Study on sediment transport in a wave and tide dominated estuary: a case study of Moyang River estuary in western Guangdong Province
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摘要: 泥沙输运是河口海岸研究的基础问题，对河口地貌演变、生态环境和工程建设具有重要的科学意义和应用价值。本文以漠阳江河口为例，基于船载和坐底三角架实测的海流、波浪和含沙量数据，分析漠阳江河口定点剖面上悬沙的沿岸和垂岸的输运趋势并计算泥沙输运通量，探讨波潮型河口的泥沙输移机制与运移规律，主要发现包括：（1）洪季口门处受径流作用主控，输沙量随着流量的增大而增大，沿岸输沙与垂岸输沙在流量最大的小潮期间达到最大值，分别为111.9 g/（m2·s）和269.5 g/（m2·s）；洪季拦门沙处则受波浪与潮流共同控制，沿岸输沙在大小潮期间皆为沿岸向西输运，垂岸输沙在大潮期间由落潮流主导离岸输沙4.0 g/（m2·s），小潮期间由波浪主导向岸输沙19.0 g/（m2·s）。（2）枯季拦门沙处受潮流和波浪主控，垂岸输沙以落潮流携沙向海输运为主，而沿岸输沙受波浪动力控制，在波生沿岸流作用下沿岸向东输沙；枯季拦门沙东侧同样受潮流和波浪主控，垂岸输沙在大潮期间为涨潮流主导携沙向岸输运，之后随着潮动力减弱转为离岸输运，沿岸输沙受波生沿岸流的影响沿岸向东输运。（3）洪季观测期间口门处向海输运显著，垂向上各水层流向一致；小潮期间出现水层流向分化，表层向海输运，底层向陆输运；拦门沙处大小潮时段垂向上各水层流向较为一致，但潮平均后大潮各水层向海输运，小潮各水层向岸输运，小潮期间受波浪作用明显，向岸输运占比达到79%。（4）漠阳江河口口门处在下泄径流与落潮流影响下以向海输沙为主，而口门外拦门沙处影响泥沙输运的最主要因素是潮流的向海输沙和波浪的沿岸输沙。Abstract: Sediment transport is a fundamental issue in the study of coastal and estuarine environments, holding significant scientific importance and practical value for the evolution of estuarine geomorphology, ecological environment, and engineering construction. This paper takes the estuary of the Moyang River as an example, based on the sea current, wave and suspended sediment concentration data measured by ship and bottom tripod, analyzes the alongshore and cross-shore transport trends of suspended sediment on the fixed cross-section of the Moyang River estuary, and calculates the sediment transport flux. It explores the sediment transport mechanisms and patterns in wave-tidal estuaries, with the main findings including: (1) During the flood season at the river mouth, the sediment transport is mainly controlled by the runoff, with the sediment transport rate increasing as the flow rate increases. The alongshore and cross-shore sediment transport reaches the maximum value during the neap tide with the largest flow, which are 111.9 g/m²/s and 269.5 g/m²/s respectively. At the mouth bar in the flood season, the sediment transport is jointly controlled by waves and tides. The alongshore sediment transport is consistently westward along the coast during both spring and neap tides, while the cross-shore sediment transport is dominated by the ebb tide during the spring tide with an offshore transport of 4.0 g/m²/s, and by waves during the neap tide with an onshore transport of 19.0 g/m²/s.(2) During the dry season, the mouth bar is primarily influenced by tidal currents and wave action. Sediment transport along the vertical shore predominantly occurs due to falling tidal currents moving seaward, while coastal transport is governed by wave energy, resulting in an eastward movement under the influence of wave-generated coastal currents. On the eastern side of the mouth bar during this season, tidal currents and waves also play a significant role; vertical shore transport is mainly driven by rising tides during spring tide periods before transitioning to offshore transport as tidal forces diminish. Coastal transport remains affected by wave-induced coastal currents and continues its eastward trajectory. (3) During the flood season observation period, the offshore transport at the river mouth is significant, and the flow direction of each water layer is consistent vertically. During the neap tide, there is a differentiation in the flow direction of the water layers, with the surface layer transporting offshore and the bottom layer onshore. At the mouth bar, the flow direction of each water layer is relatively consistent vertically during both spring and neap tides. Still, after tidal averaging, the spring tide shows offshore transport in all water layers, while the neap tide shows onshore transport in all water layers. During the neap tide, the influence of waves is evident, with the onshore transport ratio reaching 79%. (4) Under the influence of runoff and tidal current, the mouth of Moyang River estuary mainly carries sediment to the sea. The most significant factors affecting sediment transport at the mouth bar are the seaward tidal currents and the alongshore and cross-shore sediment movements driven by waves.
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图 1 研究区域（a）；双捷站位置（b）；观测站位（c）
Fig. 1 Study area (a); location of the Shuangjie station (b); Observation station location (c).
图 3 浊度与悬沙含量关系（直线为线性拟合结果）
Fig. 3 The relationship between turbidity and suspended sediment concentration (the straight line represents the result of linear regression fitting).
