Thanks for that dean's website! Hmm... This is gonna be hard now because I want to do both.
Mechanical engineering and civil engineering are very different careers and most mechanical engineers have little if any work that involves civil engineering and vice versa.
Civil engineering = infrastructure (Roads, buildings, dams, etc)
Mechanical engineering = machines and devices
Your first career is going to be an army officer and it isn't going to make any differece which degree you get. What do you want to do after the army?
In the civilian world, most civil engineering jobs are government or government funded jobs and most mechanical engineering jobs are private.