“…The shoulder line, also termed as gully-edge line (Hessel, 2002;Wu et al, 2008) or gully borderline (Daba, Rieger, & Strauss, 2003), is an apparent boundary of the U-shaped gully with a clear break in the slope angle (Hessel, 2002;Li, Zhang, Zhu, He, & Yao, 2015), which divides smooth interfluves and precipitous gully-slope lands (Song et al, 2013). As a terrain feature to characterize soil erosion and the morphological variation of landforms (Lu, Qian, & Chen, 1998;Tang, Xiao, Jia, & Yang, 2007;Yan, Tang, Li, & Zhang, 2014), the shoulder line is a natural boundary between land type and land use , as well as an adjacent boundary for positive and negative terrain, upland and gully land, slope erosion, and gully erosion (Song et al, 2013;Xiong, Tang, Yan, Zhu, & Sun, 2014;Zhou et al, 2010). The shoulder line is always located in the most active part of a gully, and its dynamics reflect the extension of gully length and the expansion of the gully area (Chen & Feng, 1992).…”