CHAPTER 9 RESEARCH ON THE APPLICATION OF
ISOTOPE TECHNIQUE IN THE MANAGEMENT
AND ASSESSMENT OF HYDROLOGY AND
CHAPTER 9 RESEARCH ON THE APPLICATION OF
The Isotope Technology plays an important function in the management and assessment of hydrology and water resources, especially on ascertaining the recharge sources, amounts and ages of groundwater, the interaction between surface water and groundwater, the effects on the pollution of surface water to groundwater, etc. We can obtain many key data with little investment, which can't be obtained by other regular methods.
9.1.1 The Brief Review
The application of Isotope Technique to the field of hydrology and water resources is started early in our country. In 1960s some experts have begun analyzing and researching the distribution of 2H and 18O in snow and ice, in the Qomolangma regions of Tibet. Then the researches of the rainfall isotope composition were raised to agenda in Beijing and Shanghai, and the rainfall isotope observation station was set in Hongkong. From 1988 to 1993, according to the study of local climate and geographic condition, ten other rainfall isotope observation stations were set in Qiqihar, Hetian, Yinchuan, Tianjin, Lhasa, Changsha, Guiyang, Nanjing, Fuzhou, Haikou. In this period the rainfall isotope was observed for a long time in these stations. Moreover, the Chinese Academy of Sciences, the former Ministry of Geology and Mineral Resources have also set some rainfall isotope observation stations. Totally there are 30 stations of this kind in our country and their data of isotope were published in GNIP by IAEA.
For many years, the Geology Institute and Geological Chemistry Institute of Chinese Academy of Sciences, the Engineering and Hydrologic Geology Institute of the National Land Resource Department, Nanjing Hydrology Science Academy of Ministry of Water Resources, the YRCC and other related graduate schools have made many efforts in the application research of isotope technique, for example: the research on the recharge sources and ages of karst water, thermal water and confined water; the invasion of seawater and salt water; sediment measurement by γ ray; soil water test by γ ray or neutron method; precipitation infiltration test of 131I; reservoir & dam's leakage; the sediment measurement in the harbor; and some basic hydrological study such as the runoff formation, the relationship of rainfall and run-off, the manner and condition of runoff production, and the division of hydrograph, etc. Good results are got through these researches.
Generally speaking, the applications of isotope technology in our country are relatively limited. There are still many problems including:(1) All the studies have been integrated little with practice but emphasize particularly on the testing research of isotope technology, which are just on the initial stages.
(2) Some new phenomena or new problems appeared in the research, but they were lack of further study and couldn't be demonstrated.(3) Most of the research projects were carried out in a small scale and with few technicians and experts. They haven't reached any common cognition on the importance and superiority of isotope technology application.
(4) The criterion and regulation are absent in applying isotope technique on the management and assessment of hydrology and water resources, which lagged the integration of isotope technique application.
Because of the serious shortage of water resources in our country, groundwater is an important source of water supply in the north of China. Some severe geological disasters occurred in many regions due to the over exploration of groundwater. In order to use the groundwater more rational we must strengthen the reconnaissance and assessment of groundwater. In many cases, we can obtain many key data with little investment by applying isotope technique, which can't be obtained by other conventional methods. In the aspect of groundwater's reconnaissance and assessment, if we integrate the isotope technology with the traditional method we can get some valuable data in a short period. In the resent years, many researches were carried out in the reconnaissance and assessment of groundwater with isotope technique as follows.
In the natural water circle, rainfall is the main source of surface water and groundwater. The forming of rainfall relates to the evaporations of rivers, lakes, and seas, while the surface water and groundwater recharge and discharge to each other. So the precipitation, surface water and groundwater compose a dynamic cycle of water. Isotope technique offers an efficient method on researching the interaction and the transforming amount between surface water and groundwater. It's particularly effective on the arid and semi-arid regions.
Being situated in the arid area in Northwest China, Heihe River is short of water resource. In the middle and lower reaches it is extremely dry and the environment is frail. Therefore, water shortage becomes the main reason of restricting the development of economy in Heihe River Basin. In order to realize the sustainable development of water resources and utilize the water resource of Heihe River rationally, we must make scientific evaluation and management on it. Getting to know the interaction between surface water and groundwater has great significance for reasonable planning of hydraulic works and unified regulation of surface water and groundwater. So we decide to research the interaction between the surface water and groundwater in Heihe River Basin with isotope technique, which get the support from IAEA. The project is organized by Hydrology Bureau of MWR, undertaken by Hydrology of YRCC, and Chinese Academy of Sciences and Hohai University are the counter parts. According to the work plan, now the project is under the way of analysis. It will be accomplished in 2004 and the results will be submitted at the same time.
