Study on the distribution characteristics of rip currents in embayed beach on Hainan Island
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摘要: 海南岛海岸以岬湾海滩为主，是我国重要的滨海旅游目的地，也是裂流引起滨海溺水事故的高发地。为研究海南岛岬湾海滩裂流的分布特征，从海南环岛54个岬湾海滩近20年的卫星影像中解译裂流的发生情况，统计裂流的分布特征，并与现场调查结果对比。结果表明：在区域分布上，海南岛东岸和南岸岬湾的裂流发生率明显大于西岸和北岸；在位置分布上，岬湾中部的海滩裂流数量高于两侧；在几何特征上，裂流的平均长度与平均宽度、平均间距均呈正相关，但裂流的平均宽度、平均数量与裂流间距均无显著相关性。波浪环境对裂流密度影响明显，表现为裂流密度随平均有效波高、平均波周期、平均入射波功率和平均入射波能的增加均减小。岬湾尺度对裂流发生数量影响明显，表现为岬湾宽度、岬湾凹入度和岬角长度与平均裂流数量均呈正相关，但岸线曲率与平均裂流数量无显著相关性。卫星影像解译裂流发生情况与现场调查结果和裂流风险评价模型的结果基本一致，相关结论可为海南岛海滩安全管理和裂流预警工作提供参考。Abstract: The coast of Hainan Island is dominated by embayed beaches, which is an important coastal tourist destination in China and also has a high incidence of drowning accidents caused by rip currents. To investigate the distribution characteristics of rip currents on embayed beaches, the occurrence and distribution characteristics of rip currents are interpreted from the satellite images of 54 embayed beaches around Hainan Island over the past 20 years, and compared with the field survey results. The results show that, in terms of regional distribution, the occurrence probability of rip currents on the eastern and southern coasts is significantly higher than that on the western and northern coasts of Hainan Island. In terms of location distribution, the number of rip currents in the middle of the headland bays is higher than that on the two sides. In terms of geometric characteristics, the average rip length was positively correlated with the average rip width, and the average rip spacing. The distribution density of rip currents is negatively correlated with significant wave height, average wave period, incident wave power, and wave energy. The scale of the headland has a significant effect on the number of rips, which is positively correlated with the bay width, the maximum bay indentation, and length of the headland, but the curvature of the shoreline has no significant correlation with the average number of rips. The results of satellite image interpretation for the occurrence of rips are consistent with the results of the field survey and the evaluation of the Ω-RTR model. These conclusions can provide useful references for the beach safety management and rip current warning work on Hainan Island.
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图 1 海南岛54个岬湾海滩的位置（基于国家测绘地理信息局标准地图服务网下载审图号为GS(2021)5449号地图制作）
Fig. 1 Location of the 54 embayed beaches around Hainan Island
图 2 54个海滩的卫星影像数、水动力参数和沉积物中值粒度统计结果
Fig. 2 Statistical results of the number of satellite images, hydrodynamic parameters and median sediment grain size for 54 beaches
图 5 从卫星影像中解译裂流的长度(L)、宽度(W)和间距(D)，其中图a、b和d表示裂流（沟槽）与海岸线垂直，图c和e表示裂流（沟槽）与海岸线不垂直
