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Chapter 12. Impact of south-to-north water transfer upon the natural environment
Liu Changming and Zuo Dakang
Institute of Geography, Academia Sinica, Beijing
INTRODUCTION
SHIWUZONG SHI YI FEN WEI ER: There are two sides to everything. The benefits of building hydraulic structures to alter the regional distribution of water for the satisfaction of human needs are obvious. Unavoidably, however, such activities also have unfavourable impacts upon the physical environment and upon social production. This duality is especially strong when water is transferred on a large scale across river basins. In order to maximize project benefits in these cases, it is necessary to study in the planning stage all the potential impacts, favourable and unfavourable, of such a transfer.
The assessment of large-scale interbasin water transfer is an extremely comprehensive, multidisciplinary subject. Its content is very broad, including various aspects of technology, social economy and the environment. In addition, the engineering plans must be adapted to meet the requirements of policies and laws. Making an overall assessment is therefore an extremely complex endeavour.
It is most important to study the impact of interbasin transfers of water on the natural environment. This is not only because the transfer itself is an enormous measure which transforms nature but also because the cost of environmental impacts is very high but hard to measure in monetary terms. In particular it is a difficult and lengthy process to restore or improve the environment once it is damaged. At the same time, the social economy cannot be considered separately from the environment, since that is where human activities take place. Generally speaking, however, environmental and economic benefits coincide and it is unrealistic to assume that an interbasin water transfer project can have very high economic benefits but be harmful to the environment.
The impact of an interbasin transfer of water on the environment is related directly to the scale of the transfer, which is generally defined according to volume. A "large-scale" project can transfer over 10 km³/annum. This designation would apply to either the Middle Route or the East Route of China's proposed south-tonorth interbasin water transfers. Unlike the north-to-south transfers of the Soviet Union and North America where both the exporting and importing regions are sparsely populated with limited industrial and agricultural development, both of China's routes are situated in densely populated industrial and agricultural centres. Environmental assessment therefore takes on particular importance in the comprehensive analysis of water transfer. To a very large extent environmental effects will determine whether the transfer can achieve its objectives. Indeed, in a certain sense, an improvement in the environment is precisely the goal of the southto-north water transfers.
OVERALL ANALYSIS OF ENVIRONMENTAL EFFECTS
Water is the most active component in the natural environment. It moves constantly and participates actively in a series of physical, chemical and biological processes which occur in the natural environment. The movement and transformation of surface chemical elements; the erosion, transport and accumulation of the ground surface; and biological growth and development are all closely linked with the circulation of moisture. In addition, moisture and heat are the most important physical conditions in the environment of the ground surface. When they are well combined they provide an important guarantee for high and stable agricultural production. Therefore the circulation of moisture and changes in water sources as well as their relationship with biological, atmospheric and geological cycles form a core problem related to the impact of interbasin water transfer on the natural environment. When water sources change, all other natural factors related to them also change.
The following generalizes the process whereby water transfer affects the environment:
Water transfer(r)change in original hydrological regime(r)change in the natural environment(r)change in the social economy (conditions of production).
A method of evaluation should be chosen before making an environmental assessment. Such a method and its contents have been recounted in an overall way by Dickert (1974), Ortolano (1979) and others. According to them, environmental assessment has three aspects: (1) identification of impact factors; (2) prediction of environmental aftereffects; and (3) impact assessment. The first aspect has been dealt with in Chapter 11 of this book and a series of articles describe the prediction aspect. Here we focus on the third, impact assessment.
The impact of any water transfer project on the environment may be divided into three different geographic regions, namely, the water exporting region, the transfer region and the importing region. These will be analyzed separately below.
