Chen Dehua, Chen Xi, Wang Zhao

(Inst.of Hydrogeol.& Environ.geol. ,Shijiazhuang 050061 ,China)

Abstract: In northern China, the natural recharge of groundwater is 293.94´10⁹m³/a and the exploitable amount of fresh groundwater resources is 152.77´10⁹m³/a. In plain areas, the natural recharge of groundwater and the exploitable amount of fresh groundwater resources are 167.53´10⁹m³/a and 108.34´10⁹m³/a, respectively. In this large region, the hydrogeological conditions are very complicated. This leads to the heterogeneous distribution of groundwater resources. The distribution characteristics of regional groundwater resources and the current situation of and problems in groundwater exploitation and utilization in northern China are elucidated in this paper.

Key words: Northern China; groundwater resources; distribution characteristics; exploitation and utilization

The administrative region of northern China includes Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Shandong, Henan, northern Jiangsu, the part of Anhui to north of the Huaihe River, Heilongjiang, Jilin, Liaoning, Xinjiang, Qinghai, Gansu, Ningxia, Guanzhong and northern part of Shaanxi. The total area is about 5.847 million km².

Groundwater is an important component of water resources and has many advantages over surface water: (i) it is reliable in dry seasons or droughts because of the large storage; (ii) it is cheaper to develop, since it requires little treatment; (iii) it can often be pumped where it is needed, on a stage-by-stage basis; and (iv) it is less affected by catastrophic events. In the arid and semi-arid areas where there is shortage of surface water, groundwater has become the main or even the only source of water supply in agriculture, industry and daily life. For instance, in Hebei, Shanxi and Beijing, groundwater accounts for 74.3%, 66.8% and 64.5% of total annual water supply. Therefore, groundwater plays an important role in the economic development in northern China.

The northern China is vast in territory. However, the water resources are not abundant. The spatial and temporal distribution is quite uneven. Shortage of water resources not only restricts the development of society and economy, but also brings about excess development and utilization and worse ecological environment. In the future the shortage of water resources will still be the key factors limiting the development of society and economy because of the increase of population, and the decrease of water resources quantity.

1 Quantity and Distribution of Groundwater Resources

According to results of investigation on the nationwide groundwater resources in 2003, in northern China, the natural recharge of groundwater resources is 293.94´10⁹m³/a, accounting for 31.8% of the nationwide amount. The volume of exploitable resources of fresh groundwater is 152.77´10⁹m³/a, accounting for 43.3% of the nationwide amount. In the plain areas, the volumes of natural recharge and exploitable fresh groundwater are 167.53´10⁹m³/a and 108.34´10⁹m³/a, respectively, which account for 65.3% and 69.4% of the amount of groundwater resources in plain areas nationwide, respectively.

1.1 Regional differences in the distribution of groundwater resources

The topography of northern China is characterized by gradually descending in elevation from the west towards the east. The regional distribution of precipitation is extremely uneven because of the great influence of such factors as the distribution of seas and lands, the sources of water vapor, terrains and landforms. The general trend is that the precipitation gradually decreases from the eastern coastal areas (600-800 mm) to the northwestern inland areas (<100 mm). As a result, the formation and distribution of groundwater resources is uneven. For example, the area of Northeast and North China accounts for 45.0% of the total area of northern China, but the natural recharge and the exploitable resources account for 54.3% and 62.4% of the total amounts, respectively; In Northwest China, the land area is 52.5% of the total area in northern China, but the percentages of natural recharge and exploitable resource are 40.3% and 30.4% of the total amount in northern China, respectively (Table 1).

Table 1 Statistics of groundwater resources in northern China (10⁹m³/a)

1.2 Difference in groundwater recharge conditions

The groundwater recharge conditions in the west are quite different from those in the east. Generally, the recharge decreases from east to the west. The module of natural groundwater recharge in North China plain shows the highest value. In the lower reach of the Yellow River, the module is 151.3´10³m³/km^2 ·a (Table 2). The modules in Northwest China are normally lower than 50´10³m³/km^{2  ·}a, for example, 17.6´10³m³/km^{2  ·}a in Hexi Corridor, which is about 1/8 of that in the lower reach of the Yellow River.

Table 2 Modules of groundwater resources in different catchments basins

In northern China, the distribution of natural groundwater recharge modules in catchment basins (Table 2) is basically consistent with the precipitation distribution. Due to the effect of geological condition, topography, rock properties and hydrological conditions on groundwater resources, the distribution of modules in a certain region might be complicated. For instance, in a region of high module, it might include a certain part of low module.

