Runoff generation characteristics on three time scales for typical stands in Jinyun Mountain,Chongqing City

To provide a basis for urban afforestation of water conservation in the Three Gorges Reservoir Area,based on the observation data of rainfall and runoff process during 2002-2005,the authors studied the runoff generation characteristics of the four typical forests on three time scales in Jinyun Mountain,Chongqing City.The results show that,1) Rainfall process distributed evenly during 2002-2005.Relative change rate of annual rainfall was 4.46% and variation coefficient was(0.061 8.) Average monthly rainfall agreed with the normal distribution.2) Both precipitation and runoff periods were obviously divided into dry season and wet season.Dry season was from October to the next March and wet season was during April to September.Most runoff volume of four forests came from the wet season.Among them,surface runoff accounted for over 85% and underground flow over 75%.3) The peak values of surface runoff and underground runoff occurred in June.The relation between monthly rainfall and surface runoff or underground runoff was performed by the unary quadratic equation.The order of annual surface runoff was given as follows: bamboo forest shrub forest mixed forest broadleaved forest.The annual underground runoff was broadleaved forest mixed forest bamboo forest shrub forest.4) Under the same rainstorm events,the order of the surface runoff coefficient was broadleaved forest mixed forest shrub forest bamboo forest,and the underground runoff coefficient was broadleaved forest mixed forest bamboo forest shrub forest.The relation between rainstorms and surface runoff or underground runoff was performed well by linear relationship.5) Both mixed forest and broadleaved forest had the better effects on flood regulation on time scales of year,month and rainstorms.The function of bamboo forest was the worst on three time scales.