Development of a preliminary ground water flow model for water resources management in the Pingtung Plain, Taiwan

Pingtung Plain is formed by Quaternary alluvial fan material from the three main rivers: Kaoping, Tungkang and Linpien. Ground water is the major water supply source on the plain. This is principally extracted from two aquifers. The natural ground water source is derived mainly from direct rainfall percolation and infiltration from the three rivers, with their catchments lying partly outside the plain. Rainfall characteristics are therefore the main factors controlling water resources availability. Pingtung Plain is an important primary production area for southern Taiwan, the comparatively warm climate allowing a long growing season, diversified cropping and the rearing of aquacultural produces. Approximately 75 percent of irrigation and domestic water supplies are derived from ground water. A water balance for the entire plain indicates that ground water resources, under optimized management, are sufficient to meet the existing multi-purpose uses. Development of a hydrogeological conceptual model is the first phase of a numerical ground water flow simulation. Preliminary results are encouraging, with the final simulations affording better insight to the hydraulic behavior of the aquifer system. Data input requirements for model operation fall into three categories: hydrological stresses, hydrogeological parameters and boundary conditions. After the model is built, the normal numerical modeling process requires significant calibration and sensitivity analyses for the hydrogeological parameters and stresses which are the most sensitive, but the least well defined. A well-calibrated simulation model can lead to a reliable and realistic management model. With this in mind, the calibration processes detailed are presented, and these data are introduced as initial values in the calibration process