Infiltration plays an important role in the urban water cycle. Infiltration has a potential to contribute to groundwater recharge in addition to runoff reduction. However, infiltration in urban areas has been considered only as a means of runoff reduction. Conventional design methods for infiltration facilities assume soils to be fully-saturated for the sake of simplicity. The amount of groundwater recharge can not be estimated properly with this scheme. Hence, the characteristics of the unsaturated soil condition need to be considered. The finite element model using SEEP/W to estimate infiltration under the unsaturated condition is presented. Infiltration tests for Joomonjin sand are performed and the infiltration behavior of Joomoonjin sand under the unsaturated condition is measured experimentally to verify the validity of the finite element model. The results from comparing infiltrated volume between the saturated and the unsaturated conditions under the same soil and rainfall conditions show that the infiltrated volume in the unsaturated condition is two times bigger than that in the saturated condition.

Keywords: Rainwater infiltration;Unsaturated soil;Finite element model;