Complex geological features are present in the mountainous regions of Taiwan. Strongly folded, faulted and highly fractured formations are common, the delineation of groundwater producing zones is, therefore, challenging. However, progress towards characterising the transmissivity in the mountainous region of Taiwan has been made. There are three major watersheds: the Dajia, Wu and Jhuoshuei River. A total of 65 boreholes have been drilled, various types of well logging, rock core inspection and packer tests carried out. Using these data gathered during the past three years, a conceptual model has been developed which delineates the spatial distribution of hydraulically transmissive conduits in the region.