5.3　Calculation of Water Inflow in Underground Mine

5.3.1　For underground mining，minimum underground water inflow during exploitation phase shall be calculated.For the mine with water drainage by phases，underground water inflow of different drainage phases shall also be calculated.During mine exploitation，when rock masses stagger to the earth surface，normal and maximum rainfall runoff infiltration volumes in subsidence area shall be calculated.

5.3.2　During estimation of rainfall runoff infiltration volume in subsidence area，the infiltration coefficient shall be the measured data of the local mine site or those of other mines with similar conditions.In case the above-mentioned data is not available，the data may be selected subject to Appendix C in terms of predicted rock mass damage conditions and features.

5.3.3　Rainfall runoff infiltration volume in the subsidence area shall be estimated in terms of the designed frequency storm volume of 24 hours.The storm frequency in the design shall be 5% for superlarge and large mine，10% for medium-scale mine and 20% for small-scale mine.For the underground mine shifted from open pit，the rainfall infiltration volume in the subsidence area may be estimated according to this clause.