黄土高原丘陵沟壑区浅沟对切沟发生和发育的影响

Influence of ephemeral gullies on the occurrence and development of permanent gullies in the Loess Hilly Gully Region of China

浅沟和切沟是侵蚀沟的重要组成部分,二者之间是否存在较为明显的关联性,成为新时期黄土高原沟道侵蚀治理的关键问题之一。为探究黄土高原切沟沟头上方浅沟对其下方连通的切沟发生、发育的影响,该研究在陕西子洲岔巴沟流域上、中、下游各选1个典型小流域为研究区,基于厘米级无人机航摄和高精度野外实测,系统分析黄土高原丘陵沟壑区浅沟与切沟连通性现状及这一连通性对切沟在极端暴雨情景下新成和之后3 a时间尺度发育的影响。结果表明:1)在极端暴雨情景下,有浅沟的坡面更有利于切沟的发生,3个小流域在陕北2017年“7.26”极端暴雨中共发生43条新成切沟,其中67.44%与浅沟连通。2)切沟沟头上方是否存在浅沟对切沟形态特征具有重要影响,和浅沟连通的切沟长度显著大于和浅沟不连通的切沟,在切沟宽度上这一影响不显著。3)切沟沟头上方浅沟对其下方连通的切沟发育也有显著的影响。在2017年“7.26”暴雨后3 a时间尺度上,相比与浅沟不连通的切沟,与浅沟连通的切沟在后续发展过程更加活跃。有浅沟连通条件下沟头发育的新成切沟和原有切沟的占比分别是无浅沟连通的1.67倍和3.11倍,沟头前进速率分别是其1.80倍和2.17倍。该研究可为黄土高原丘陵沟壑区沟道侵蚀精准治理提供理论依据。

Ephemeral and permanent gullies are vital components of erosion gully system,and the existence of a significant correlation between them has become one of the critical scientific questions in the control of gully erosion on the Loess Plateau in the new era.This study aims to explore the effect of ephemeral gullies above the head of permanent gullies on the occurrence and development of the connected permanent gullies in the Loess Plateau.Three typical small watersheds were selected as the research area located in the upper,middle,and lower reaches of the Chabagou watershed in Zizhou,Shaanxi Province.This study systematically analyzes the current connectivity between ephemeral and permanent gullies in the hilly-gully region of Loess Plateau and the impact of this connectivity on the formation under extreme rainstorm and their further development were explored at a three-year time scale based on unmanned aerial vehicle(UAV)aerial photography and high-precision modern measurement technology.The results showed that:1)The hillslopes with ephemeral gullies were more conducive to newly formed permanent gullies under the'7.26'extreme rainstorm in northern Shaanxi in 2017.A total of 43 newly formed permanent gullies occurred in the three small watersheds during the rainstorm,of which 67.44%were connected with ephemeral gullies.2)The existence of ephemeral gully in the upstream of permanent gully head had an important influence on permanent gullies morphological characteristics.The permanent gullies connected with the ephemeral gullies were significantly longer than that disconnected with the ephemeral gullies,and the width of the permanent gullies was not significantly influenced.3)Upslope ephemeral gullies also significantly affected the development of permanent gullies connected downslope.On the 3 a time scale after the'7.26'rainstorm in 2017,the permanent gullies connected with ephemeral gullies were more active in the subsequent development process than the ones not connected with ephemeral gullies.The proportion of gully head development in permanent gullies for newly formed permanent gully heads connected with ephemeral gullies was 1.67 times that of non-ephemeral gully-connected permanent gullies.and the gully headcut retreat rate was 1.80 times.For the existing permanent gullies,the above rates were 3.11 times and 2.17 times,respectively.This study can provide a theoretical basis for more effective management of gully erosion in the hilly-gully region of Loess Plateau.