Dean,

You could do it with this limitation:

The positive pressure will be limited to less than the pond height while water is flowing through the siphon and to the pond height when the valve at the bottom is shut.

I would prefer there be no valve at the end of the siphon that manages your water level. It may be better to create an irrigation siphon additionally out of a smaller diameter polypipe that would service the irrigation system..

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers