A series of flume experiments were conducted at the condition of different runoff discharge

slope gradient and slope length. The Purple soil with a clay texture is the typical soil in the upper reaches of the Yangtze river.The flume with the size of 30 cm wide and 10 m long were used.eleven slope lengths including 0.5 m

1 m

2 m

3 m

4 m

5 m

6 m

7 m

8 m

9 m and 10 m were used. The flume were divided into 3 rills and the rill width is 10 cm. Three slope gradients including 5°

15° and 23°and three flow discharges with 5 L/min

15 L/min

25 L/min were used in the experiments. All experiments were repeated three times and there were total 297 test sessions. The results showed that rill erosion was affected by flow hydraulic characteristics

soil properties and slope characteristics

with the increase of flow sediment concentration

the rill erosion rate showed a trend of decrease; The greater the flow rate and slope gradient

the bigger rill flow detachment and the rill erosion rate. Under the condition of 5 l/min of small flow discharge

rill erosion rate restricted by detachment rate and had no strict linear relationship with sediment concentration

but under condition of 15 l/min

25 l/min

rill erosion rate was linear correlation with sediment concentration. At the beginning of the rill

the rill erosion rate is the biggest

with the increases of rill length

the flow energy consumption for sediment transport

so sediment detachment decreased rapidly. The rill erosion rate and the rill length had a exponentially decreasing relationship by correlation analysis

and the correlation coefficient R2 changed between 0.45 to 0.98. By regression analysis

the average purple soil erodibility was 0.005 3 s/m

and the average critical shear stress was 2.92 Pa under experimental condition. The results provide data support for establishment and application of distributed physical model and serve as the further research of slope soil erosion of purple soil.