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The Main Fuctions of Three Gorges Project
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The installation of ship locks is intended to increase river shipping from 10 million to 100 million tonnes annually, with transportation costs cut by 30 to 37%. Shipping will become safer, since the gorges are notoriously dangerous to navigate. Each of the two ship locks is made up of 5 stages taking around 4 hours in total to complete and have a capacity of 10,000 tons. Critics argue, however, that heavy siltation will clog ports such as Chongqing within a few years based on the evidence from other dam projects.
The locks are designed to be 280 m long, 35 m wide and 5 m deep (918 x 114 x 16.4 ft).That is 30 m longer than those on the St Lawrence Seaway, but half as deep. Before the dam was constructed, the maximum freight capacity of the river at the Three Gorges site was 18.0 million tonnes per year. From year 2004 to 2007, there were total of 198 million tonnes of freight passed through the Three Gorges Dam ship locks. The freight capacity of the river increased 6 times and the cost of shipping reduced by 25%, comparing to the previous years. The total capacity of the ship locks is expected to reach 100 million tonnes.
In addition to the canal locks, the Three Gorges Dam will be equipped with a ship lift, a kind of elevator for vessels. The ship lift is designed to be capable of lifting ships of up to 3,000 tons. In the original plan its capacity was to be 10,000 tons. The ship lift was not yet complete when the rest of the project was officially opened on May 20, 2006.Construction of the ship lift started in October 2007 and is anticipated to be completed in the year 2014.
Flood Control & Drought Relief
The most significant function of the dam is to control flooding, which is a major problem of a seasonal river like the Yangtze. Millions of people live downstream of the dam, and many large and important cities like Wuhan, Nanjing and Shanghai lie next to the river. Plenty of farm land and the most important industrial area of China are built beside the river.
The reservoir's flood storage capacity is 22 km3(18 million acre feet). This capacity will reduce the frequency of major downstream flooding from once every 10 years to once every 100 years. With the dam, it is expected that major floods can be controlled. If a "super" flood comes, the dam is expected to minimize its effect.
In 1954 the river flooded 47.75 million acres (193,000 km2) of land, killing 33,169 people and forcing 18,884,000 people to move. The flood covered Wuhan, a city with 8 million people, for over three months, and the Jingguang Railway was out of service for more than 100 days.In the event of a recurrence of the 1954 flood that carried 50 billion m3 of water, the Three Gorges Dam could only divert the water above Chenglingji, leaving 30 to 40 billion m3 of flood water to be diverted.Also the dam will not protect the large tributaries such as the Xiangjiang, Zishui, Yuanshui, Lishui, Hanjiang, and Ganjiang from flooding,due to the location of the dam.
In 1998 a flood in the same area caused billions of dollars in damage. The Chinese government asked for support from its military to fight the flooding. Two thousand and thirty-nine square kilometers of farm land was flooded. The flood affected more than 2.3 million people, and 1,526 were killed.
Reduction of Air Pollutant & Greenhouse Gas Emission
According to The National Development and Reform Commission of China, it takes 366 grams of coal to generate 1 kWh of electricity in China(2006).Therefore, the Three Gorges Dam will potentially reduce the coal consumption by 31 million tonnes per year, cutting the emission of 100 million tonnes of greenhouse gas,millions of tonnes of dust, 1 million tonnes of sulfur dioxide, 370 thousand tonnes of nitric oxide, 10 thousand tonnes of carbon monoxide and a significant amount of mercury into the atmosphere.The elimination of the fossil fuel also reduces the energy consumption in mining, washing and transporting about 31 million tonnes of coal from northern China to the load centre in south and east China.
Since the dam started generating power on July 10, 2003, total power production is equivalent to 84 million tonnes of standard coal and reduces carbon dioxide emission by 190 million tonnes, sulfur dioxide by 2.29 million tonnes and nitroxides by 980,000 tonnes.
