Optimization Of The Groundwater Level Monitoring Network Density In A Karst Collapse Area Of Wuhan

The groundwater monitoring of Wuhan began in the 1970 s, and it provides a large number of basic data information for the urban construction development and scientific researches. However, the quality and precision of the data obtained by the current monitoring network are hard to be effectively guaranteed, and the existing problems are also increasingly obvious. The main problems are inadequate control and discontinuous monitoring data, etc. Furthermore, carbonate rocks are distributed in this area widely where the geological conditions are complex. Coupled with the increase in major engineering, a series of geological environment problems especially karst collapses take place frequently, and the groundwater regime has a great impact on the occurrence of karst collapses. Therefore, real-time monitoring and analysis of groundwater is of very important realistic significance, and the optimization design of monitoring networks is inevitable. At present, the optimization methods mainly include the hydrogeological analysis method, the Kriging method, and the Kalman filter method and so on.This dissertation takes the groundwater level monitoring network in Wuhan as the research object, and the Kriging method is used to evaluate the existing Quaternary groundwater and karst water monitoring networks, respectively. The mean error variance is 9.57 and 5.05, and there are some monitoring blank areas exist. A region is selected as a typical area, the monitoring wells of the Quaternary are concentrated at the first Yangtze River’s Terrace in the confined aquifer, due to lack of monitoring of the unconfined aquifer, the variance is 2.37 to 2.62. Karst water monitoring wells are distributed in each karst belt, and the variance is 0.14 to 4.54. The groundwater level monitoring network in this area can be optimized by the delineating groundwater regime zone map method. By analyzing the factors that affect the dynamics of groundwater levels, the groundwater regime type is divided into different areas, according to this graph and combined with the design principles of the monitoring network, by making full use of the existing special monitoring wells, the groundwater level monitoring network optimization scheme is put forward in this area.There are 59 wells altogether in the monitoring network after optimization, 5 existing Quaternary groundwater monitoring wells and addition of 17 wells; 7 existing karst water monitoring wells and addition of 19 wells, and 11 multi-layer groundwater monitoring wells. Using the Kriging method to analyze the optimized monitoring network, the variance value of the Quaternary groundwater level monitoring network is 3.29 to5.54, the value increases relatively because the monitoring wells are closely distributed in a small region before, after optimization the density in the whole study area is smaller, but from a practical point of view the layout is more reasonable. The variance of optimized karst water level monitoring network is 0.21 to 2.98, the fluctuation range of error variance is reduced, high value area reduced as a whole and the low value area expanded. The optimization scheme is reasonable and meets the objective of optimization and the original intention of the research. The optimized monitoring network fills the blanks of monitoring in this area and ensures to obtain sufficient information about the temporal and spatial variation characteristics of groundwater, and further ensures the rational and sustainable use of groundwater. It is helpful in getting a more efficient prediction about the change of groundwater conditions, and realizing the management of groundwater in the future or auxiliary monitoring and prevention of geological hazards.