Modeling the Shore-Normal Profile Shape Evolution for an Accretional Tidal Flat on the Central Jiangsu Coast
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摘要: 在泥质、砂质物质共存的淤长型潮滩, 其剖面的塑造受到潮流作用下堆积过程的控制.为探讨这种潮滩剖面的演变过程, 以江苏中部海岸为研究对象建立了大小潮周期性作用下的潮滩剖面演变模型, 模拟了潮滩均衡态剖面形态与初始坡度、潮差、沉积物供应量之间的关系及潮滩的持续淤长剖面.模拟结果表明: (1)淤长型潮滩剖面达到均衡态时的形态是上凸的, 且与初始形态无关; (2)在外源一定的条件下, 潮滩的宽度与潮差呈正相关; (3)外源物质供应越丰富, 潮滩宽度越大; (4)潮滩的冲淤状态由沉积物的供应量决定; (5)对大潮高潮位附近的无沉积带进行充填可实现对其长期持续淤长剖面的模拟; (6)有丰富沉积物来源的潮滩, 在调整至均衡态后仍持续向海淤长, 并在淤长过程中保持均衡态; (7)当在模型中输入有关江苏海岸的参数时, 模拟的潮滩宽度和坡度与江苏海岸的潮滩一致.Abstract: The evolution of the shore-normal profile shape of an accretional tidal flat is controlled by the transport of muddy and sandy sediments by tidal currents. To understand the evolution processes, a model is established to simulate the tidal flat profile changes in response to spring-neap tidal cycles, and it is applied to the accretional tidal flat on the central Jiangsu coast to investigate the interrelationships between the initial profile shape of the inter-tidal flat, tidal range, sediment supply, the equilibrium profile shape of the intertidal flat, and the long-term behavior of a prograding profile. The modeling output indicates that: (1) the shape of the accretional tidal flat tends to be convex when reaching its equilibrium state; (2) equilibrium of the intertidal flat morphology is independent of the initial profile shape; (3) if the sediment supply remains stable, then the width of the intertidal flat is positively correlated to tidal range; (4) the width of the intertidal flat increases with sediment supply and the accretion or erosion status of the intertidal flat is determined by sediment supply; (5) there is a need to design an algorithm to treat the area close to high water on springs to simulate long-term growth of the tidal flat; (6) the intertidal flat associated with abundant sediment supply will progradeg towards the sea, and at the same time its equilibrium shape will be maintained; and (7) the width and gradient of the intertidal flat from the model output are consistent with those of the Jiangsu coast, when inputting parameters derived locally for the model.
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Key words:
- tidal flats /
- sediment transport /
- sedimentology /
- shore-normal profile shape /
- equilibrium /
- Jiangsu coast
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图 1 研究区示意(王颖和朱大奎，1994)
Fig. 1. Sketch map of study area
图 2 对潮间带大潮高潮位附近的无沉积带进行充填的算法示意
Fig. 2. Diagram showing the algorithm to fill in the non sedimentation zone near high water level on springs on the tidal flat
图 3 水域左边界的控制与否对潮滩地形演变的影响
a.水域左边界不控制；b.水域左边界加以控制；潮滩的初始坡度为0.7‰，平均潮差为3.62 m，涨潮阶段开边界悬沙浓度为0.5 g/L
Fig. 3. Influence of the treatment of the left side boundary (i.e., the non sedimentation zone) on the model output of the profile evolution
图 4 不同初始坡度潮滩剖面的演变及其均衡态
a.潮滩初始坡度为0.5‰；b.潮滩初始坡度为0.9‰；涨潮阶段开边界悬沙浓度为0.5 g/L，平均潮差为3.62 m
Fig. 4. Evolution process and the equilibrium of the intertidal flat with different initial gradients
图 5 潮差对潮滩宽度的影响
a.平均潮差为2.66 m；b.平均潮差为4.66 m；潮滩初始坡度为0.7‰，涨潮阶段开边界悬沙浓度为0.5 g/L
Fig. 5. Effect of tidal range on the width of the intertidal flat
图 6 沉积物供应中止时潮滩剖面的演变
初始潮滩坡度为0.5‰，平均潮差为3.62 m
Fig. 6. Evolution of the intertidal flat when sediment supply was cutoff
图 7 外源量的变化对潮滩剖面的演变及其均衡态的影响
a.涨潮阶段开边界悬沙浓度为0.5 g/L；b.涨潮阶段开边界悬沙浓度为1.0 g/L；潮滩初始坡度为0.7‰，平均潮差为3.62 m
Fig. 7. Effect of variations in sediment supply on the evolution of the intertidal flat profile and the equilibrium status
图 8 潮滩长期持续淤长剖面
潮滩剖面初始坡度为0.7‰，平均潮差为3.62 m，潮滩阶段开边界悬沙浓度为0.5 g/L
Fig. 8. Long-term intertidal flat profile evolution
表 1 动力学模型中的有关参数取值
Table 1. The parameters in the model
参数类型 参数名称 数值 潮汐参数 与M2相联系的涨潮历时Tmf(s) 19 656 与M2相联系的落潮历时Tme(s) 25 056 与M2相联系的潮位循环时间Tm(s) 44 712 与M2相联系的最大潮差Rm(m) 3.495 8 与S2相联系的涨潮历时Tsf(s) 18 900 与S2相联系的落潮历时Tse(s) 24 300 与S2相联系的潮位循环时间Ts(s) 43 200 与S2相联系的最大潮差Rs(m) 1.160 8 大小潮循环时间T(s) 1 277 486 潮滩沉积物粒度参数 沉积物密度ρs(kg/m3) 2 650 砂的粒径Ds(mm) 0.07 泥的粒径Dm(mm) 0.01 砂的临界起动流速Ucs(m/s) 0.30 泥的临界再悬浮流速Ucm(m/s) 0.25 泥的临界沉降切应力τm(N/m2) 0.19 泥的临界侵蚀切应力τe(N/m2) 0.19 悬沙沉降速率ωs(mm/s) 0.5 海水物理性质 海水密度ρ(kg/m3) 1 025 动力黏度系数μ(kg/m/s) 1.4×10-3 运动黏度系数υ(m2/s) 1.4×10-6 距离底床100 cm处的拖曳系数C100 3.0×10-3 卡门常数κ 0.4 底床物理性质 粗糙长度Z(m) 1.98×10-2 再悬浮常数E(kg/m2/s) 1.0×10-5 底床沉积物的空隙率ε 0.4 其他参数 空间步长(m) 200 时间步长(s) 120 地形更新时间(s) 1 277 486 
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