Then he cut the heavy stones from his feet, and the sea carried him and threw him onto the shore. what literary device is used to describe what the sea dose to gilgamesh

Flashbacks: The Story of the Flood is told in the form of a flashback. In this case the story is used to explain parts of the plot and to pull the reader deeper into the story. Another use of flashback can be seen when Enkidu relates to Gilgamesh his dream that foretells his own death. In this case it is used as a plot device to foreshadow Enkidu's death. 

Repetition: "After two leagues the darkness was thick and there was no light, he could see nothing ahead and nothing behind him. After three leagues the darkness was thick, and there was no light, he could see nothing ahead and nothing behind him. At the end of five leagues the darkness was thick and there was no light, he could see nothing ahead and nothing behind him. At the end of six leagues the darkness was thick and there was no light, he could see nothing ahead and nothing behind him. When he had gone seven leagues the darkness was thick and there was no light, he could see nothing ahead and nothing behind him. When he had gone eight leagues Gilgamesh gave a great cry, for the darkness was thick and he could see nothing ahead and nothing behind him." 
Another example of the repetition of the exact phrasing is when the youth tells his father about sighting Enkidu then runs of to find Gilgamesh and tells him what the youth told his father word for word. 

Imagery: The Imagery of the Forest is very important. Our two heroes, Gilgamesh and Enkidu must pass through this intimidating and dangerous forest to validate their heroism and slay the monster Humbaba. This imagery could represent several different things. Often forest imagery is used to represent danger. In this case it probably represents the heroes' dangerous rite of passage.