近50年来珠江河网区水动力对地形的响应

自20世纪50年代以来,珠江三角洲发生的河道采沙、航道整治等人类活动对河网区河床形态的自然演变过程产生了较大影响,引起河网区水动力产生相应的调整。根据平原感潮河网水力特性建立一维河网模型,并对50年代和90年代珠江河网区水动力过程进行了模拟,同时结合数值试验探讨了珠江河网水动力对地形变化的响应。结果表明,河床形态变化导致西、北江干流洪季水位及水位梯度较50年代明显下降,西江水位梯度由7.2 cm/km下降至4.1 cm/km,北江水位梯度的下降主要集中在上游地区,其中三水至三围由9.3 cm/km降至5.0 cm/km,而三围至口门变化不大,两个年代分别为4.9和4.8 cm/km,北江干流平均水位梯度由7.1 cm/km下降至4.9 cm/km。两个年代枯季水位梯度变化不明显,不同区域日均水位有升有降。数值试验结果同时表明,地形变化导致各主要节点分流比也产生不同程度调整,三水-马口、天河-南华等地形变化显著的区域分流比变化较大。

Impact of Channel Evolution on Hydrodynamics in the Pearl River Delta in the Last 50 Years

The Pearl River Delta (PRD) is a complex river network system, its hydrodynamic process is controlled both by runoff and tide,different from other estuaries in the world. During the last 50 years, the PRD area had undergone some large scale human activities (such as floodgate building, sand excavation, channel regulation), which changed the morphology of the river bed, and resulted in the hydrodynamic characteristics different from the 1950s. 1D river network hydrodynamic model was developed to simulate the river flow of 1950s and 1990s.The results show that the water level in flood seasons of the PRD was significantly lower than that in 1950s,and the surface grads of two main rivers (Xijiang and Beijiang) were dropped from 7.2 cm/km and 7.1 cm/km to 4.1 cm/km and 4.9 cm/km,respectively. In dry seasons,the change was not so significant. A numerical experiment was conducted to figure out the impact of channel evolution on the hydrodynamic process.In the experiment, the water surface level of the Xijiang river and Beijiang were dropped from 7.1 cm/km and 7.2 cm/km to 4.2 cm/km and4.7 cm/km,respectively,under the same conditions,which indicates that the main reason for low of water level in the PRD was the change of river bed. The experiment also figures out that the divided flow ratio was re adjusted heavily where the river bed changed dramatically.