Hydro-dynamic parameters of overland flow during laboratory rainfall experiments under grass coverage

Laboratory rainfall experiments were performed in order to investigate the variation of hydro-dynamic characteristics of overland flow for 2 typical loess soils under artificial grass coverage. Grass coverage was the major factor and soil texture and rainfall intensity were the minor factors in the analysis. The results showed that, for the same grass coverage, runoff rate and flow velocity both increased when rainfall intensity increased, while runoff rate and flow velocity both decreased when cover age increased. Flow velocity increased when rainfall duration was prolonged, while the curve of flow velocity variation over time was totally elevated when rainfall intensity increased. The curve of flow velocity variation over time was totally degraded when cover increased. Average flow depth decreased with increasing flow velocities. When cover age increased at the same rainfall intensity, Froude number increased, Renolds number decreased and both Darcy-Weisbach and Manning friction coefficients increased correspondingly. At the same grass coverage, when rainfall intensity increased, both the Froude and Renolds number increased, with both Darcy-Weisbach and Manning friction coefficients decreasing correspondingly. Therefore, the hydro-dynamic characteristics were improved, the flow velocities decreased and the friction and roughness increased when the grassland coverage increased.