In order to study runoff movement process and its hydraulic characteristics on composite slopes

runoff velocity was measured for 7 runoff rates (10

15

20

25

30

35 and 40 L/(min·m)) and 25 combinations (5 uniform linear slopes

10 concave slopes

and 10 convex slopes) of slope gradients (5o

10o

15o

20o and 25o) by a series of simulated soil flume experiments in laboratory

and corresponding runoff depth

Reynolds number

and Froude number were calculated as well. Total experimental treatments were 175. Results indicated that runoff velocity on uniform linear slope increased with flow path and progressively tended to be steady

and it increased with the slope gradient or runoff rate. Runoff velocity on the downslope segment of convex slope was greater than that on the upslope segment

while the runoff velocity on the downslope of concave slope was smaller than that on the upslope segment. Runoff depth on uniform linear slope decreased with flow path and tended to be steady

and it increased with the runoff rate or decreased with slope gradient. Runoff depth on the downslope segment of convex slope was smaller than that on the upslope segment

but an opposite tendency existed for concave slope. The Reynolds number (Re) of runoff was a constant value along with flow path

and it increased significantly with the increase of runoff rate but was less affected by slope gradient and the combination of slope gradients. The Froude number (Fr) of runoff increased with flow path

and it increased significantly with the increase of slope gradient or runoff rate. Under experimental conditions

Re value was ranged between 200～800

and Fr value was smaller than 2.5. Runoff belonged to laminar flow when runoff rate was smaller than 25 L/(min·m)

otherwise it was turbulent flow. The runoff on upslope segment of convex slope was subcritical flow while that on its downslope segment was torrent flow

and the runoff on concave slope usually belonged to torrent flow status in most cases.