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Chapter 7. Natural conditions in the proposed water transfer region
Wei Zhongyi and Zhao Chunian
Institute of Geography, Academia Sinica, Beijing, China
THE SOUTH-TO-NORTH water transfer region in east China denotes the area Iying between 110° to 120° E and 30° to 40° N affected by the proposed East and Middle Routes. From the north to the southwest it is framed by the Yan, Taihang and Funiu Shan, the Qin Ling, and the Daba and Dabie Shan. It then reaches the main course of the Chang Jiang in the south, and faces the Bo, Huang (Yellow) and Dong (East) Hai (Seas) in the east. It encompasses all or part of nine provinces (Hebei, Henan, Shandong, Anhui, Jiangsu, Hubei, Shaanxi, Shanxi and Liaoning), two municipalities (Beijing and Tianjin) and an autonomous region (Inner Mongolia). It covers a total area of about 860,000 km², of which approximately 360,000 km² are plains, including the lower Chang Jiang Plain north of the river. The Chang Jiang, Huang He, Huai He and Hai He (some of China's major rivers) flow through the region. The Hongze, Gaoyou and Nansi lakes are found in this region, as are the Guanting, Miyun and Danjiangkou reservoirs. The Huang-Huai-Hai Plain, largest in China, is located here, with nearly 20 million ha of cultivated land. This plain is one of China's most important industrial and agricultural bases.
In general, this region is elevated in the west and low in the east. The plain abuts the Yan Shan in the north, the Taihang Shan in the west and the Qin Ling and Huaiyang Shan in the south. These mountains have an elevation of 1,000 to 3,000 m above sea level, with individual peaks above 3,000 m. In the east, most of the low mountains and hills of Shandong are lower than 500 m, although Tai Shan is 1,524 m. Fault zones join the Shandong range with the Huang-HuaiHai Plain in the north and the southwest. The proposed East Route passes through a string of lakes, including the Nansi and Dongping, which are located near the northwesterly Southwest Shandong Fault Zone. The Taihang mountain range with a strike of NNE is the place of origin for many of the tributaries of the southern Hai He system (Figure 1). The Funiu Shan, the eastern extension of the Qin Ling Range into western Henan Province, have an abrupt eastern rim where the HuangHuai-Hai Plain joins the lower Han Jiang Plain in the Nanyang and Xiangyang basins. The proposed Middle Route passes through the Nanyang-Xiangyang Passage, which offers favourable topographic conditions for interbasin water transfer. To the east of this area is the Huaiyang Upland, including the low (only about 1,000 m) Tongbai and Dabie Shan and, at its eastern edge, a stretch of low hills called the Zhangba Ling.
Figure 1. Geomorphological Sketch-map of the Huang-Huai-Hai Plain
The Huang-Huai-Hai Plain, lying mostly at less than 100 m above sea level, covers an area of about 300,000 km², not including the plain on the north bank of the lower Chang Jiang. This area contains one-fifth of China's population and cultivated area and is one of its most important agricultural regions. The plain has been formed by the common alluvium of the Huang, Huai and Hai He and their tributaries. In particular, the Huang He has played an extremely important role in moulding the great plain. Together with the Yongding He and the Zhang He, the Huang He carries huge amounts of silt from the loess plateau in the west. After flowing out of the mountains, each of these streams deposits a large amount of silt on the plain. The channels are notorious for silting up and for dike breaches. There is a wide variation in the geomorphological features going from the mountains to the coast: fans of various sizes are distributed in the piedmont areas; the central part is a broad alluvial plain; and the east is composed of coastal plains and deltas. Owing to the continuous silting up of the channels and the construction of dikes in response, the alluvial belts of the rivers have become dividing ridges of the plain. In consequence, relatively low-lying depressions have been formed between pairs of alluvial fans or river channels. This feature has not only determined the rolling relief and the differences in surface sediment of the present plain, but it has also had a great effect on the water-salt regimes of the surface runoff and the shallow groundwater. The entire plain can be divided into the following three geomorphological types:
(1) The piedmont diluvial-alluvial plain. Situated in the stretch from Beijing to Xinyang in the eastern piedmont of the Taihang Shan and the Qin Ling, this piedmont plain consists of interlaced diluvial-alluvial fans descending from west to east, 30 to 100 m above sea level. The eastern piedmont of the Taihang Shan north of the Huang He is roughly delineated by the 100 m contour line. The surface gradient between the 100 m and 50 m contours is generally about 1:600, becoming gentler as one goes eastward. Relatively large alluvial fans have been formed by the Zhang He, Hutuo He and Yongding He. As the Huang He has flowed across the centre of the plain it has formed a huge wide fan below Mengjin, the front edge of which approaches the southwest fringe of the Shandong Hills. The river channel between Mengjin and Lankou is the ridge axis of the fan. There is a marked dip from this axis north towards the Hai He Plain and to the south towards the Huai He Plain. In the past, when the Huang He overflowed its banks or shifted course, it usually occurred in this stretch. The piedmont plain is composed of tremendously thick coarse sand gravel or sand pebbles. Most of the proposed Middle Route diversion scheme will pass through this region, so attention should be paid to controlling canal seepage.
