I made my anti-vortex plates. A simple way to do this is to wrap a stiff sheet of flexible metal around the top of the entrance pipe and bolt in place like a hood sticking into the pond beyond the pipe. The plate keeps a whirl-pool from forming and sucking air into the pipe.

Some specs for the emergency spillway: https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_023318.pdf

On one of my ponds, I built a trash rack from pieces of hog panels and put a solid top on it made from a piece of roof metal. Anything that shields the top of the pipe to prevent air from being sucked in once the pipe is full should do the trick.

http://www.livingthecountrylife.com/homes-acreages/ponds/creating-and-fixing-pond-spillways/