三峡变动回水区典型淤沙浅滩土脑子河段河型变化特点分析

土脑子河段是川江三大淤沙河段之一，三峡水库蓄水前为弯曲分汉河型，遵循汛淤枯冲的规律。三峡工程蓄水运用后，该河段汛后冲刷的特性被改变，河型也出现了转化的趋势。依据河道实测资料．分析了该河段在三峡蓄水前后的河床演变。着重探讨了河型的变化以及河型变化对航道的影响。分析表明．蓄水后土脑子河段已基本完成由凸岸深切河曲向宽浅河曲变化的过程。将会进一步转化为凹岸深槽的河曲。目前蓄水位下河道累积性淤积以及断面形态的变化对航道的影响不大，这种情况在156m时期将会继续，远期随着水库蓄水位的抬高，河段完成由凸岸深切河曲向凹岸深槽河曲的转化，航道条件将会得到根本改善。

Evolution Process of Tunaozi Shoal at the Fluctuating Backwater Area of the Three Gorges Project

Tunaozi Shoal is one of the three severe sediment depositing shoals in the Yangtze River. Before the impounding of the Three Gorges Reservoir, it is a branching and meandering river, and follows the law of sediment deposition on high-water period and sediment erosion on low-water period. After the impounding, the feature of deposition and erosion was changed and the river pattern evolved accordingly. Based on the field data, bed evolution before and after the impounding, esp. the variation of fiver pattern and the influence of fiver pattern on waterway are analyzed. The results reveal that after the impounding, Tunaozi Shoal transformed basically from convex-bank entrenched meander to shallow broad river, and will further develop to a concave-bank deep channel. The sedimentation has not much influence on the waterway under the present water lever. The condition of waterway will be improved accordingly with the rise of water lever in the future.