1. Integrated Approach for Assessing the Characteristic of Groundwater Recharge in Basin Scale Hsin-Fu Yeh*, Cheng-Haw Lee, Kuo-Chin Hsu Department of Resources Engineering, National Cheng Kung University, Tainan 701, Taiwan (*Corresponding author: hfyeh22@gmail.com) 2. Assessment of the Groundwater Recharge Potential Zone [Yeh et al. 2009] 1. Introduction An integrated approach is presented for the assessment the characteristic of groundwater recharge using remote sensing (RS), geographic information system (GIS), stable-base-flow (SBF) analysis, and environmental stable isotopes techniques considering Chih-Pen Creek basin, southeast Taiwan as a study area. First, the RS and GIS techniques are used to integrate five contributing factors: lithology, land cover/land use, lineaments, drainage, and slope. The weights of factors contributing to the groundwater recharge are derived using aerial photos, geological maps, a land use database, and field verification. Second the SBF is established to estimate the groundwater recharge in mountainous basin scale. The concept of the SBF is to use the base-flow separation from the total streamflow discharge to obtain a measure of groundwater recharge. Finally, stable isotopes of oxygen and hydrogen are used to evaluate the sources of groundwater and seasonal contributions of precipitation to groundwater recharge in basin.. Fig. 3 The interactive influence of factors concerning recharge property. Table 1 Relative rates for each factor. Table 2 Score of each recharge potential factor. Fig. 1 Location of the study area. Fig. 2 Methodology flowchart for the groundwater potential zone. Table 3 Categorization of factors influencing recharge potential in the Chih-Pen Creek basin. Fig. 4 GIS technology used in spatial integration and analysis to demarcate basin groundwater recharge potential zone. 3. Estimating Groundwater Recharge [Yeh et al. 2007] Fig. 5 The diagram of the stable-base-flow analysis Fig. 8 The location of the study region. Sampling sites of precipitation (circles), river water (squares), and groundwater (triangles) samples are shown. Fig. 6 Result of monthly mean base-flow separation at Chih-Pen gauging station of Chih-Pen Creek basin, 1980-2007. Fig. 7 Result of stable-base-flow analysis. 4. Groundwater recharge sources evaluation [Yeh et al. 2011] Fig. 9 Plot of δD versus δ 18 O for precipitation samples. GMWL and LMWL represent the global meteoric water line of Craig (1961) and local meteoric water line, respectively. Fig. 10 A comparison of seasonal changes of δ 18 O, δD, d-values, precipitation, evapotranspiration, and temperature. where A is the precipitation stable isotope value of the basin; B is the river water stable isotope value of the mountain watershed; C is the groundwater stable isotope value of the basin; V A is the amount of precipitation; V B is the amount of river water; X is the recharge proportion of river water; and (1-X) is the recharge proportion of precipitation. Mass Balance Analysis 5. Summary and Conclusions In this study, an integrated approach for assessing the characteristic of groundwater recharge using RS, GIS, SBF, and environmental stable isotopes techniques has been proposed in the Chih-Pen Creek basin, southeast Taiwan. First, this study produced a groundwater recharge potential map of the mountainous basin. The results indicate that the most effective groundwater recharge potential zone is located downstream. In this region, the gravelly stratum and agricultural land have a high infiltration ability. Additionally, the concentration of drainage also indicates the ability of streamflow to recharge the groundwater system. The upstream region is least effective for groundwater recharge, mainly due to its metamorphic limestone. Second this study has used the water balance conceptual model in a mountainous basin to estimate the groundwater recharge. This study used base-flow record estimation of streamflow information to carry out groundwater recharge calculations of the mountainous watershed. From the results of base-flow separation, the stable- base-flow days of each basin cannot be obtained, leading to a higher result of the estimated groundwater recharge. Finally, this study examined the stable isotopic composition of precipitation, river water, and groundwater in the Chih-Pen Creek basin. The results show that 79% of the groundwater in the study basin is derived from river water of the mountain area and 21% is from the meteoric water in the plain area. This indicates that the groundwater of the basin is mainly recharged from river water of mountain basins. References Yeh H. F., C. H. Lee, and K. C. Hsu (2011), Oxygen and hydrogen isotopes for the characteristics of groundwater recharge: a case study from the Chih-Pen Creek basin, Taiwan, Environmental Earth Sciences. 62, pp.393-402. Yeh H. F., C. H. Lee, K. C. Hsu, and P. H. Chang (2009), GIS for the Assessment of Groundwater Recharge Potential Zone, Environmental Geology, 58, pp.185-195. Yeh H. F., C. H. Lee, J. F. Chen, and W. P. Chen (2007), Estimation of Groundwater Recharge Using Water Balance Model, Water Resources, 34(2), pp.171-180.