(2) The main part of the Huang-Huai-Hai Plain is an alluvial plain. Historical records show over 1,600 shifts in river course or dike breaches. There have been six major changes in river course since 602 BC, affecting an area from Tianjin in the north to Huaiyin in the south. In a broad sense, this plain can be regarded as a major alluvial plain of the Huang He. Research into the distribution of ancient river channels on the alluvial plain and how they are buried is of great significance to the exploitation and utilization of shallow fresh groundwater and to the use of these channels as underground reservoirs to store and regulate water resources.
The alluvial plain on the north side of the Huang He slopes from the southwest to the northeast. Historically this plain has been widely affected by the Huang He and even now there are still traces of the ancient Huang He on the surface. In addition, there are numerous swamps and depressions in the plain. The largest depressions are the Ningjinbo-Daluze, Baiyangdian and the Wenanwa. The plain is principally composed of sandy and loamy sediments, with loam predominant. The sandy sediments are distributed in lines or bands along runways, shoals and ancient river channels. The ground surface is extremely level, with a slope of about 1:10,000.
The Heilonggang District, located in south-central Hebei Province, lies between the Zhang He in the south, the Fuyang He and the Ziya He in the west and the Wei He and the Nan Yunhe (South Grand Canal) in the east. It covers an area of about 15,300 km² and includes 47 counties and county-level municipalities in Handan, Xingtai, Hengshui, Cangzhou and Langfang prefectures and a portion of Tianjin Municipality. The district contains numerous saucer-shaped depressions, ancient river channels and rolling sand dunes. Because of inadequate drainage, the water table is high and heavy evaporation causes extensive soil salinization.
The Huaibei alluvial plain north of the Huai He and south of the Huang He slopes from northwest to southwest. Formed by the accumulation of silt from the Huai He and its tributaries, the face of this plain has also been affected to a certain degree by the Huang He which in historical times has appropriated the Huai He channel as an outlet to the sea. The plain is flat with a gradient of approximately 1:1,000. The sediments are predominantly alluvial phase clayey soils, silty mildly clayey soils and sandy soils.
(3) The coastal plain has an elevation in general less than 5 m above sea level. It is mostly from 30 to 40 km wide, but extends over 100 km in the northern Jiangsu plain. Its surface slope is extraordinarily gentle. The plain has flat shallow depressions and lagoons of various sizes. Recent deltaic plains lie at the mouths of the Huang He and Luan He. The apex of the Huang He delta is in the vicinity of Lijin County about 80 km from the sea. There are many abandoned river channels left in the delta (Editorial Department, 1975),which is growing rapidly at a rate from dozens to over two hundred metres per annum.
The proposed water transfer region crosses the north subtropical and warm temperate zones. Roughly speaking, the area to the south of the Huai He together with the upper reaches of the Han Jiang lie in the north subtropical humid climatic zone, while the broad expanse to the north of the Huai He is in the temperate semihumid climatic zone. The entire region has a distinct summer monsoon from the southeast. It has the following temperature and precipitation conditions.