Thinking of the over-exploitation of groundwater in the bank area of Weihe and branch of Yellow River, the Hydrology Bureau of Shanxi Province and the Chinese Academy of Sciences are also studying the interrelation between surface water and groundwater in this area by using of the isotope technique. It is deadly short of water in Erdors basin, which is in northwestern China. As the National Land Resource Department arranges the reconnaissance of groundwater there, they also operate the study of the interaction between surface water and groundwater. The two projects were supported by IAEA and began to work in 2001. They planed to achieve the results before 2004.
9.2.2 Research of Thermal Waters
Based on the research of thermal water, if the thermal water in one area has the same content of δD as its precipitation, which indicates the thermal water in that area mainly comes from precipitation. The groundwater is recycling among rocks, the content of δO increases along with the augment of the depth, temperature and pressure of the groundwater cycle. Therefore, we can judge the depth of groundwater cycle on the basis of the content of δO in the local thermal water.
Professor Sun Zhanxue (East China Geological Institute) and some other experts studied the isotope in the nature hot-spring water Lushan, Ma Anping and Xunwu in Jiangxi , they found that the value of δD, δ18O is values of the geothermal waters in the province are roughly in accord with the regional meteoric line, which indicates that the thermal water is mainly of meteoric origin. Altitude isotope variation of natural water in these areas reveal that the recharge areas of the geothermal waters are mountain regions. According to the study of dating the thermal water by Ra/Rn and tritium, the residence time of most of the thermal waters are ranging from decades to several hundred years, which demonstrate that the geothermal waters belong to thermal water resources of active circulation. The study on the isotope of rare gas in Xunwu hot-spring shows that the hot-spring gas in this area originates from the deep earth, and partly from the mantle source.
Tao Shuhua (Bureau of Geology & Mineral Resources of Shanxi Province) has analyzed characters of the isotope of hydrogen and oxygen in local thermal water. The result indicates that the local groundwater is mainly recharged by rainfall, and the source is the glacier in Qinling Mountain area 2000 m above sea level. According to the result dated by 14C, the age of recharged groundwater is 10 to 30 ka Bp, which is belong to a secondary glacial period in late Quaternary.
After working over the isotope of hydrogen and oxygen and the components of the dissolved gas in the hot-spring water in the south of Zhangjakou, Wang Jihua ( Geology Institute of China Earthquake Bureau) and some other experts get to know that hot spring water is mainly originated from meteoric water. In the deep circle, the water comes from rainfall is heated by magma and terrestrial heat, and it blocked and begins to move upward along the fracture. On account of some joined superficial water, its temperature begins to low and changes into hot-spring at the rift of rocks.
During the research on Seepage flow in dam or embankment, we can get the direction, speed, route, percolation coefficient and other observation data. And using isotope to show water trace is also an efficient way to do the research.
In Guangdong Province, Beijiang Embankment is a key engineering to protect floods at the lower reaches of Zhujiang River. One of the parts of the embankment lies in Shijiao town of Qingyuan city where the dykes were broken for many times in history. Although we had treated the embankment by anti-seepage technology since 1990 to 1994, water gushed from apertures during the floods from 1994 to 1997. Experts have different ideas on the reason that leads this kind of seepage, but getting to know the trace of seepage flow is the key to prevent it. Liu Jiangang , Chen Jiansheng and other experts of Hohai University studied the cause of formation of piping by using isotope to show water trace, then they drew a conclusion that piping was caused by base-rock seeping. It provides the important reference for anti-seepage engineering of embankment.
Reasons on the complicated hydrology and geology of the Xiluodu water power plant dam area in Sichuan Province, Zhang Shishu and other experts in Chengdu Reconnaissance Design Academy, National Electric Power Corp. analyzed the groundwater of the dam area by using the isotope technology. Then they mastered the supply of the groundwater, the water trace and the condition of drainage and provided the reference for engineering.
