Saraswati is among the most discussed rivers in the context of Indian history, the waters of which once flowed from the Himalayas to the Arabian Sea, separate from the other historically famous Indus(Sindhu) river. More than five thousand years ago, The mighty river Sarasvati was flowing in full strength through the arid desert of Western Bharat into the Arabian Sea.
Sarasvati is mentioned in Rig Veda and ancient sanskrit text, the oldest being the, Rig Veda, the Saraswati is described as the best and the purest among all rivers, which is fast-flowing and ocean-like, and it flows from the mountains to the sea. The later text epic Mahabharata too mentioned the Saraswati as lost in the desert sands, and then reappearing at different places in its downstream course, thus making it clear that the composer was aware of Saraswati losing its flow strength. According to the Sattelite image of ISRO, The Ghaggar Hakra river is identified was indeed the Vedic Saraswati River mentioned in the Rig Veda. several European scholars, as early as 1810s, reported that in the couplets sung by the common people in Rajasthan, the depopulation in the desert areas was blamed on the absorption or disappearance of the Saraswati or Ghaggar-Hakra.
They also observed high quality antique structures buried in sand which perished as the river dried up. several research papers published at the time and later identifies the Ghaggar-Hakra stream as the erstwhile river Saraswati. The identification of a river Saraswati in the region was well-accepted since the time of the British Raj and the argument that the river is just a poetic figment of imagination, came later by AIT/AMT proponents.
Drying of river Saraswati a time frame-
1. 2700 BCE - Kalibangan earthquake. This led to creation & activation of Yamuna tear faults in the Siwalik hills.
2. 2200 BCE- Second earthquake in Dholavira, which led to the next episode of tectonic shifts and creation of new faults lines.
3. 2000 BCE- Yamuna moves eastward towards Ganga, abandoning Saraswati that loses >50% of its water volume and Sutlej turns westward, abandons Saraswati, and joins Sindhu (Indus). Now Saraswati loses almost its entire volume of the glacier waters.
4. 1800 BCE- By this time the river stopped flowing into the sea at Rann of Kutch, from being a perennial ice-fed river, Saraswati now becomes a weak rain-fed stream.
5. Between 600-500 BCE, Unfortunately, owing to the monotonic weakening of Monsoons in the Siwalik areas that had set in long back, the rain-fed stream could not retain the previous heavy flow.
6. Further tectonic activities that created ridges (across Haryana and Rajasthan) turned this already dying rain-fed stream into a series of lakes & pools (the water bodies are still visible from flights). As the mighty Saraswati dies, people migrate to the Ganga Yamuna doab areas.
Ghaggar (the upper part of saraswati as it is named now) is still there as a thin monsoon time stream. It was the remnant of the Rig Vedic Saraswati river, which used to be a mighty river once which flowed all the way to the modern day Arabian sea. Rig Veda does not mention the drying of the Saraswati River - we can say that the Rig Veda was composed sometime atleast by 2000 BCE, So the forced dating of Rig Veda to1500 BCE is also incorrect.