The region's cumulative temperature >= 0° C is 4,500° C to 5,500° C and that >= 10° C is 3,800 to 4,900° C, increasing from northwest to southeast. Apart from areas along the coast and south of the Huai He, temperature rises rapidly in the spring and drops quickly in the autumn. The mean temperature in the HuangHuai-Hai Plain is 11° to 16°C higher in May than in March and is 10° to 12° C lower in October than in August. The seasonal rise and fall in temperature is more sudden than in areas south of the Chang Jiang. Furthermore, the annual duration of sunshine is longer, mostly 2,100 to 2,800 hr. increasing from southeast to northwest, just the opposite from the temperature distribution. Sunshine may exceed 2,800 hr/annum in the Hai He plain. The potential evaporation capacity varies from 700 to 900 mm/annum and exceeds 800 mm in most parts of the Huang-Huai-Hai Plain. The degree of aridity (measured as the ratio of annual potential evaporation capacity to annual precipitation) is greater than 1.
Annual precipitation varies between 500 mm and 1,200 mm in the region, tending to decrease from south to north and from mountainous areas to the plains or intermontane basins. Precipitation may exceed 700 mm/annum in the Yan and Taihang Shan but declines from there northwest to the plateaux and east to the plains. It exceeds 800 mm/annum in the upper reaches of the Han Jiang, may reach 1,200 mm in the Dabie Shan and is about 1,100 mm in the lower reaches of the Chang Jiang. From 500 to 1,000 mm/annum falls on the Huang-Huai-Hai Plain, except for the area around Xian, Hengshui and Sulu counties in southern Hebei Province, where it is less than 500 mm (Figure 2).
Figure 2. Isohyetal Map for Mean Annual Precipitation of East China Water
Precipitation varies greatly from year to year. The Huang-Huai-Hai Plain has one of the largest relative rates of annual variation in China (Zhu, 1962),20 to 34 per cent in most areas. The highest variation is along a line connecting Jinan, Tianjin and Zhangjiakou. The rate of annual variation in the region as a whole increases with latitude from 16.3 per cent in Nanjing to 17.8 per cent in Hefei, 23.5 per cent in Zhengzhou, 30.1 per cent in Jinan and 31.5 per cent in Beijing. Data recorded over the last thirty years reveals a difference of 4 to 6 times between wet years and dry years in many localities. For instance, annual precipitation in Beijing was 1,406 mm in 1959 but only 261.5 mm in 1965. In Bengbu it has ranged from 1,559 mm in 1956 to 442.1 mm in 1978. In addition, both rainy years and dry years occur in relatively long successions, leading to serious drought or flooding and to very unstable agricultural yields.
Winter and spring are dry with scant rainfall as precipitation is highly concentrated during the summer monsoon. Besides the uneven seasonal distribution, there is a wide intraseasonal difference in precipitation between areas north and south of the Huai He. In most areas to the north of the Huai, spring (March to May) precipitation is but a few dozen mm, less than 15 per cent of the annual total. Sixty to seventy-five per cent of the year's precipitation is concentrated in the summer (June to August). Autumn precipitation is generally higher than in the spring, while winter is the driest season. In areas south of the Huai, spring precipitation, exceeding 150 mm, amounts to over 20 per cent of the annual total, with an additional 40-50 per cent falling in the summer. In most places the autumn is drier than the spring. Most of a year's precipitation is concentrated in July and August storms. The main storm regions are situated on the windward side of the Taihang, Yan, Dabie and Funiu Shan.
To sum up, crop growth on the Huang-Huai-Hai Plain is benefited by favourable sunshine conditions together with a quick rise in temperature and low relative humidity during the spring. On the other hand, evaporation is high, annual precipitation is too low and precipitation varies greatly from season to season and from year to year. In consequence there are successive spring droughts and summer storms can lead to flooding.
