Variations in sediment concentration and velocity after turbidity current confluence in submarine canyon
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摘要:
高速的浊流具有强大的破坏力，威胁着海底结构物的安全。海底峡谷是浊流向深海运动的重要通道，其中许多海底峡谷具有多条分支峡谷，而分支峡谷与主干峡谷浊流发生汇流后，含沙量、速度可能会增加，进而破坏力增强。本文通过室内水槽试验和数值模拟，研究了分支峡谷中的浊流汇流到主干峡谷中含沙量和速度的变化，并与仅有主干峡谷浊流的情景进行了对比。研究发现，发生汇流时，浊流的高度、含沙量和速度在头部均有增加，在汇流发生过后会有所减小，但含沙量和速度仍大于不发生汇流时的情况。本文试验结果可为有分支峡谷发生浊流汇流的现场监测位置及项目、速度推算提供指引。
Abstract:High-speed turbidity currents are very destructive and threaten the safety of seabed constructions. An important channel for turbidity currents to move to the deep sea is submarine canyons, of which many have multiple branches. Once a branch meets the canyon with turbidity currents, the sand content and the velocity of turbidity currents could be increased, and so the destructive power. We studied the changes in sand content and movement velocity of turbidity currents in branch canyons converging into the main canyon, to which the scenario of turbidity currents in main-canyon-only was compared. Result show that the height, sand content and velocity of turbidity currents were increased at the head when confluence occurred, and decreased after the confluence occurred. However, the sand content and the velocity were still larger than those without confluence. This study provided guidelines for site selection and velocity calculation for field monitoring when turbidity currents confluence occurs in branch canyons.
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Keywords:
- submarine canyons /
- turbidity currents /
- confluence /
- velocity /
- sediment concentration
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图 1 海底峡谷汇流模型概况图
a：模型平面布置图，b：模型地形等高线图。
Figure 1. Image of the submarine canyon confluence model
a: top view of the model, b: model terrain contours.
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图 4 总含沙量随初始配置浊流含沙量的变化
a：汇流点S1， b：继续流动点S2。
Figure 4. Variation in total sand content with initial configurated turbidity currents sand content
a: Confluence point S1, b: continued flow point S2.
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图 5 主流和汇流情景下浊流各层含沙量随初始浊流含沙量的变化
a：100 g/L，b：200 g/L，c：300 g/L，d：400 g/L，e：500 g/L。
Figure 5. Variation in sand content in each layer of turbidity currents with initial turbidity currents sand content in main flow and confluence scenarios
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图 6 数值模拟模型构建
a：模型立体图，b：网格划分。
Figure 6. Construction of numerical simulation model
a: model stereogram, b: meshing.
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图 7 初始含沙量为200 g/L的浊流模拟流速与实测流速对比
a：vA处主流情景，b：vB处主流情景，c：vA处汇流情景，d：vB处汇流情景。
Figure 7. Comparison of simulated current velocity and measured current velocity for turbidity currents with initial sand content of 200 g/L
a: Main current scenario at vA, b: main current scenario at vB, c: confluence scenario at vA, d: confluence scenario at vB.
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图 8 浊流在取样点S1、S2处的垂向速度剖面
a、c、e、g、i：S1处的垂向速度剖面；b、d、f、h、j：S2处垂向速度剖面。速度负值代表反向流动。
Figure 8. Vertical velocity profiles of turbidity currents at sampling points S1 and S2
a, c, e, g, i: Vertical velocity profile at S1; b, d, f, h, j: vertical velocity profile at S2. The negative values of velocity represent reverse flow.
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图 9 200 g/L的浊流在主流情景时的模拟结果
a：浊流到达S1处，b：浊流到达S2处。
Figure 9. Simulation results of turbidity flow at 200 g/L in the main currents scenario
a: turbidity currents arrives at S1, b: turbidity currents arrives at S2.
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图 10 浊流运动中的头部流场（x方向）图
Figure 10. Diagram of the head current field (x-direction) in turbidity currents motion
表 1 试验浊流初始含沙量配置表
Table 1 Configuration in initial sand content in the turbidity current experiment
序号 试验情景 浊流含沙量/(g/L) 主流 支流 1 主流 100 0 2 汇流 100 100 3 主流 200 0 4 汇流 200 200 5 主流 300 0 6 汇流 300 300 7 主流 400 0 8 汇流 400 400 9 主流 500 0 10 汇流 500 500 
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表 2 含沙量样品编号与取样盒层位对应关系
Table 2 Correspondence between sand content sample serial number and sampling box layer
取样盒分
层名称距底高度
范围/cmS1处各层
样品编号S2处各层
样品编号上层 8～12 S1-3 S2-3 中层 4～8 S1-2 S2-2 底层 0～4 S1-1 S2-1
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表 3 初始含沙量为200 g/L的浊流模拟流速最大值与试验流速最大值对比
Table 3 Comparison between the maximum simulated currents velocity and the maximum experimental flow velocity for turbidity flow with initial sand content of 200 g/L
项目 主流情景
vA点主流情景
vB点汇流情景
vA点汇流情景
vB点试验值/(m/s) 0.275 0.304 0.306 0.356 模拟值/(m/s） 0.270 0.291 0.305 0.351 绝对误差/(m/s) 0.005 0.013 0.001 0.006 相对误差/% 1.91 4.42 0.42 1.63 注：相对误差的计算方法为相对误差=|模拟值−试验值|试验值。
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