Does descent of Ganga or Gangavataran on Earth have roots in Rig Veda?

 

Descent of Ganga or Gangavataran has been described in Valmiki Ramayana as follows:

When the eldest son Asamanja is with sinister activity, a torturer of goodmen, and delighter in the undesirable activities towards citizens, his father king Sagara expatriated him from the city.

The ritual horse released by Emperor Sagara is snatched away by Indra in order to cause hindrance to the ritual. The ritual cannot proceed to culmination without the horse. 

Then Sagara orders his sixty thousand sons to search for that horse, asking them to dig earth to trace it, if it is not found on earth. And the princes will dig earth when they have not found the horse on earth, to the grief of beings living in netherworlds.

Sagara's sons dig out all the quarters of earth and when they enter northeast to find out the horse thief, there they find Sage Kapila, i.e., Vishnu in the semblance of a sage. When they wanted to attack that sage Kapila, he renders them to heaps of ashes by his yogic powers.

Asamanja's son Amshuman's search for horse reveals that Kapila rendered his paternal-uncles to ashes. When he wanted to offer water oblation as obsequies to their souls he did not find water. 

Then Garuda, the Eagle-vehicle of Vishnu and maternal uncle of Amshuman advises him to get River Ganga onto earth whereby the souls are cleansed and they go to heaven. Amshuman reports the same to King Sagara, but Sagara not finding any way to get River Ganga onto earth departs to heaven at the end of his time.

Amshuman and his son Dileepa could not make any effort to bring the divine river to earth. But Bhageeratha, the son of Dileepa, staunch at heart tries earnestly to get her onto earth. Brahma agreeing for this descent of Ganga designates lord Shiva to bear the burden of the onrush of Ganga, because the earth cannot sustain it.

Ganga descends to earth by the extraordinary effort of Bhageeratha. Shiva agrees to the alighting of Ganga on His head and from where she is released into a lake called Bindu sarovar, and from there she flows in seven courses. 

On land Bhageeratha ushers her up to netherworld dug by his ancestors, where heaps of ashes of his grandparents are there, and she enters accordingly to inundate those mounds of ashes according salvation to the souls.

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Rig Veda I.32 tells of Indra’s most significant victory, his triumph over Vrtra (वृत्र) and the release of the waters. 

Vrtra was a gigantic cobra who lay coiled around a mountain within which all the waters were entrapped. 

In his battle with Indra, Vrtra spread his “shoulders,” his cobra’s hood, and struck at Indra with his fangs, but Indra finally killed Vrtra with his mace, broke open the mountain, and let the waters pour out. 

They then flowed to Manu, who was the first sacrificer, and by implication to his descendants. Vrtra’s name means “obstacle,” and this victory over “Obstacle” is therefore paradigmatic for Indra’s victory over all obstacles.

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Most of the Rig Vedic mantras are to be understood in esoteric sense only.

Here, Manu, the human being to get Self Realisation, got over his obstacles, Vrtra, in spiritual journey, with the aid of Indra, an epithet of the formless BRAHMAN or Almighty.

The release of water is to be understood also in esoteric sense, which means getting ENLIGHTENMENT.

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The story of Indra releasing waters, which reach Manu, mentioned in Rig Veda was described in Valmiki Ramayana in descending of Ganga from Heaven to Earth and to reach Netherworlds.