If anyone can make this work, he/she's my hero..........
Trying this because with complex water displacement rendering takes ages, and accuracy is not always important (such as in a fast flowing river). There is a way around (by masking), but that's a crude way and not by depth.
You can cheat the depth with making a depth mask from a HF......
With a little bit of displacement, it doesn't look too bad.
What I did find with the above clip file, is that I did have to centre the lake to the HF. I also uped the compute terrain patch size to 0.05 to make the HF, and dropped it back down afterwards.
Thanks for diving into deep water, Jon. I just tried but couldn't get it to work yet. I'll take some more time. Problem is probably that my HF is already quite complicated, with all sorts of warps and masks, and calculating might even take more time than a more crude way of faking or just using the water shader after all. I already used the transparency only close by, the rest is just reflective.