The Water Exporting Region
The main impact of a water transfer will occur at the point of transfer and in the river reaches below it. In the East Route this would be the lower reaches of the Chang Jiang below Sanjiangying. The stretch from Sanjiangying to the estuary, over 200 km in length, belongs to the delta of the Chang Jiang. The surrounding terrain is flat with a crisscrossing water network. Known as the land of fish and rice, this area has one of China's most flourishing economies, with numerous urban areas, a dense population and highly developed industry. Because of its location, the entire area is subject to tidal intrusion from the ocean. Water transfer would reduce the flow in the Chang Jiang. In particular, the reduction in the river's flow during the dry season would markedly change the water regime of the lower reach river channel and the estuary. The possible aggregation of sea water intrusion and its effect on industrial and agricultural production and municipal water supply in Shanghai Municipality and the coastal areas of the lower reaches is dealt with in this volume by Shen Huanting et al and by Xu Yuexian and Hong Jialian (Chapters 25 and 11 respectively), while Yu Xuefang (Chapter 27) provides a detailed discussion of the impacts on the ecology of aquatic organisms and on fisheries in the estuary and inshore areas. We will therefore not go into detail on these matters.
The mouth of the Chang Jiang is a tidal estuary. Influenced by the weakened runoff in the Chang Jiang and intensified tidal currents, a southward flowing ocean current carries a vast amount of sediment from the coast of northern Jiangsu into the north branch of the estuary. This is particularly apparent during the winter. For more than a decade the water and silt of the north branch have intruded into the south branch, with 43.6x 106 tons of silt per annum entering into the Chang Jiang in this way.
The reduction in Chang Jiang runoff and tidal action have made it difficult for the river's sediments to be transported far. This has resulted in serious sedimentation during recent years at the southern channel outlet. In addition, tidal action and the salt water wedge have reduced the dynamic action of the water to a minimum. This has inevitabl led to the accelerated settling of fine particles and the expansion of sand bars blocking the estuary of the Chang Jiang.
All of these factors are unfavourable to navigation in the estuary. It is therefore necessary to carry out intensive studies on the problems of water transfer during the low-flow season in the Chang Jiang.
The Middle Route begins with a diversion of water from the Danjiangkou Reservoir. The water transfer would affect districts along both sides of the main channel of the middle and lower reaches of the Han Jiang downstream from the reservoir. The main channel is 650 km long from Danjiangkou to Hankou, and the nearly 79,000 km² in the middle and lower reaches is an important component of the commodity grain base of the Han Jiang Plain. It is planned to expand the present approximately 300,000 ha of irrigated land to 630,000 ha, but the water transfer would impair irrigation water use.
Since Danjiangkou began storage operations in November 1967, maximum reservoir discharge has been stable for the most part at 1,000-1,500 m³/sec, reaching a minimum of 360 m³/sec. A comparison of statistics from 1960 to 1975 reveals a total reservoir sediment content of 625X106 m³ due to the interception of the silt of the upper reaches of the Han Jiang. The resultant discharge of clear water has had a great impact on the downstream river channel.
According to research by the Department of Geomorphology, Institute of Geography, Chinese Academy of Sciences, the clearwater discharge has greatly reduced the transport concentration and spatial concentration of the sediment. The original river course has changed from alluvial to scouring. Scouring has deepened the main channel and widened the main fork so that the flow returns to the main channel. The branch forks have silted up and multiple channels have become double or single channels. At present, these bed-forming actions, which may reach all the way to the confluence of the Han Jiang and the Chang Jiang, are extremely favourable to navigation and bed stability. If water is transferred northward, however, the reservoir's downstream discharge will decline, causing water depth and the flow velocity to diminish further. This would not be favourable to navigation.
Although the discharge from the Han into the Chang Jiang would decline considerably, it is estimated that there will be no marked impact on the amount of water in the Chang Jiang below Hankou. This is due to the countervailing influence of some lakes in the Hanjiang Plain, including Dongting and Poyang lakes.
Sedimentation in the Chang Jiang is found mainly in the stretch from Yichang to Hankou. A further decrease in the river discharge downstream from Danjiankou will certainly weaken the silt-scouring action at the convergence of the Han and Chang Jiang. This may be detrimental to the Wuhan harbour which is located there. Furthermore, sediment in the Han Jiang may accumulate at the convergence of the two rivers as a result of the incursion of the Chang Jiang into the Han Jiang and the blocking action of the backwater.
The foregoing are only possible problems. Further research is necessary to determine their probability.
