基于潮沟定点观测的潮间带水、沙、盐交换研究——以长江口九段沙一潮沟为例

INTERCHANGE OF WATER-SEDIMENT-SALINITY OVER AN INTERTIDAL FLAT IN JIUDUAN SHOAL IN THE CHANGJIANG RIVER ESTUARY

为研究潮间带和潮下带的水、沙、盐交换,于夏、秋两季在长江口九段沙一典型潮沟的固定点利用OBS-3A和ADP-XR进行了水深、浊度、盐度、流速流向剖面和回声强度观测。结果表明:(1)夏季大潮、冬季中-大潮、冬季小潮的潮周期垂向平均流速分别为26.5、15.9和8.4cm/s,夏、冬季观测到的最大流速分别为84cm/s和35cm/s。(2)夏季盐度变化范围为0.65—4.91,平均盐度2.14;冬季盐度变化范围为3.5—10.3,中-大潮和小潮平均盐度分别为6.26和7.98。(3)高悬沙浓度出现在涨潮初期和部分落潮末期的低水位阶段;涨潮阶段的平均悬沙浓度是落潮阶段的1.11—7.0倍。(4)涨、落潮阶段的水体和盐输运量大体上趋于平衡;(5)无论是冬夏季或大小潮,潮沟在潮周期内的净输沙方向均指向陆,即落潮输沙量小于涨潮输沙量(平均小40%);平均每个潮周期内净输沙量为6102kg,结合潮盆面积推算的潮周期沉积速率为0.0112mm/tide,或8.2mm/a。

To understand the interchange of water-sediment-salinity in the tidal flat of Jiuduan Shoal, Changjiang(Yangtze) River estuary, the water depth, turbidity, salinity, speed and direction of vertical current, and echo intensity were measured using OBS-3A and ADP-XR during spring tide in summer and middle-spring and neap tide in winter. Results show that:(1) the average speed of vertical current in winter middle-spring and neap tide were 15.9 and 8.4 cm/s, respectively, while in summer the current speed reached 26.5 cm/s. The biggest speed during observation in summer and winter were 84 and 35 cm/s;(2) salinity was higher in winter than in summer, in the ranges of 0.65–4.91 in summer(2.14 in average) and 3.5–10.28 in winter(6.28 and 7.98 in middle-spring and neap tide in average);(3) high SSC(suspended sediment concentration) occurred during shallow water stage at the beginning and the end of inundation. The average SSC was higher in flood period than in ebb period. The average SSC became higher from surface to bottom gradually;(4) The discharge of water and salinity in-and-out the tidal basin were in balance, while about 40% of sediment discharge transported during flood tidal period was detained in the tidal basin. The average sediment discharge carried during every tide was 6102kg, and the accretion rate was 0.0112mm/tide. The results show that the tidal basin was in accretion at rate of 8.2mm/year.