Consider the following statements:
1. In an open channel flow, an energy grade line is obtained by adding the datum head, pressure head, and velocity head.
2. In an open channel, the hydraulic grade line is the free surface itself.
3. For a pipe and an open channel of source dimension, the hydraulic gradient line is located at the same height above the datum.
4. Energy gradient line of an open channel is always horizontal.
Which of these statements are correct?