基于主控因素分析的河控三角洲形态定量表征

Quantitative characterization of river-dominated deltaic morphology based on analysis of dominant controlling factors

针对不同因素控制下河控三角洲形态对其生长过程的响应缺乏系统的定量研究。基于分形几何和控制变量的思路,利用构型尺度沉积正演数值模拟方法,确定河控三角洲主体和河坝复合体朵叶的形态类型和特征,明确沉积物供给速率、沉积物组分和盆地水深对形态的控制作用,建立形态特征值与生长过程主控因素之间的定量表征模型。结果表明,三角洲主体和河坝复合体朵叶的形态可以由初始河口主分流河道间夹角、节点间距、单一河口或节点处河坝复合体数量、主分流河道数量和主分流河道比例进行表征。随着河流流量增大且沉积物浓度较小时,三角洲主体由分支间湾型向河网砂坝型转化;随着沉积物流量增加或沉积物粒度减小,三角洲主体向分支间湾型转化且收敛性减弱,河坝复合体朵叶由多水道复合指状朵叶向少水道复合指状朵叶转化;随着盆地水深增加,三角洲主体趋于单一的主分流河道椭圆状河坝复合体朵叶。

Dominated by different controlling factors,the response of river-dominated deltaic morphology to its growth pro⁃cesses is short of systematic quantitative study.On the basis of fractal geometry and variable controlling,we utilized sedi⁃mentary forward numerical modeling at an architecture scale to extract morphological types and features of river-dominated deltaic main bodies and channel-mouth bar complex lobes(CMCLs)and verify the controlling effects of sediment supply rates,sediment compositions,and basin bathymetry on morphology.Also,we established a quantitative characterization model relating the values of morphological features to dominant controlling factors of growth processes.The results indicate that the morphology of deltaic main bodies and CMCLs can be characterized by included angles between main distributary channels at initial river mouths,joint distance,the number of channel-mouth bar complexes at a river mouth or a joint,and the number and proportion of main distributary channels.In the case of low sediment concentration,deltaic main bodies are transformed from branching deltas with inter-distributary bays to sand-bar deltas with distributary networks when the river discharge rises.With the increase in the sediment discharge and the decrease in the sediment grain size,deltaic main bod⁃ies turn into branching deltas with inter-distributary bays and have weakened convergence,and CMCLs are transformed from complex finger lobes with multiple channels to complex finger lobes with few channels.Deltaic main bodies tend to be oval CMCLs with main distributary channels when the basin bathymetry increase.