|Long Distance Water Transfer: A Chinese Case Study and International Experiences (UNU, 1983)|
Wang Jinghua and Liu Yonghe
Institute of Geography, Academia Sinica, Beijing
GENERAL CONDITION OF WATER QUALITY IN THE RIVERS OF THE PROPOSED WATER TRANSFER REGION
THE QUALITY of the natural river water in the proposed south-to-north water transfer region is relatively good, soft and medium-hard bicarbonate with a mineralization of 200 to 500 mg/l. But the development of pollution in these waters has produced a number of problems.
River pollution is directly related to the existing conditions of pollution sources in the region. The proposed trunk conveyance canal would receive pesticides and fertilizers from the Huai He and Hai He drainage basins. At the same time, about 2.55 x 106 tons of waste water would be discharged each year from industrial pollution sources. These would be certain to affect the quality of transferred water.
According to available data, the conditions of principal pollutants such as phenol, cyanide (CN-), arsenic (As), mercury (Hg) and chromium (Cr) are quite different in the rivers of the region. The current water quality conditions in several major rivers are as follows.
The Chang Jiang
At present the water quality of the Chang Jiang is good. The water has a pH value of 7.0 to 8.5 and a total hardness of 4 to 9 degrees. Dissolved oxygen content exceeds 7 mg/l. BOD5 content is mostly 1 mg/l or so, with only 1.2 per cent of the water samples taken during the high flow period containing more than 4.0 mg/1. Just 3.7 per cent of those drawn in the low flow period have this high a BOD5 content.
Some pollution does appear in the river, however, after it flows through certain cities. For instance, the annual mean value for phenol is 0.003 mg/1 in the Wan county reach, 0.002 mg/1 in the Jiujiang and Wuhu reaches, and 0.004 mg/1 in the Shanghai reach. An analysis of 2,700 samples taken during the low flow period reveals the highest determining percentage for phenol, 22.5 per cent. Nevertheless, only 6.3 per cent of water samples have a phenol content reaching or exceeding the state's standards for surface water. The determining percentage of the remaining four pollutants is rather low (Figure 1).
Since it has a large and swift flow, the Chang Jiang has a very strong capacity for diluting and purifying pollutants. The speed of self-purification is especially marked for phenol compounds, which are volatile and easily decomposed. Heavy metal trace elements are adsorbed onto suspended matter or enter into sediment. Localized pollution may therefore result from the large amount of industrial waste water and domestic sewage which the Chang Jiang receives as it flows through some cities. The extent involved varies, from hundreds of metres to several kilometres, and the width is normally confined within the lines of the main current. In general, pollution is somewhat more serious in low flow periods than in high flow periods.
The Huai He
The Huai He drainage basin is only subject to pollution in the vicinity of industrial cities and towns. For instance, organic pollution is most conspicuous in the Bengbu reach, causing the dissolved oxygen content to drop. The average phenol content in the river water is 0.005 mg/1 and As content, 0.002 mg/l. Figure 2 gives the variation in the annual mean value of phenol content in the Bengbu reach during the period 1975-1979. It shows a marked increase in phenol content since 1978.
Phenol content is 0.002 mg/1 where sewage water enters around Lake Hongze but no phenol, CN- or As pollution has ever been found in the central part of the lake.
The Huang He
Monitoring data show that the Huang He is markedly polluted in the Lanzhou reach where phenol concentration reaches 0.004 mg/1 and CN-, 0.003 mg/1, mainly due to industrial waste water. But both these pollutants have remarkable self-purification capacities in the Huang He. Studies show that the self-purification coefficient value K for phenol ranges from 0.003 to 0.030 km-i in the Lanzhou reach, being affected mostly by temperature (Xu, 1980). Arsenic concentration rises in the river below Shaanxi Province with an annual average value of 0.336 mg/1, 8.4 times higher than the surface standards. The arsenic in the river does not stem from industrial pollution but is contained in the soil of the Loess Plateau which enters the river as a result of erosion.
In the stretch below Zhengzhou, industrial waste water cannot be discharged into the river because the channel bed is higher than the surrounding ground. In addition, the river carries a high sediment content, so the pollutants are adsorbed by the silt, and precipitate gradually along the course. As a result water quality remains good.
The Xiaoqing He, which flows through the city of Jinan, has been seriously contaminated by industrial waste water and domestic sewage. It has a phenol content of 0.03 mg/1; As, 0.01 mg/1; and Cr. 0.017 mg/1.
