交汇角度对黄河上游高含沙交汇区淤堵影响的试验研究

黄河上游支流——十大孔兑的高含沙洪水在入黄交汇区形成沙坝、淤堵干流的过程是一种典型的干支流交汇现象，对交汇区河床演变、防洪和工农业生产有重大影响，因此研究减轻高含沙交汇区沙坝淤堵的治理措施是一项十分必要和迫切的工作。本文通过模型试验研究了干支流不同交汇角度对孔兑与黄河高含沙交汇区沙坝淤堵规模的影响。模型试验以产生的高含沙洪水淤堵黄河干流次数最多、危害最大的孔兑之一——西柳沟与黄河交汇的干支流河段为模拟对象，采用黄河高含沙水流动床模型相似律进行模型设计，选取90°、60°、30°和15°作为试验交汇角度，分别开展了清水和浑水交汇试验，获取交汇区水流分区特性和沙坝淤堵规模特征。研究结果表明：随着交汇角增大，支流对干流的顶托作用增强，交汇口上游壅水区流速逐渐减小，水深增大；交汇角较小时交汇口下游形不成回流区，交汇角增大到30°以后回流区形成并随交汇角增大而增大，伴随着高流速带向对岸移动；壅水区和回流区沙坝尺度随交汇角增大而增大，交汇角较小时形不成壅水区淤积体和回流区淤积体，但易形成交汇口对岸淤积体，其尺度随交汇角增大而减小，与回流区淤积体互为消长。交汇口以上主槽的淤堵由壅水区淤积体构成，交汇口下游主槽淤堵由回流区淤积体和对岸淤积体共同构成，当交汇角为30°时交汇口上下游主槽总体淤堵规模最小。从河道淤堵规模和河岸稳定方面综合分析认为，在现状河道和水沙条件下，30°是有利于减轻孔兑与黄河高含沙交汇区淤堵的较优交汇角，这对交汇口河道整治具有重要指导作用。

Experimental Study of Influence of Confluence Angle on Sandbars at River Confluence with Hyperconcentrated Tributary Flow

The hyperconcentrated floods of the ten tributaries of upper Yellow River formed sandbars at the confluence, blocking the main channel of Yellow River and having adverse impact on local river bed evolution, flood control and industrial and agricultural production. It is necessary to explore the measures to reduce the scale of the sandbar and thus to alleviate its impact. In this paper, the influence of confluence angle on sandbar morphology at the confluence with hyperconcentrated tributary flow was investigated through physical model experiments. The confluence of upper Yellow River and Xiliugou River, one of the ten tributaries the hyperconcentrated floods from which resulted in most of the sandbar blocking events, was chosen as the simulated target. The model was designed by the physical model similarity laws for hyperconcentrated river flow which was applied widely. The angles of 90, 60, 30, and 15 degrees were set as the confluence angles in the experiments. It was found that, with the increase of the confluence angle, the main stream blocking was strengthened. The flow velocity of the backwater area upstream of the tributary river mouth slowed down gradually and the water depth increased. When the confluence angle increased to 30 degree, the separation zone came into being and then expanded gradually with the increase of the confluence angle, companied with the high velocity area shifting towards the opposite bank. The scales of the sandbar in backwater area and separation zone both increased with the growing of the confluence angle. When the confluence angle was small, there was no sandbar formed in those two areas, but a sandbar adjoining to the opposite bank of the tributary river mouth would be formed. The scales of the opposite bank sandbar decreased with the increase of the confluence angle. The main channel immediately upstream of the river mouth was blocked by the sandbar in the backwater area, while the main channel immediately downstream of the river mouth was blocked collectively by the opposite bank sandbar and the sandbar in the separation zone. As a whole, the scale of the sandbars in the main channel was the smallest when the confluence angle was 30°. It is believed according to the analysis on the sandbar scale and the river bank stability that, under the current river channel and water-sediment conditions, the confluence angle of 30°is a relatively optimal angle which can reduce the sediment deposition at the confluence.