iPad design dimensions

I am designing for iPad (canvas dimensions 768 x 1004) using the attached mock-up resource. However, I was wondering whether I need to factor the lower navigation bar into my design? I was planning on having a menu bar at the bottom and wondered whether this can sit over that navigation bar or whether I need to work above it. If this is a permanent fixture and I need to work around it then I will crop it off the canvas. Many thanks in advance for your answers.