Study on Groundwater Flow System Along the Chaobai River and Yongding River, North China Plain

STUDY ON GROUNDWATER FLOW SYSTEM ALONG THE CHAOBAI RIVER AND YONGDING RIVER, NORTH CHINA PLAIN

KAISAR AJI1, TANG CHANGYUAN1, KONDOH AKIHIKO2, SAKURA YASUO3, SONG XIANFANG4, KANEKO SHINOBU1 AND YU JINGJIE4 1 Graduate School of Science and Technology, Chiba University, Japan 2 Center for environmental Remote Sensing Chiba University Japan 3 Department of Earth Sciences, Faculity of Science, Chiba University, Japan 4 Inst.of Geog & Nat.Res, CAS

This paper will try to give a simple description about considering regional groundwater flow system from recharge area to discharge area in region of the Chaobai River and the Yongding River, which sources are from the Yanshan Mountian, the north boundary of NCP between 39o to 41o N latitude. In our study, it was found that changes of EC and pH coincided with groundwater flow from recharge area to discharge area. EC values were low as 300 - 500 s/cm in shallow groundwater of recharge area and high on the piedmont alluvial fan where high populated, urbanization Beijing were about 900 - 1700 s/cm in shallow groundwater. In discharge area, EC values were around 600 - 800 s/cm in deep groundwater. EC values also decreased with increasing with well depth. Tracing of groundwater in NCP has a good corresponding relation with stable isotope such as 18O and D. Groundwater D - 18O values are light in deep groundwater and heavy in shallow groundwater. In deep groundwater D value is range between –92.9‰ and –68.1‰, the 18O value is range between –11.12‰ and –8.6‰. In shallow groundwater D value is range between –76.7‰ and –43.8‰.

INTRODUCTION

Groundwater flow system is very important issue in the hydrological cycling with regional climate. Especially study on groundwater flow system in arid and semi arid region like of the North China Plain (NCP) would bring to great benefit for normal use the groundwater resources. NCP is China’s leading industrial and agricultural area, but it is suffers from the systematic problems of population growth and water shortage. Therefore, better use of groundwater resources in the NCP is an urgent task. By considering the variations of groundwater use in past forty years, the groundwater quantity and quality was obviously affected by both nature and anthropogenic factors. Water table is going decrease year by year. In this paper, attentions have been focused into the spatial distributions of EC, pH and stable isotopes (D and 18O) of groundwater in the basins of Chaobai River and the Yongding River. Further, the characteristics of groundwater in recharge, urban (Piedmont alluvial fan) and lowland discharge areas were separately discussed. SITE DESCRIPTIONS AND METHODS

The annual rainfall ranges from 400 to 600 mm in study area, and 70 to 80% of annual rainfall are found from July to August. There are only 40 mm to 60 mm of rainfall or even no rainfall available in more than one hundred days in Spring. The variation of seasonal precipitation is so large that it is the common case to have dry Spring and flooding Summer. Figure 1 shows the map of study region which includes all places around the Beijing city, Tianjin city and Hebei province between latitude 40º54’′43” to 39º5’47” and longitude 118º39’11” to 115º31’′47”. Quaternary deposits of the NCP represent an ample groundwater reservoir. They have been deposited within a subsiding area, and are underlain by impermeable strata. The origin of the sediments is very complicated. In front of the mountains the Quaternary sequences consist of alluvial, pluvial sdiments. In the middle of plain they are mostly layers of alluvial and lacustrine sediments, and alluvium constitutes the main part near seashore plain which contains several marine deposit layers. Quaternary deposits chiefly consist of monotonous loesslike sediments interbedded with sand (sometimes with gravel). On the basis of lithologic, hydrologic and structural criteria the mentioned sediments have been subdivided into three genetic and aquifers series from the surface: deposits of the recent alluvial of the Yellow River with river channel and interchannel zones; deposits of widespread piedmont cones; and old alluvial plain deposits with a narrow margin of piedmont cones. Water supplies in Beijing depend largely on groundwater and reservoirs. Since almost all rivers in the study region have no water more than 300 days/year. At the same time, the income flows for the reservoirs decreased sharply in past twenty years. Also, it can be found that most of water table is above 20 meters in around Beijing. Over- pumping contributed the most declination of water table. Comparing with observation data in the last forty years, the water table in the Beijing has declined more than twenty meters. From August 23 to September 5th, 2003, our research group went to field surveying. During this period, pH, EC and temperature of groundwater were measured in situ. Information such as groundwater usage, well depth etc. has Figure 1. Map of study regions and sampling points been gotten by well users or farmers. Totally, we had brought groundwater, surface water samples from 55 different points. All anions and cations were analysed in Chiba University, 18O and 2H are also measured by mass spectrometer (Delta S, Themoquest) in the laboratory at Chiba University.

