|Long Distance Water Transfer: A Chinese Case Study and International Experiences (UNU, 1983)|
Institute of Geography,
Academia Sinica, Beijing, China
CHINA, a country with a vast territory, is situated in the southeastern part of Asia facing the Pacific Ocean in the east. It is not too distant from the Indian Ocean in the south and adjoins the centre of the Eurasian continent in the northwest. Influenced by this kind of an oceanic and continental location and a monsoon climate, annual precipitation in China in general decreases from south to north and from southeast to northwest. Annual precipitation is less than 500 mm northwest of the Yan Shan, the Taihang Shan and the Qin Ling, and more than 500 mm to the southeast. The 500 mm isohyet stretches along the western slope of the Da Xing'an Ling and the middle reaches of the Liao He, then runs through the Yan Shan and the Taihang Shan to north of the Qin Ling. Precipitation is even less in the northwestern part of the country, including Gansu and Qinghai Provinces and the Xinjiang Uygur, Inner Mongolian and Ningxia Hui Autonomous Regions, with an annual average around 150 to 250 mm or less. In the east around the Huai He, precipitation is about 900 mm and in the middle and lower reaches of the Chang Jiang (Yangtze River) it is around 1,100 mm.
Annual precipitation is not only unevenly distributed by area but it also varies greatly between seasons of the year. With few exceptions, the heaviest rainfall occurs in summer throughout the country. The higher the latitude, the wetter the summer months, with rain usually coming in the form of storms. For example, while summer rainfall makes up 40 to 55 per cent of the total annual precipitation in areas south of the Huai He, it amounts to 60 to 75 per cent on the Huang-HuaiHai Plain north of the Huai He and in the northwest. Water surplus or deficiency is mainly determined by the amount of rain in summer storms. Precipitation varies greatly from year to year as a consequence of large changes in the number and frequency of storms in these regions. Spring is the sowing time for autumnharvested crops and the growing period for wheat and other crops, so it is the season when more water is needed for agriculture. Precipitation is scanty in the spring in many parts of China. For example, it accounts for about 20 per cent of the annual average in areas south of the Huai He but less than 15 per cent in the Huang-Huai-Hai Plain north of the Huai He. The latter is one of the regions receiving the smallest amount of spring rainfall in the country. The air temperature rises very quickly during the spring on the Huang-Huai-Hai North China Plain. The air is dry and there are numerous heavy winds. The evaporation potential is strong and may reach three to four times the amount of precipitation in the corresponding period. Hence this area frequently suffers from "nine droughts in ten years", seriously limiting agricultural development.
The temporal and spatial distribution of surface runoff coincides in the main with the distribution tendencies of annual precipitation. It also decreases progressively from south to north and from the southeast to the northwest in the continental interior. For instance, the annual runoff depth along the banks of the middle and lower reaches of the Chang Jiang ranges from 400 to 500 mm, while in areas north of the Huang He (Yellow River) it is less than 100 mm and mostly below 50 mm on the lower reaches of the Hai He Plain.
Precipitation is the decisive factor for the distribution of river runoff during the year. River runoff in the eastern monsoon region is greatest in the summer and lowest in winter. Summer river runoff constitutes 60 to 70 per cent of the year's total volume and in spring it is below 10 per cent on the Huang-Huai-Hai Plain, which receives the smallest proportion of spring runoff in eastern China. Winter is the dry season there with runoff below 8 per cent of the annual total. The uneven distribution of runoff during the year, combined with the absence of sufficient regulating and storage facilities, leads to a large volume of water flowing into the sea during the flood season and wet years, and highlights the difference between the supply of water and the requirements for it in the spring.
Year-to-year variations in river runoff are related to factors such as the amount of precipitation and the size of rivers. For example, the coefficient of variation C, of the annual runoff of the Chang Jiang, the most stable river in China,is 0.12 to 0.15, while that of the Huai He is 0.55 to 0.65 end that of the Hai He reaches 0.60 to 0.75. In addition, wet years or dry years often occur in succession.
