Comparing Q-Tree with Nested Grids for Simulating Managed River Recharge of Groundwater

Abstract

The use of rivers to recharge groundwater is a key water resource management method. High-precision simulations of the groundwater level near rivers can be used to accurately assess the recharge effect. In this study, we used two unstructured grid refinement methods, namely, the quadtree (Q-tree) and nested grid refinement techniques, to simulate groundwater movement under river recharge. We comparatively analyzed the two refinement methods by considering the simulated groundwater level changes before and after the recharge at different distances from the river and by analyzing the groundwater flow and model computation efficiency. Compared to the unrefined model, the two unstructured grid refinement models significantly improve the simulation precision and more accurately describe groundwater level changes from river recharge. The unstructured grid refinement models have higher calculation efficiencies than the base model (the global refinement model) without compromising the simulation precision too much. The Q-tree model has a higher simulation precision and a lower computation time than the nested grid model. In summary, the Q-tree grid refinement method increases the computation efficiency while guaranteeing simulation precision at a certain extent. We therefore recommended the use of this grid refinement method in simulating river recharge to the aquifers.

Simulation Study on the Environmental Impact of Rare Earth Ore Development on Groundwater in Hilly Areas: A Case Study in Nuodong, China

“…To improve accuracy and computational efficiency, the study area model is constructed based on an unstructured grid (MODFLOW-USG) on a quadtree grid. Using MODFLOW-USG, refinement can effectively reduce the area occupied by stream cells, thus enhancing the drainage area near the stream and making the model calculation more accurate and efficient [28][29][30]. The model was composed of three layers with a total of 46,038 active cells referring to the stratigraphic structure of the geological model.…”

Combining river replenishment and restrictions on groundwater pumping to achieve groundwater balance in the Juma River Plain, North China Plain

“…The model domain was discretized with the quadtree refinement method in MODFLOW-USG, which achieves a high simulation precision in modeling river recharge to aquifers (Cui and Hao, 2020). The finest grid was 250 m × 250 m, and the cell size gradually increased to 500 m × 500 m away from both sides of the river.…”

“…General groundwater models often have difficulty in precisely simulating local groundwater level changes near rivers with large groundwater level changes. In this study, we used local grid refinement to finely characterise groundwater level changes near the river, and Cui and Hao (2020) have successfully applied this method to numerical simulations with ecological water replenishment of rivers. This study was conducted in the Juma River Plain, which flows through the Juma River, one of three ecological replenishment rivers.…”