Effects of Cynodon dactylon grassland with 90% coverage on reducing single rainfall runoff.

We studied the effects of Cynodon dactylon grassland with 90% coverage on the generation process of surface runoff on bare land at each rainfall event and the reduction of total runoff by means of simulated rainfall experiment. The results showed that C. dactylon grassland had a remarkable effect in extending the initial runoff time, with the minimum 4′2″, the maximum 29′8″, and the average of 11′42″. The grassland had a remarkable runoff reduction rate of 59.04% of the total runoff on the bare land, with an average of 47.76%. Grassland can well delay the peak runoff time compared with the bare land. Time for runoff generation rate tending to be stable on grassland and bare land was also shortened with the slope degree and rainfall intensity increasing, and the stable rate of runoff generation was also increased. The difference in stable rate of runoff generation between grassland and bare land was smaller as the slope degree increased, and the capacity of grassland to reduce total runoff tended to decline. Rainfall intensity and slope gradient were negatively correlated with reduction rate,following the equation of E=I－0.23(1－sin θ)0.58×e4.93×100%, with statistical significance on both sides.