广西钦江河口枯季水动力特征及其对冷空气的响应

Hydrodynamic characteristics of the Qinjiang estuary in Guangxi during the dry season and its response to cold front

中文关键词:  沉积动力  侵蚀-沉降  悬沙输运  冷空气  钦江河口

英文关键词:sediment dynamic  erosion-deposition  suspended sediment transport  cold front  Qinjiang estuary

中文摘要:

      河口作为陆海相互作用的关键带，是河流入海泥沙及污染物的主要归宿地。钦江作为广西第二大河流，在茅尾海资源开发利用和生态环境保护与修复中发挥着重要作用。为进一步认识钦江河口地区的沉积动力过程，2021年10月27日至12月8日在此展开水动力和水体环境要素的连续观测。现场观测与分析结果表明，观测期间钦江河口潮汐类型为正规全日潮，浅水分潮显著，平均潮差为3.07 m，具有落潮优势；潮流以全日分潮流为主导，平均流速为0.12 m/s，运动形式主要为往复流；余流流向主要为西南方向。钦江河口潮汐和潮流性质较外湾和茅尾海中部海域全日潮特征更显著。枯季期间河口表层沉积物随潮汐运动表现为侵蚀－沉降交替的变化规律，垂向上侵蚀通量大于沉降通量，水平方向上悬沙净向海输运。冷空气过境带来的降雨使得钦江河口水体盐度降低、浊度增大，悬沙浓度及输沙量增加，同时冷空气南下时北风增强引起钦江河口减水效应并使潮差略有增加，水动力强度增大，增加表层沉积物的活动性，从而引起底部沉积物再悬浮强度和频率增加。

英文摘要:

      As the key region of land-sea interaction, estuaries are the main destination for river sediment and pollutants. The Qinjiang River, as the second largest river in Guangxi, holds significant importance in the development and utilization of resources, as well as the protection and restoration of the ecological environment in the Maowei Sea. To gain deeper insights into the sedimentary dynamics processes in the Qinjiang estuary area, the hydrodynamic process and water environment parameters near bed were continuously measured in the Qinjiang estuary from October 27 to December 8, 2021. The measured results show that the tidal type of the estuary is regular diurnal, and shallow water over-tides are significant. The mean tidal range is 3.07 m, with the ebb tide dominance during the observation. The tidal currents are mainly characterized by diurnal current, and dominated by reciprocating flow with a mean value of 0.12 m/s. The residual current is mainly in the southwest direction. The diurnal characteristics of tide and tidal current in the estuary are more obvious than those of the outer bay and the central part of the Maowei Sea. During the dry season, the surface sediments in the estuary exhibited alternating erosiondeposition patterns with tidal action. In the vertical direction, erosion fluxes were found to be greater than settling fluxes, while in the horizontal direction, there was a net seaward transport of suspended sands. The rainfall brought by the cold front led to decrease in the salinity of near bed water in the estuary, in addition, it causes increase in turbidity, suspended sediment concentration, and sediment transport. At the meanwhile, the enhanced north wind causes the water reduction effect in the estuary and slightly increases the tidal range during the cold front southward, which further increases the estuarine hydrodynamic, enhancing the activity of surface sediment, and then enhances the intensity and frequency of bottom sediment resuspension of the estuary.