MODELING WATERSHED RESPONSES TO TYPHOON EVENTS - A CASE STUDY OF WULIN CATCHMENT IN TAIWAN

Chichiawan stream in the Wulin catchment, Taiwan is the natural habitat of the Formosan landlocked salmon. Recently, human and agricultural activities have negatively impacted water quality and, thus, the habitat of this fish. To protect and manage the habitat of the Formosan landlocked salmon, it is necessary to understand possible watershed responses to rainstorms and land-use activities. This study investigates watershed responses in the Wulin catchment to several typhoon events in Taiwan in 2004. Specifically, this study examines the influences of typhoon events on high-nutrient runoff, and the relationship between land-use planning in the Wulin catchment and aquatic biosphere quality for the Formosan landlocked salmon. The analytical results show that rainfall characteristics can exert a complex influence on watershed responses. Peak flows are not always proportional to the level of precipitation during a storm event. Land-use planning in the Wulin catchment is not observed to significantly influence peak flows during typhoon events. However, strategies that limit agricultural activities can significantly reduce nutrient exports. Since the results of sub-basin analyses show that most nutrient exports are induced by agricultural regions, land-use planning in the Wulin catchment has the potential to significantly protect valuable fish species and create a sustainable water environment.