It has significant meaning to study the age of water in confined water on the research of Hydrology and geology. The isotope technology has special superiority on this research. By isotope technique Zhou Lian from Chinese Geology University and some other experts confirmed the age of the third layer of Quaternary aquifer of confined water is 250 ka, and the fourth layer is 300 ka in Cangzhou region of Hebei Province. After analyzing the confined groundwater system of Ejin Banner basin in the lower reaches of Black River, by using the radioactive isotope 14C, Wu Xuanmin and other experts in China Geology Environment Observation Academy has confirmed the age is between 5600 and 13000 years old.
Because of over-exploiting the groundwater, the invasion of seawater has become a serious problem in the littoral of China. It is a high efficient method of using the isotope technique to analyze the invasion of seawater. Zhang Shouquan and other experts in Chinese Academy of Sciences studied the groundwater system of Laizhou Bay in Shandong Province, and achieved the research fruits on the invasion of seawater.
On account of the conditions of geography, topography and climate, flood took placed in China frequently all through the ages. According to the random of flood, the frequency calculation is the main method to reckon the average odds of flood as the reference for engineering. But because of lacking of the information of spot observation, the calculated data come from the simple records of flood in history is not precise. It will affect the precision of frequency analysis. We can improve the precision of the analysis calculation on research of ancient floods and relatively analyze the flux of flood and expand the goal period of flood by using the isotope technique; even we can avoid the error of expanding the goal period of flood by using mathematic method.Professor Zhan Daojiang and Xie Yuebo from Hohai University studied the isotope of sediment caused by ancient floods in Changjiang Three Gorges engineering, Huaihe Xiang Hongdian reservoir, Gangnan and Huangbi village reservoir in Xituo River, Huanghe Xiaolangdi reservoir and some other places. They achieved the relevant flux of many ancient flood peaks. Through reasonable analysis, they think that research on ancient floods can help us to reduce the error of flood designs, level off the results and balance the different section on parameter.
REFERENCES Liu Jiangang, Chen Jiansheng and Chen Liang (2001), Evaluation of rock seepage and analysis of formation mechanism for Shijiao Part of Beijiang Embankment, Hydrogeology and Engineering Geology 28(4): 23-25 (in Chinese). Liu Xiaoyao, & Chen Jansheng (1999), Use Isotope Technology to Survey Well, Nanijg, Jiangsu Province Science & Technology Publishing Co. (in Chinese). Sun Zhanxue & Li Xueli (2001), Studies of geothermal waters in Jiangxi Province using isotope techniques, Science in China, 44(supp.): 144-150 (in Chinese). Tao Shuhua (2001), The source of replenishment of geothermal water around Xi'an, Science in China, 44(supp.): 165-167 (in Chinese). Wang Jihua, Lin Yuanwu, Liu Chenglong, & Liu Wuzhou (2000), Evidence to the hydrogen-oxygen stable isotopes and gas composition formed from hot springs in southern area in Zhangjiakou, Hydrogeology and Engineering Geology, 27(4): 30-33 (in Chinese). Wang Jiyang & Sun Zhanxue (2001), Brief review on the development of isotope hydrology in China, Science in China, 44(supp.): 1-5 (in Chinese). Wu Xuanmin, Shi Shengsheng, Li Zhiheng, Hao Aibing, Qiao Wenguang, Yu Zhishan and Zhang Shunbao (2002), The study on groundwater flow system of Ejina Basin in the Lower Reaches of Black River North-west of China, Hydrogeology And Engineering Geology, 29(1): 16-20 & 29(2): 30-33 (in Chinese). Zhan Daojiang & Xie Yuebo (2001), The Study on Ancient Floods, China Irrigation and Waterpower Publishing Co. (in Chinese). Zhang Shizhu, Cui Changwu, Chen Kui, Liang Xing and Wang Chuan (2002), The groundwater environment isotope analysis of the inclined tunnel over the River in Xiluodu Hydrostation Dam Zone, Hydrogeology and Engineering Geology, 28(1): 35-37 (in Chinese). Zhang Shouquan & Dai Fuchu (2001), Isotope and hydrochemical study of seawater intrusion in Laizhou Bay, Shandong Province, Science in China 44(supp.): 86-91 (in Chinese).