Environmental impact of Hsuehshan Tunnel on water quality at Feitsui Reservoir and its tributaries

To investigate the possible impact of the traffic flow of mountainous roads and the construction and operation of a long tunnel on the water quality of a reservoir, this study conducts statistical analysis on water quality, meteorological, and traffic data of the Feitsui Reservoir and its upstream tributaries over the last three decades. Results from statistical regression analysis indicate that in the upstream area where the traffic flow is low, water quality varies insignificantly with rainfall and traffic flow, providing as a background reference of natural environment. Water quality near a conventional highway on which many vehicles travel through the catchment area is significantly affected by both rainfall and traffic flow since the drainage system of a conventional highway sends its gathered water into adjacent rivers. Not only does traffic flow generate contaminants, but also the construction of the Hsuehshan Tunnel of the No. 5 Expressway, Taiwan, in the catchment area of the Feitsui Reservoir generates pollution. Drainage, silt settling and retarding basin, and wastewater treatment facilities near the construction site mitigate the impact of tunnel construction and traffic flow on the environment. The No. 5 Expressway makes good use of viaduct and tunnel structures, collecting water from pavements within the catchment area into sewage facilities, filtering it, and then emitting it outside the catchment area, forming a closed system over the Feitsui Reservoir. The Expressway now shortens travel time from two hours to 40 min and accommodates 7–13 times previous traffic flows, insignificant influencing water quality in the upstream tributaries of the reservoir, demonstrating the effectiveness of its environmental protection measures.