Groundwater Resources in the North China Plain FEI ,IIN The Institute of Hydrology and Engineering Geology Zhengding, Hebei, China ABSTRACT / Shallow groundwater is a major object of exploitation in the North China Plain. About 20 billion m3/yr of

Introduction

The North China Plain is located in the eastern part of the People's Republic of China. It borders on the Bohai Sea in the east and reaches the Yellow River in the south. The Taihang Mountains border on the west and the northern boundary of the plain is the Yanshan Mountains. The North China Plain is one of the most important economic areas in China, has a total area of about 260,000 km ~, and a population of approximately 70 million. The normal annual precipitation is generally from 500 to 600 mm (Fig. 1). The monthly distribution of annual precipitation is uneven, with about 70 percent occurring within three m o n t h s - - f r o m J u n e to August. The yearly changes in annual precipitation are significant with the difference of precipitation during dry and wet years as much as three to four times. There are three river systems in the plain: the Haihe, Launhe and the Yellow River. There are also some dry rivers which drain nearby waterlogged areas in rainy seasons; such rivers are the Douhai, Majia, and Heilonggang (east of the Grand Canal). Most of the rivers are seasonal, usually dry because of the reservoirs in their upper reaches. The amount of surface water available as a water supply is 20 billion mS/yr in normal years and 12.4 billion mS/yr in extremely dry years (Xie Jinrong, unpub, data). The groundwater in the North China Plain is mainly from Quaternary aquifers from depths down to 400 meters. Aquifers

Quaternary formations range in thickness from 200 to 600 m, however, the greatest thickness is more than 1,000 m. The aquifers are composed of unconsolidated pebble, pebble and gravel, sand and gravel, coarse sand, medium to coarse sand, fine sand, fine sand and silt, silt, clay, sandy clay, and clayey sand. From west to east, the particles of quaternary aquifers become finer, and the thickness of individual aquifers decreases. Environ Geol Water Sci Vol. 12, No. 1, 63-67

fresh groundwater and about 20 billion ma/yr of surface water are available. Present water demand is about equal to or exceeds the utilizable water resources in the North China Plain. Strict economy of water use is needed along with strengthened water control, a restructured development plan, and artificial recharge.

Aquifers at depths from 0 to 400 m can be divided into two groups (Fig. 2). The first group ranges from 0 to 80 m deep, and the second aquifer group is from 80 to 400 m in depth. In the piedmont area (area A in Fig. 2) to the west and the north of the plain, the aquifers are better recharged, more permeable, have good water quality (bicarbonate type, TDS less than 1 g/l) and the water table is deep. In the middle part of the plain (area B in Fig. 2), the shallow fresh water aquifers are, primarily, fine sand, and, secondarily, fine-medium sand and silt - - f i n e sand. The cumulative thickness of shallow freshwater aquifers is 5 to 30 m, and the hydrochemical types of water are bicarbonate, bicarbonatesulphate, bicarbonate-chloride, and sulphate-chloride waters with TDS less than 2 g/l; the specific capacity ranges 2 to 30 mS/h.m. Deeper freshwater aquifers are distributed evenly throughout the region and consist primarily of medium-fine and fine sands, generally with a cumulative thickness about 40 m and buried to a depth greater than 100 m; in most places these deeper aquifers have specific capacity of 10-30 mS/h.m. The hydrochemical types of water are bicarbonate, bicarbonate-chloride, sulphate-chloride, chloride-sulphate waters with TDS less than 1 g/l. In coastal areas (area C in Fig. 2) in the North China Plain, there are saltwater-freshwater relationships. Only in a few places are there isolated bodies of shallow freshwater. In the river mouth area of the Yellow River, both shallow and deep aquifers contain saltwater. The deep freshwater aquifers in the coastal area consist of medium-fine sand with a cumulative thickness of 50-70 m and a depth greater than 100 m. The hydrochemical types of deep freshwater are bicarbonate, bicarbonate-sulphate, bicarbonate-chloride, sulphate-chloride, or chloride-sulphate waters, and locally, chloride water. E v a l u a t i o n of G r o u n d w a t e r

Resources

Beginning in the 1950s, the fresh groundwater resources in the North China Plain have been evaluated 9 1988 Springer-VerlagNew York Inc.

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Figure 2. (Cont.) many times. The quantitative concept of groundwater resource is defined as the amount of groundwater which can be drawn technologically and economically at a rate of exploitation that will not result in a serious decline of the water table (or the pressure head), serious deterioration of the water quality of the aquifer, or any other unexpected consequences. In the North China Plain, there are three ways to assess groundwater; for places with relatively limited area, such as a city, a county, a district, or big industrial plants and mines, mathematical modeling is usually applied to evaluate the exploitable amount from either shallow or deep groundwater. For example, as a result of the United Nations Project, "Groundwater Resource Evaluation in Huang-HuaiHai Plain," the Institute of Hydrogeology and Engineering Geology under the Ministry of Geology and Mineral Resources has developed mathematical models for the Nanggong District (170 km 2, 600 nodes) and the alluvial fan of the River Hutou (10,600 km 2, 864 nodes). Using the modified program of T. A. Prickett and C. G. Lonnquist, the results are satisfactory (T. A. Prickett and C. G. Lonnquist 1971). Regarding the evaluation of deep groundwater resources for the entire plain, mathematical modeling has not been applied due to the limitation of both data and computer capabilities. Due to practical experience in places like Tianjin, Hebei, and to the results of mathematical modeling for other individual places, most hydrogeoiogists in China believe that the recharge time of deep, fresh groundwater in the North China Plain is extremely long. Deep freshwater being exploited comes mainly from elastic reserves due to the compaction of aquifer, upper and h)wer confining beds, and also due to the elastic expansion of the con-

