The purpose of the project near Chiang Mai in northern Thailand is to link the Mae Ngad reservoir to the Mae Kuang reservoir, in order to better utilize the capacity of both reservoirs in case of locally different precipitation. In particular the Mae Kuang reservoir has shown a deficit in water supply in years of lower rainfall. Alignment studies based on hydraulic requirements and geotechnical conditions led to the selection of a tunnel of a length of approximately 23 km, with an overburden thickness up to 550m.