基于水槽沉积模拟实验的不同类型辫状河心滩坝发育特征及主控因素分析

Characteristics and key controlling factors of channel bar in different types of braided river based on flume tank experiments

辫状河具有较多的沉积类型和复杂的形成机理,易形成优质储集沙体。为研究不同类型辫状河心滩坝发育特征及其主要控制因素,结合不同地区的辫状河类型,以底形坡度、河道宽度及河岸类型为地质变量,基于水槽沉积模拟实验,设计3种类型辫状河,即开阔型辫状河、限制-开阔型辫状河和限制型辫状河;控制不同水流大小和加沙量,根据水槽沉积模拟实验结果,分析不同类型辫状河心滩坝沉积特征及定量表征参数。结果表明:开阔型辫状河心滩坝长宽比介于3~11,平均为6,以纵向沙坝为主;限制-开阔型辫状河心滩坝长宽比介于2~5,平均为3,以纵向沙坝和侧向沙坝为主;限制型辫状河心滩坝长宽比介于1~3,平均为2,以侧向沙坝和横向沙坝为主。底形坡度、水流强度与河岸类型是影响不同类型辫状河心滩坝沉积差异的主要因素,其中,不同因素引起辫状河心滩坝形态特征及几何规模的差异,可为古辫状河心滩坝沉积的精细表征提供定量参数和理论依据。

Many sedimentary types are formed in braided river,whose formation mechanisms are complicated,and channel bar is often high-quality reservoir sand body in them.In order to investigate the characteristics and key controlling factors of channel bars in different types of braided river,in flume tank experiment open braided river,restricted-open braided river and restricted braided river were designed on the basis of the slope,channel width and bank type of natural braided river in different area.By changing flow and sediment supply,different braided rivers are simulated in flume.The sedimentary characteristics and quantitative parameters of channel bars in different types of braided river were studied on the basis of experiment results.The experimental results show that in the open braided river,the longitudinal bar dominates river,and the ratio of length to width of channel bar is mainly from 3 to 11 with an average value of 6;in the restricted-open braided river,the longitudinal and diagonal bar dominate,and the ratio of length to width is from 2 to 4 with an average value of 3;in the restricted braided river,the diagonal and transverse bar dominate,and ratio of length to width is from 1 to 3 with an average value of 2.The main factors that affect the sedimentary difference of channel bars in different types of braided river are bed slope,flow magnitude,and the river bank type,and they lead to the different morphological characteristics and geometric scale of the channel bars in different types of braided river,which provides theoretical support for quantitative characterization of ancient channel bar sedimentation.