The Role of Plant cover (Forest) in decreasing runoff in North of Iran (Polrud basin)

Plant cover in every zones, especially in mountainous area decrease the rate of surface runoff and caused to reduce soil erosion as well as infiltration and considerably decreased flood water destruction. This study evaluated the role of plant cover on reducing Max discharge in Khorasan Poshteh (Polrud basin) which situated in north of Iran , of one small forestry basin in an area about 2.535 km².After evaluation physiological, geological , pedological and plant covers parameters, from totally 150 precipitation data and discharge collected in the study area , 41 precipitation which has suitable intensity and duration selected and used in linear regression, relation between rain intensity and special discharge with correlation coefficient being about 0.85. Analyzed information showed that in forestry basin concerning with 70 percent plant cover has highly effect on reducing Max discharge, runoff which derived from precipitation in a forestry unit calculated 45.2 percent and study showed that the highest factor on increasing the rate of discharge could be slope in the forestry area.