But during the shallow coal seam mining,the Quaternary pore water has local direct hydraulic connection,and the focal point of to keep away is gob water and fault conducted water,because of calamities bring about may be .

Especially, the water of old kiln, construct and fall pillar is more dangerous to production of the coal mine.

According to the time between hydrops formed in the goaf and mine field exploit,the goafs are classified into two types:the old mine area before mine field exploit,the normal goaf formed in the period of normal coal recovery in the mine.