1.3 Types and distribution characteristics of groundwater

In northern China, according to the nature of aquifer space, groundwaters can be classified as three types, i.e., pore water, karst water and fissures water.

Pore water (natural recharge 182.35´10⁹m³/a, exploitable resources 116.67´10⁹m³/a) mainly distributes in the major plains and basins, and is a predominant component of groundwater resources. In northern China, the pore water mainly distributes in the Mesozoic-Cenozoic tectonic basins of large scale, which are composed of thick loose sediments. In these sediments, abundant groundwater is stored. (1) In the inland basins in west. At the piedmont parts of the basin, the recharge of groundwater is normally abundant due to the plenty of precipitation in the mountain area and the thawing of perennial snow. Large amount of water is stored in thick sandy gravel aquifer and the runoff condition is good. However, in the middle part of the basin, where is mainly covered by sand dunes and the climate is arid, there is a shortage of groundwater. (2) In the Huang-Huai-Hai Plain and Song-Liao plain. Large amount of groundwater is stored in the very thick Quaternary sediments. The groundwater resource is relatively homogeneously distributed. The circulation of groundwater is mainly in vertical direction. The groundwater flow in horizontal direction is very slow. (3) In the Loess Plateau. Groundwater types mainly include loess pore water and loess fissure water. The groundwater resources are scarce. The formation and distribution of loess groundwater shows unique characteristics. In loess, groundwater transports mainly through the holes and fissures, but is mainly stored in pores.

Karst water (natural recharge 19.76´10⁹m³/a, exploitable resources 13.33´10⁹m³/a) distributes mainly in Shanxi, Shandong and Hebei. The temporal and spatial distribution is uneven. The aquifers consist of the carbonate rocks from Sinian to Ordovician. Karstification degree is lower than that in southern China. The karst water mainly crops out as springs, such as Tianqiao spring and Niangziguan spring in Shanxi and Baotu spring in Shangdong.

Fissure water (natural recharge 91.83´10⁹m³/a, exploitable resources 22.77´10⁹m³/a). Bedrock fissure water distributes mainly in mountainous and hilly areas. Aquifers are composed of clastic rock, metamorphic rock and magmatic rock. Due to the differences in lithology and inside and outside agents, the development of fissure varies in different locations. This results in the difference in fissure water distribution. In the alpine zone of the northwestern arid areas, as a result of climate vertical zonation, precipitation is abundant in the mountain area. Therefore, the recharge of bedrock fissure water mainly occurs in this area. Finally, this recharge becomes an important source of the groundwater in the plains.

2 Exploitation and Potential of Groundwater Resource

2.1 Exploitation of groundwater

According to the water supply data in 1999, groundwater plays the most important role in North China. In the total water supply, groundwater supply accounts for 74.3% in Hebei, over 60% in Beijing and Shanxi, 56.7% in Henan, over 40% in Shandong, Liaoning and Shaanxi Provinces, respectively. The water supply in most cities in northern China is mainly from groundwater. 70% of urban and rural residents rely on groundwater as drinking water. In some cities, such as Hohhot, Baotou, Xining, Hengshui and Cangzhou, groundwater is the only source for water supply. This indicates that groundwater is of great importance in the industry and agriculture and urban drinking water supply.

In northern China, in average 66.07% of the total amount of groundwater is consumed in agriculture. In Jilin, Hebei, Xinjiang, and Inner Mongolia, it accounts for over 70%. In Gansu it reaches 80.15%. In average, 18.37% and 15.56% of total groundwater water is used in industry and daily life, respectively (Table 3).

Table 3 Exploitation of groundwater for different purposes in each province (city, autonomous region) in northern China(10⁹m³/a)

2.2 Exploitation potential of Groundwater

The history of groundwater exploitation in China is very long. With the rapid development of economy and improvement of people's living standard, more and more water is needed. In northern China, where there is shortage of surface water, groundwater has become the main or even the only source for water supply. In 1950s and the early 1960s, in a few big and medium-sized cities, groundwater was used as the source of urban water supply, based on the systematic prospecting and exploitation planning. In late 1970s, the rapid urban development and construction of industrial bases led to a growing demand for water. Some cities and areas met the problem of shortage of water resources. Due to insufficient surface water supply, water supply was mainly dependent on the exploitation of groundwater. In northern China, the groundwater extraction volume was 6.379´10⁶m³ at the end of the 1970s, and reached 8.439´10⁶m³ in 1999 (which is 32.3% higher than that at the end of the 1970s). In Hebei, Henan and Shandong provinces, the groundwater extraction volume was more than 1.20´10⁶m³/a (in Hebei, the highest reached 1.495´10⁶m³/a). This accounted for 47.7% of the total extraction volume of groundwater (Figure 1).