Earthquakes occurred frequently after the Danjiangkou Reservoir began to store water. Fifty-eight tremors were measured between 1969 and 1973, the largest with a magnitude of 4.7. The existing height of the dam is 162 m above sea level with a normal water storage level of 157 m and a total storage capacity of 21 km³. Increasing the dam height to 175 m and normal storage level to 170 m would increase storage capacity to 33 km². Whether or not this large a storage will lead to an increase in the number and magnitude of earthquakes is a matter which deserves serious study.
The Chinese Anopheles mosquito is a carrier of contagious malaria. Its larvae propagate mainly in static water bodies such as reservoirs, paddy fields and puddles. In recent years, the incidence of malaria has increased in the area around the Danjiangkou Reservoir. The considerable enlargement of the static water surface necessary for northward water transfer could lead to an expansion of malarial epidemic regions. Research should be strengthened to search out effective methods of disease control.
Diversion via the Middle Route would have only a slight effect on the water conditions of the principal river of the Chang Jiang while the East Route diversion would have a large impact on its lower reaches and estuary. The Middle Route would worsen production conditions in the middle and lower reaches of the Han Jiang by reducing the water available for navigation and irrigation. This could be compensated for, however, by building a canal from
Shashi to Shayang which would divert 360-540 m³/sec from the Chang Jiang into the lower reaches of the Han Jiang. It is estimated that the water level in the principal river of the Chang Jiang would only fall by an inconsequential 0.2-0.3m. Of course, since East Route water would be diverted from the lowest reaches of the Chang Jiang where the river itself has a very large discharge, that transfer would have a great impact on the natural environment of the estuary if it is timed according to the amount of flow in the Chang Jiang.
The Transfer Region
This refers in the main to the affected environment along both sides of the conveyance canals and surrounding the water bodies used for storage. The main conveyance canal of the East Route would be 1,150 km long. That portion south of the Huang He must pass through a number of lakes, including the Hongze, Luoma and Nansi. The diverted water of the Chang Jiang would raise the level of these lakes or maintain a high water level for a relatively long period of time. In the meantime, lacustrine water flows and sediments would be changed. All these factors would exert a definite influence on the aquatic ecosystems of the lakes. Yu Xuefang (see Chapter 27) estimates that there would be a decrease in the number of large herbivorous fish and an increase in the number of small fish which take open waters as their habitat.
Seven plains reservoirs are planned north of the Huang He along the East Route with a total surface area of approximately l 30,000 ha, where fisheries would be developed. If the water table adjacent to the reservoirs cannot be controlled effectively, however, secondary salinization of the soil could occur.
The main conveyance canal of the East Route would pass through four major drainage systems, those of the Chang Jiang, the Huai He, the Huang He and the Hai He. The route of the main canal should be considered in conjunction with the overall plans for control of these four systems. For example, the Huang He is famous for being an "elevated river" whose bed is several metres, sometimes over 10 m above the ground surface in the lower reaches. Over the past 30 years the channel there has risen by an average of about 7 cm/annum. Further conscientious research is necessary on the problems of preventing breaches during high-flow years and of protecting the lives and property of the people along both banks. If it is necessary for the river to shift its course, as it has done numerous times in the past, this will have an enormous impact on the natural environment of broad areas of the Huang-Huai-Hai Plain. The plans for the main East Route canal to cross the Huang He would also have to be considered anew.
The 1,265 km long main canal of the Middle Route would be newly excavated. It would cross 168 rivers. Where the canal intercepts the river flows it would affect the flood discharge and sediment in those channels. The canal would be lined to prevent seepage but, nonetheless, some water would percolate into the ground. It is estimated that salinization would not be serious along either side of the canal south of the Huang He. Although the water table is relatively low north of the river, however, the conveyance of water in the canal over a long period of time could cause it to rise, so we still need to pay attention to the problem of soil salinization. Since the main canal of the Middle Route would cross piedmont alluvial fans it is also possible to consider using the water percolated from the canal to recharge the groundwater along the east side of the canal. Since no natural lakes exist in the transfer region it would be necessary to build reservoirs for water regulation and storage in addition to utilizing the existing reservoirs in the vicinity of the canal. For example, the Yanshan Reservoir in Henan Province will have a control area of 1.3 million ha. A reservoir of this size will also have an impact on the environment.
