Hydraulic parameters of surface runoff in typical forest sites of Jinyun Mountain, Chongqing City of southwestern China

We selected four land use types, i.e. bare field, mixed broadleaf-conifer forest, evergreen broadleaved forest and bamboo forest, and carried out scouring experiments with five different flows of 0.12, 0.18, 0.24, 0.30, and 0.36L/min to study the eco-hydrological processes of forest vegetation in Jinyun Mountain, Chongqing City of southwestern China. The hydraulic parameters of surface runoff under saturated storage were measured. The results showed that: 1) Darcy-Weisbach coefficient of the four types of forest lands decreased with increasing flow rate, indicating that litters, organic matters and roots on the ground may increase the roughness and surface resistance effectively. As the flow increased, rills were formed after litters and organic matters were flowed away, then the effects of shallow root system against runoff would be enhanced significantly. However, the amount of coefficient of woodland with deep roots gradually approached to that of bare field. 2) The flow velocity of four land use types had a positive correlation with flow rate. Litter and roots could slow down the runoff velocity, especially in bamboo forest while in higher flows. 3) As the amount of flux increased, the Reynolds number increased and runoff characteristics transformed from laminar to turbulent; Froude's number decreased to a minimum value at the amount of flux between 0.18 and 0.30L/min and then increased. Under the same flow amount, the order of Reynolds and Froude's number was bare field > mixed broadleaf-conifer forest > evergreen broadleaved forest > bamboo forest.