Numerical simulation of karst groundwater and dynamic prediction of spring water level in the Mingshui spring area , Ji’nan City

The Mingshui spring area is located at the transition zone from the mountainous region to the piedmont tilting plain in central Shandong Province. It is bounded by the Wenzu fault in the west, Yuwangshan fault in the east, metamorphic rocks and the floor of Lower Cambrian series in the south, and the Ordovician limestone roof 600 m below surface in the north, respectively, with an area about 660 km2. The overall direction of karst groundwater flow is from south to north in the spring area. The spring water mainly originates from the area with outcropped limestone and abundant karst cracks in the south. The infiltration of precipitation and surface runoff result in abundant karst-crack water. This water flows along the dip direction of strata from south to north. When reaching the most low-lying area in the northern spring area, the karst ground water is blocked by the coal measures strata, and then the water ascends through cracks to become spring groups. The main recharge of karst groundwater of the Mingshui spring area is precipitation, followed by seepage supply of the Qingyang river and Dongbalou river, as well as agricultural irrigation supply. The dominate drainages are spring water drainage, artificial mining, and coal mine drainage.To provide technical basis for the rational development and protecting karst groundwater resources，and the management of karst groundwater resources in the Mingshui spring area, this work has established a 3D numerical model of groundwater for the Mingshui spring area using the groundwater modeling software GMS. Then we conducted karst groundwater numerical simulation and water balance analysis of the spring area, calculated and evaluated the karst groundwater resources, and estimated the recoverable karst groundwater amount on the condition that perennial springs spewing. On the basis of above study, this research predicted the dynamic levels of spring water using the time series analysis method. Results show that the mean annual (2003-2014) groundwater recharge of the Mingshui spring area is 1.23×108 m3·a-1, the groundwater discharge is 1.36×108 m3·a-1, and the water balance is -1.30×108 m3·a-1. The model predicts that in the next 20 years, the lowest spring water level is 55.65 m, the highest spring water level is 68.72 m, and the average spring flow is 34.6×104 m3·d-1, respectively.