2.1 Study area
The research area of this study is the Zhoutungou watershed (36°42’10” N to 36°47’10” N, 109°09’00” E to 109°13’45” E) (Liu et al. , 2021), a typical small watershed in the hilly and gully region of the Loess Plateau, with an average altitude of 1,235.37 m. The total watershed area is 33.6 km2, of which the valley is 18.7 km2, accounting for 55.57% (Jiang et al. , 1999). The location of the research area is shown in Fig. 1. The climatic characteristics and soil properties of the watershed are available in Liu et al. (2021). The main valley in the watershed runs north to south, with the number of branch valleys gradually increasing from north to south. The main valley and branch valley sections are in ‘U’ shape, with the terrain of each valley comprising hills, slopes, and channels.