粘性泥石流入汇区河床堆积动力学研究的问题与展望

粘性泥石流入汇主河极大地改变了入汇区的河床堆积地貌,其动力学实质是非牛顿流体与牛顿流体的交互作用,合理描述粘性泥石流入汇区河床堆积动力过程对于划定粘性泥石流风险区范围和认知流域地貌演化具有重大意义。粘性泥石流入汇区河床堆积体时空演化过程有别于粘性泥石流在地表的纯堆积过程,通过回顾国内外学者在泥石流入汇区堆积动力学方面的研究成果,可以发现在粘性泥石流入汇区内堆积现象复杂,存在"阵性"输移、"元堆积"和龙头"水滑"等特殊现象。但目前的研究对泥石流和水流交互机制都进行了简化,一是将粘性泥石流视为挟沙水流,直接采用异重流方法;二是将粘性泥石流视为"半固态",只考虑水流的输沙特征,研究认为基于这样的简化不足以描述粘性泥石流入汇的物理过程和特殊现象,也低估了粘性泥石流交汇区冲击速度和堆积范围。同时,根据粘性泥石流入汇区河床堆积动力过程的研究现状,结合粘性泥石流入汇的特殊运动过程,提出未来可开展的工作:一是粘性泥石流入汇的物理过程和其交互机制的合理简化;二是普适性高的粘性泥石流-水流堆积动力学模型的建立。 

Fundamental problems and prospects in the study of deposition dynamics of viscous debris flow in the gully-river junction

Viscous debris-flow deposits in the junction with mainstream channel may greatly change the morphology, and the dynamics relies on the interaction between the Newtonian fluid and non-Newtonian fluid. The deposition under water differs much from that on the surface, and properly describing the subaqueous process is significant for zoning the danger area and understanding the river evolution. This review provides a comprehensive survey of studies on subaqueous deposition of debris flows and puts forward some questions for the future. We found several new phenomena during the deposition under water, such as the intermittent transport, the "unitary" deposit due to separate surges, and the "water slip" of the surge front, which have been long ignored in previous studies. The existing studies are all based on oversimplification of the water-flow interaction, which considers debris flow as sediment-load flow and adopts the method of density flow, or treats debris flow as a semi-solid state and takes into account only the sediment transport by water flow. Such paradigms do not match the complexity of the real processes and usually underestimate the deposition scale. Then we suggest that further studies, based on the special phenomena, should be emphasized on 1) finding a new framework of the water-flow interaction in the junction, and 2) establishing a new model for debris-flow deposition under water.