基于动力过程的冰湖溃决洪水侵蚀演化特征研究

Study on erosion evolution characteristics of glacial lake break flood based on dynamic process

冰湖溃决洪水具有范围广、持续时间长、危害大并经常伴随有泥石流发生等特点。目前针对冰湖溃决洪水动力演化特征的定量研究相对匮乏。为此,对次仁玛错冰湖溃决洪水灾害演化特征进行研究,以实地调查及多期遥感影像为基础,并采用泥沙输移模型和水动力模型耦合方法揭示冰湖溃决洪水侵蚀演化特征。模型基于精度为12.5 m的数字高程(DEM)地形数据,模拟反演1981年次仁玛错冰湖溃决洪水动力演化过程,与实测结果进行对比,验证模型的适用性和可行性,并对冰湖再次溃决进行预测分析,定量评价冰湖溃决洪水在演进过程中流深、流速、侵蚀和沉积特征。溃决洪水在演进过程中对章藏布支沟冰碛物及下游沟岸松散坡积物进行冲刷侵蚀,高含沙洪水逐渐演化为稀性泥石流,在707滑坡处流深8~10 m,最大流速13.7 m·s^(-1),侵蚀深度8~9 m。稀性泥石流在主沟沉积形成堰塞坝,坝高9~11 m,短暂堵塞波曲河。稀性泥石流对樟木口岸下游滑坡群坡脚进行冲刷侧蚀,侵蚀深度约10~13 m,易引发大规模次生灾害,稀性泥石流到达水电站处,淤埋水电站进水口,导致水电站失效。整体来看,溃决洪水在演进过程中,洪水对上游沟床及沟岸进行强烈的侵蚀夹带,洪峰流量增强,在中游,稀性泥石流对沟岸进行侧蚀,在沟道狭窄处流速增大,下切侵蚀增强,在沟道宽阔处,流速降低,固体物质沉积,整体达到冲淤平衡,洪峰流量随距离逐渐衰减,至下游,沟道地形开阔,流速放缓,稀性泥石流逐渐沉积,同时对沟道两岸进行侧蚀,整体为沉积。模型可以良好地揭示冰湖溃决洪水灾害侵蚀演化动力特征。

Glacial lake outburst floods are characterized by wide range,long duration,high hazard and often ac⁃companied by debris flow.At present,there is a lack of quantitative studies on the dynamic evolution character⁃istic of glacial lake outburst floods.To this end,the evolutionary characteristics of Cirenmaco glacial lake out⁃burst flood disaster are studied based on field survey and multi-period remote sensing images,and the sediment transport model and hydrodynamic model coupling method are used to reveal the evolutionary characteristics of glacial lake outburst flood erosion.The model is based on the digital elevation model(DEM)topographic data with an accuracy of 12.5 m,simulating the inversion of the 1981 Cirenmaco glacial lake outburst flood dynam⁃ics evolution process,comparing with the actual measurement results,verifying the applicability and feasibility of the model,and conducting prediction analysis of the glacial lake outburst again,to quantitatively evaluate the characteristics of flow depth,flow velocity,erosion and deposition of glacial lake outburst flood in the evolution process.The outburst flood scours erosion on the moraine deposit of the Zhangzangbu branch ditch and the loose colluvium of the downstream ditch bank during the evolution,and the high sediment concentration flood gradual⁃ly evolves into turbulent debris flow.At the 707 landslide,the flow depth is 8~10 m,the maximum flow veloci⁃ty is 13.7 m·s^(-1),and the erosion depth is 8~9 m.The turbulent debris flow formed a barrier dam at the main ditch deposition,with a dam height of 9~11 m,which briefly blocked the Boqu River.turbulent debris flow to the downstream landslide group of Zhangmu port for scouring side erosion,erosion depth of about 10~13 m,easy to trigger large-scale secondary disasters,turbulent debris flow reaches the hydropower station,siltation buried hydropower station intake,resulting in the failure of the hydropower station.On the whole,outburst flooding in the evolution process,the flood water to the upstream ditch bed and ditch bank for strong erosion en⁃trainment,flood peak flow enhanced.In the midstream,turbulent debris flow laterally erodes the gully bank,and the flow velocity increases in the narrow part of the gully,and undercut erosion is enhanced.In the wide part of the channel,low velocity decreases,solid materials deposition,overall reach the balance of flushing and siltation,flood peak flow gradually decay with distance,to the downstream,channel topography open,flow velocity slows down,turbulent debris flow gradually deposition,while the lateral erosion on both sides of the chan⁃nel,overall for deposition.The model can well reveal the evolutionary dynamics of glacial lake outburst flood disaster erosion characteristics.