Groundwater is an important component of water resources. The hydrogeological departments have calculated the combined volume of shallow groundwater recharge when the water table drops to an average depth of 4 m on the Huang-Huai-Hai Plain (see Chapter 18). The results of their calculations indicate that a total of 47.6x109 m³ of freshwater resources (mineralization<2 g/ 1) is available within an area of nearly 0.3 x 106 km² on the Huang-Huai-Hai Plain each year. The present extraction rate is 25 x 109 m³ per year, of which an average 8.8 x 109 m³ is in Hebei Province and 9.3 x 109 m³ is in Henan Province. After making a comparative analysis of the amount of groundwater reserves and the current state of extraction, they have held that there is still great potential for shallow groundwater exploitation on the plain. Cangzhou and Hengshui Prefectures in Hebei Province, where groundwater extraction is relatively heavy, exemplify this. Shallow freshwater extraction intensities in the two prefectures were 67,000 m³/km² and 70,000 m³/km² respectively in 1974 (an average year) and 94,000 m³/km² and 105,000 m³/km² respectively in 1975 (a dry year) comprising merely one-third to one-half of the groundwater recharge resource. This shows that the shallow groundwater has not yet been fully extracted.
The Chang Jiang is the largest river in China with abundant water resources. Its total annual river runoff is 980 x 109 m³. This volume is 18 times as much as that of the Huai He system (53 x 109 m³),20 times that of the Huang He (48.6 x 109 m³) and 35 times that of the Hai He-Luan He drainage basin (28.3 x 109 m³). The abundance of water in the Chang Jiang can be seen in that its average annual runoff constitutes 38 per cent of the national total while that of the Huai He is 2 per cent, the Huang He 1.9 per cent, and the Hai He and Luan He together 1 per cent.
There is much water and little land in south China and the opposite in north China. The phenomenon of having much land and little water is even more pronounced in northwest China. According to Yao Bangyi and Chen Qinglian (see Chapter 9), the existing cultivated land in the Chang Jiang basin adds up to 24 million ha which is about a quarter of the total in China. Runoff volume averages 41,700 m³/ha. There are 12.6 million ha and 13.1 million ha of cultivated land in the Huai He and Huang He basins respectively. Runoff volume averages 4,230 m³/ha in the former and 4,290 m³/ha in the latter, each only one-tenth the average amount in the Chang Jiang river basin. Arable land totals 11.3 million ha in the HaiLuan river basin and runoff averages only 2,500 m³/ha, merely 6 per cent that of the Chang Jiang basin.
Both the Chang Jiang basin and the Huang-Huai-Hai Plain are centres of China's economic and cultural activity. Industrial and agricultural uses of water are bound to increase with the further development of the national economy. Taking into account the abundance of water in the Chang Jiang basin and its deficiency in the Huang-Huai-Hai Plain and the northwest, and especially the serious water shortages there in the spring plus the extreme imbalance of water and land resources, the water conservancy department carried out some studies on northward water diversion from the upper reaches (West Route), the middle reaches (Middle Route) and the lower reaches (East Route) of the Chang Jiang during the early 1950s. From 1959 to 1961 the Chinese Academy of Sciences organized scientific research personnel, engineers and technicians to conduct field investigations of the water transfer in the upper reaches of the Chang Jiang. The northwest of China consists of arid and semi-arid regions where water transfer is urgently needed for industrial and agricultural development. However, after the investigation it was felt unanimously that the topographic conditions are extremely complex in the region which the West Route passes through, that the water transfer route is too long and that the engineering is difficult because the route will have to pass through a large number of high mountains; and therefore it will be hard to solve this problem within the century. In recent years, there have been droughts and water deficiencies in vast areas of the Huang-Huai-Hai Plain, so the subject of interbasin water transfer from the middle and lower reaches of the Chang Jiang to the Huang-Huai-Hai Plain and the cities of Tianjin and Beijing has been put on the agenda once again. Basing their efforts on the programme from the 1950s, water conservancy departments restudied the route for transferring water by pumping from the lower reaches of the Chang Jiang and in 1976 issued a preliminary planning report. Following this, research was also carried out on the water transfer route from the middle reaches of the Chang Jiang. In 1979 and 1980, the Ministry of Water Conservancy organized engineers, technicians and scientific research personnel to conduct rather detailed on-site investigations of the two routes. The present monograph deals mainly with research on the impact on the natural environment of south-to-north water transfer via the Middle and East Routes.
Diverting large quantities of water from the Chang Jiang into the Huang-HuaiHai Plain through the Middle and East Routes will inevitably cause changes in the ecosystems of the plain, including those of the farmlands and of rivers and lakes. If we do not think things out carefully, take proper measures or have good management, we will be unable to promote what is beneficial and eliminate what is harmful so as to realize our goal of improving industrial and agricultural production on the plain. What is worse, disastrous consequences could follow if we violate the laws of nature. At present there are already 2.7 million ha of saline soil on the Huang-Huai-Hai Plain. Would a northward transfer of Chang Jiang water aggravate the spread of secondary salinization in the soil? How can we prevent the occurrence of secondary salinization? These are questions which cause great concern. After a south-to-north water transfer, a considerable amount of water in irrigated areas and canals will pass below the surface. If there are no complete drainage systems in the irrigated areas to control the water table, drastic changes in groundwater dynamics occur and we anticipate that these may cause the aggravation and development of soil salinization in these areas.
Water transferred from the lower reaches of the Chang Jiang will have to cross many lakes, so aquatic life in the lakes and rivers is bound to be affected because of changes in the ecological environment of the lakes and the Chang Jiang estuary. Salt water intrusion in the Chang Jiang estuary has already affected industrial and agricultural production in Shanghai. How much will sea water intrusion, siltation and navigation be affected if water is diverted from the lower reaches of the Chang Jiang (especially during the dry season)?
Of greatest concern to people is water quality. Some of the rivers and lakes located in the section from which water is to be diverted in the lower reaches of the Chang Jiang and along the water conveyance route have already suffered varying degrees of pollution from industrial waste water, waste solids and chemical pesticides. In some rivers phenol, cyanogen and mercury concentrations have already exceeded the set standards. How to strengthen the protection of water sources, strictly implement the Environmental Protection Law and prevent polluted water from being transferred northward are issues which must be studied conscientiously. In addition, research must be carried out on how to prevent the incidence and spread of disease brought by water diversion as well as the effects of water diversion on the climate of irrigation districts and areas adjacent to them.
The purpose of water transfer from south to north lies in transferring water northward, that is to say, in resolving the problem of water deficiency in areas north of the Huai He. What is the amount of water resources in this area? In particular, just how much groundwater is there? We should study whether it is really necessary to transfer water if we carefully consider the water requirements of future industrial and agricultural development based on the improvement of water resource management and the economic use of water. If it is necessary, then how much should be transferred? From which river should water be diverted? What are the alternative routes?
Although water is abundant in the Chang Jiang, only 2,890 m³ per capita is available in the basin each year. Moreover, according to the statistics, the average annual runoff decreased by 14 per cent during the 20 years from 1956
to 1975 compared with that in the ten years from 1946 to 1955, although there was no reduction in annual precipitation. If we take into account the great development in industry and agriculture likely in the future in the Chang Jiang basin, how much surplus water will be left which can be transferred from the Chang Jiang? In-depth studies have yet to be carried out on all these problems related to matters such as the calculation of water resources, the balance of water supply and water requirements, and investment in projects and their economic benefits.
The south-to-north water transfer is a gigantic project involving a human transformation of the environment. It will have a tremendous impact not only on the natural environment but also on the social environment and the productive activities of society as well. Hence, extreme interest has been expressed in this project by many engineers and technicians as well as scientific workers in the fields of water conservancy, agriculture, soil science, geology, biology, environmental protection, hydrology, geography and economics. With this in mind, the Chinese Academy of Sciences held a symposium in 1978 on the impact of south-to-north water transfer on the natural environment and entrusted its Institute of Geography with the responsibility of organizing the relevant scientific research units, institutions of higher learning and industrial departments within China to work together to draw up a scientific research plan and divide up the research work. The two main topics were water balance in the south-to-north water transfer regions and comprehensive evaluation of water resources, with research on the balance of water supply and requirements and on water regulation and storage. Topics concerning the impact of south-to-north water transfer on the natural environment were: control of secondary salinization in irrigated areas; the effect of water transfer on climate in irrigated areas and surrounding districts; the effect of water transfer on hydrogeological conditions; and the effect of downstream water transfer on the estuary and seacoast of the Chang Jiang as well as on the environment of lake waters and on aquatic life ecology along the transfer route. Additional topics were the evaluation and evolution of water quality; the rational utilization of land after water transfer; and cropping patterns and prediction of benefits from increases in agricultural production. In 1979, the Chinese Hydrological Society held a symposium in Tianjin on south-to-north water transfer schemes. Over two hundred experts, professors, scientists and technicians gave presentations and exchanged scholarly opinions. In October 1980, the Chinese Academy of Sciences and the United Nations University co-sponsored an investigative tour by Chinese and foreign experts covering the areas along the Middle and East Routes on the topic of the impact of south-to-north water transfer on the natural environment. A symposium followed in Beijing focusing discussion on two subjects, namely, the necessity of water transfer from south to north and the impact of water transfer on the natural environment. This monograph is one of the products of the workshop and contains some of the research results and opinions offered by the Chinese and foreign experts on the impact of interbasin water transfer on the natural environment and related topics.