RIVERS AND HYDROLOGIC CHARACTERISTICS
The Main Water Systems and River Channels
From south to north, the major rivers in the region are the Chang Jiang, Huai He, Huang He, Hai He and Luan He. These empty into the Dong, Huang and Bo Hail The largest tributary of the Chang Jiang, the Han Jiang, merits some separate consideration. The region embraces the middle and lower reaches of the Chang Jiang, the lower reaches of the Huang He, and the entire drainage basins of the remaining rivers. The following is a brief description of these rivers:
Chang and Han Jiang. The abundant water of these rivers is a potential source for transfer along both the East Route and the Middle Route. The Chang Jiang is the largest river in China with a drainage basin of about 1.8x106 km² and a total length of 6,300 km. After it enters into the region under consideration, the river channel becomes gentle with a surface width of 2 to 3 km under normal conditions. Water is extraordinarily abundant in the Chang Jiang and its annual average runoff is 980x 109 m³. The annual average discharge at the Datong station on the lower reaches is 29,200 m³/sec with a maximum of 43,100 m³/sec in 1954 and a minimum of 22,100 m³/sec in 1972. The maximum observed peak flood discharge recorded was 92,600 m³/sec in 1954 and the minimum flow was 6,020 m³/sec in 1923. The coefficient of variation for annual runoff is a relatively low 0.15.
The Han Jiang has a basin of about 0.17X106km² and is 1,532km long. Its upper reaches are in the mountains, where gorges alternate with basins. The middle and lower reaches flow into a plains area commonly known as the JiangHan plain. The river's average runoff is 48X109 m³. The large-scale Danjiangkou Reservoir on the upper reaches is the site for water transfer into the proposed Middle Route.
Huai He. This river is large with many tributaries but no outlet of its own to the sea. Its drainage basin occupies 0.26X106 km², including the river systems of the Yi He, Shu He and Si Shui. The main course has a length of 1,000 km, originating in the Tongbai Shan in Henan Province. After flowing into Hongze Lake, the majority of the river's water passes through Gaoyou Lake and converges with the Chang Jiang while a smaller amount empties into the Huang Hai through the North Jiangsu Canal. The northern and southern tributaries of the Huai are very asymetric. Those in the north are numerous and long and originate either in the Funiu Shan or below the southern embankment of the Huang He. These are mostly plains rivers with gentle flows. Some of the channels have become "elevated rivers" due to the diversion of the silty Huang He into them over a long period of time. The less numerous tributaries originate in the Dabie Shan and are short and swift.
The average annual runoff observed in the Huai basin is about 49.9x 109 m³. The discharge over the year at Bengbu station in the middle reaches averages 855 m³/sec with a maximum of 2,280 m³/sec in 1921 and a minimum of 117 m³/sec in 1966. The maximum observed peak flood discharge was 26,500 m³/sec in 1931 while during the driest period the river ceased flowing. The coefficient of annual variation in runoff is as high as 0.63, the greatest of all the major rivers in China.
Huang He. This river, 5,464 km long and with a drainage basin of about 0.75X106 km², has an enormous silt content, with 1.6X109 tons per year entering the lower reaches where the channel widens and the gradient flattens. Over a long period of time the highly silt-laden flows have turned the channel into an accumulational stretch. The river bed is now several metres-in some places over 10 m-higher than the surrounding land surface. Over the past thirty years the main channel in the lower reaches has risen at a rate of 10 to 20 per year. This flow characteristic of the lower reaches of the Huang He makes the crossing project a key one for the proposed East Route. At present the ideal site for this is the narrowest section of the lower reaches, located between Weishan and Xieshan. The mainstream width here is about 280 m. The huge amount of silt which has to be dealt with each year precludes the use of the Huang He channel itself to convey Chang Jiang water northward. Hence the only option is to bore a tunnel under the river bed.
Although the Huang He is the second largest river in China, its observed annual runoff is only 48.6x 109 m³. The average discharge over a year recorded at the Shenxian station in the middle reaches is 1,350 m³/sec, with a maximum of 2,091 m³/sec in 1937 and a minimum of 635 m³/sec in 1928. The maximum observed peak flood discharge was 22,000 m³/sec in 1933 and the minimum just 145 m³/sec in 1928. The Huang He has been one of the largest rivers in China most affected by human activities, especially since the founding of the People's Republic of China in 1949. Large diversions from both banks for irrigation and the construction of other kinds of projects of all sizes have led to a reduction in the natural runoff of the river.
