A concrete gravity dam of 22m height will be constructed on the Quaternary glaciofluvial accumulation layer. The leakage of the reservoir is resulted in the difference of the water head between the upstream and downstream of the dam. A great deal of leakage could cause the reservoir water stage not up to the designed level and then influence the engineering effect. The osmosis from the leakage could cause the depravation and seepage damage of the dam foundation

and influence the safety of the dam. On the basis of field investigation

numerical stimulation method is used to estimate the seepage of the reservoir and calculate hydraulic gradient of the dam base on the condition that a blanket of 175 m length is designed in the reservoir. Because the seepage volume and the hydraulic gradient are very large

many measures such as inverted filter

etc. are suggested to offer the reference for designing and decision.