fined water after the exploitation starts. A considerable part of the exploited groundwater comes from adjacent aquifers through leaky confining beds. The lateral flow from the recharge area is considered negligible. Consequently, in most places the pressure head of deep freshwater has been declining rapidly and continuously after exploitation has started, thus inducing land subsidence and other unexpected results. It is therefore suggested that the deep freshwater in the North China Plain be regarded only as an emergency source of drinking water and not allowed for large scale exploitation. On the basis of exploitation, experience, and the results of mathematical modeling for individual places in the plain, the estimate~t exploitable amount of deep confined freshwater is about 2 billion mS/yr (Chen Mengxiong, unpub, data). Shallow, fresh groundwater is the major object of groundwater exploitation and utilization at present due to its shallow buried depth rapid recharge by rainfall and surface waters. Due to the shallow depth of water table, a considerable part of water is wasted through natural evapotranspiration. Exploitation of shallow, fresh groundwater in the plain may be potentially intensified by lowering the water table and controlling natural evapotranspiration. This will maximize the recharge by infiltration of precipitation and other surface waters. The exploitable amount of shallow, fresh groundwater has-not been evaluated for the entire plain with mathematical modeling because of the limitation of data and computer capabilities. The method that should be used to assess the exploitable amount of shallow fresh groundwater for the whole plain is termed the "method of regional water balance." Shallow groundwater resources in the North China

Groundwater in North China Plain

Plain have been evaluated according to the regional water balance method, and the result is as follows: the allowable exploitive amount of the shallow groundwater is 14-20 billion m3/yr; about 54 percent of the amount is in the piedmont area of the Yanshan and Taihangshan Mountains, about 45 percent of the amount is in the middle part o f the plain, and the exploitive amount of the shallow groundwater in coastal areas is less than 1 percent. Recharge sources, 7 0 - 8 0 percent of the allowable exploitive amount of shallow freshwater, come from the infiltration recharge from precipitation; the other 2 0 - 3 0 percent comes primarily from the infiltration of seepage water from canals, ditches, rivers, and irrigated water; the lateral flow from recharge regions in mountainous areas, however, accounts only for about 2 percent of the total allowable exploitive amount (Chen Mengxiong 1986). Total resources of all fresh groundwater (shallow and deep aquifers) in the North China Plain are about 16-22 billion m3/yr; with the surface water available for water supply, the total utilizable water resource is 3 0 - 4 0 billion M~/yr. However, according to statistics, industrial and agricultural water demand has already reached 40 billion ma/yr, and consequently, an intense water supply problem exists in the North China Plain.

3.

4.

Conclusion T o solve this problem, many hydrologists suggest diverting water from the south m the n o r t h - - f r o m the Yangtze River and Yellow River to the North China Plain. Such a project is so large that it can hardly be supported by the nation's present economic capability. Possible changes in the environment caused by the proposed project are still to be studied carefully. More realistic ways to solve the tense situation are outlined as follows: 1. Eliminate water waste. The present waste of water is serious. For example, the water use in some metallurgical industries is as much as 5 - 6 times more than that of developed countries; likewise the waste of water by agricultural irrigation is serious. 2. Strengthen the control o f water resources,

5.

67

especially groundwater. Groundwater in the North China Plain is still being exploited arbitrarily. According to statistics, about 700,000 wells have been drilled (Xie Jinrong, unpublished data). Make a rational plan for industrial and agricultural development according to water resource availability. Enhance the regulation and management of surface water. At present, existing reservoirs cannot be regulated properly. During wet years, a great amount of water stored in the reservoirs must be drawn off and diverted into the sea to prevent flooding. However, artificial recharge to groundwater is promising. In piedmont areas o f the mountains of Taihan and Yanshan, distribution of shallow gravel and coarse sand layers is more than 15,000 km 2, where depth of the water table is greater than 20 m. It has been estimated that more than 40 billion m 3 of water can be stored underground in these areas through artificial recharge. T h e results of artificial recharge experiments conducted in those areas show that recharge rate can be as large as 1.5 m3/sec, therefore it would be possible to transfer a great amount of surface water u n d e r g r o u n d in a short time. T h e stored water can be pumped and utilized during dry seasons and dry years, and, thus, the efficiency of water resource utilization can be enhanced. Research ways to increase the amount of utilizable water, such as reutilization of industrial waste water, desalinization of groundwater, and sea water utilization.

References Cited T.A. Prickett and C.O. Lonnquist, 1971, Selected Digital Computer Techniques for Groundwater Resource Evaluation, Illinois State Water Survey, Urbana, Bulletin 55, p. 9, 25, 29, 32, 36, 39, 45. Mengxiong, C., 1986, Regional characteristics and assessment of groundwater resource in China: Journal of Natural Resources, v. 1, no. 1, p. 18-27.