Officials of the Public Works Department say the pool of water was apparently had its source from a peculiar spring on an otherwise dry Cauvery river bed.
While the local people alleged that the pool of water had been stagnant in a trench caused by unauthorised mining of sand, the Public Works Department officials said a sand quarry was functioning about half-a-kilometre downstream the accident spot in Perugamani. However, they did not discount the possibility of a trench being left behind by sand being scooped away in bullock carts by local people on the sly.
The PWD officials conducted an inspection of the site and enquired with the local people.
“From what we hear from the locals, the pool of water had been there for quite some time.
“There was apparently a spring at the spot, creating a pool with water to a depth of about four to five feet. The water was spread in a radius of about 15 metres. Locals say that they were aware that the water was deep, but the victims could have been caught unawares,” a senior PWD officer told The Hindu.
The officer, who did not wish to be identified, said the spring could have loosened the top soil on the river bed and such spots are extremely difficult to identify.
The victims had probably stepped on one such place. As they were being pulled inside, they could have panicked leading to the tragedy, he said.
Incidents of drowning in quick sands on the river bed are reported almost every year after a fresh flow of water in the river after the summer, especially at the Mukkombu picnic spot on the outskirts of the city.
In the absence of water flow now, this was apparently not quick sand which are normally characterised by swirling waters at a particular spot, officials said.
At the behest of District Collector Jayashree Muralidharan, the PWD officials are taking steps to place signboards cautioning people against venturing into such vulnerable spots.