ONGC have confirmed that the major course of a river ran through the present-day Ghaggar River. The supposed paleochannel of the Hakra is actually a paleochannel of the Sutlej, flowing into the Nara river bed, presently a delta channel c.q. paleochannel of the Indus River. At least 10,000 years ago, well before the rise of the Harappan civilization, the sutlej diverted its course, leaving the Ghaggar-Hakra as a monsoon-fed river. Early in the 2nd millennium BCE the monsoons diminished and the Ghaggar-Hakra fluvial system dried up, which affected the Harappan civilisation. Paleochannels and ancient course While there is general agreement that the river courses in the Indus Basin have frequently changed course, the exact sequence of these changes and their dating have been problematic. Pre-Holocene diversion of the Sutlej and Yamuna Older publications have suggested that the Sutlej and the Yamuna drained into the Hakra well into Mature Harappan times, providing ample volume to the supply provided by the monsoon-fed Ghaggar. The Sutlej and Yamuna then changed course between 2500 BCE and 1900 BCE, due to either tectonic events or "slightly altered gradients on the extremely flat plains," resulting in the drying-up of the Hakra in the Thar Desert. More recent publications have shown that the Sutlej and the Yamuna shifted course well before Harappan times, leaving the monsoon-fed Ghaggar-Hakra which dried-up during late Harappan times. Clift et al. (2012), using dating of zircon sand grains, have shown that subsurface river channels near the Indus Valley civilisation sites in Cholistan immediately below the presumed Ghaggar-Hakra channel show sediment affinity not with the Ghagger-Hakra, but instead with the Beas River in the western sites and the Sutlej and the Yamuna in the eastern ones. This suggests that the Yamuna itself, or a channel of the Yamuna, along with a channel of the Sutlej may have flowed west some time between 47,000 BCE and 10,000 BCE. The drainage from the Yamuna may have been lost from the Ghaggar-Hakra well before the beginnings of Indus civilisation. Ajit Singh et al. (2017) show that the paleochannel of the Ghaggar-Hakra is a former course of the Sutlej, which diverted to its present course between 15,000 and 8,000 years ago, well before the development of the Harappan Civilisation. Ajit Singh et al. conclude that the urban populations settled not along a perennial river, but a monsoon-fed seasonal river that was not subject to devastating floods. Khonde