Sanduoping Three Gorges Dam Project TGP Construction Site

Dam site
The dam site is at Sanduoping,Yichang City, Hubei province. The total catchment area is about 1,000,000 square meters and there is 451,000,000,000 cubic meters of average annual runoff.
At the location of the Sandouping dam site, the river valley is relatively open and broad, with a small islet known as Zhoubaodao in the river, which is favorable for a river diversion scheme with phased construction. As regards communications, there is a railway to Yichang and a waterway to the dam site. A 26 km-long expressway has also been constructed from Yichang to the dam site. The bedrock at the dam site is sound, intact granite with a compressive strength of 100 developed. The rock mass has only very slight permeability.

Project layout
The main elements of the project are the dam, two power plants, and the navigation facilities.
The spillway dam section is in the center of the river channel, that is, on the original main river course, while the intake and non-overflow sections are arranged on each side. The powerhouses are to be located at the toe of the intake section. The navigation structures are on the left bank.

Dam
The dam is of the concrete gravity type. The total length of the dam axis is 2309.47m, with the crest elevation at 185 m, and a maximum height of 181 m.
The spillway section is 483m long, with 23 bottom outlets and 22 surface sluice gates. With a maximum discharge capacity of 102,500 cubic meters, the project is designed to discharge the probable maximum flood PMF.

Powerhouses
The two powerhouses will be at the toe of the dam. Fourteen sets of generating units will be installed in the left bank powerhouse, and 12 units in the right one. The turbines will be of the Francis type each with a rated capacity of 700 MW.
There will be 15 transmission lines, with 500 kV AC lines to Central China and Chongqing and ± 500kV DC lines to East China.
The permanent navigation structures consist of the permanent ship lock and a ship lift. The design capacity for annual one-way navigation is 50,000,000 t.
The ship lock is designed as a two-way, five-step flight of locks; each lock chamber is 280*34*5m.capable of accommodating a 10,000 t barge fleet.
The ship lift is designed as a single-stage vertical hoisting system with a ship container sized at120*18*3.5m.capable of carrying one 3000 t passenger or cargo boat each time.

Scheduling of the dam
The total construction period will be 17 years, with the three stages being as follows:
Preparation and first stage 5 years (1993 to 1997)
Second stage (construction) 6 years (1998 to 2003)
Third stage (construction) 6 years (2003 to 2009)
River diversion is being phased, and the construction schedule is divided into the three stages.
In the first stage, the part of the river on the right side of the islet has been enclosed. Advantage was taken of the islet to build an earth- and rockfill cofferdam. In this stage, the open diversion channel was excavated and the longitudinal cofferdam was constructed. Meanwhile, construction of the temporary shiplock was being finished on the left bank. During this construction phase, the river flow and navigation have continued to be through the main river course.
In the second stage, now under way, the transverse cofferdam is being constructed, to form, together with the completed longitudinal cofferdam, the second stage construction pit, where the spillway, the intake dam and the powerplant on the left bank will be built. Simultaneously, the permanent shiplock and the shiplift are being constructed on the left bank. In this stage, the river flow will be diverted through the diversion channel, and the boats will be able to pass either through the open channel or the temporary shiplock.
In the final stage, the third stage cofferdam is to be built in the open channel, and the reservoir impounded up to el.135 m. The left bank power station and permanent shiplock will then be put into operation. In the meantime, the third stage cofferdams, together with the longitudinal cofferdam, will form the third stage construction pit so that the right bank dam and powerplant can be built. During this period, the river flow will be discharged through the outlets in the spillway dam, and the boats will pass through the permanent shiplock.