The major differences between the aftereffects on the natural environment in the transfer regions of the main conveyance canals of the East and Middle routes are as follows:
(1) By passing through lakes, the main conveyance canal of the
East Route would significantly disturb the aquatic ecosystem. The
newly excavated Middle Route canal would encounter no natural
lakes along its course, ruling out any impact on an aquatic
ecology.
(2) The Middle Route canal has more river crossings than does the
East Route, so it would have a greater disturbance on natural
flows. This problem can only be solved by making a much larger
financial investment in the engineering works. Seepage would
cause the water table along both sides of the main East Route
canal to rise. This would retard the eastward flow of the
groundwater in areas north of the Huang He, which in turn could
lead to secondary salinization of the soil. The main Middle Route
canal would not have this problem.
(3) A water pollution problem would exist along either route, but
it would be easier for the East Route to receive sewage water.
Because the Middle Route canal is to be newly excavated, however,
it would be relatively simple to handle the sewage problem by
moving the canal north of the Huang He suitably to the west
(taking the high line). This would improve the safety of the
canal by widening the distance between it and cities or
industrial areas.
The Water Importing Region
In many areas there is no sharp delineation between the water importing region and the transfer region just discussed. The importing region is scattered in patches along the main conveyance canals and would be quite extensive. It is planned that the two routes would expand or improve the irrigated area by 9.40 million ha. Because areas north of the Huang He are the driest, water consumption in either route would be greater there than south of the Huang. The impact of imported water on the natural environment would be higher than in the Huai He basin south of the Huang, where precipitation and
humidity are both higher. As shown by Zhu, Wang and Hseung (see Chapter 28), potentially saline soils are widely distributed in the Hal He Plain area north of the Huang He because of the high soil salt content there. Irrigating with imported water would cause the water table to rise, making salinization more likely and even inevitable as long as large amounts of water are applied in irrigation and a drainage system has not yet been established.
In general, the environment will improve markedly after water is imported into currently water-deficient cities and industrial or mining centres. Nonetheless, these areas should pay attention to rational water usage in order to prevent new industrial pollution.
Secondary salinization of the soil exists in irrigated areas north of the Huang He along either route, but to different degrees. Districts along the East Route are more prone to secondary salinization after irrigation because of their low-lying terrain and higher water table (generally about 2 m below the surface), together with inadequate natural drainage. The terrain to be irrigated along the Middle Route is higher with adequate natural drainage and a lower water table (generally about 4 m below the surface).
Different water storage conditions in areas north of the Huang He would lead to different environmental effects along the two routes. Unlike the East Route regions, the area along the Middle Route has conditions for underground storage which, if utilized, would reduce any unfavourable effects on the environment.
The area now irrigated by wells and canals in the Hai-Luan river basin is 6 x 106 ha. Plans provide for new or improved irrigation in this area on 2.0 X 106 ha for the East Route and 2.2 x 106 ha for the Middle Route. The surface area of various other water storage bodies would also be increased. All this would produce a certain effect on the meso- and microclimates which would be especially distinctive in the area under irrigation and its vicinity. A rise in soil humidity would increase evaporation and air humidity and reduce diurnal fluctuations in soil and air temperature. In addition, surface reflectivity would decrease and the absorbed heat of solar radiation would increase. It is estimated that these factors would have a favourable effect on the mesa- and microclimates of the importing region but little impact on its macroclimate.
The above has only roughly presented some of the main aspects of the effects on the natural environment in the three types of regions. From an overall point of view, we have come to understand the following: Firstly, in the exporting regions it is possible that the negative aspects of environmental effects may be greater than the positive aspects. The benefits to the importing regions are clearer, but attention must be paid to avoiding unfavourable results as much as possible, particularly the problem of secondary salinization of the soil. Secondly, both positive and negative aspects have a regional duality. For instance, the large-scale fish production in the southern lake area along the East Route may decline while new fishery production can be developed in the newly built reservoirs in the north. The water exporting region in the lower reaches of the Chang Jiang may suffer losses and the water importing region in the Hal Plain may benefit. Thirdly, the main inducement to environmental change is the change in hydrological regime. The control of unfavourable environmental consequences should begin with appropriate control of the hydrological regime.
