入湖三角洲水道结构对流量的随机响应试验研究

Experiments on Stochastic Response Characteristics of Lacustrine Deltaic Channels to Discharge

在温和的外部环境条件下,入湖三角洲的形态演变过程始终表现出一定的随机特性,这给河-湖区域环境监测和水资源管理带来较大的不确定性.本研究在传统确定性的调查方法基础上,通过设置两种不同量级流量条件并分别重复两次的物理模型试验,进行了入湖三角洲水道结构对流量的确定性和非确定性响应规律研究.对准周期相似的三角洲水道的几何特征进行定性观察及其波动变化进行定量统计,一方面,确定性地揭示出随流量的变化,主流水道长度指标与它的正相关性,和三角洲中游各阶汊道分汊位置指标的波动特征、高阶汊道各项几何特征指标的平均波动周期的与它的非正相关性;另一方面,非确定性地分别揭示出低流量条件下三角洲上游分汊位置指标和汊道长度指标的平均波动周期与其均值的正相关性和负相关性.本研究提升了对三角洲水道分汊不确定性规律的认识,并为三角洲形态发展的随机模拟研究奠定了基础.

The development of river-delta systems exhibits some stochastic characteristics even under slow-varying external conditions,which pose considerable uncertainties for environmental monitoring and resource management on deltas.Instead of using traditionally deterministic investigation methods,in this study,we used two sets of repeated physical modeling experiments under two average-constant discharge conditions to explore both deterministic and nondeterministic effects of the upstream river-inflow on channelized configurations of a lacustrine shallow-water delta.The qualitative observations and quantitative statistics of the fluctuations of the geometrical characteristics of the obtained quasi-periodically similar deltaic channels show that,on the one hand,deterministically,along with the change of discharge,the single-main channel length increased positively,and both the fluctuation characteristics of the branching position indicator of different-order branching channels and the average period of all the geometrical indicators of higher-order branching channels in the middle delta underwent nonpositive changes;on the other hand,non-deterministically,results highlighted the positive and negative correlations between average period and average value,on the indicators of the branching position and the branching channel length respectively in the upper delta under low-discharge conditions.This study improves our understanding of bifurcation instability and makes the foundation for stochastic modeling of lacustrine-delta morphology.