基于多波束地形测量的上荆江典型河段沙波形态特征分析

沙波形态影响水流结构、泥沙输移及动床阻力。本研究采用多波束测深系统首次精细测量了上荆江典型河段的床面地形,采用改进后的沙波形态量化算法统计了各类沙波形态参数,分析了不同水流强度下沙波形态的变化特征。计算结果表明:(1)测量河段小型与大型沙波的平均波高分别为0.16～0.81和0.96～2.31 m,波长分别为13～27和16～41m;沙波尺度相较于水深较小,小型与大型沙波的波高分别不超过水深的0.045和0.150倍;(2)沙波背流面坡度基本不超过14°,小于泥沙水下休止角,其与陡度之间的关系可以用线性方程描述;(3)中洪水流量对沙波形态尺度的塑造作用强于枯水流量,且对浅水区大型沙波形态尺度的塑造作用强于深水区。本研究量化了天然河流的沙波形态,较好地反映了沙波形态特征,能为大型冲积河流沙波形态的量化及特征参数的统计分析提供参考。

Analysis of sand wave geometry in a typical sub-reach of the Upper Jingjiang Reach using multi-beam topographic survey

Sand wave geometry affects flow structure, sediment transport and movable bed roughness. In this study, a multi-beam sounding system was used to measure the detailed topography of a typical sub-reach in the Upper Jingjiang Reach for the first time. An existing quantization algorithm of sand wave geometry was improved to calculate and determine various geometric parameters of sand wave, and variation characteristics of sand wave geometry were analyzed under different flow intensities. The results indicated that: (i) the average heights of small and large sand waves in the study reach were 0.16-0.81 m and 0.96-2.31 m, respectively, while the corresponding wavelengths were 13-27 m and 16-41 m. The scale of sand wave was small, as compared with the magnitude of water depth, and the heights of small and large sand waves were less than 0.045 and 0.150 times of water depth respectively; (ii) the angle of leeside slope was basically less than 14° and less than the submerged repose angle of sediment. The relationship between leeside slope and steepness was well described by the linear equation; (iii) medium-to-flood flows had a stronger shaping effect on geometric scale of sand wave than low flows, and had a stronger shaping effect on large sand waves in shallow water depths than in deep water depths. This study quantified the sand wave geometry in natural rivers, and also demonstrated the geometric characteristics of sand wave. It provides a perspective for the quantification, statistics and analysis of sand wave geometric parameters in large alluvial rivers.