PROTECTION OF NATURAL RESOURCES
Either transfer project would involve vast areas of east China. The allocation of the water resources of four major rivers would be affected. One-fifth of China's cultivated land would be involved. In addition, there would be an impact on resource utilization, for example in lacustrine aquatic production, coal mines and oilfields. How to protect these natural resources while carrying out the south-tonorth water transfer projects should be an essential topic in any comprehensive assessment of environmental effects.
The following points should be heeded in protecting water resources:
(1) The amount of water diverted must be calculated on a
strictly scientific basis. The suitable amount of water to be
diverted should be determined through an integrated balance which
considers both exporting and importing regions. Measures must be
taken to minimize the effect on water resources in the exporting
region, such as rationally utilizing water in the importing
region. Attention must be paid to the development of scientific
water usage techniques so as to make every effort to develop the
full potential of local water resources, strengthen local water
storage and save water by every possible means. It is extremely
important to raise the canal system utilization coefficient for
farm water supply, to adopt methods to circulate water in
industry and collect fees volumetrically in agriculture as well
as industry.
(2) Since pollution sources are present along the water transfer
routes it is extremely necessary to enact a law on the protection
of water quality of the southto-north transfer to prevent the
Chang Jiang water from being contaminated in the transfer regions
(see Chapter 26).
(3) In order to enable the transferred Chang Jiang water to meet
industrial and agricultural water supply needs most effectively,
the canals should be lined to reduce seepage losses. Forest belts
should be planted to break the wind and reduce evaporation
losses.
The following steps should be considered to protect soil resources:
(1) At present there are about 2.7 million ha of saline soil
and about 4.7 million ha of potentially saline soil in the North
China Plain. Positive measures must be taken to improve these
soils. Research on scientific irrigation methods is needed if
transferred Chang Jiang water is to be used for irrigating crops.
A complete drainage system must be in place prior to the
development of irrigation. The transferred water may be used to
flush out salts. Irrigation and drainage may be done by combining
the use of canals and wells. The transferred water may be used to
improve salt water in the shallow aquifer. These combined with
other methods to improve saline soil would enable the quality of
the soil to improve continuously.
(2) The water level in the main conveyance canals should as much
as possible be kept below the groundwater critical depth. This is
an important measure to protect the land along both banks from
marshification and secondary salinization.
(3) The newly built main conveyance canals and reservoirs will
necessarily occupy a large area of land which in the North China
Plain is extraordinarily valuable. For example, about 50,000 ha
of land will be taken up by the 1,265 km long main canal of the
Middle Route, not including the Yanshan Reservoir or the
subsidiary canals. A considerable amount of land would also be
occupied along the East Route to build the plains reservoirs
north of the Huang He. Therefore, in choosing between water
transfer plans, we should consider most strongly how the project
can occupy less land.
The following should be heeded in protecting aquatic and mineral resources:
(1) The water level, flow velocity, sediments and the like
must be controlled properly when the East Route passes through
lake areas such as those of the Hongze, Luoma and Nansi so as to
protect the fishing industry. Alternatively, the idea of
separating the canal from the lakes may be taken into account
when schemes are compared and selected.
(2) Fisheries in the Chang Jiang estuary and coastal areas could
be affected to a certain degree by East Route water transfer.
This impact can be minimized by selecting suitable times and
amounts for diversion.
(3) When a conveyance canal passes through a mining district such
as the coal fields of Yu County, Henan Province along the Middle
Route, the canal route should make a suitable detour so as to
avoid interference with the coal-mine.
CONCLUSION
The proposed south-to-north water transfer project is a magnificent engineering work which would transform nature. We need to consider not only its various impacts on the natural environment and protect our natural resources to the fullest extent possible, but we must also improve and beautify the environment as well as develop agriculture, industry and tourism so as to create benefits for future generations.
References
Dickert, T.G., 1974, "Methods for Environmental Assessment: A Comparison". In Environmental Impact Assessment: Guidelines and Commentary, Editors T. G. Dickert and K.R. Domeny, University Extension, University of California, Berkeley.
Ortolano, L., 1979, "Environmental Assessments in Water Resources Planning". In Interregional Water Transfers, Editors G. Golubev and A. K. Biswas, Pergamor Press, Oxford, pp. 159-176.