panteradon,

L X W X D X 7.5 (gallons per sq. ft.) = 1080. You need a pump that turns over 1000 GPH. The head pressure that is needed is determined by height (3 feet), length of pipe, and turns (joints) in pipe. I gather this pump is an in-water type. I guess (roughly) 5 feet of head pressure. If it is more than needed, the water flow can be controlled by a ball valve.

By the way, what are you having in this pond? Plants? goldfish? koi? All have different set-ups/ minimum reqs. Planning / talking it out (other ponders, books, internet) is the best course to minimize the mistakes in building your pond.

LP