图 4 洪季L1、L2站大、小潮流速剖面及垂向均值（黑色虚线）时间变化图（x轴0点代表观测周期起点时刻）
Fig. 4 Velocity profiles of large and small tidal currents at L1 and L2 stations and time variations of the vertical mean value (black dashed line) in the flood season (0 point on the x-axis represents the starting point of the observation period )
图 5 洪季L1、L2站大、小潮悬沙含量剖面及垂向均值（黑色虚线）时间变化
Fig. 5 Suspended sediment content profiles of large tides and neaps at L1 and L2 stations and temporal variation of vertical mean value (black dashed line) in flood season
图 7 洪季L1、L2站逐时平均垂岸输沙通量等值线图（x轴0点代表观测周期起点时刻）
Fig. 7 Contour map of hourly average vertical sediment transport flux of L1 and L2 stations in the flood season (point 0 on the x axis represents the starting point of the observation period, the same below)
图 8 洪季L1、L2站逐时平均沿岸输沙通量等值线图（x轴0点代表观测周期起点时刻）
Fig. 8 Contour map of hourly average alongshore sediment transport flux of L1 and L2 stations in the flood season
图 9 枯季K1、K2站逐时平均沿岸输沙通量
Fig. 9 Average hourly alongshore sediment transport fluxes at K1 and K2 stations in dry season
图 10 枯季K1、K2站逐时平均垂岸输沙通量
Fig. 10 Average hourly cross-shore sediment transport fluxes at K1 and K2 stations in dry season
图 11 双捷站逐时流量图，红色部分为定点观测时间段（a）； 大潮观测期间流量（b）；小潮观测期间流量（c）
Fig. 11 Hourly discharge chart for Shuangjie station, the red part is the fixed point observation period (a); discharge during the spring tide observation period (b); discharge during the neap tide observation period (c).
图 12 大潮逐时平均沿岸输沙通量（a）；小潮逐时平均沿岸输沙通量（b）；大潮逐时平均垂岸输沙通量（c）；小潮逐时平均垂岸输沙通量（d）
Fig. 12 Hourly average alongshore sediment transport flux during the spring tide (a); hourly average alongshore sediment transport flux during the neap tide (b); hourly average cross-shore sediment transport flux during the spring tide (c); hourly average cross-shore sediment transport flux during the neap tide (d)
图 13 洪季L2站逐时有效波高,红色部分为定点观测时间段（a）；枯季K1站逐时有效波高（b）；枯季K2站逐时有效波高（c）
Fig. 13 Significant wave height for station L2 during the flood season, with the red part indicating the observation period (a); significant wave height for station K1 during the dry season (b); significant wave height for station K2 during the dry season (c)
图 14 漠阳江河口悬沙输移模式示意图
Fig. 14 Schematic diagram of sediment transport model in Moyang River estuary.
表 1 观测仪器参数设置
Tab. 1 Parameter Settings of observation instruments.
观测系统 测量仪器 参数设置 观测项目 船载观测 OBS-3A 整点下放，采样频率1 Hz 剖面浊度、深度 ADCP（Workhorse II Monitor ADCP 1 200 kHz） 整点开测，层厚0.25 m，
采样频率0.1 Hz，入水深度
0.5 m，盲区0.05 m剖面流速 座底观测 OBS-3A 采样间隔10 s，
采样时间10 s单点浊度、深度 AWAC（1 MHz） 采样频率2 Hz，采样间隔
10 min，采样时间512 s，
距底高度1.2 m，盲区0.4 m单点波高、波向 ADV （Vector
6 MHz）采样频率32 Hz，采样间隔
10 min，采样时间1 min，
距底高度0.3 m单点三维高
频流速
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表 2 各动力项潮周期输沙量和方向[垂岸方向正值表示垂岸向陆，沿岸方向正值表示沿岸向东，单位： g/(m2·s)]
Tab. 2 Tidal-averaged suspended sediment flux and direction of each dynamic term [positive value in the cross-shore direction indicates movement towards the land, and a positive value in the alongshore direction signifies eastward transport along the coast, unit: g/(m2·s)]
站位及
方向T1 T2 T3 T4 T5 平流输
沙项潮流输
沙项总输沙 L1大潮垂岸输沙 8.67 12.75 5.68 –21.58 –14.40 21.43 –30.30 –8.87 L1大潮沿岸输沙 20.55 21.20 19.49 22.71 21.63 41.75 63.84 105.59 L1小潮垂岸输沙 –34.40 –46.82 –47.52 –46.94 –43.44 –81.21 –137.90 –219.11 L1小潮沿岸输沙 14.23 18.92 19.21 19.9 18.47 33.15 57.58 90.73 L2大潮垂岸输沙 –0.62 –0.60 –0.63 –0.52 –0.44 –1.22 –1.59 –2.81 L2大潮沿岸输沙 0.48 0.40 0.38 –0.37 –0.16 0.89 –0.14 0.75 L2小潮垂岸输沙 2.65 2.64 2.50 1.75 1.93 5.29 6.17 11.48 L2小潮沿岸输沙 –0.87 –1.52 –1.05 –0.24 –0.68 –2.39 –1.97 –4.36
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