Rajesh Kocchar, after a detailed analysis of the Vedic texts and geological environments of the rivers, concludes that there are two Sarasvati rivers mentioned in the Rigveda. The early Rigvedic Sarasvati, which he calls "Naditama Sarasvati", is described in suktas 2.41, 7.36, etc. of the family books of the Rigveda, and drains into a "samudra". The description of the "Naditama Sarasvati" in the Rigveda matches the physical features of the Helmand River in Afghanistan, more precisely its tributary the Harut River, whose older name was "Haraxvatī" in Avestan. The later Rigvedic Sarasvati, which he calls "Vinasana Sarasvati", is described in the Rigvedic Nadistuti sukta (10.75), which was composed centuries later, after an eastward migration of the bearers of the Rigvedic culture to the western Gangetic plain some 600 km to the east. The Sarasvati by this time had become a mythical "disappeared" river, and the name was transferred to the Ghaggar which disappeared in the desert. The later Rigvedic Sarasvati is only in the post-Rig Vedic Brahmanas said to disappear in the sands. According to Kocchar the Ganga and Yamuna were small streams in the vicinity of the Harut River. When the Vedic people moved east into Punjab, they named the new rivers they encountered after the old rivers they knew from Helmand, and the "Vinasana Sarasvati" may correspond with the Ghaggar-Hakra river.