Abstract: The geological structure in the middle reaches of Bailong River in Gansu and Sichuan Province,China is composed of a series of east-west folds and faults,and the formation lithology is exposed from Silurian to Quaternary.The soft rocks and hard rocks are interlayer or interbedded superimostion,and the dry valleys have obvious climatic characteristics,which is the most active geological unit of landslides.Soil and water erosion in this area has reached extremely serious viscous debris flow property,and the spatial distribution is related to geological,geomorphic,climatic and human activity factors,showing vertical zonal differentiation characteristics.Most debris flow channels are formed gully with small drainage area and “scoop” shape.The geomorphologic process is orderly in space,forming a process of precipitation convergence—water and soil mixed-transport and soil erosion.Taking the small watershed of Ganjiagou as an example,using the orderly characteristics of spatial structure,the combination of arbor and shrubs is adopted in the precipitation gathering area to create 1 300 hm2 of soil and water conservation forest and grass,which effectively intercepts precipitation.In the unfavorable geological action areas such as landslide collapse,16 km of drainage ditch is arranged to take the surface water out of the landslide area; sloping farmland builds 580 hm2 of horizontal terraces to reduce runoff on the slope.Erosion gully layout of 25 masonry stone lanes,interception of sand and stones,the stability of the gully bed,fixed slope.Thirteen sand barriers were built in the transport area to raise the erosion standard in sections,reduce the gully bed ratio and destroy the groove boundary conditions.The dam body drainage and water sand separation were used to make the channel gradually silt,disperse fluid along the capacity.Drainage ditches will be set up in the accumulation areas to set aside super-standard flood channels,protect downstream villages,farmland and important infrastructure,fully configure the prevention and control system of water and soil conservation,and realize the comprehensive control of mountains,rivers,fields and forests.After years of observation and follow-up investigation,no debris flow disaster has occurred in the basin since the treatment was completed in 1998.Practice has proved the comprehensive management mode of small watershed of Ganjiagou use soil and water conservation ecological measures to change the mountain micro-geomorphology structure,artificially intervenes to transform the channel boundary conditions,and combines the treatment of gully and slope,unblocking and blocking,and highlighting the ecological,Which is the effective way of administer landslide and debris flow disasters under currently local economic and technological conditions,and provides an effective reference for establishing comprehensive management models in similar areas.

Key words: dry valley, geographical environment, soil erosion, Bailong River