When completed in 1994, the storage of Nanhwa Reservoir is 154 million m3. The reservoir is an important potable water supply source in southern Taiwan. The Southern Water Resources Bureau of Water Resources Agency, Ministry of Economic Affairs is undertaking the development of a sedimentsluice tunnel for Nanhwa Reservoir. The purpose of the project is to reduce rate of siltation in the reservoir and to increase flood discharge capacity in light of climate changes. In an operating reservoir, it is very difficult to construct the intake of a tunnel which is 45 m below the design water level in the right abutment for sediment sluicing during storms. Special features of this project include intake construction (including cofferdam an underwater work), fabrication and installation of high pressure large gates, and excavation of a large scale underground cavern. The project is designed to discharge 1 000 cms at reservoir level EL.180.0 m. It is estimated that an average annual silt sluicing of 72×105 m3 can be achieved, or about 24% of average annual sediment inflow.