山溪性强潮河口分汊河道演变机制——以瓯江江心屿河段为例

山溪性强潮河口是中国东南沿海的一种典型河口，水动力强劲、泥沙运动活跃，对人类活动响应迅速。自然条件与人类活动共同驱动下山溪性强潮分汊河道演变机制尚需进一步研究。以径潮流作用下滩槽演变剧烈的瓯江江心屿分汊河段为例，采用实测资料分析与二维水沙数学模型计算的方法，分析了20世纪70年代以前自然演变、70年代至90年代末上村丁顺坝建设影响期、21世纪以来人工采砂等影响下的河道演变机制。结果表明，丁顺坝建设等人类活动改变了该河段自然条件下主支汊周期性交替的演变规律; 21世纪以来人工采砂等造成河床大幅下切，近20 a来潮差增大0.5 m、涨潮流量增大约47%，分流与分沙不均匀性分别减弱0.08~0.30和0.28~0.54，涨落潮流速差异减小，有利于减缓支汊萎缩态势，河道演变机制受到自然-人类活动双重因素主导。研究成果可为类似河流演变和保护利用提供借鉴。

Study on the evolution mechanism of bifurcated branches in the macro-tidal estuary with a mountain stream: case study of the Jiangxinyu reach in the Oujiang River

The macro-tidal estuary with a mountain stream is a typical estuary on China′s southeast coast, characterized by intense dynamic forces, active sediment movements, and a robust response to human activities. It demands further investigation of its evolution mechanism under both natural conditions and anthropogenic stresses. This paper takes the Jiangxinyu reach of the Oujiang River estuary as a case example to explore the river′s evolution under the influence of human activities, including effects of longitudinal dam construction, sand mining, and shoreline adjustment since the 1970s. Measured data analysis and a two-dimensional flow and sediment mathematical model were used. The results confirm that anthropogenic stresses have altered the natural periodic alternation of the river′s main and side branches. Moreover, the undercutting of the riverbed caused by sand mining from the beginning of this century has increased tidal range by 0.5 m and tidal prism by 47%, while weakening the discharge asymmetry and sediment transport asymmetry indices by 0.08—0.30 and 0.28—0.54, respectively. The undercutting of the riverbed has also weakened the ebb and flood asymmetry. These conditions have subsequently helped slow down the shrinkage of the side branch. The evolution mechanism is dominated by both natural and human activities. Overall, the research findings may be a reference for river evolution and protection under the influence of human activities.