| Zhangye Basin is iocated in the middle reaches of Heihe River and is the area with the highest utilization degree and largest utilization amount of water resources in Heihe River Basin, it is also the key region controlling the evolution of water cycle in this basin area. However, surface water in Zhangye Basin was over irrigated which was caused by the population growth and economic development, making the Heihe River Basin water resources become more and more serious and the fragile ecological environment situation become worse and worse downstream. In order to save and improve the ecological environment of natural oasis downstream, the State Council approved the "Recent Management and Planning of Heihes River Basin" in August 2001 and clearly states the need to ensure the discharged water in Zhengyixia. This requires the increase of the exploitation of groundwater in Zhangye basin and the ratio of groundwater in the total water consumption, as well as the program to optimization and the allocation of water resources. In addition, in recent years, the groundwater level of Ganzhou City in Zhangye and the surrounding areas continued to rise, which brought greater harms to the city building; there exists the phenomenon of more serious over-exploitation in some irrigation and phenomenon of great variation within the development and utilization of groundwater in different sections. Therefore, making risk assessments of groundwater irrigation development in Zhangye Basin and thus exploring sustainable ways to the use and development of groundwater resources are of great significations to the study of rational development and utilization of groundwater resources in the research region.In this paper, our study focuses on the risk of groundwater development, with the analysis of its main effective factors. Due to the particular characteristics of groundwater system in Zhangye Basin, we have taken previous research results and specific circumstances of groundwater system into consideration within the comprehensive evaluation index system of groundwater development risks. Therefore, the index system is same to the previous system on the aspect of structure, however, its specific characteristics are suitable to the research of assessment of groundwater development risks. On the base of catastrophe theory, we use catastrophe evaluation model to evaluate the groundwater development risks in Zhangye Basin. Firstly, convert the original index value of membership function to mutation series of 0 to 1 in accordance with the evaluation steps. Then make comprehensive calculation from single index layer to target layer using normalized formula. Assessment results showed that risk values of groundwater development in each irrigation region within the groundwater system in Zhangye Basin were between 0.6257-0.8339, which belonged to the moderate risk area (0.5-0.85) according to the grade criteria of risk category.In order to control the groundwater development risks, numerical evaluation model was established. By the identification and calibration of this model we found that the water level values of observation wells were meet to the accuracy needs. Those above indicated that the generalization of aquifer layers, identification of hydrologic geology parameters and the treatment of terms of source and sink were reasonable. Therefore, the model established could be used to make simulation and dynamic forecasts of groundwater. According the scheme of diversion of water in the middle and lower reaches of Heihe River watershed, we determine the increase or decrease of the amount of groundwater development in accordance with the potentiality of each irrigation region and input values to the calibrated model. Results indicated that if we increase the amount of groundwater development according to the planning, there was a decline trend of spring water (spring water flow varied from 56448×104m~3/a down to 51245×104m~3/a, decreased by 9.2%). However, due to the decrease of groundwater level, phreatic evaporation was controlled effectively, which was reduced from 28924×104m~3/a reduced to 20683×104m~3/a, reduced by 28.5%. In addition, on the one hand, the increase of the amount of groundwater development could enhance the river recharge from surface water to groundwater, with the recharge amount increase from 31450×104m~3/a to 34014×104m~3/a. On the other hand, because the canal system usage efficient of surface water was higher to groundwater, then increase groundwater development amount could replace surface. According to the coupling relationship of surface water and groundwater we could calculate that when the development amount was 7600×104m~3, surface water could be saved by 1.01×108m~3, with the deduction of river recharge amount, 2564×104m~3 and runoff amount in river increased to 7536×104m~3. Those above not only could increase utilization efficiency, but ensure the discharge water amount in Zhengyixia. Along with the defuse of groundwater development risk, we could also obtain environment and society benefits, then we could achieve sustainable developments of water resources, ecological environment and socio-economy.
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