Study on multi-objective emergency allocation of groundwater resources for small towns in karst area: A case study of Zhijin county

In order to solve the problem of discrepancy between the water supply and water demand in urban area and to put forward an emergency allocation scheme for groundwater resources in karst areas under drought conditions. In this paper, we take Zhijin county north Zhucang water storage syncline structure as an example; and the runoff modulus method was used to simulate the development and utilization of the water resources in the study area. According to the principles of mixed integer linear programming and multi-objective linear programming, following the principle of "giving priority to the protection of domestic water and taking into account the maximization of economic benefits", a drought emergency allocation model for the resources at different targets , i.e. E-MIP (Emergency Multi-objective Integer Programming) model, was constructed and applied to the study area. As a result, the groundwater resources in the city of Zhijin county emergency scheme during 2010-2030 were put forward. The research result shows that, (1) In the north of Zhucang anticline, the exposed water from the fractured-karst aquifers mainly discharges through the underground river, with an average flow rate of 62.04 m3·s-1; and in porous-fractured bedrock are springs mainly discharge groundwater in an manner of dispersion, with an average flow of only 2.14 m3·s-1.(2) The elevated degree of drought not only restricts the amount of water resources used, but also directly stimulates and improve the water use efficiency and social and economic benefits. In the period of 2010-2030, the severe drought rate in Zhijin county was 21.25% which was lower than that of the mild drought, but its social and economic benefits increased by 5.84 times. Meanwhile, the supply and demand balance of groundwater resources under severe drought has changed from 35.68% surplus rate to 47.98% water shortage rate, but the GDP of Zhijin urban area was 47.96×108 yuan, rising to 280.27×108 yuan year by year. (3) The emergency allocation principle of groundwater resources is a priority to protect residents living water demand; secondly, according to the water use efficiency and the weight order, the distribution of the surplus groundwater resources is allocated; in addition, the emergency allocation scheme of water resources for the years of 2020 and 2030 in Zhijin was further predicted, respectively which has laid the foundation for improving the state of emergency under the rational and scientific use of resources. The above research indicates that with the increase of water use efficiency, the social and economic benefits of the allocation of groundwater resources in the northern part of Zhucang syncline will gradually increase, and domestic water will become the key object of emergency allocation of water resources, so that making the social benefits greatly exceed its economic benefits.