软岩-半成岩区泥石流物源特征及形成机制——以云南南涧县大箐河泥石流为例

Material source characteristics and formation mechanism of debris flows in soft rock-semi-lithologic areas： A case study of Dajing River debris flow in Nanjian County， Yunnan Province

摘要:

云南南涧县城区是典型软岩和半成岩发育区，县城北西侧泥石流灾害发育。基于野外调查，结合多源多期次遥感解译和地形测绘等结果，总结了软岩-半成岩区泥石流物源特征和活动特征，分析了泥石流的形成机制，结果显示：大箐河沟域内泥石流物源有坡面侵蚀物源、崩滑物源和沟道堆积物源，其中坡面侵蚀物源发育范围广，成为该沟最重要的物源类型；北侧沟谷泥岩发育范围更广，南侧沟谷半成岩更发育，抗风化和抗侵蚀性能不同，使得北侧沟谷物源更发育，南北两条沟谷因软岩-半成岩的岩性组合与强度差异呈现明显物源空间分异性，主沟中游成为最强效物源补给区，呈现点多面广的特征；该沟历史上暴发过7次泥石流灾害，短历时集中降雨是激发泥石流活动的主要因素，大箐河泥石流属典型暴雨沟谷型水力类泥石流灾害，后续在极端降雨条件下暴发泥石流的可能性依然存在，沟口为县城核心区域，泥石流危害和风险依然较突出。

Abstract:

The area of Nanjian County， Yunnan Province， is a typical area of soft rock and semi-lithologic， and debris flow disasters are developed behind the county town. Based on field investigations and combined with multi-source and multi-period remote sensing interpretation and topographic mapping， the material source characteristics and activity characteristics of debris flows in the soft rock-semi-lithologic area were summarized， and the debris flow formation mechanism were analyzed. The results show that there are sources of debris in the Dajing River Basin： slope surface erosion source， collapse and landslide source， and channel accumulation source. Among them， the erosion source on the slope surface is in a wide range and has become the most important source type in this river basin. The mudstone in the northern gully develops over a wider range， while the semi-rock in the southern gully is more developed. The different resistance to weathering and erosion result in more developed material sources in the northern gully. Due to the lithological combination and strength differences of soft rocks and semi-rocks in the north and south gullies， there is a significant spatial differentiation of material sources. The middle reaches of the main gully have become the most effective material source recharge area， characterized by many points and wide distribution. In the historical record， seven debris flow disasters have occurred in this gully， and short-duration concentrated rainfall is the main factor triggering debris flow activities. The Dajing River debris flow is a typical rainstorm gully-type hydraulic debris flow disaster， and the possibility of debris flow occurrence still exists under extreme rainfall conditions. The gully mouth is the core area of the county town， so the hazard and risk of debris flow remain prominent.