Figure 1. Exploitation of groundwater at different periods in each province, autonomous region or municipality directly under the Central Government in northern China

The large plains and basin in northern China are the main agricultural areas of our country and also the areas where the groundwater is most intensively exploited. In the six basins in Shanxi, the exploitation degree (extraction volume/exploitable volume) was 106.6%. In Guanzhong Plain, Huang-Huai-Hai Plain and Hexi Corridor, the exploitation degree exceeds 60%. For example, the exploitation degrees in Tianjin, Hengshui, Weiwu regions are 340%, 155%, and 130%, respectively. In the regional scale, the overexploitation and the potential exist at the same time. In North China, in most areas, generally speaking, there is no exploitation potential of groundwater any longer, except the zone along the Yellow River in shangdong and piedmont region of Yanshan mountain. In Northeast China, in Songliao and Sanjiang plains, the groundwater exploitation degree is less than 50%. In most regions, there is certain potential of groundwater exploitation. In Northwest China, the groundwater resource is not abundant, in the cities using groundwater as main water source and the drainage basin of Shiyang River, the overexploitation of groundwater is a very serious. Problem. However, due to the low amount of water needed in most areas, the degree of overall exploitation of groundwater is low. Therefore, there is still a certain potential of groundwater exploitation (Table 4).

3 Problems in the Groundwater Exploitation

3.1 Lack of systematic planning and scientific management

The layout of exploitation wells is not quite rational and the exploitation is not well planned. This leads to serious regional decrease of groundwater level. In recent years, groundwater extraction in urban area was basically under control. However, the groundwater exploitation for agricultural irrigation was still at a uncontrolled state. In the mid-east part Hebei Plain, due to the shortage of shallow fresh groundwater, deep groundwater (90% from the third aquifer) was over-exploited, which accounts for 50% of the total extraction volume. This caused the continuous drop of deep groundwater level

Table 4 Exploitable potential of groundwater resources in the plains and basins in northern China (10⁹m³/a)

*: Statistics in 2003

3.2 Lack of comprehensive planning in the utilization of surface water and groundwater resources

In the exploitation and utilization of surface water and groundwater, there is a lack of overall planning. The dams in upstream cause the shortage of surface water resource and reduce the recharge of groundwater in downstream areas as well. This is especially problematic in the northwestern inlands. The reservoirs and impermeable channels artificially changed the water circulation conditions and led to the lowering of the water table in the piedmont plain, decreasing of spring flow rate, vegetation regression in lower reaches of a river, development of desertification, and deterioration of eco-environment. In the agricultural area irrigated by water from the Yellow River, there is a problem of water waste. Meanwhile, overuse of water in agriculture also caused the soil salinization.

3.3 Serious waste of water resources

In agriculture irrigation, water resources are not well managed. In some regions, flood irrigation method, which has a high irrigation ration, is still used. In northern China, normally the irrigation ration is 700-1000 m³/mu. In Ningxia Plain, the irrigation reaches 1537m³/mu, which causes serious waste of valuable water resources and results in soil secondary salinization. The waste of water in industry is also serious. Water has not been well recycled. Both shortage and waste of water resources highlights the contradiction between inadequate water supply and demand.

3.4 Weakness in well management

In some areas, the poor quality in well construction caused not only the low production of groundwater in each well, but led to the mixing of waters from different layers. In some cases, this caused the intrusion of brackish/saline water into the fresh groundwater unit. Consequently, the groundwater resource was deteriorated. According to data from Hebei province in 1990s, 10% of wells in Changzhou, Hengshui, Handan, Langfang, and Qinhuangdao were discarded due to deterioration of groundwater quality, causing huge economic losses.

3.5 Serious pollution of water resources

Even the government has intensified law enforcement on environmental contamination, the discharge of industrial wastewater and sewage in some places caused serious environmental pollution. In the peripheral regions of some cities, groundwater has already been contaminated to a certain extent, making water resources more scarce.