Risk Assessment of Groundwater and its Application. Part II: Using a Groundwater Risk Maps to Determine Control Levels of the Groundwater

With the rapid development of economy, demand of water resources is becoming larger and larger, and over-exploitation of groundwater is common in many areas. Due to over-exploitation of groundwater over many years, a number of potential adverse hydrogeological problems have raised. To reduce such adverse effects, it is necessary to carry out strict groundwater management in over-exploited areas. And to achieve the strictest management of groundwater, it is critical to determine control levels of groundwater including the blue line levels (proper levels) and red line levels (warning levels). According to the establishment of evaluation model of shallow and deep groundwater exploitation and utilization risks, it can be observed that the groundwater level index factor is included in the evaluation index system in different groundwater function zones. Therefore, there is a corresponding relationship between the risk grade and groundwater level of different underground aquifers. The risk grade of different groundwater function zones in Tianjin is divided into five grades, which contributes to the risk management of groundwater, avoiding the arising of a wide range of risk management measure. However, to determine the key groundwater level, the standard of five grades cannot meet the requirements. The risk grades need to be divided more subtly. Hence, in this paper, the risk grade was divided according to the standard of sixteen grades based on that of five grades in the first place. The higher the grade is, the greater the risk. And then the occurrence frequency of risk grade for each aquifer was counted in each administrative district or country. The corresponding water level of the risk grade, whose occurrence frequency was the highest, served as the base level. The water level of groundwater that would be exploited and utilized in the future cannot be below this base level. In consequence, this water level that served as the red line level was the minimum requirement in the planning years, while the corresponding water levels of other risk grades that were inferior to this risk grade can all be seen as red line levels. And the planning period the long-term corresponding groundwater level of the aquifers under mining-banned condition can be used as blue line control levels of the different planning years. Finally, according to the determinate range of red line level change amplitude in each district or country, as well as the ultimate restoration aim of groundwater levels (blue line levels), corresponding measures were taken step by step to achieve the overall rising of groundwater levels. The obtained determinate control levels can provide a scientific basis for dynamic management of groundwater.