hills on both sides of the river are fairly flat with a small islet called Zhongbaodao in the river, which is favourable for the river diversion scheme with phased construction. As for outside communications nearby, there exists a railway to Yichang, only 40 km to the dam site, and meanwhile a high standard highway from Yichang to the dam site and a bridge on the Yangtze River at the dam site have been constructed and opened to traffic in 1996. On the early stage of construction, there already exist direct accesses by a low-standard highway and waterway to the dam site. Now, several docks have been constructed. The navigation conditions have surely been improved especially for handling of heavy items of equipment.

The bedrock of the dam site is sound and intact granite with 100 MPa of compressive strength. The faults and fissures in the bedrock are less developed and most of them are well cemented. The permeability of the rock mass is slight in nature. The weathered layers in the hills on both sides are a bit thick, ranging from 20 to 40 m, while few layers exist on the main river channel.

In the vicinity of about 15 km around the dam site, there are no major disadvantageous geologic structures. The regional seismic activities are small in intensity and low in frequency. The whole area of the dam site belongs to a slight seismic area ranking as Degree VI of seismic intensity classified by the state authority department concerned.

2.2 Layout of the Project

The project is composed of the dam, two power plants and navigation facilities' For a long time, efforts were engaged in the in-depth studies and researches on various schemes to determine the structural pattern, configuration and layout of the structures. And it was not until undergoing analysis by scientific researches and tests regarding hydraulics, sedimentation, structure and material, etc., that these issues were finally determined. The overall layout of the project is as the following.