RESULTS

Information about the evolution of water table, EC and pH in this region are very important for water resources development. Figure 2 shows the changes of pH value with the depth of wells. It was found that the pH values in groundwater of the study area were almost larger than 7.0. pH values increased with increase depth of aquifer. In recharge are pH values range from 7 to 8, in Piedmont alluvial fan where around the Beijing pH values are range from 7 to 7.5, in lowland discharge area pH values close or over to 8. Especially, the pH is higher than 8 around the Tianjin city where groundwater belongs to the deep aquifer. From Guanting Dam to Bohai Sea along the Yongding River ( figure 1 ) the ph values increase with great changeable, and in other side where from Myun Dam to Bohai Sea along the Chaobai River ( figure 1 ) the pH values also increase but not with such a great changeable.

Figure 2. Relation between PH and Figure 3. Relation between EC and depth of well. depth of well.

Figure 3 shows the relation between EC and the depth of well. EC values also decreased increasing with well depth. EC values were low as 300 - 500 s/cm with shallow groundwater in recharge area. EC values were high on the Piedmont alluvial fan where high populated, urbanization Beijing were about 900 - 1700 s/cm with shallow groundwater. In lowland discharge area where near the Tianjin EC values were around 600 - 800 s/cm with deep groundwater. So in this area deep groundwater is main drinking resource for human being. Based on the data appear that EC values in ground water were low around the Guanting Dam and Miyun Dam which main resource of

Figure 2. Relation between pH and depth of well. drinking water for Beijing area. From Miyun Dam to Bohai Sea along the Chaobai River (figure 1) the EC values range from 300 to 700 s/cm, From Guanting Dam to Bohai Sea along the Yongding River (figure 1) the EC values range from 300 to 1700 s/cm. EC values sharply increased in the Piedmont alluvial fan where around the Beijing and far northern side of Tianjin city. On the other hand, EC values lower in high elevation and low population northern recharge area, and higher in low elevation, high population, agricultural head lowland urban discharge area, at last low again the discharge area with deep groundwater.

Figure 4. The relation between δD and δ18O in the study area Figure 4 shows that groundwater D - 18O values of study area in NCP typically plot to the right of the global meteoric water line (GMWL). All of the points are located near the GMWL, which means that groundwater originate from precipitation. D - 18O values light in recharge area with shallow groundwater, which D value is range between -92.9‰ and -57.6‰, the 18O value is range between -9.36‰ and -7.11‰. Heavy in hillside urban area with shallow groundwater which D value is range between -72.8‰ and -43.8‰, the 18O value is range between -9.09‰ and -3.86‰. Light in lowland discharge area with deep groundwater which D value is range between -81.9‰ and -62.1‰, the 18O value is range between -10.1‰ and -7.23‰.

) -40.0 D o

% GMWL (

D Shallow G H -60.0

-100.0

-120.0 -16 -14 -12 -10 -8 -6 -4 -2 0 18O (%o)

Figure 5. The relation between δD and δ18O in shallow and deep ground water Figure 5. The relation between δD and δ18O in shallow and deep ground water.

In Figure 5 the groundwater D - 18O values are light in deep groundwater and heavy in shallow groundwater. In deep groundwater D value is range between –92.9‰ and –68.1‰, the 18O value is range between –11.12‰ and –8.6‰. In shallow groundwater D value is range between –76.7‰ and –43.8‰.

DISCUSSIONS AND CONCLUSIONS

Groundwater in front of Yanshan Mountain is a local shallow circular system. Along the runoff direction from north to south, both EC and pH increases. It was found that changes of EC and pH coincided with groundwater flow from recharge area to discharge area. The EC and stable isotopes data indicate that the natural region of the groundwater system of the Quaternary aquifer has been affected greatly by intensive exploitation, especially in areas in Beijing and Tianjin. It also found that both D and 18O became lighter and light with depth in the discharge area, which means that there exist different aquifers in the study area with different recharge area. Based on the isotopic data of groundwater in the study area, an equation of D=5.7118O+20.34 was obtained. In brief, in this study area groundwater flow system has special characteristics from recharge area to discharge area. Groundwater flow is flowing in several separate aquifers from recharge area such as shallow and deep aquifer to discharge area. In the Piedmont alluvial fan groundwater pumped from shallow aquifer, and where in lowland discharge area pumped from deep aquifer.

ACKNOWLEDGEMENTS

The authors would like to thank Dr. Li Huadong and Dr. Yang Chong from Inst.of Geog & Nat.Res, CAS, for their helps during the field works. This work was supported by MEXT through scientific grant No.15310006.

REFERENCES

[1] Sakura, Y., Tang, C., Yoshioka, R., and Ishibashi, H. (2002): Intensive use of groundwater in some areas of China and Japan. In Intensive Use of Groundwater (Eds. By Llamas M.R. and Custodio, E., A.A Balkema Publication.) 337-353.