Abstract: The riverbed evolution characteristics  and sediment transport in the diversion area of  underground hydropower station have great effects on the water-intake and power generation. According to terrain data of the diversion area of the underground power station measured three times from April, 2006 to August, 2011 in the initial impoundment of Three Gorges Project, in association with model test results, the authors investigated the sedimentation and scour in the diversion area, as well as the desilting effect when the desilting outlets were opened. It's believed that since the diversion area was influenced by boundary conditions and flow characteristics, the deposition on the riverbed was accumulated. What's more, the desilting outlets of the underground powerhouse mainly functioned as keeping the water in front of the station clean by producing a scoured funnel, but did little good for the desilting in the whole diversion area. In view of this, further model tests on the sand-flushing effect of the desilting outlets should be carried out. The desilting measures should be refined to guarantee the water diversion safety of the underground hydropower station.

Key words: Three Gorges Project, underground power station, sedimentation and scour, sand-flushing effect