Gravity dams are so named because they are held to the ground by gravity – they weigh a lot, and are typically made from concrete or stone. Engineers must de-water the river where the dam is meant to be built. This is done by diverting the river through a tunnel that runs around the intended construction zone.
Answer:First, they dug tunnels from below the dam to above the dam. Then, they put the cofferdam in place, and opened the tunnels. The water flowed around the site where the permanent dam would be built until they were done, at which point the cofferdam was removed.
When light enters from air to water i.e. it is moving from rarer to denser medium, it changes its original path as there is a change of speed of light and deflects itself towards the normal. This is known as the refraction of light and this is why a pencil in a cup of water looks as if it is broken and larger.
