低含沙条件下黄河下游花园口河段床面形态研究

Study on the Characteristics of Bed Form in Huayuankou Reach of the Lower Yellow River Under the Condition of Low Sediment Concentration

采用多波束测深系统对低含沙条件下黄河下游花园口河段床面形态进行观测,分析床面形态特征及变化规律。2016—2018年6—8月在花园口河段主槽范围内观测得到不同流量条件下长度为2.4~3.7 km、宽度为65~120 m的三维床面地形数据。经分析,低含沙条件下花园口河段床面表现为波长差异较大的两级沙垄叠加而成的复合沙垄形态。一级沙垄波长均值范围为388~955 m,波高均值范围为1.47~3.03 m,迎水面波长占比均值范围为0.43~0.68,背水面倾角均值范围为0.26°~0.77°;二级沙垄波长均值范围为4.71~9.18 m,波高均值范围为0.24~0.55 m,迎水面波长占比均值范围为0.51~0.57,背水面倾角均值范围为7.51°~14.59°。一级沙垄和二级沙垄几何特征值之间的关系相似,波高与波长呈正相关关系,迎水面波长占比与波长没有明显的趋势性关系,背水面倾角与波长呈负相关关系,但对于一级沙垄,波长大于500 m时背水面倾角与波长不再有趋势性关系。在观测流量范围内一级沙垄波长、波高、迎水面波长占比、背水面倾角都随流量增大先增大后减小,拐点出现在流量为1500 m^(3)/s时;二级沙垄波长、波高、背水面倾角都随流量增大而增大,流量超过1500 m^(3)/s时不再有趋势性变化。

Multi⁃beam sounding system was used to observe the bed surface morphology of Huayuankou section in the Lower Yellow River un⁃der low sand content,and the morphological characteristics and change regularity of the bed surface were analyzed.The main channel of the Huayuankou reach was chosen for survey from June to August in 2016-2018,the bed form data of the channels with the length of 2.4-3.7 km and the width of 65-120 m under different flow conditions were collected.The results show that under the condition of low sediment concen⁃tration,the bed form of the river reach of Huayuankou of the Lower Yellow River is featured compound dunes formed by the superposition of first⁃order and secondary dunes.The average wavelengths of the first⁃order dunes are 388-955 m,the average wave heights are 1.47-3.03 m,the average non⁃dimensional lengths of the upstream face are 0.43-0.68 and the average lee slope angles are 0.26°-0.77°.The av⁃erage wavelengths of secondary dunes are 4.71-9.18 m,the average wave heights are 0.24-0.55 m,the average non⁃dimensional lengths of the upstream face are 0.51-0.57 and the average lee slope angles are 7.51°-14.59°.The relationships between the geometrical properties val⁃ues of the first⁃order and secondary dunes are similar.The wave heights are positively correlated with wavelength.There is no obvious rela⁃tionship between the non⁃dimensional lengths of the upstream face and the wavelength.There is a negative correlation between the lee slope angles and the wavelengths.The wavelength,wave height,non⁃dimensional lengths of the upstream face and lee slope angles of the first⁃order dunes increase first and then decrease with the increase of the flow discharge,and the discharge of the critical point is about 1500 m^(3)/s.The wavelength,wave height and back water surface inclination of the secondary sand ridge are all increased with the increase of the flow rate,and there is no trend to change after the flow rate exceeding 1500 m^(3)/s.