调水调沙以来黄河尾闾河道冲淤演变及其影响因素

2002年开始的黄河调水调沙改变了进入黄河口的水沙条件,必然引起尾闾河道地貌的显著调整。根据黄河尾闾河道利津以下的断面实测高程数据,建立基于正交曲线网格的河道DEM,结合河床形态与水沙条件变化,综合研究黄河尾闾河道冲淤的时空演变及其影响因素。结果表明,调水调沙以来尾闾河道冲刷明显,2002—2017年累计冲刷6240万m ³,根据冲淤速率可以分为3个阶段：快速冲刷阶段（2002—2005年）冲刷速率为1443万m ³/a;冲刷减慢阶段（2006—2014年）冲刷速率为139万m ³/a;以及淤积阶段（2015—2017年）,淤积速率为263万m ³/a。其中,调水调沙初始4年尾闾河道的冲刷量占总冲刷量的80%,2006年以后冲刷强度逐渐减弱,甚至转为淤积。从季节上看,主要表现为汛期冲刷,非汛期淤积;从空间上看,越往口门方向,冲刷强度越小。调水调沙改变了入海水沙的年内分配,造成了尾闾河道的持续冲刷,入海流路也发生多次调整。但经过多年冲刷,河床整体下切,加上河口淤积延伸影响,调水调沙对尾闾河道的冲刷效率在持续降低。受河口海域淤积影响,近口门段在经历冲刷后转为淤积,河道纵比降减缓,增加了尾闾的不稳定性。

Spatiotemporal evolution of Yellow River estuarine channel and its influencing factors since the water-sediment regulation scheme

The implementation of the Water-Sediment Regulation Scheme(WSRS) since 2002 has changed the water and sediment entering the Yellow River Estuary, which may lead to adjustment of the estuarine channel. Based on the elevation data of 41 transects from 2002 to2017 in the estuarine channel downstream from Lijin, we established a digital elevation model(DEM) based on curved orthogonal grids to investigate the spatiotemporal characteristics of channel erosion and deposition, and further analyzed its controlling factors combining the morphological changes of river mouth and water-sediment data. The results show that the Yellow River estuarine channel has undergone significant erosion with a total sediment volume of 62.4 × 106 m³ since 2002. The channel evolution process can be divided into three stages according to the rates of erosion or deposition, namely: rapid erosion(2002-2005), slow erosion(2006-2014), and slow deposition(2015-2017). Approximately 80% of the total eroded sediment was depleted in the first stage. The erosion flux has shown a significant decreasing trend after 2006, and the overall characteristic of the channel transferred from erosion into deposition afterwards. On a seasonal scale, the estuarine channel was eroded in the flood seasons and deposited in the non-flood seasons;from the spatial perspective, the erosion intensity decreased in the downstream direction. The operation of the WSRS changed the distribution of water and sediment entering into the sea during a year, most of which was delivered in a short time(no more than 20 days), thus caused the continuous erosion of channel as well as the morphological adjustments of the estuarine channel. As a result of the intensive erosion in the first stage, the estuarine channel riverbed has lowered so much, and accompanied by the impact of the extension of river mouth, the erosion efficiency decreased continuously.Besides, the channel reach near the mouth has undergone significant siltation after the first stage causing the decline of riverbed longitudinal slope, which increased the instability of the estuarine channel.