I have been using the Miri Airport bypass for a long time and not long ago, I noticed this structure and immediately, I knew that it is a dike because when I was young, we used to have a simpler structure.
Just in case you don't know, dike is used to control water level or flood prevention.
This structure was built across the small river. In this case, it was made of concrete walls on both side with a metal "door" that can be lowered or lifted up. If flood water prevention is desired, the door would be lowered when the tide was low. When water retention is desired, the door would be closed when the tide came in.