Changes in groundwater flow in an unconfined aquifer adjacent to a river under surface recharge.

The groundwater level in an unconfined aquifer near a river is strongly affected by rainfall and river level. The linearized Boussinesq equation has been used in numerous studies to analytically investigate the changes in groundwater level. A perturbation method was used to determine the non-linear term of the Boussinesq equation. The generalized integral transform technique (GITT) was subsequently used to obtain a semi-analytical solution. We compared this solution with a linearized analytical and non-linear numerical solution and investigated the influence of each parameter that affects the number of convergent terms in analytical solutions. To estimate the recharge volume, two methods, the Horton infiltration formula and a method in which the fraction of rainfall intensity is considered, were employed. Subsequently, the simulated groundwater levels were compared with the field data. Finally, the recharge type, namely unimodal, with and without the Horton infiltration formula was used to model the groundwater flow. [ABSTRACT FROM AUTHOR]