐深槽动力地貌过程及工程效应研究--以渤海湾曹妃甸近岸海区为例.博士学位论文.南京:南京水利科学研究院,2008]
17 Lu Y J,Ji R Y,Zuo L Q.Morphodynamic responses to the deep water harbor development in the Caofeidian sea area,China’s Bohai Bay.Coast Eng,2009,56:831-843
18 Lu Y J,Zuo L Q,Ji R Y,et al.Effect of development of Caofeidian harbor area in Bohai bay on hydrodynamic sediment environment(in Chinese).Adv Water Sci,2007,18:793-800[陆永军,左利钦,季荣耀,等.渤海湾曹妃甸港区开发对水动力泥沙环境的影响.水科学进展,2007,18:793-800]
19 Zuo L Q,Lu Y J,Ji R Y,et al.Field observation and analysis on fluid mud and sediment concentration during windy days in Fengnan port,Tangshan(in Chinese).Technical Report,Nanjing Hydraulic Research Institute,2012[左利钦,陆永军,季荣耀,等.唐山丰南港区底质采样、浮泥与大风天含沙量现场观测及分析.技术报告,南京水利科学研究院,2012]
20 Ji R Y,Lu Y J,Zuo L Q.Coastal geomorphology and stability analysis in Fengnan coast,Tangshan(in Chinese).Technical Report,Nanjing Hydraulic Research Institute,2011[季荣耀,陆永军,左利钦.唐山丰南段岸线海岸动力地貌及岸滩稳定性分析.技术报告,南京水利科学研究院,2011]
21 Tang C B.Averaged velocity for sediment incipient motion(in Chinese).J Hydraul Eng,1963,(4):1-12[唐存本.泥沙起动规律.水利学报,1963,(4):1-12]
22 Nielsen P.Coastal Bottom Boundary Layers and Sediment Transport.Singapore:World Scientific,1992
23 van Rijn L C.Principles of Sediment Transport in Rivers,Estuaries and Coastal Seas.The Netherlands:Aqua publications Amsterdam,1993
24 Wang Y P,Gao S,Jia J J.Flow structure in the marine boundary layer and bedload transport:A review(in Chinese).Mar Geol Quatern Geol,2000,20:101-106[汪亚平,高抒,贾建军.海底边界层水流结构及底移质搬运研究进展.海洋地质与第四纪地质,2000,20:101-106]
25 Sleath J F A.Velocities and shear stresses in wave-current flows.J Geophys Res,1991,96:15237-15244
26 van Rijn L C.Unified view of sediment transport by currents and waves.II:Suspended transport.J Hydraul Eng,2007,133:668-689
27 Zuo L Q.Modelling and analysis of fine sediment transport in wave-current bottom boundary layer.Doctor Dissertation.Delft:TU Delft and UNESCO-IHE,2018
28 Grant W D,Madsen O S.The continental-shelf bottom boundary layer.Annu Rev Fluid Mech,1986,18:265-305
29 Te Slaa S,van Maren D S,He Q,et al.Hindered settling of silt.J Hydraul Eng,2015,141:4015020
30 Camenen B,Larson M,Bayram A.Equivalent roughness height for plane bed under oscillatory flow.Estuar Coast Shelf Sci,2009,81:409-422
31 Yao P,Su M,Wang Z B,et al.Experiment inspired numerical modeling of sediment concentration over sand-silt mixtures.Coast Eng,2015,105:75-89
32 Zuo L Q,Roelvink D,Lu Y J,et al.On incipient motion of silt-sand under combined action of waves and currents.Appl Ocean Res,2017,69:116-125