Explanation:

There are three rivers originating from Baralacha Massif situated in Lahul valley, which are Chandra, Bhaga and Yunam. Chandra and Bhaga meet at Tandi and form Chanderbhaga Sangam whereas Yunam moves to other direction in Zanskar.
According to Shiv Puran, the mountain range starting from Chanderkhani in Kullu region to Drilbu Ri in Lahul is called Chanderbhag Parvat, so the river flowing underneath was named Chanderbhaga whereas one river was called Chandra and second one Bhaga.
Chanderbhaga name for the combination of two rivers in Lahul Valley is found more visible in old Hindu texts called Puranas. The ancient name of this river in Vedic period was Asikni(Chenab River).