三峡工程运用后沙市段洲滩形态调整特点分析

Analysis on evolution of mid-channel sandbars in Shashi reach after the Three Gorges Project operation

为了研究三峡工程运用后沙市河段的洲滩调整过程,采用该河段1999—2016年实测水沙地形资料及2003—2016年从卫星遥感影像中提取的洲滩面积数据,定量分析了该河段的洲滩形态调整特点及影响滩体面积变化的相关因素。计算结果表明:三峡工程运用后,沙市河段洲滩整体呈逐渐萎缩趋势,其中太平口心滩先淤后冲,滩体面积(30 m等高线)在2010年达到最大值(2.38 km^2),至2016年滩体面积较最大值减小约62.6%;三八滩与金城洲持续冲刷,其滩体右缘均有明显崩退,2016年滩体面积(较2002年)分别减小了约91.2%和70.1%;腊林洲边滩对沙市河段心滩调整的控制作用在2003—2010年间逐渐减弱,2010年后太平口心滩、三八滩及金城洲明显出现相互影响的现象。此外还建立了太平口心滩、三八滩及金城洲的滩体面积与前5年平均的汛期水流冲刷强度的幂函数关系,用于反映滩体面积随水沙条件的变化过程。

The mid-channel sandbars in the Shashi reach have recently undergone significant evolution owing to the operation of the Three Gorges Project（TGP）. This paper reports an analysis on this evolution and its influencing factors using the 1999-2016 hydrological and topographic data and the 2003-2016 satellite remote sensing images. The results show that generally these sandbars have degraded and withered since the TGP operation commenced. The mid-channel sandbar at Taipingkou was first deposited and then scoured, shrinking in area（30 m contour） from the maximum（2.38 km^2） occurred in 2010 to a value of 62.6% smaller in 2016. The mid-channel sandbars at Sanbatan and Jinchengzhou were scoured during 2003-2016, decreasing in area by 91.2% and 70.1% respectively relative to the values in 2002, with their right sides collapsing and retreating significantly. We demonstrate that the period of 2003-2010 saw a gradual weakening in the impact of the point sandbar at Lalinzhou on the mid-channel sandbars in the Shashi reach, and that among these mid-channel sandbars an obvious mutual interaction has started since 2010. In addition, we develop empirical relationships of the mid-channel sandbar areas versus the flood-season average fluvial erosion intensity over previous five years, revealing the sandbars＇ tendency and response to changes in flow and sediment regime.