荆江河段4次裁弯后干流河道调整研究

Channel Adjustments Induced by Four Meander Cutoffs in the Middle Yangtze River( Jinjiang reach)

1949~1979年长江中游的荆江河段共发生4次裁弯,包括2次自然裁弯(碾子湾和沙滩子)和2次人工裁弯(中洲子和上车湾),裁弯后上下游的河床和河势发生显著调整。基于实测水文资料和遥感影像(1955~2016年),计算2次人工裁弯后新河道的冲刷量,并验证老河道的淤积量,分析裁弯后4个牛轭湖的发展过程与现状,并指出荆江4个牛轭湖的快速衰退主要受当地人类活动影响。荆江河段的裁弯增加了河床比降,引起水流功率的调整,促使河床长期冲刷下切和床沙粗化。荆江4次裁弯完成后,直至1990年代荆江河床才基本达到冲淤平衡,且下荆江略有淤积。

The riverbed and channel planform in the middle Yangtze River（ Jinjiang reach） was significantly changed along with the four systematic cutoffs including two natural cutoffs（ at Lianziwan and Shatanzi） and two artificial cutoffs（ at Zhongzhouzi and Shangchewan） occurred during 1949-1979. Using the hydrological data and remote sensing images from 1955 to 2016,we calculated the erosion volume of new channels and deposition volume of old channels（ i. e.,oxbow lake）,and analyzed the evolution process and the current status of the formed oxbow lakes. We found that the oxbow lakes were mainly influenced by local human activities. The increase of the channel gradient due to the four cutoffs causes adjustment of stream power along the channel and forces erosion of the channel bed in the long term and coarsening of bed material. The channel bed of the Jinjiang reach adjusts to its erosion-deposition equilibrium state until 1990 s,with a slight deposition in the lower Jinjiang reach.