5.2　Calculation of Water Inflow in Open-pit Mine

5.2.1　Water inflow calculation for open pit shall include underground water inflow and rainfall runoff at the pit.And normal and maximum water inflow shall be calculated.

5.2.2　During calculation of rainfall runoff at the pit，the storm frequency in the design shall be determined by comprehensive analysis according to mine scale，service life，flooding time and damages caused.The designed storm frequency shall be 5% for super-large and large mine，10% for medium-scale mine and 10%-20% for small-scale mine.

5.2.3　Surface runoff coefficient shall be the data measured at mine area.When the data is not measured，the coefficient shall be selected in terms of Appendix B.