岔巴沟流域暴雨山洪水沙特征

Water and Sediment Characteristics of Flashflood Caused by Heavy Rainfall in Chabagou Basin

受极端降雨事件影响,黄土丘陵沟壑区易发生暴雨山洪,造成重大灾害损失。为进一步了解工程与非工程措施导致的下垫面变化下的产流产沙特征,探究暴雨山洪的形成及致灾机理,基于"7·26"暴雨事件,以岔巴沟流域为研究区域,采用现场调查结合实测资料分析的研究手段,分析岔巴沟流域暴雨山洪特征。分析表明,在历时短、强度大、雨量多的极端暴雨事件条件下,岔巴沟流域形成流量较大、输沙量较低的陡涨陡落型山洪。径流量大的原因在于降雨量高、降雨强度大;输沙量较低的原因在于多年的退耕还林、封山禁牧等政策措施及水土保持工程措施。虽然岔巴沟的植被覆盖度较高,下垫面显著改善,但自然恢复的植被相对较少,坡面上仍存在大量坡耕地,在极端降雨事件下,仍会产生携带一定泥沙的山洪。

Affected by the extreme rainfall events,flashfloods often occur in the loess plateau,which may cause significant losses.In order to further understand the features of runoff and sediment yield under the change of underlying surface caused by engineering and non-engineering measures,and explore the formation and disaster-causing mechanism of flashfloods,taking the"7·26"rainfall in Chabagou basin as the research object,the flashflood characteristics are analyzed by means of field investigation and field data analysis.The results show that under the conditions of the extreme rainfall of short-duration,strong-intensity and heavy-quantity,the steeply rising and rapidly falling flashflood with large runoff and low sediment transport is formed in Chabagou basin.The reason for large runoff is heavy-quantity and strongintensity rainfall.The reason for low sediment transport lies in the policy measures such as returning farmland to forest,grazing prohibition and water and soil conservation engineering measures.Although the vegetation coverage of Chabagou is increasing and the underlying surface is significantly improved,the vegetation of natural restoration is relatively small,and there is still a large amount of sloping farmland on the slope.The flashflood that can still carry a certain amount of sediment occurs when there is an extreme rainfall event.