怒江干流堰塞坝特征及稳定河床机制

Morphological characteristics and mechanism for riverbed stabilization of the barrier dams in Nujiang River

滇西怒江是青藏高原东缘地形急变带内深切河流的典型代表,因崩塌、滑坡和泥石流等地质灾害在干流形成数百个稳定堰塞坝,有效抑制了河流下切。为探究怒江堰塞坝发育及提升河床稳定性的负反馈机制,通过野外考察和卫星影像,总结了怒江干流沿程和堰塞坝地貌特征,基于地貌水力特性对堰塞坝分类,并量化评估不同类别堰塞坝的稳定性和消能率特征。研究结果表明,怒江干流的堰塞坝分布密度较高,且与单宽水流能量正相关。干流堰塞坝可分为崩塌滑坡(崩滑)堰塞坝与泥石流堰塞坝。崩滑堰塞坝可在特大洪水中保持稳定,泥石流堰塞坝则可在一般性洪水中稳定。两类堰塞坝的消能率接近自然阶梯-深潭结构。崩滑堰塞坝消能率随单宽水流能量增大而提高,而泥石流堰塞坝则因较大的河谷横向空间汛期单宽水流能量增长较慢。干流堰塞坝的稳定性和消能特点均与当地单宽水流能量特点匹配,从而持久高效地消耗水流能量,提升河床整体稳定性。

Nujiang River in western Yunnan Province is a typical example for the incised rivers in the topographic steep zone,at the eastern edge of Qinghai-Tibet Plateau. Hundreds of barrier dams were formed in the mainstream owing to geological hazards such as collapses,landslides and debris flows,which effectively restrain river incision. In order to explore the negative feedback mechanism of the Nujiang River to enhance riverbed stability by barrier dam development,we collected data from the field and satellite images.The geomorphological characteristics of the main stream and barrier dams in the Nujiang River were summarized,based on the classification of the barrier dams. The stability and energy dissipation properties of the barrier dams were evaluated quantitatively by category. The results show that the distribution density of barrier dams is high and positively correlated with unit width stream power. The barrier dams are classified into two categories,barrier dams formed by collapses or landslides,and formed by debris flows. The former type can remain stable during historic exceptional floods while the latter stays stable in ordinary floods.Both types of barrier dam demonstrate similar energy dissipation ratio with natural step-pools. The energy dissipation ratio of the barrier dams by collapses or landslides increases with unit width stream power. In contrast, the unit width stream power increases relatively slowly owing to the larger transverse valley for the other barrier dam type. The barrier dams in the mainstream exhibit the stability and energy dissipation ratio matching the local unit width stream power,and therefore,can dissipate flow energy enduringly and efficiently and increase the overall riverbed stability.