| The Jiuquan basin is located in the middle of Heihe River in the Gansu Province, which is one of the typical large—scaled inland river basins in the northwest arid inland river. The basin is besieged by the fault of Qilian Mountain in the south,the apophysis of North Mountain in the north and the West and East is separately the fault of Jiayuguan,the groundwater watershed of Yumu mountain. Meanwhile, the Jiiuquan Basin is the important industry, the agricultural production base and the area of supplied water, which is approximately 250.0km in long and 10.0—15.0km in width. Since the Quaternary, Jiuquan basin has violently subsided and deposited massive loose sediments. Under the control of fluviation and geology, the sediment components gradually change from grits to clay and sands from south—west to north—east, while the thickness becomes thin little by little. These alluviums and fluvial sediments consist of the aquifer changed from single—aquifer to multiply—aquifers, and provide a well space of groundwater movement with recharge, flow and discharge conditions.In recent years, massive hydraulic engineering have been constructed in order to meet the needs of development of industry and agriculture in the basin, and the population is getting larger and larger, which caused this groundwater resources to be at a seriously excessive usage stage. At the same time, the massive activity of construction is changing the relation of recharge, runoff, discharge and hydrologic cycle in the groundwater system itself and affects the weather, climate and the hydraulic cycling on a regional scale in the study area. All the above factors have caused serious ecological environment questions such as the groundwater level declining, the ecology vegetation dying, the soil secondary solidification, the desert expending, and the sand storm worse and worse and so on. Therefore, it is vital to reasonably appraise, plan, exploit and manage the groundwater resource for the Sustainability development of the study area and Heihe River. Collecting the geology and hydrology geology of the study area, based on the fluent equation of continuity and the energy, the author built the 3D numerical model of the groundwater system, with the help of GIS technique and FEFLOW, and calibrated the established model by the observed data of wells, meanwhile us ing the calibrated model, evaluated the groundwater recourse. The main achievements of the study are as follow: (1) Established the three—dimension hydrogeology conception and math model of the aquifer system, based on the geological cross sections and drill holes of the study area, and built up the corresponding numerical model by FEFLOW. Through many a times of adjusting the parameters, resolving, and calibrating the results of the model, it is indicated that the established model can well reflect the conditions of the study area, and can be used to optimize, manage, and attempter the groundwater resource of the Jiuquan basin as scientific basics.(2) The model coves 4127.0 km~2 or so, and most boundaries of the model are selected at the natural body's boundaries (such as faults, watershed, etc), thus enhancing the precision of simulation. The research indicated that the total recharges vol. was about7.0562×10~8m~3, and the discharge vol. was about 8.2146×10~8m~3on the present situation year (2003). Of the recharges, the North and South irrigation of Taolai River was 2.7464×10~8m~3, the Qingshui irritation was 0.5961×10~8m~3, the Linshui irritation was 0.8253×10~8m~3, the Hongshui irritation was 1.2626×10~8m~3, the Hongshan irritation was 0.3445×10~8m~3, the Ganshan irritation 0.0542×10~8m~3, the Fengle irritation was 0.5938×10~8m~3, and the Maying irritation was 0.6334×10~8 m~3.(3) By the calibrated numerical model, forecasted the recharge, discharge and the flow fields of unconfined aquifer on the P=50%, 75%, 95% different surface—runoff frequency. The results of the forecast are that: on P=50% condition, the total recharge is 7.7346×10~8m~3, the discharge is 8.7208×10~8m~3, and the balance is -0.9862×10~8m~3; On P=75% condition, the recharge is 7.1663×10~8m~3, the discharge is 8.3789×10~8m~3, and the balance is—1.2126×10~8m~3; and on the P=95% condition, the recharge is 6.3610×10~8m~3, the discharge is 7.8477×10~8m~3, and the balance is -1.4867×10~8m~3.
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