Hai He. This is the largest river in north China, with a drainage area of about 0.26x 106 km². The Hai He plain is the principal area to be benefited by the proposed water transfer projects. The Hai river system is fan-shaped, with five major tributaries: the North Canal (including the Ji Canal, the Chaobai He and the North Canal), the Yongding, Daqing and Ziya He and the Wei Canal. These tributaries converge into the Hai He from the north, west and southwest in the vicinity of Tianjin. The mainstream of the Hai is a flat, shallow meandering channel with a total length of about 75 km. The Tuhai and Majia He, which empty into the sea through their own outlets, are ordinarily included in the Hai river basin. The average annual runoff in the basin is roughly 22.6x109 m³ and comes mainly from the mountains. The flatness of the plain provides inadequate conditions to create a flow.
All the rivers in the Hai He basin rise in the Taihang Shan or the Loess Plateau and flow through them. In the upper reaches the river systems are well developed, with steep beds, deep gorges and many stretches where gorges alternate with basins, providing good dam sites for reservoir construction. However, when the rivers flow out of the mountains, their stream beds flatten abruptly, the flow becomes gentle, silt is deposited and the channels become shallower. Some stretches have turned into "elevated rivers".
Luan He. This 877 km long river rises in Fengning County in the Yan Shan and drains about 54,000 km². Its upper and middle reaches are torrential flows with rich water sources. The Luan has an average natural runoff of 5.75 X 109 m³/annum.
The estimated annual runoff of the entire region averages about 1.15X 1012 m³, 43 per cent of the national total. The Chang Jiang has about 88 per cent of the region's water. Just as with the Huang He, human activities have had quite a striking impact on the runoff and its process of change in the Huai and Hai He. The construction) of numerous water projects has brought much of the mountain runoff under control in the upstream areas of these two rivers. In addition, increases in industrial and agricultural water use have affected runoff.
The following makes use of some basic characteristics of variations in annual runoff to analyze the hydrologic conditions of the proposed water transfer. The distribution of annual runoff depth (Figure 3) tends to coincide with that of annual precipitation (Physical Geography Editorial Committee, 1981). Annual runoff in the region decreases from over 600 mm in the Dabie Shan to 400-600 mm in the upper reaches of the Chang Jiang, 200-300 mm in the Yan and Taihang Shan, less than 200 mm in the Huang-Huai-Hai Plain, and (an average of) merely 50 to 100 mm in the Hai He plain, where in most areas it is less than 50 mm and the annual runoff coefficient is under 0.1.
Year-to-year variations in annual runoff are also extraordinarily pronounced. The coefficient of variation is over 0.6 for the entire region and exceeds 0.8 for most parts in the Huang-Huai-Hai plain, one of the most labile regions in China.
These big rivers have relatively long periods of wet years and dry years. For instance, the longest low flow periods on record are 5 years for the Huai He (at Bengbu station), 11 years for the Huang He (at Shanxian station) and 9 years for the Yongding He (at Guanting station). At the same time high and low flow years are very rarely synchronized between the major rivers. This provides favourable conditions for interbasin water transfer along either the Middle Route or the East Route.
The rivers of the region are mainly rain-fed. Variations in runoff during the year are closely correlated with the distribution of precipitation but are more extreme due to the influence of topography and human activities. Areal differences are even more pronounced. The spring flow in many rivers does not show an obvious increase because rainfall then is sparse, the temperature rises quickly and evaporation is high. North of the Huai, spring runoff constitutes only 6 to 10 per cent of the annual total; south of the Huai it is 10 to 20 per cent.
Summer runoff accounts for 40 to 50 per cent of the annual total in areas south of the Huai and along the Han Jiang; 50 to 60 per cent in the Taihang Shan; and up to 60 to 70 per cent in the plains areas. The Huang, Huai and Hai have been known historically for their summer floods.
