Hualian River is abundant in runoff and high in sediment transport capacity. Most surface water is utilized for agricultural purposes, whereas domestic and industrial water usage relies on the copious amount of available groundwater. To understand the use of water resources in this basin, the fundamental characteristics and recharge of the groundwater need to be analyzed. In this study, the weight of different factors for potential groundwater recharge and the score under various characteristics were assessed based on the characteristics of the study area. A GIS approach was used to integrate five contributing factors: lithology, land cover/land use, lineaments, drainage, and slope. The results demonstrated that about 1.2% of the study area is designated as excellent potential groundwater recharge. Good, moderate and lower potential groundwater recharge areas cover 11.6, 11.7 and 29.9%, respectively; the area with poor potential groundwater recharge covers 45.6%. The results indicate that the most effective groundwater recharge potential zone is located in the Huatung Valley. In this region, the gravelly stratum and the concentration of drainage also help the streamflow recharge the groundwater system

In this study, the stable isotope values of oxygen and hydrogen were used to identify the seasonal contribution ratios of precipitation to groundwater recharge in the Hualien River basin of eastern Taiwan. The differences and correlations of isotopes in various water bodies were examined to evaluate the groundwater recharge sources for the Hualian River basin and the interrelations between groundwater and surface water. Proportions of recharge sources were calculated based on the results of the mass balance analysis of the isotope composition of hydrogen and oxygen in the basin. Mountain river water accounted for 83% and plain rainfall accounted for 17% of the groundwater recharge in the Huanlian River basin. Using the mean d-values, a comparison of d-values of precipitation and groundwater indicates the groundwater consists of 75.5% wet seasonal sources and 24.5% dry seasonal sources, representing a distinct seasonal variation of groundwater recharge in the study area. Comparisons between hydrogen and oxygen isotopes in rainwater showed that differences in the amount of rainfall resulted in depleted oxygen and hydrogen isotopes for precipitation in wet seasons as compared to dry seasons. The river water contained more depleted hydrogen and oxygen isotopes than was the case for precipitation, implying that the river water mainly came from the upstream catchment. In addition, the hydrogen and oxygen isotopes in the groundwater slightly deviated from the hydrogen and oxygen isotopic meteoric water line in Huanlian. Therefore, the groundwater in this basin might be a mixture of river water and precipitation, resulting in the effect of the river water recharge being greater than that of rainfall infiltration.