Now comes the tough part in determining the Timeline for Kaveri River.From Chola Copperplates evidence of Thiruvalankadu and the genealogical table by the Purans,it becomes evident that Cauvery River was brought to earth by Chitradhanvan Chola, emulating his ancestor Bhagirath who brought Ganga River to Earth.This would place Cauvery River timeline and consequently date of Poompuhar to Treata Yug,which is atleast a 900,000 years ago( We are in Kaliyug now; Dwapar Yug preceded this lasting for 8,64,000 years).

However, dating of Ramayana places it around 5114 BC, that is about Seven thousand years ago.

The conundrum is because of Time being Cyclic and not Linear.

The origin of Kaveri river is associated with Sage Agastya and it was brought to earth by him.We find references to Agastya ,apart from references to him in Puran, Vedas,is mentioned in Vedas. He imparted Adhitya Hruday stotra to Sri Rama to shrug of his depression when Lakshmana was felled by Ravana’s Mohanastra. Agastya is reported to have come down south . This time frame is validated by Star Canopus, Agastya Nakshatra visibility in the southern hemisphere.And Ramayana lists over Thirty Rivers.

Our minds do not accept such vast scale of Time. Can we then ,place Cauvery River and Poompuhar date around 7000 years ago.

But we have archeological evidence from Poompuhar that Poompuhar to support a date of around atleast 11,000 years ago.

So as a compromise, we may assign the Date of Cauvery River to atleast 11000 ago?

Now, Indra Vizha celebrated in Poompuhar also supports this timeline because Uparichara Vasu was a Chola King who ruled Chedi Kingdom and was a friend of Indra. Indra is reported to have given him Bamboo Pole.

Uparichara Vasu was a king of Chedi belonging to the Puru Dynasty. He was known as the friend of Indra. During his reign, Chedi kingdom had a good economic system and contained much mineral wealth, which made a lot of merchants around the world, come to the Kingdom. It was abundant in animals and corn. There were many towns and cities in the kingdom. He possessed a very special chariot. He introduced a festival in his kingdom in the honour of Indra. The festival involved planting of a bamboo pole every year, in honour of Indra. The king will then pray for the expansion of his cities and kingdom. After erecting the pole, people decked it with golden cloth and scents and garlands and various ornaments.

Chedi Kingdom

Indra Vizha , Festival was celebrated with great pomp in Poompuhar. Failure to conduct it had resulted in a great Tsunami consuming Poompuhar, Tamil Sangam Classics, including Silappadikaram aver.

So this shall place Poompuhar being intact before Kaliyug that is Chola Perunarkilli , who is recorded to be the first Chola King in Kaliyug.

Hence ,it is safer to postulate the date of Poompuhar to about 11000 years ago.

Cholavarman’s son was Rajakesarivarman and Rajakesarin’s son was Parakesarin (vv. 30 and 31).  These two names were used as titles alternately by the Chola kings in the order of their coronation (v. 32).  Parakesarin’s son was Chitraratha; his son was Chitrasva and his son, Chitradhanvan (v. 33).  It is stated that this last king Chitradhanvan brought into his dominions the river Kaverakanyaka, i.e., Kaveri, just as Bhagiratha brought into the earth Ganga, the river of the gods (v. 35).( Chitradhanvan was an ancestor of Sri.Rama and therefore Kaveri was in flow during Ramayana)

Thiruvaalangadu Copperplates

V. 36.) In that family was (born) Suraguru who was the hereditary abode of the maiden, the Lakshmi of victory.  This king having conquered by his glory the god of Death in his own territory acquired the name Mrityujit.

(V. 37.) In his race was born king Chitrartha called Vyaghraketu from his banner-cloth bearing (the figure of) a tiger, who was a store of great heroism and who wore as an ornament on his head the flowers of the dhataki (Grislea Tomentosa).

(V. 38.) The Treta-age having come to a close, a son of this king known as Narendrapati became the ruler.  The diadems of (subordinate) kings dropped down their gems ; (because their) fastenings had become loosened by the constant rolling at his footstool.

(V. 39.) From him was produced the head-jewel of the powerful Solar race, (king) Vasu, who was the cause of the destruction of the demons (and) who (known) by the significant surname of Uparichara moved in any direction he liked in a celestial car which was presented (to him) by the lord of gods (i.e., Indra).

(V. 40.) At the end of the Dvapara (-age) was born in the family of this head-jewel of kings a conqueror of all hostile kings named Visvajit.[30]https://www.whatisindia.com/inscriptions/south_indian_inscriptions/volume_3/no_205b_aditya_ii_karikala.html

Kings after Muchukunda Chozha.

Mandhata
Muchukunda
Valabha
Prithulaksha
Parthivachudamani
Dirghabahu
Chandrajit
Sankriti
Panchapa
Satyavrata
Rudrajit
Sibi
Marutta
Dushyanta
Bharata
Cholavarman
Rajakesarivarman
Parakesarin
Chitraratha
Chitrasva
Chitradhanvan. https://www.whatisindia.com/inscriptions/south_indian_inscriptions/volume_3/no_205_aditya_ii_karikala.html