分汊河道主支汊交替主导因子的转换模拟

进口水流条件及河道周界特征的改变是促使分汊河道主支汊交替的两大主要因素，不同类型的汊道对两者敏感性存在差异，辨析不同汊道主支汊交替的主导因素是预测汊道演变的前提。以长江中游分汊河道为参考，通过调整进口水流动力轴线走向及两汊的长度比设置了30种概化方案，采用平面二维水沙数学模型探讨上述两种因素对主支汊交替的影响。结论表明：两汊长度比存在一个临界值，当汊长比低于此临界值时，进口主流动力轴线的偏移是影响主、支汊交替的主要动力因素；超过此临界值后，进口水流条件变化对汊道分流格局的影响将会明显减弱，影响主支汊交替的主导因子将转换为汊道间的阻力对比关系；通过概化计算得到此临界值约为1.5。

Simulation of dominant factors transforming on major-minor branches alternation in anabanched rivers

Variations of inlet water flow and riverbed boundary conditions are the dominant factors that precipitate alternating major-minor branches in anabranched rivers,which have different sensitivities to different subtypes. Distinguishing the main factors affecting the alternating major-minor branches of different anabranched reaches is needed to determine/understand the fluvial evolution. Taking the anabranched reaches in the middle of the Yangtze River as reference,30 generalized schemes are established for the inlet water flow and riverbed perimeter variations. A depth-integrated two-dimensional mathematical model is adopted to explore the effects of the aforementioned factors on major-minor branch alternation. By numerical simulation,a critical branch length ratio of 1.5 is obtained. Hydrodynamic axis shifting is the dominant factor affecting major-minor branches alternation when the branch length ratio is less than 1.5;otherwise,the dominant factor will become the resistance difference between branches,and effects of inlet hydrodynamic conditions on the diversion patterns will weaken significantly.