Dams and Impounded Rivers - River Dynamics and Integrated River Management - page 450

the slope soil saturated with water has in sufficient time to dewater and may slide down to the river.
There are about 1,000 potential landslides in the Three Gorges area, of which 140 landslides and
rockfalls each measure 1 million m 3 or more in size. Along the 1,300 km-long banks there are 22 large
slopes that are unstable or may slide down once the reservoir is filled with water. These slopes vary in
size from several million to 80 million m 3 . However, after 10-20 years of operation, most of the potential
landslides will become stable again. The overall stability conditions of the slopes of the Three Gorges
Reservoir are basically firm.
Studies have indicated that any collapse of slopes that might occur after the Three Gorges Reservoir if
silled, would not clog the Yangtze River nor form a blockage. The total mass of the 22 unstable slopes is
only 380 million m 3 . Even if the entire bulk slides into the reservoir, it will only fill up 2.2 percent of the
reservoir at the 145-m water level.
7.4.3.3 Impact on Local Climate
It was estimated in the planning of the project that any change induced by the reservoir on the climate of
the surrounding areas would be negligible. The average annual wind velocity would increase by 15%-40%
and the relative humidity may rise by 2%-8% in the reservoir. Any impact on the frequency of foggy
days, or volume and distribution of rainfall would be slight. Summer temperature might drop slightly by
0.9 to 1.2 ć on a monthly basis, but in winter the temperature might rise slightly by 0.3 ć to 1.3 ć , with
the minimum temperature up to 3 ć .
In the first three years after the impoundment of the reservoir in 2002 there was no obvious climate
change. In 2006, however, a severe drought, the worst in 100 years, occurred in Chongqing municipality
and Sichuan Province. At least 14 million people and 15 million livestock suffered from a shortage of
drinking water as continuous droughts and searing heat ravaged the area. Some scientists blamed the
Three Gorges Project for the severe drought. The Sichuan and Chongqing Basin is enclosed by mountains
and the main moisture flow path is the Yangtze River valley linking central China and the basin. The Three
Gorges Dam has blocked the moisture inflow. Thus, the precipitation in the basin has been reduced greatly.
Meteorological experts said that there is no relation between the severe drought and the Three Gorges
Project. The global greenhouse effect is the chief reason for droughts, especially in upper latitude regions
of the northern hemisphere. Chongqing Municipality and Sichuan Province, the worst-hit areas, are located
in these regions. According to the experts, the global greenhouse effect had led to rising temperatures,
abnormal climate change and severe drought. The direct reason for the drought is the impact of abnormal
air movements over the Qinghai-Tibet Plateau. Caused by booming human activities, deforestation and
industrial projects in urban areas, the heat island effect around big cities also plays a role in producing
the hot weather and rising temperatures. The heat island effect around Chengdu, capital of the Sichuan
Province, and Chongqing has partly led to a dry summer and a lack of rainfall. According to experts at
meteorological stations in Sichuan and Chongqing, constant typhoons, which landed in coastal areas in
southern and eastern China in the summer in 2006, have prevented the entry of cold air fronts into the
Sichuan Basin. Without cold air, the basin is covered solely by high-pressure currents and has no chance
to produce rainfall.
7.4.3.4 Water Quality
The annual runoff at the dam is over 400 billion m 3 ; and the total wastewater discharged into the reservoir is
about 1 billion tons. Now the water quality of the river, however, remains good, except for pollution belts
along the banks near cities. Generally speaking, after impoundment the pollution in the reservoir worsened
to some extent due to lower flow velocity and higher water level. Therefore, it is necessary to strictly
control the discharge of wastewater from surrounding factories, mines, towns and cities, and to treat