珠江三角洲河道近期冲淤特征初步分析

近20多年,在人为因素影响下,珠江三角洲网河区和口门区的水沙分配发生了 重大变化．水沙东输,加速了伶仃洋的淤积,其年均淤积量、水域缩减面积、滩涂的年 均增长率,分别为磨刀门的2．4倍、1．7倍、6.4倍．网河区河道由淤转冲,过水断面面 积扩大13．9％～31．9％;冲刷速率12～21cm／a．

Preliminary study on the characteristics of scouring and sedimentation of river channels in recent decacles in the Zhujiang Delta

In recent decades, the ratios of flow and stream load of Beijiang River increase obviously resulting in the transportation of flow and stream load eastwards. This change is caused by excessively quarrying the sand from river channel which makes the drop of river bed and water level and thus the flow of Xijiang River intrudes into Beijiang River. Because of increase of water and strengthen of hydro-dynamics, the channels tend to be scoured. From 1980s to 1990s the sectional area of flowing water in the two main channels of Beijiang River Delta enlarged 19.6%-31.9% in average with a scouring rate of 12-13cm/a. In the main channels of Xijiang Rive Delta, the enlargement rate and scouring rate is 13. 9% and 21 cm/a, respectively. The (?)/H of main channels in upper course became smaller extensively, showing the scouring and downcutting of river channel. From 1987 to 1999, the ratio of stream load of the eastern four estuaries increased from 47.7% to 56. 8% , resulting in the acceleration of accumulation process in Lingdingyang estuary. The annual accumulation rate, reduction area of sea region and annual natural increase rate of shallow in Lingdingyang estuary is 2.4,1.7 and 6.4 times larger than those in Modaomen estuary, respectively. The ratio of stream load after five years in the eastern estuaries is predicated to be 57%. However the annual accumulation rate may be still less than the annual average value. After ten years the ratio will increase to 57.7% and the accumulation will be larger than the average value. The transportation of flow and stream load eastwards is unfavorable for the protection of Lingdingyang estuary. The main channels and their tail course in braided five regions will be scoured extensively.