PRELIMINARY HYDROGEOMECHANICAL NUMERICAL SIMULATION OF IMPACTS OF GROUNDWATER PUMPING AND INJECTION ON GROUNDWATER FLOW AND LAND DEFORMATION IN A FLUVIAL AQUIFER

A series of numerical simulations using a fully coupled hydrogeomechanical numerical model COWADE123D (Kim, 1995, 2006) was performed to analyze groundwater flow and land deformation in a fluvial aquifer due to groundwater pumping and injection. The aquifer is located along the Nakdong River in the Andong area, Korea. The aquifer consists of the weathered bedrock and fluvial sediments, and can be subdivided into the four layers of weathered rock, weathered soil, gravel, and sand in ascending order. A groundwater well is located at the center of the modeling domain, and its screen interval is installed in the middle of the gravel layer. The results of the numerical simulations show that the groundwater pumping and injection in the fluvial aquifer have significant impacts on the mechanical deformation field as well as the groundwater flow field. After the groundwater pumping, the pressure and hydraulic heads rapidly decreases for 1 day and then gradually decreases. The depression zone of watertable expands radially until it meets the area where the weathered soil is exposed at the surface, and then it becomes more irregular in shape. The temporal and spatial distributions of the vertical displacement are similar with those of the watertable drawdown. It means that the ground subsidence spreads outward from the pumping well, and an irregular subsidence area appears due to layered heterogeneity of the aquifer. On the other hands, for the case of groundwater injection, all the hydrological and geomechanical responses appear opposite to those under the groundwater pumping. It is expected that the numerical simulation technique and its results presented this study can be utilized as practical method and reference data for decision making processes of the sustainable water resources or safe underground space management. Further numerical simulations based on the field tests and their monitoring data are recommended to secure the validity and applicability of the numerical simulation model and its results. This work was supported by the Under Ground Safety (UGS) Convergence Research Department Project of the Electronics and Telecommunications Research Institute (ETRI) funded by the National Research Council of Science and Technology (NST), Ministry of Science, ICT and Future Planning, Republic of Korea.