1. Surface Water
The average annual runoff of all the rivers in China has been estimated at 2,711 billion m3, equivalent to the mean runoff depth of 284 mm. China's total annual runoff ranks sixth in the world, after Brazil, the former U.S.S.R., Canada, the United States, and Indonesia. However, the per capita amount of runoff—estimated at 2,134 m3/year—is only about a quarter of the world mean. The availability of water per hectare of cultivated land is estimated at 28,000 m3, which is about two-thirds of the world average.
Water resources in China are characterized by uneven regional distribution (Table 1). The runoff of the Yangtze River and the river systems in the south accounts for 81% of the total runoff in the country, whereas the runoff of the large rivers to the north of the Yangtze River is only 14.4% of the total runoff.
The groundwater in China is classified as two types, based on the recharge characteristics. Shallow aquifers hydrologi-
Table 1 Surface Water Resources of China (by Region)
Mean Surface Annual Runoff
Drainage Area (km2)
II Hai He-Luan He basin
III Huai He basin
IV Yellow River basin
V Yangtze River basin
IX Interior basins
Source: Department of Hydrology, Ministry of Water Resources (1992).
cally and hydraulically interconnect with river flows and recharge by local precipitation. These aquifers serve as the major source of base flow of the rivers. In the low-lying areas of China, groundwater from shallow aquifers is widely used for irrigation and domestic water supply. It is renewable and is replenished yearly during the rainy season. The deep aquifers are formed over a long period of time and depend very little on precipitation and surface runoff.
In mountainous areas, groundwater from subsurface deposits and upstream flows are the major recharge sources. The total volume of groundwater in the mountainous areas throughout the country has been estimated at 676.2 billion m3.
The silt concentration is critically high in many rivers of China. Approximately 3.5 billion tons of sediment annually is transported to rivers from the mountains and hilly areas, of which about 60% discharges into the sea, while the remaining 40% deposits in the river courses in the middle and lower reaches, as well as in lakes and reservoirs. During flood periods, the sediments are transported to the lower reaches of the rivers, where they are deposited in the flood plains or diverted into the irrigation areas. With its annual transportation of about 1.6 billion tons, the Yellow River ranks highest among the world's largest rivers in terms of sediment transport. It accounts for 50% of the total river sedimentation of China; the annual runoff accounts for only 5% of the total.
Since the end of the 1970s, water quality has deteriorated because of arbitrary disposal of wastes in rivers. Industrial wastes and city sewage are the main point sources, whereas most of the nonpoint sources, mainly comprising pesticides and chemical fertilizer, originate from the agriculture sector. The comprehensive assessment of water quality of rivers in China conducted in 2000 indicates that the water quality is acceptable for most users along only about 58.7% of the total length of rivers.
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