Background As an important ecological security barrier area in the upper reaches of Yangtze River, the gully in Liangshan prefecture is widely distributed, which leads to a serious soil loss and the continuous increase of river sediment. The development of gully is a complex process under the interaction of multiple factors such as topography, geology, soil, and human activities. The Mibume small watershed was selected as the study area due to its severe gully development, critical topography and land use. The study aims to investigate the spatial distribution of gully and its key impact factors in this typical mountainous watershed.

Methods Based on GF-2 image, remote sensing visual interpretation was selected for extracting basic information of gully. Then field survey, GIS statistics and analysis were combined to integrate gully information and study its spatial distribution. Geographical detector was selected to compute the key factors of gully distribution and its influencing effects.

Results 1) The gullies in this study area had a large number and a wide distribution. They were mainly concentrated in the southeast (upstream) area of this small watershed with a gradually decreasing trend towards the northwest (midstream and downstream). The highest density of gullies in this small watershed reached 6.53 km/km². The area of gullies above moderate erosion intensity reached 103.38 km², accounting for 58.12% of the total area of this watershed. 2) Sorted by level of impact, the key factors influencing the spatial distribution of gullies were stratigraphic lithology, elevation, soil type and land use. The gullies were concentrated in the area with elevation of 3 020-3 150 m, stratigraphy of Xiaoba Group or Wutoushan Group, soil type of subalpine scrub meadow soil, and land use of bare land or abandoned farmland in the sub-basin.

Conclusions The special impact factors(stratigraphic lithology, elevation, soil type and land use) of this small watershed led to a wide distribution and a large number of gullies, which were concentrated in higher altitude areas. The research results of this paper can promote the layout of soil erosion projects and the application of soil conservation measures in Daliangshan, besides it is also beneficial to the construction of local ecological civilization and the development of agricultural production.