Autumn runoff is generally higher than in the spring and may reach 35 to 40 per cent of the annual total in the upper reaches of the Han Jiang. It exceeds 30 per cent in the Hai He plain and is 20 to 30 per cent in other localities. Autumn flooding is common. The winter is the low flow period when ice forms in numerous rivers north of the Huang He. Aside from the Taihang Shan where it exceeds 10 per cent, winter runoff occupies only 6 to 8 per cent of the annual total in the region. It is even less than that in the Luan He basin.
Figure 3. Isoline Map of Annual Runoff Depth of East China Water Transfer Region
In general, surface water resources in the Huang-Huai-Hai plain are not plentiful and hydrologic conditions are extremely unstable. Surface runoff is lacking in the winter and spring and successive spring droughts occur over large areas. In summer, however, when the flood waters flow into the plain's river channels, dikes are often breached and banks overflowed, resulting in inundations. Since the 1950s the Huai He and then the Hai He have been controlled, greatly transforming both rivers. The fan-shaped drainage system of the Hail has been basically remoulded, providing some control of the mountain flood waters. The chaotic river network of the dower reaches of the Huai has been realigned.
The groundwater of the mountains surrounding this region is mainly bedrock crevice water and, secondarily, phreatic void water stored in unconsolidated Quaternary diluvial-alluvial strata. The drainage from streams into the subsurface water provides a steady supply source of water to other streams. Groundwater is quite complex in depth and distribution in the mountains. Because of structural, geomorphic and hydrogeological conditions, only a few localities have abundant groundwater there.
Quaternary deposits have settled on the Huang-Huai-Hai plain in great thickness, 200 to 600 m. From the piedmont to the coastal plains hydrogeological conditions change with marked regularity. Aquifer materials become finer, individual aquifers become thinner and more numerous, and the water quality worsens. The water-bearing strata composed of Quaternary unconsolidated deposits can be divided into the shallow aquifers at a depth of 50 to 60 m or more, and the deep aquifers which are even farther below the surface. The former contain phreatic water or slightly confined water; the latter, confined water.
Since the Quaternary period, the sedimentary environments have differed on either side of the Huang He, so there is a great disparity in hydrogeological conditions. The piedmont diluvial-alluvial fans to the north are well developed with aquifers thicker than 100 m composed of relatively coarse materials, mainly sand and either gravel or pebbles. Subsurface runoff conditions are good. This area has abundant pure fresh water. Specific capacities of wells here are 20 to 50 m 3/fur or greater and the groundwater lies mostly at a depth greater than 5 m. South of the Huang, no piedmont diluvial-alluvial fans have developed, the aquifers are 20 to 30 m thick and consist predominantly of coarse to medium grain sand. Specific capacities of the wells are 10 to 30 m³/hr. In sum, the piedmont plain possesses the most favourable conditions in the region for groundwater extraction.
Throughout the alluvial plain, variations in the lithological characteristics, structure and thickness of the unconsolidated deposits are extremely complicated with sands of different grain sizes interbedded with clayey soils. The aquifers are numerous but not thick, with a water-yielding capacity which is both inferior to that in the piedmont plain and which decreases monotonically eastward. The specific capacities of wells here are 5 to 30 m³/hr. The table of phreatic or slightly confined water is generally 2 to 4 m below the surface in the alluvial plain and within 2 m in some depressions. The phreatic water flows from southwest to northeast in areas north of the Huang He and from northwest to southeast in areas to the south. Evaporation is the main way phreatic water is removed due to the flatness of the terrain, the relatively weak permeability of the fine particules comprising the aquifers, the gentleness of the groundwater hydraulic gradient and the extreme slowness of the flow.
Confined water is distributed throughout the alluvial plain. The confined aquifer is shallow (40 to 50 m) in the west and deep (200 to 300 m) in the east, with a confined water table lying mostly within 3 to 5 m of the ground surface. As the rate of groundwater extraction increases the piezometric pressure head of water drops constantly, thus forming cones of depression in places where water withdrawal has been the heaviest. Although the intensity of extraction of deep confined water which was formed through recharge within an historical period is lower than that for shallow groundwater, the level in the centre of the cone has nonetheless fallen very quickly, at a rate up to 2 to 6 m per annum. The deeper the aquifer, the greater the rate of drawdown. According to estimates made in Tianjin, Dezhou, Cangzhou and Hengshui, the extractable volume is 2,000 to 3,000 m³/km²/annum when the deep confined water level drops by 1 m/annum. Effective measures, most importantly artificial recharge, must be employed to prevent the depletion of groundwater.
