Have beavers in an irrigation lake. After five years of killing them and more moving in I convinced the owner he needs an exclusion fence. How high above the pipe and how far away from the pipe should the fence be?

Depends on pipe size, it's location, and water depth at the pipe.

If it's a typical culvert type pipe under a dam or roadway, the easiest way is to build a grate-type device that can be installed/removed by hand or tractor FEL. The owner can, as needed, lift the grate and the force of water will push most mud/small debris thru. Then, put grate back in place. Most places, if this is done a couple or 3 times per year, there will just be mud and small woody debris pushed up against it. The longer you wait, the larger the debris the beavs bring up there.

If you need to build an excluder (that seems to confound the beaver), then use goat panel (squares a beav can't get thru.) If water is shallow enough, then the height of the panel may be sufficient. Most designs allow water to keep flowing. Beavers can't figure out what they need to do to stop the flow. I'll try to find some pics of a small excluder I built a couple years ago.....it's still working.

These are not my pics, but the top left one (V-shaped) is how I built the one that contines to work well.

This is right helpful. Got a farmer friend that’s played heck with a culvert. Gonna share the v-shaped design with him.

I used three 16' panels and about ten 7' t-posts. Used the aluminum t-post wire twists, pliers, bolt cutters, and a t-post driver.

Water depth was only thigh deep. I installed it in about 2 hours without assistance.

Thinking about a circle using 2 hog panels. Would be be 10'2.5' in diameter. A couple of feet taller than the pipe. Retired hog farmer. What he has on hand,

That should work as well as the V-shaped.