溪洛渡库区支流拦门沙形成机理

Study on formation mechanism of barrier sandbar of tributaries in Xiluodu Reservoir

水库蓄水后,水深增加使得河道干支流水动力条件发生改变,干流泥沙倒灌造成支流淤积,影响水库有效库容和航运安全。以溪洛渡水库为例,基于实测资料和三维水沙数学模型,研究库区干流和支流的水沙输移规律,分析支流河口段泥沙淤积特性及拦门沙形成机理。结果表明:①库区支流河道淤积泥沙来自支流上游和干流倒灌,其中,支流上游来沙是库区支流河道淤积的主要来源。②干流倒灌库区支流河口形成对流和环流区,泥沙易于淤积,西溪河和牛栏江坡度较缓,存在形成拦门沙的风险较大;美姑河坡度较大,存在形成拦门沙的风险较小。③对于西溪河、牛栏江和美姑河,干流倒灌的距离随着流量的增加而增加,高水位运行时,水位对干流倒灌的距离影响不明显;而对于金阳河和西苏角河,干流倒灌的距离随着流量的增加基本不变,干流倒灌的距离随着水位的增加而增加。研究成果为新水沙情势下库区支流拦门沙风险防控提供依据。

After the reservoir is impounded,the increase of water depth changes the hydrodynamic conditions of the river channel,the backfilling of the incoming sediment from main stream to the tributaries resulted the sedimentation of tributary mouth,affecting the effective storage capacity of the reservoir and the safety of navigation.In this paper,taking Xiluodu Reservoir as an example,the characteristics of water and sediment transport in the main stream and tributaries was studied,and the formation mechanism of barrier sandbar at the tributary mouth was analyzed based on the measured data and the three-dimensional mathematical model.The results is indicated that:the deposited sediment of tributaries mainly comes from the upstream incoming sediment and the backfilling of the main stream sediment,and the upstream incoming sediment is the main source of the sedimentation of tributaries;the main stream backflows into tributaries near the tributary mouth,and a convective and circulation zone are formed,where the sediment is easy to be deposited.The slope of Xixi River and Niulan River is slow,and the risk of the barrier sandbar formation is large,while the slope of Meigu River is large,and the risk of the barrier sandbar formation is small;for Xixi River,Niulan River and Meigu River,the distance of main stream backfilling into the tributary increases with the increase of discharge,and the influence of water level on the distance of main stream backfilling into the tributary is not obvious when the Xiluodu Reservoir is operating at high water level.In Jinyang River and Xisujiao River,the distance of main flow backfilling into the tributary is basically unchanged with the increase of discharge,and the distance of main stream backfilling into the tributary increases with the increase of water level.The research results provide a basis for controlling the risk of barrier sandbar formation at the tributary mouth of reservoir under the new condition of water and sediment.