There is marked variation in the mineralization of groundwater in the HuangHuai-Hai Plain. The piedmont plain contains freshwater with a mineralization less than 1 g/ 1. Most portions of the alluvial plain have slightly saline water with a mineralization of 1 to 3 g/1. Highly mineralized saline water predominates in the coastal areas, generally greater than 5 g/1 and sometimes even in excess of 30 g/ 1. There is a gradual transition in groundwater hydrochemical types from heavy carbonates and sulphate chlorides in the west to chloride sulphates and chlorides in the east. Vertically, shallow groundwater in the centre of the plain generally exhibits belts of fresh water in shallow ancient channels overlying a saline water body which in turn overlies confined fresh water mineralization generally less than 1 g/1 (No. 4 Hydrogeological Team, 1977). The base of the saline body is an undulating surface which deepens from west to east. It normally lies 60 to 100 m beneath the surface but may be as deep as 200 m. The groundwater in part of the coastal plain is almost entirely saline. Where fresh water is present over the saline water, it is 20 to 50 m deep (maximum 80 m).
Shallow freshwater in the Hail He plain is correlated closely with the distribution of ancient channels. For instance, the bottom layer of the shallow fresh water is 30 to 50 m from the surface (in some places 50 to 80 m) within the ancient channels of the Huang and Zhang He in the counties of Daming, Linxi, Guchang and Jing. The water quality type, both horizontally and vertically, is relatively uniform in the vast plain extending from south of the Huang He to the Huai He region-mainly heavy carbonates with a mineralization generally below 1 g/1 (I to 3 g/1 in some localities). Saline water covers 100,000 km² of the HuangHuai-Hai Plain, or one-third of the region's total area.
Calculations based on long-term observations of groundwater dynamics conducted by the Ministry of Geology indicate that the average annual freshwater contained in the shallow aquifers of the Huang-Huai-Hai Plain is 47.6x109 m³ (20.4X109 m³ north of the Huang He and 27.2x109 m³ south of it), and saline water is 9.1X 109 m³ (3.0x 109 m³ north of the Huang He and 6.1x109 south of it).
The annual recharge of shallow groundwater in the piedmont area north of the Huang He is generally 0.2 to 0.25x 106 m³/km² (0.3 to 0.5x 106 m³/km² in the Beijing piedmont plain), 0.2 to 0.25x106 m³/km² in the east Henan plain along the Huang He; and 0.15 to 0.2x 106 m³/km² in most of the plains of north Shandong, north Jiangsu and north Anhui, but only 0.1 to 0.1 5x 106 m³/km² in some parts of those plains.
SOIL AND VEGETATION TYPES AND PROPERTIES
Areas north of the Huang He are in the warm temperate burozem and drab soil zones with broadleaf deciduous trees and sparse trees and shrubs. The basins of the Huai He and the middle and lower reaches of the Chang Jiang south of the Qin Ling as well as the Han Jiang are in the northern subtropical mixed evergreen and deciduous broadleaf forest zone. Most of the natural vegetation has been destroyed by long-term reclamation. Natural vegetation remains only on a few higher mountain ridges or where cultivation has not been possible. The predominant type of tree is oak.
Drab soil prevails in the mountains and piedmonts of north China. Brown earth is found on the low mountains and hills of Shandong Province and the mountains of north Hebei Province. In the main, cultivated burozem is distributed on the Qin Ling and Huaiyang Shan (Figure 4), with some brown earth as well (Nanjing Pedology Institute, 1978). These are all zonal soils. The scarcity of natural vegetation has led to serious erosion and poor moisture or fertility retention capacity. The mountains south of the Huai He are mainly covered by oak (Quercus) or pine or mixtures of the two. In addition a certain portion of this area has been planted in China fir and mao bamboo. The limited amount of natural vegetation remaining north of the Huai He is predominantly oak, with pine (Pinus rabulaeformis) second.