Fig. 5 Interpretating the rip length (L), rip width (W) and rip distance (D) from satellite images, where figures a, b and d indicate that rips (channels) are perpendicular to the coastline, and c and e indicate that rips (channels) are not perpendicular to the coastline
图 7 从卫星影像和无人机图像中解译各海滩的裂流发生情况(a)，基于卫星影像解译(b)和现场调查(c)的2022年12月24日海棠湾海滩的裂流发生情况
Fig. 7 The occurrences of rips were interpreted from satellite images and drone images (a), the occurrence of rips at Haitang Bay on December 24, 2022 based on satellite image interpretation (b) and in situ observation (c)
图 8 54个岬湾的宽度、凹入度和发生裂流的平均数量统计结果(a)，19个岬湾海滩发生裂流的平均长度、平均宽度和平均间距统计结果(b)
Fig. 8 The width of 54 embayed beaches and average number of rips (a), statistical results of the average length, average width and average spacing of rips on 19 embayed beaches (b)
图 9 裂流几何特征变量之间的拟合关系
Fig. 9 Fitting relationship between the geometric characteristic of rip currents
图 10 54个岬湾海滩的状态和裂流风险判别结果，数字对应图1中的海滩编号
Fig. 10 Results of beach states and rip hazard evaluation for 54 embayed beaches, numbers correspond to the beach numbers in Fig. 1
图 11 裂流数量和分布密度与近岸波浪环境的拟合关系
Fig. 11 Fitting relationship between the number of rips and wave environment, fitting relationship between rip density and wave environment
图 12 平均裂流数量与岬湾尺度特征间的拟合关系
Fig. 12 Fitting relationship between the average number of rips and the bay scale features
图 13 裂流特征与岬湾尺度特征间的拟合关系
Fig. 13 Fitting relationship between the characteristcs of rips and the bay scale features
图 14 54个岬湾的朝向、平均入射波角度和平均裂流数量
Fig. 14 The opening direction, mean incident wave angle and average number of rips of 54 headland bays
表 1 从卫星影像解译各类裂流特征的方法
Tab. 1 Criteria for interpreting rip current types from satellite images
类型 特征 地形控制型 沟槽裂流 裂流出现在有沟槽垂直或斜向切割的沙坝或台地，沟槽两侧波浪破碎有白沫，槽内无或少白沫且水色偏深 聚焦裂流 入射波峰线向岸呈现韵律状弯曲，波高沿岸规律性变化，裂流在小波高处出现，沿岸有白沫出现，通常存在物质离岸输运而使水色变深 水动力控制型 瞬变裂流 波浪为正向入射的短峰波风浪，裂流出现在短峰之间区域，伴随短波峰的瞬变演化而间歇出现 剪切不稳定裂流 波浪斜向入射，裂流出现在近似平直海岸不稳定沿岸流，表现为离岸迁移的大尺度涡运动。碎波带内出现窄裂流颈，
存在物质离岸输运使水色偏深边界控制型 偏斜裂流 裂流出现在垂直海岸结构物的迎浪侧，存在物质离岸输运使水色偏深 阴影区裂流 裂流出现在垂直海岸结构物背浪侧的波影区，边界处出现白沫 混合型 沟槽−瞬变裂流 波浪为几乎垂直入射的风浪，裂流在沙坝沟槽处出现，沟槽附近有白沫 边界−沟槽裂流 垂直海岸结构物边界附近存在沟槽地形，沟槽双侧有白沫出现 聚焦−沟槽裂流 裂流出现在双沙坝地形，外部沙坝的白沫不明显，内部沙坝被沟槽分割，沟槽宽一般较大且呈规律性分布 
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表 2 基于地形动力学模型的海滩状态和裂流风险等级判别
Tab. 2 Beach state and rip hazard evaluation method based on morphodynamic model
海滩组别 Ω RTR 海滩类型 风险等级 反射型 $ \varOmega < 2 $ $ {\mathrm{RTR}} < 3 $ 完全反射型（R） 低 $ 3 \leqslant {\mathrm{RTR}} \leqslant 7 $ 有裂流沟槽的低潮台地（LTTR） 中 $ {\mathrm{RTR}} > 7 $ 无裂流沟槽的平坦低潮台地型（LTT） 低 中间状态 $ 2 \leqslant \varOmega \leqslant 5 $ $ {\mathrm{RTR}} < 3 $ 沿岸沙坝和裂流沟槽交替的沙坝型（B） 高 $ 3 \leqslant {\mathrm{RTR}} \leqslant 7 $ 低潮时伴有冲流沙坝和裂流沟槽的低潮沙坝裂流型（LTBR） 高 消散型 $ \varOmega > 5 $ $ {\mathrm{RTR}} < 3 $ 沙坝消散型（BD） 中 $ 3 \leqslant {\mathrm{RTR}} \leqslant 7 $ 无沙坝消散型（NBD） 低 超消散型 $\varOmega > 2$ $ {\mathrm{RTR}} > 7 $ 超消散型(UD) 低
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