Project Layout and Hydraulic Structures

Dam Site

After repeated study and analysis on 15 dam site alternatives, the dam site of the TGP is finally selected at Sandouping with the crystalline rock as its foundation. The total water catchment layout of the Three Gorges project area hereof is about one million km² with 451 billion m³ of average annual runoff and 530 million tons of annual sediment discharge.

Here at the location of Sandouping dam site, the river valley is relatively open and broad, the mountains on both sides of the river are fairly flat with a small islet called Zhongbaodao in the river, which is favourable for river diversion scheme with phased construction. As for the outside communications nearby, there exists a railway to Yichang, with a distance of 40 km to the dam site and a high standard express from Yichang to the dam site, and a bridge on the Yangtze River has been constructed and was open to traffic in 1996. Besides, there are direct accesses by a standard highway and waterway to the dam site.

The bedrock of the dam site is sound and intact granite with 100 MPa of comprersive strength. The faults and fissures in the bedrock are less developed and most of them are very well cemented. And 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, low in frequency. Therefore, the whole area belongs to a slight seismic area ranking as 6 degree of seismic intensity classified by the state authority department concerned.

Layout of the Project

 The The project is composed of a dam, two power plants and navigation facilities. For a long time, efforts were engaged in the in-depth study and research 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.

The spillway is placed in the center of the river bed, i. e. , on the original main river course, while the intake dam sections and non-overflow dam sections are arranged on its both sides. The power plants are placed on the back of the intake dam, and in addition, an underground power plant on the right bank is to be built in future. The permanent navigation structures are located on the left bank side.

Dam

 The dam is of a concrete gravity type. The total length of the dam axis is 2,309.47m, with the crest elevation at 185 m and a maximum height of 175 m.

The spillway section, which is located in the middle of the river course, is 483 m long in total. In this section, there are 23 bottom outlets and 22 surface sluice gates. The dimensions of the bottom outlets are 7 * 9 m, with the elevation of the inlets at 90 m. The net width of the surface sluice gates is 8 m, with its sill elevation at 158 m. In the downstream part of this section, flip bucket for energy dissipation is provided.

On both sides of this section, there will be arranged the intake - dam and non- overflow dam sections.

The maximum discharge capacity of the Project can reach 116,000 m³/s, which is able to discharge the possible maximum flood.