Flood Control: Dams and Reservoirs

Mainly with the construction of dams and reservoirs but also with other forms of infrastructure, the flood control system in China has played an important role in managing flood disasters. As a result, 46.8 million hectares of farm land and 598.5 million people have been protected. The flood control systems on major rivers in China can basically defend the level of the largest floods occurred since the founding of New China in 1949. The accumulated direct economic benefits of flood control between 1949 and 2009 totalled 4 trillion Yuan, and the annual death toll caused by flooding has decreased by 83% from 8900 in the 1950s to 1500 in the early 2000s.

Other than flood control, dams and reservoirs also play a role in electricity generation, and irrigation water supply. Hydropower energy generation in China has increased from 1.2 billion kWh in 1949 to 721 billion kWh in 2010. In 2007, China’s gross installed hydropower capacity and hydropower energy generation reached 145.3 million kW and 486.7 billion kWh, both highest in the world. The share of hydropower energy in total energy supply has remained relatively stable at around 16% since 1990. This share is expected to increase in the future. In 2007, China issued the Medium- and Long-term Plan of Renewable Energy Development, and proposed a gross installed capacity of hydropower of 300 million kW by 2020, which is more than double the size in 2007. Also, China issued the national climate change programme, and planned to enhance the proportion of renewable energy in primary energy supply. Considering the higher energy demand and more emphasis on clean energy, it is inevitable that China will continue its effort to explore hydropower in the near future.

Another benefit of building dams and reservoirs is the ability to farm the huge areas of arable land that had not been usable before by temporally changing distribution of regional water resources to meet the seasonal demands of agricultural production. Dam/reservoir-fed irrigated land increased to account for about one-third of total effective irrigated area in 2009, indicating the significant role of dams/reservoirs in sustaining irrigation for agriculture in China.

Irrigation: Water Supply to Agriculture

Irrigation plays a key role in China’s agriculture and food security. Accounting for about 45% of the arable land, irrigated land produces about 70% of the total grain, 80% of the cotton, and 90% of the vegetables and fruits in China. Irrigation has enabled an significantly higher crop yield in the main food-producing regions like the North China Plain, where irrigated wheat yield is 70% higher than rainfed wheat yield.

A strong relationship exists between grain production and irrigated areas in China, during 1985–1999 and 2004–2009. In both periods, expansion of irrigated area was an important reason for the increased crop production. The exception was in 2000–2003, when irrigated area remained almost unchanged but grain production sharply decreased. This was mainly attributed to the decline in the planted area of grain due to urbanisation and implementation of the 1999 Grain-to-Green Program which consisted of large-scale ecological projects to convert rainfed cropland on steep slopes to forest and grassland.

Despite the close relationship between expansion of irrigated area and growth of grain production, there is no clear correlation between agricultural water use and grain production. This is largely due to the fast development and extensions of water-saving technology in China, especially since the 1990s. The Chinese government has been heavily investing in research on water-saving agricultural techniques since the beginning of the Seventh Five-Year Plan.

Water Transfer: For Better Water Allocation

A direct benefit of water diversion projects is the transfer of water from water-surplus to water-deficit regions to alleviate water shortage in the receiving areas. These water diversion projects mainly aim to supply water for domestic and industrial uses, although some also serve for irrigation.

Environmentally and ecologically oriented water diversion projects also have recently emerged. A typical example for water quality improvement is the Yin Jiang Ji Tai project that diverts the Yangtze River water into Taihu Lake. As the third-largest freshwater lake in China, Taihu Lake serves as a major water source for drinking, aquaculture, and industrial needs, as well as being a popular tourist attraction. The Taihu basin accounts for 0.4% of the total area of China, 2.9% of the national population, but 14% of China’s GDP. With economic growth and population increase, Taihu Lake began to suffer from several environmental problems, including deterioration of its water quality and consequently increasing frequency of noxious algae blooms. Started in 2001, the Yin Jiang Ji Tai project increased flow velocity, improved self-purification capacity, reduced the water exchange period, and alleviated degradation of Taihu Lake. By the end of 2006, it had transferred 7.42 billion m³ of water from the Yangtze River into Taihu Lake basin, of which 3.24 billion m³ went into Taihu Lake. Despite the positive short-term effect of improving water quality in Taihu Lake, its long-term function is a concern because of the large net input of nitrogen and phosphorus from the river to the lake.

Restoring degraded ecosystems caused by reduced water inputs is a typical application for ecologically oriented water diversion projects. An exmaple of ecological water diversion projects is associated with the Heihe River, the second-largest inland river. Due to the overexploitation of water resources in the middle reach of the river, serious environmental degradations, such as river-flow interruptions, shrinkage of lakes, groundwater-level drawdown, disappearance of vegetation cover, and desertification, occurred in the lower reach. To alleviate these environmental problems, the Heihe River Management Administration launched “Integrated Water Resource Management of the Heihe River Basin” in 2000. A core part of the plan was to increase stream discharge by diverting water from upstream and midstream man-made reservoirs to lower reaches using a man-made channel. From 2000 to 2006, a total volume of 5.29 × 10⁹ m³ of water was delivered to the lower Heihe River through intermittent water diversions for over 20 times. As a result, East Juyan Lake, which is the end of the river and dried up in 1992, was replenished to an area of 38.6 km²by 2006.