东江下游河段溯源侵蚀特征与机理

Mechanism study of retrogressive erosion in the lower reach of Dongjiang River

1980年以来，东江下游及三角洲发生了高强度的采沙活动，由此导致水文条件发生显著变异，河床形态出现溯源变形，根据不同历史时期的地形与水文资料的对比分析，东江下游段溯源变形特征主要表现为：①大规模采沙直接引起同流量条件下水位大幅下降，尤以枯水期表现最为显著，博罗站水位～流量关系曲线表现为逐年右偏；②采沙引起河床高程大规模降低，即为一级溯源变形，其显著的特征是水面比降大，由此引起河床发生强烈冲刷，遂派生出河床演变的二级溯源变形，二级溯源变形的长期发展将使河床变形趋于平缓；③采沙河段必然发生河床断面形态及尺度的物理变形，按其发生的时间过程分为各具特色的3段：变形完成段（东江网河区）、变形进行段（石龙到博罗段）及变形影响段（博罗以上河段）。

Since 1980s, the intensified sand dredging activities in the lower reach and the delta of Dongjiang River have caused significant changes in river hydrodynamics, which results in retrogressive riverbed deformations. The mechanisms and characteristics of the retrogressive erosion are studied through analysis of the river bathymetric and the hydrological data collected during the different sampling periods. The finding suggests that because of the large-scale intensified sand dredging in the reach and delta： （ 1 ） For the same discharge, there is a significant decline trend detected in the corresponding water level time series especially during the dry seasons, the stage-discharge relation of Boluo station exhibits a tendency to right deflection after 1980; （2） a significant reduction in riverbed altitudes has led to an increase in water surface slopes, this is the first-stage retrogressive deformation, which in turn will cause an intensified riverbed erosion and result in the second-stage retrogressive deformation that will stabilize riverbeds in the long run; （3） the changes in river cross-sections are inevitable and divided into three parts, which are deformed reaches （Dongjiang River network）, deforming reaches （Shilong to Boluo） , and deformation effected reaches （above Boluo）, respectively, according to processes of their changes.