Rod, our elevation is 6500. Pond bottom is clay from decomposed Mancos shale. Surface water temps rise to mid 70s in the heat of summer. Irrigation water inflow is cool enough to keep trout alive all summer.
My biggest concern is that the roots will freeze in winter when the water level drops below where either iris or pickerel is growing.
Yep, that is what I was afraid of in your situation. What is your frost line there?
I suspect your plant roots MAY not go deeper than your frost line. However, many plants can survive having their roots spend the winter in frozen ground. My wife frequently divides iris bulbs (garden variety) with our neighbors. They are planted very shallow and our frost line is around 24". (More importantly, Boondoggle's link shows they can survive in cold zones.)
Maybe try a few plantings on your north bank? (south facing) Also, the frost line on slopes is not horizontal, rather it roughly parallels the slope. If you plant them on your steeper banks, then their feet should be a little warmer during the winter.
Also, even if the plants go out of the water during winter, the adjacent pond will actually keep your banks a little bit warmer.
P.S. Any of outcrops of the Mancos Shale on your property? In some locations, the concretions (nodules) may hold treasures like ammonites or shark teeth.
