I would like to let my native water turtle hibernate, but my pond is only about a foot deep. Will this be successful?
There are two problems with water that shallow. One is that it is not deep enough to maintain a constant temperature when we get warm days and cold nights. Water warming on sunny days can harm turtles that normally go to deep water to avoid temperature fluctuations. They need to stay cold during hibernation / brumation. The other problem is that it can ice over solid at the top, preventing the turtle from getting surface air. The only way to maintain a water turtle in shallow water is to have it in full shade during it's brumation time and trickle a hose in it if it freezes. A hole drilled a few inches below the surface of the pond will prevent the water from overflowing and the escape of the turtle. Then when it is time to come out of brumation (and you won't really know when that is) it has to be moved back to a sunny area. And then back to full shade when the water temperature reaches 85 degrees. Pretty tricky.
If a shallow pond is the only option, I would bring it in and keep it warm, active and feeding through the winter. A problem with this, however, is that females will often need to lay offseason when overwintered indoors, and if your turtle does not have access to land, she will very likely try to retain her eggs. This can result in eggbinding - a grave and potentially fatal situation for turtles.
If your turtle is a female, even if she has never mated, she could form infertile eggs. Fully aquatic housing (without access to a land area) is not at all appropriate for them.
These big water turtles need big ponds. A foot of water can overheat and kill turtles in the summer. Unless you have a large in-ground pond with a land area easy accessible to the turtle, she really should be released in the spring.