The characteristics of erosion and deposition of viscous debris flow gully bed are different from that of water flow or landslide. Gully bed of viscous debris flow exists with special mechanism

i.e.

scouring and silting of gully bed is mainly controlled by debris flow characteristics

flow type and scale among a year or once. Gully bed change during intermittent flow is mainly embodied by variety of depth of residual layer. Field observing debris flow at Jiangjia gully in Dongchuan City of Yunnan province and located observing of scouring and silting of gully bed were made. Gully bed evolution of observed section before and after intermittent flow passing through is measured by supersonic debris flow depth meter. According to field observed data

the relationship is analyzed among depth of viscous debris flow

velocity

drag force and scouring and silting of gully bed; as the debris flow depth is less than 2.0 m

velocity is less than 8.0 m/s

and discharge is less than 1 500 m3/s. We can find that scouring and silting of gully bed doesn′t have obvious nonlinear relationship with above-mentioned three conditions and scale of scouring and silting of gully bed isn′t large

about between -0.8m and 1.0 m. According to the analysis

we attain the expression of gully bed′s maximum scouring depth of viscous debris flow. The equation has good physical meaning and it is correspondent to data in field.