Analysis And Identification Of Hierarchical Groundwater Flow System In Jinan

A reliable delineation of groundwater flow patterns is essential for the proper management of groundwater resources. Groundwater flow system theory is a useful tool in the research of groundwater circulation and evolution, revealing the systemic and structural properties of groundwater flow. Based on the groundwater flow system theory, the present research was focused on the Jinan karst groundwater system, taking the thermal groundwater in northern Jinan and cold karst water in the south as a whole. According to the hydrogeological conditions in the study area, multiple approaches were combined to identify different groundwater flow hierarchies and analyze groundwater circulation patterns.Taking groundwater discharge areas as the fingerprint of groundwater flow system, multi-parameters, including geological conditions, groundwater level dynamics, hydrochemical and isotopic data, etc., were combined to identify groundwater circulation patterns. Shallow groundwater primarily belonged to the local flow system with high nitrate concentration and enriched stable isotopic contents, recharged by the infiltration of local precipitation. Non-thermal karst water may be attributed to the intermediate flow system with uniform HCO3-Ca(Mg) facies and low nitrate concentration, recharged by the lateral inflow from limestone outcrop areas in the range front and discharged through artificial exploitation or in the form of springs. Thermal groundwater has high chloride, TDS concentrations and lightest 8 H and δ18O values, derived from a regional flow system with largest circulation depth and longest residence time. It was recharged by precipitation in the high lands of northern piedmont of Mt. Tai, about 26.68-13.44 ka BP, presumably under a colder climate in the late Pleistocene.Taking into consideration the time attribute of groundwater flow system, the discontinuity of groundwater residence time distribution was used to identify different groundwater flow hierarchies. A three-dimentional numerical model of groundwater flow system was set up and real digital elevations in Jinan were imported to the model to represent the complex topographic relief. Residence time corresponding to the inflection point in the probability density functions of residence time, was used to divide the residence time field in the groundwater basin and to identify different groundwater flow hierarchies. Different factors, including the intensity of infiltration recharge, anisotropy and heat transport, were added to the numerical model. The influences of these factors on the groundwater flow system, were quantitatively analyzed according to the changes of residence time fields, as well as the recharge amounts and volume variations of each flow hierarchy.A typical hydrogeological profile was selected to set up a groundwater flow-age coupling numerical model. The simulation results were consistent with the groundwater conceptual model. Hierachical groundwater flow systems, with nested local, intermediate and regional subsystems, were developed from the northern piedmont of Mt. Tai to Qiguang Fault. The scales of these flow subsystems were controlled by the topography. Aquifer lithology variations largely influenced the groundwater flow system. Groundwater age distributions were closely related to the flow system. Groundwater became older along the flow paths and groundwater age increased sharply near the local stagnant point, which was a significant sign of the boundary between different groundwater flow hierarchies.The results of the present research not only deepened the understanding of groundwater circulation regimes in Jinan karst groundwater system, promoting the rational development and utilization of groundwater resources, but also provided references for the pratical applications of groundwater flow system theory.