To find out, whether the sand bars at Rameshwaram are man made or not, we need not do any research at the site.
But let us read bit of Valmiki Ramayan!
Valmiki Ramayan says (yudha kanda), the Nala and Monkeys constructed a bridge of 100 yojans length and 10 yojans wide. One yojan is about 12.87 kms. This means that they constructed 1287 kms long and 128.7 kms wide bridge. But distance between Rameshwaram and Mannar (including Ramar sethu) is only 21 kms.
According to Valmiki Ramayan, Starting point of Ram's bridge is near Mahendragiri - that is close to Kanyakumari, and not at Rameshwaram.
Further, Valmiki Ramayan says, Ram went on top of Mahendragiri, hoping to view the Lanka - where Sita was prisoned. However, the sea was so huge, he could not see the beaches of Lanka-it adds. Mahendragiri is as tall as 5000 feet, and about 5 kms west of the ocean. Normally, with this height, a person can comfortably see a place situated about 70-80kms far - despite the earth's curving effect.
In addition, suppose, at Rameshwaram, if there was a mountain as small as 400 feet, Ram would have seen the Lanka - comfortably - because the distance is very small. But, there is no mountain near Rameshwaram.
In addition, it is interesting to note that %u2018yudha kanda%u2019 explains the star%u2019s position of the sky - when the bridge construction work started. It talks about a Rasi %u2018Sabtharishi Mandal%u2019 surrounding the Dhruv star at the North Pole. Sabtharishi Manda
