Rainfall-runoff Reduction Measures by Land Use Patterns of Xi'an

Based on the model of DRAINMOD for water balance calculation on the impervious surface,then the different patterns of rainfall excess on the pervious and impervious surfaces were analyzed from 1988 to 2007,and finally the viable options for reducing urban runoff and increasing rainfall infiltration through model simulation were discussed.The results showed that the annual runoff coefficients ranged from 0 to 0.414 on the pervious surface and varied from 0.667 to 0.844 on the impervious surface in Xi'an over the 55 year simulation period.The land use,soil infiltration capacity and rainfall intensity were major factors affecting the rainfall-runoff relationship.When the area ratio of permeable to impermeable surface was less than 50%,the runoff coefficient would reach above 0.8.Increasing the depth of the permeability could increase runoff infiltration,and had significant reduction of surface runoff,but it had limited effect on reducing runoff from maximum 24-hour storm.