Abstarct: Sedimentation due to the reduction of the reservoir active capacity, instability of dam and economic losses is one of the issues that has always been investigated by researchers and engineers. In addition, seepage in earth dam is an essential and important issue regarding the high hydraulic gradient, porosity of the body of the dam foundation and also economic issues. In order to prevent water seepage from earth dam foundation, the dam is sealed which although it reduces a large amount of foundation seepage, it imposes significant costs which sometimes does not seem economical. In the sedimentation phenomenon, the sediments deposited in the reservoir gradually accumulate on each other and while increasing the density of the previous sediments, they affect the thickness of the sedimentation and decrease the permeability of the reservoir floor so that it can be expected that the permeability of the reservoir floor will be very limited practically after a few years, which means no other foundation sealant systems will have a role in reducing the water seepage from the dam. In this research, modeling was done by seep/w for the Bidvaz earth dam and analysis was performed for four cases: presence of a cutoff wall with sediment, a cutoff wall without sediment, sediment without a cutoff wall and short cutoff with sediment Then they were compared with each other. Furthermore, considering the results obtained from the software, the costs of building a cutoff wall and the amount of water seepage from the dam foundation, assuming the loss of all water leaked from the foundation in the state of without a cutoff wall with sediment, water rate of 1200 tomans per cubic meter and the comparison of costs with each other it was determined that a lot of money is saved by removing the cutoff wall.