河床下切影响下珠江三角洲潮流不对称时空变化规律

Spatial-temporal variation patterns of tidal current asymmetry in the Pearl River Delta under influence of riverbed descending

潮流不对称对三角洲地区的泥沙净输运和地貌演变有着重要作用,近年来珠江三角洲的大规模采砂活动引起河床大幅下切,因此研究河床下切后珠江三角洲潮流不对称的时空变化规律具有重要意义。利用1999年和2010年珠江三角洲河口河网地形数据,建立珠江口平面二维水动力模型,模拟珠江河口河网枯季水动力过程。结合非稳态调和分析方法分解流速信号,用偏度方法量化分潮组合、余流及分潮和余流相互作用对潮流不对称的贡献程度。研究结果表明:1)珠江三角洲潮流不对称受余流影响呈现出落潮占优的特性;2)河床下切后,各分潮组合的不对称性增大,潮流不对称在下游河道有所减弱、中上游河道有所增强,且珠江三角洲中上游河道变化大于下游河道;3)分潮和余流相互作用的变化是导致该现象产生的主要原因。

Tidal current asymmetry plays an important role in the net sediment transport and morphological evolution in the delta,and large-scale sand excavation activities in the Pearl River Delta(PRD)have caused significant descending of the riverbed in recent years,so it is important to study the spatial and temporal variation patterns of tidal current asymmetry in the PRD after riverbed descending.This paper establishes a two-dimensional hydrodynamic model which using topographic data of the PRD in 1999 and 2010 to simulate the hydrodynamic process in the Pearl River estuary network during the dry season.Using nonstationary harmonic analysis method to decompose velocity signals,the skewness method is used to quantify the contribution of tidal combinations,residual flow and interaction between tidal components and residual flow to tidal current asymmetry.The study shows that:1)Tidal current asymmetry is ebb dominant in the PRD due to the influence of the residual flow.2)After riverbed descending,contribution of tidal combinations to tidal current asymmetry shows increasing trend,tidal current asymmetry weakens in the lower reaches and strengthens in the middle and upper reaches,and the change of the middle and upper reaches of the PRD is greater than that of the lower reaches.3)Changes in the interaction between tidal components and residual flow are the main cause of this phenomenon.