The Hai He basin
The Hai is one of the main drainage systems in the North China Plain. It includes the Yongding He, formed by the Sanggan He and the Yang He, which rises in Shanxi Province and is polluted by the industrial cities and towns along its course. Phenol, Cr and Hg concentrations all reach the surface standards. The Yongding replenishes groundwater reserves in Beijing after entering into the Guanting Gorge via the Guanting Reservoir. Water quality measurements over a long period of time show: phenol, 0.001 to 0.009 mg/1; CN-. 0.001 to 0.02mg/1; As,0.001 to 0.04mg/1; Cr,0.001 to 0.01 mg/1; Hg, 0.0005 to 0.002 mg/l; and both cadmium and 666, zero.
To the south, phenol content in the Fu He around Baoding is 0.033 ma/ I, over three times higher than the standard for surface water. The Fuyang He is polluted by phenol, CN- and Hg from industrial waste water in the Xingtai-HandanHengshui region.
In the Tianjin reach, COD and C1- concentrations have exceeded the standard requirements. The average COD value in 1977-1979 was 5.73 mg/1, with a maximum of 13.0 mg/1. Concentrations of phenol, CN-, As and Hg were 0.004, 0.004, 0.01 and 0.0003 mg/1 respectively, all below the surface water standards.
Three conclusions follow from the above. First, the river water in the vicinity of the industrial cities and towns of the proposed water transfer region has been polluted to differing degrees by industrial waste water. This condition is continuing to develop.
Second, the chief pollutants are phenol and CN-. Of over 500 samples, the number with levels of phenol, CN-, Cr and As exceeding the standard values amounted to 44.9 per cent, 28.5 per cent, 6.8 per cent and 0.8 per cent respectively. Since phenol and cyanide are volatile pollutants, both concentrations decline in the course of being transported downstream owing to constant decomposition and self-purification.
Third, water quality in the region changes from high flow to low flow periods. Generally speaking, pollution eases during the high flow period but there is a tendency for the Hg and As contents to increase. During the low flow, pollution worsens in general with a tendency for organic materials, phenol and CNto increase.
EFFECT OF THE PROPOSED WATER TRANSFER ON RIVER QUALITY
Water in the Chang Jiang is of the HCO3-Ca++ type with a mineralization of about 200 ma/ 1. Mineralization of river water increases progressively from the Chang Jiang towards the north and the water types change correspondingly. Mineralization may exceed 500 mg/1 in the lower reaches of the Hai He with CI--Na+ type of water. It would therefore make sense to divert water from the Chang Jiang to improve the natural water quality of the surface waters of the north. Nonetheless, further research is necessary on the issues of water pollution and the effect of changes in the physical environment on the evolution of the quality of water involved in interbasin water transfer.
Effect on the Water Quality of the Diversion Reaches of the Chang Jiang
The diversion of water from the Chang Jiang during the low flow period would lead to a strengthening of tidal current action and the intrusion of sea water, an increase in chlorinity, and a reduction in solute runoff (e.g., Si, Fe and organic matter). All this in turn would affect fish activity in the adjacent sea areas. At the same time, the expansion of seawater intrusion may retard the discharge of polluted water from the Huangpu Jiang and aggravate pollution. The effect of tidal intrusion can only be relieved after the low-flow period discharge of the Chang Jiang has been increased with the completion of the Sanxia (three gorge) Reservoir project upstream.
Water pollution is relatively serious in the reach of the Chang Jiang from which water would be diverted along the East Route. Urban sewage discharge amounts to 2.07x106 tons/day at the inlet of the East Route in the Naming reach. Of this, 82 to 91 per cent is released from Nanjing alone. The main pollutants are phenol, CN-, organic matter, and oil. These would seriously affect the quality of transferred water.
Effect on the Main Conveyance Canals
A number of oil and coal fields and important cities and towns are situated along the two conveyance routes. The discharge of a huge amount of sewage would affect the water quality of the main conveyance canals and river channels, especially along the East Route. The pollutants are chiefly phenol and CN-. Heavy metal pollution occurs in some places. Water quality is good in the lakes through which the East Route would pass. But if a large quantity of nutritive material and urban and domestic sewage enters these lakes, they would suffer from organic pollution, even eutrophication, affecting water quality along the main route.
Effect on the Hai He Drainage Basin
At present, the volume of the Hai He that empties into the sea and the solute runoff are constantly dropping while pollution is increasing. An analysis of monitoring figures shows a phenol content of 0.002 mg/1 but a determining percentage of the samples of only 15 per cent, while CN- content is 0.009 mg/1 with a determining percentage of 31.8. Under such circumstances, if adequate measures are not taken to control strictly the quality of transferred water and if industrial and domestic sewage mix in along the way, the pollutant load in the Hai He basin is bound to increase. Furthermore, if the return flow from irrigated fields along the route also flows in, large quantities of pesticides and chemical fertilizers applied to the fields will appear in the Hai He.
If the quality of the large volume of transferred Chang Jiang water is guaranteed against pollution, the mineralization of the Hai He will certainly be improved and the amount of fresh water increased. This would be highly beneficial for water supply in Tianjin and for coastal agricultural activities.
