Numerical Simulations for Artificial Recharge of Takaoka Groundwater Basin, Tosa City, Japan

摘要

The lowering of groundwater levels in the Takaoka basin poses a significant threat to sustainable utilization of its scarce ground-water resource. A transient, two-dimensional groundwater flow model was developed for a single-layered unconfined aquifer system and was solved by the finite-element method (FEM), Using this numerical model, present and future groundwater scenarios for dry periods are presented by simulating various groundwater management strategies. The response of the Takaoka basin to some artificial recharge techniques was also investigated, and two techniques are proposed for its rehabilitation. The model estimated recharge from the Niyodo River to be about 22.24 × 10~3 m~3/d in a no-pumping situation. A decline equal to or greaterthan 0.5 m in the Niyodo River water level considerably lowers the basin's groundwater levels. Any increase in pumping from the present rate will aggravate the overdraft problem. Modeling results suggest a cutback of about 30% in pumping as a preliminarymeasure to mitigate groundwater mining. The worst groundwater scenario during drought years emphasizes the immediate rehabilitation of the basin. Further, simulation results of two artificial recharge techniques—viz., groundwater barrier and Niyodo River modification—indicated promising potential for rehabilitating the depleting aquifer, While the influence of the proposed barrier is limited, a weir of height 4.5 m from the dry period water level in the Niyodo River is sufficient to meet the presentgroundwater demand and thereby stabilize the aquifer.