Establishment and Application of A Methodology for Numerical Model Calibration for Regional Groundwater Flow System - A Case Study of Hualien River Basin in East Rift Valley

　In order to properly manage the groundwater resources, we need a well calibrated numerical model to assess the effectiveness of various management strategies.
　This study aimed to be based on the methodology of numerical model calibration for regional groundwater flow system at home and abroad, then be supplemented and systematized to establish a set of numerical model calibration method, and applied which on Hualien River Basin in East Rift Valley for surveying its feasibility.
　The methodology proposed in this study is composed of 3 phases, including the identification of source/sink of groundwater system, parameter testing of a steady numerical model and parameter testing of a transient numerical model. First of all, to understand the feature of flow of regional groundwater system, the methodology utilized groundwater hydrograph analysis and oxygen isotopic tracer method to estimate the water balance and the recharge sources in study area. Secondly, the spatial distribution of source, sink and hydraulic conductivity were checked in steady-state simulation separately. Finally, the spatial distribution of storage coefficient and specific yield were checked in transient simulation. The process was iteratively corrected until the subdivision of storage coefficient and specific yield were fitted the previous corrected value.
　The results of the identification of source/sink of groundwater system practiced on the case of Hualien River Basin in East Rift Valley between 2008 to 2012 showed that, its annual average amount of recharge was 787 million tons ( recharge of precipitation accounted for 11.70%, recharge of river represented 63.53%, and the outer zone of groundwater recharge occupied 24.77%), the annual average loss amount was 813 million tons (pumping took up 7.03%, coastal loss constituted of 31.23%, and the seepage to the river stood at 61.74%) and the average annual storage changes was -26 million tons.
　The results of the numerical model of regional groundwater flow system used in the case of the daily model of Hualien River Basin in East Rift Valley indicated that, its annual average amount of recharge was 804 million tons ( recharge of precipitation accounted for 11.92%, recharge of river represented 67.03%, the outer zone of groundwater recharge occupied 21.05%, and the number difference between the total amount of recharge and the results of the system identification was 2.16%), the annual average loss amount was 773 million tons (pumping took up 7.39%, coastal loss constituted of 30.46%, the seepage to the river stood at 62.15%, and the number difference between the total amount of the outflow and the results of the system identification was 4.92%) and the average annual storage changes was 30 million tons. The root-mean-square error of Nanhua, Wuquan, Darong, Changqiao and Dafu reached to 2.52 meters, 0.29 meters, 1.65 meters, 2.90 meters and 2.57 meters, respectively. The hydraulic conductivity and specific yield were regulated within 1 order of magnitude.
　The results showed that the calibration method established in this study could initially simulate the groundwater flow situation of Hualien River Basin in East Rift Valley. Likewise, it could be used as a reference for simulations and various analyse in the future.