EVALUATION OF WATER QUALITY IN THE PROPOSED WATER TRANSFER REGION
Data were collected from over 500 monitoring points in the proposed water transfer region. It was necessary to use a unified method of handling them in order to compare and evaluate the degree of water pollution in the region (Nemerov, 1974).
Currently, river pollution monitoring in China focuses on the five pollutants phenol, CN-, As, Hg and Cr (Guan et al., 1980). In order to compare and assess the actions of these five pollutants on river bodies, we use the following "pollution index":
Where Ki = pollution index;
Ck = unified standard value, temporarily defined as 0.1;
Coi = maximum allowable concentration of different pollutants in surface water;
Ci = measured concentrations of different pollutants.
Using this index as well as the percentage of determining values of the pollutants that exceed the surface water standards, we can establish the following grades of pollution:
Ki £0.1 non-polluted water, indicating that the sum of the various pollutants
does not exceed the unified maximum surface water standard;
Ki = 0.1 slightly polluted water, indicating that at least one pollutanthas exceeded the allowable standard for surface water; Ki ³0.3 polluted water, indicating that at least two pollutants have exceeded the allowable standards and that at least one of them has caused serious pollution.
We have used this formula to calculate the pollution index for some of the major river reaches in the proposed water transfer region from the Chang Jiang to the Hai He basins and have drawn up Figure 3. From this figure one can see that:
(1) The water quality of most of the rivers in the region is good with a
pollution index 0.1
(2) Where pollution exists, the greatest proportion of the water is slightly polluted. This includes the river flows in Beijing, Tianjin, Dezhou and Shijiazhuang.
(3) Pollution is serious in some individual localities. Of the pollutants, phenol is the most prevalent, with concentrations far in excess of the permissible surface standards. For example, the Xiaoqing He in Jinan has a pollution index of 2.7, with phenol pollution predominant, being 3 to 20 times higher than the standards.
Figure 4 uses available data to show the intemporal variation of the pollution index between 1972 and 1978 at Huang He monitoring points at Huayankou, Gaocun, Aishan, Loukou and Lijin. The figure shows that the pollution index increased sharply beginning in 1974 or 1975. The main pollutant in the river is arsenic, amounting to over 90 per cent of the total index for the five pollutants. Both the variation and increases in the pollution index for the Huang He are due principally to arsenic.
WATER SOURCE MANAGEMENT AND PROTECTION MEASURES FOR SOUTH-TO-NORTH WATER TRANSFER
Water quality is basically good in the rivers of the proposed water transfer region. In contrast to some rivers in the world (Durum and Haffty, 1963), pollution in these Chinese rivers is primarily caused by phenol and cyanide. Heavy metal pollution has not been reported on a wide scale. Water source protection will remain a major problem with the development of China's industry and the completion of the water transfer project. To this end, we present some views regarding water source and protection measures for the south-to-north water transfer:
(1) Water source protection must be regarded as a specific category to be
included in the overall planning of the water transfer project. It should be
given sufficient attention from the very beginning of the project's operation. A
correct assessment should be made of the current and future conditions of water
quality in the rivers of the region.
(2) Once the project is put into effect, feasible measures must be taken to protect water sources so that the main canals are not used as sewage discharge channels and industrial waste water is not permitted to flow in. The waste water in the larger industrial cities along the routes must be handled in a unified way and other discharge routes found for it.
(3) The most fundamental measure to solve the problem of protecting the source of the water transfer is to strengthen the control over pollution sources. The waste water of major factories and enterprises along the routes should be brought under control prior to the completion of the project. Priority should be given to river stretches where serious pollution has already occurred.
(4) Water source protection districts should be established. These should be drawn up in the water transfer region in accordance with the level of water pollution, the capacity of the environment for self-purification and the social conditions and economic structures of human activity. Comprehensive programmes to prevent and control water pollution should be drafted for each district.
(5) River pollution monitoring should be improved and monitoring points be set up along the main conveyance routes.
(6) Laws should be drawn up providing rights to sue and demand compensation for losses from units that wilfully discharge waste water into the conveyance canals.
Guan Boren, Wang Huadong and Zheng Yingming, 1980,''A summary of research on river pollution in China," Environmental Science, No. 3.
Durum, W. H. and Haffty, J., 1963, "Implication of the Minor Element Content of Some Major Streams of the World", Geochime et Cosmochim. Acta, Vol. 27, p. 1.
Nemerov, N.L., 1974, "Scientific Stream Pollution Analysis", McGraw-Hill, New York.
Xu Yunlin, 1980, "A preliminary study of the role of self-purification played by some degradable pollutants in rivers". Environmental Science, No. 1.