彩沙示踪研究九龙江河口湾北侧湾口海区底沙运动

Bedload movement in north mouth of Jiulongjiang Estuary using colored sand tracing

1998年 11月 6～ 7日在九龙江河口湾鸡屿北侧沙洲进行了彩沙示踪试验研究 ,取得沙洲底沙运动数据 :(1)两个主要运动方向及其最大运移速度为 :NW向 6 1m/d ,SW向 32m/d。 (2 )一个全潮周日的最大扩散范围为 :NW SE向 74m ,SW NE向 42m ,垂直扩散深度 3cm左右。 (3)底沙运动过程中粗粒沙滞留在沙洲 ,细粒沙被搬走。 (4 )垂直鸡屿北岸的断面净输沙率为朝NW方向 717t/d。证实了鸡屿北侧沿岸存在着一股反向 (朝NW向 )输移的泥沙流 ,这一反向输沙是由往复潮流中涨潮流占优势和偏东向波成沿岸流的耦合作用所造成 ,从而造成河口湾北侧湾口海区的底沙年内变化呈顺时针方向旋回运动的势态。底沙向E(正向 )运动及河流洪水冲刷所致 ,结果导致海区东部浅滩区大量泥沙堆积。各水道水流交汇、偏东向波浪以及涨潮流占为优势的水动力环境使浅滩区底沙先向SW迁移 ,继而平行鸡屿北岸向NW迁移 ,最终沉积于鸡屿NW海底。一旦发洪水 。

In Nov.6-7,1998, a study on the colored sand tracing on bedload movement of sand bar to the north of the Jiyu Islet in the Jiulongjiang Estuary was carried out. The quantitative data of the bedload movement were obtained as follows: (1) Main moving directions and the maximum moving speeds were 61m/d in NW direction, and 32m/d in SW direction. (2) The maximum spread distances in a tidal periodic day were 74m in NW SE cross section, and 42m in SW NE cross section; the maximum vertical mixed depth was about 3cm. (3) In the bedload movement process, coarse sand tended to stay on the sand bar, find sand was brought away. (4) Net discharge of the sand in the cross section, which was vertical to shoreline of north Jiyu Islet and via the laying point of the tracing sand, was 717t/d in NW direction. The data confirmed a reverse(NW direction) silt flow in the shore zone of north Jiyu Islet. The reverse bedload transportation was caused by the action of stronger flood stream than ebb stream and shore current dominated by the eastern wave action.It was advanced a yearly clockwise cyclic bedload movement pattern in north mouth of the Estuary. The bedload transported towards E by powerful scouring when the flood caused a large number of silt depositing in shoal on east of the sea area. The confluence of waterways, the easterly waves, and the stronger flood stream environment brought the shoal bedload to remove towards SW, then to remove towards NW with roughly parallel the shoreline of north Jiyu Islet, and to deposit on sea floor to the NW of the Jiyu Islet. In case of the river was in flood, the bedload movement went round and began towards E.