Figure 4. Soil Map of the Huang-Huai-Hai Plain
The Huang-Huai-Hai Plain is mostly cultivated and nearly without natural vegetation. The principal trees on the plain are Chinese toon and elm and the main grasses are xerophilic Themela Triandra (var. japonica), Bothriochloa ischaemum and Artemisia. The Huang-Huai-Hai Plain is flat with a thick soil horizon. Cultivated meadow soil, China's principal dry farming soil, is concentrated here. This kind of soil, formerly called alluvial soil or light-coloured meadow soil, is formed in the alluvial plain under the influence of groundwater activity and matured through cultivation. In this region it can be divided into yellow meadow soil, light grey meadow soil and sajong meadow soil.
Yellow meadow soil is comprised of loessial deposits which have been matured through cultivation. Most of the soil of the Huang-Huai-Hai Plain falls in this category. There is little accumulation of organic matter on the surface, imbuing the soil with a rather light colour. There is only about 0.5 per cent organic matter in the cultivated horizon, which is rich in calcium with a slight alkaline reaction. There is considerable variation in texture with both sandy soil and clayey soil. Most soil profiles are arranged in horizons formed by different textures.
Because of the high water table (generally 1 to 3 m), salinization accompanies humidification in the alluvial plain. Saline soils are mainly distributed in eastern Hebei, northwest Shandong, the Nansi Lake plain, the Huai He plain and in the depressions around Huang He, covering a total area of 2.7 million ha.
Light-grey meadow soil is comprised of sediments in the middle and lower reaches of the Chang Jiang which have been matured through cultivation. It is often accompanied by a strong leaching process with lime, exhibits a moderate to slight acidic reaction, and is relatively high in organic content.
The Huaibei alluvial plain is low and flat. Sajong meadow soil is broadly distributed in locations here which regularly accumulate water and where drainage is poor. It has a black humus horizon and a sajong gley horizon and exhibits a moderate to slightly alkaline reaction.
In addition, there are several other types of soil in the region: coastal solonchak, paddy soil and bog soil. The coastal solonchak is mainly distributed in the coastal areas of Hebei, Shandong and Jiangsu. Because these areas are low and flat with poor drainage, a high (1 to 2 m) water table, highly mineralized groundwater and tidal effects, the soil salt content is excessively high, generally over 1 per cent and in some cases as much as 30 per cent. The salts are comprised mainly of chlorides. These areas are extensive salt deserts where natural vegetation cannot grow. Only Huangxu cao and Tamarix chrnensis are found, covering less than 10 per cent of the area.
Paddy soil is most concentrated in areas south of the Qin Ling and the Huai He but it is also found in the Yinhuang (Huang Diversion) Irrigation District and in the regions of Nansi Lake and Tianjin's Xiaozhan and Lutai. This type of soil is unique and is formed through long-term paddy cultivation in different kinds of soil. The soil in the double-cropped paddy areas south of the Qin Ling and the Huai He exhibits moderate to slight acidity, while that in the single-crop paddy areas north of the Huai is slightly alkaline in most cases. In some districts when the soil is not being planted to paddy rice it is still undergoing salinization.
Bog soil is distributed in some lake basins or depressions such as Nansi Lake, Baiyangdian and Wenanwa. Here water accumulates to different degrees on the ground surface during the year, the water table is high and there is pronounced gleying of the soil. Drainage measures must be adopted if this soil is to be utilized.
Editorial Department, Annals of China's Geography, 1975, Data on the physical geography of north China, Science Press, Beijing.
Nanjing Pedology Institute, 1978, Chinese Academy of Sciences, Soils in Chino, Science Press, Beijing.
No. 4 Hydrogeological Team, Bureau of Geology, Hebei Province, 1977, The exploitation and utilization of groundwater in plains irrigation districts, Science Press, Beijing.
Physical Geography Editorial Committee, Chinese Academy of Sciences, 1981, Surface water, Science Press, Beijing.
Zhu Binghai, 1962, Climate in China, Science Press, Beijing.
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