Thanks, guys. It seems that I pick up something new with each project. This time it was ZBrush, an application I tried to avoid but now wonder how I ever managed without. And always learning new things with Terragen, of course. All the help and advice on this forum have been invaluable.
This one set a record for rendering time -- the original 6,000-pixel frame took almost 158 hours. MPD was 0.5 and AA was 10 (with customized sampling) to reduce noise in the water and V3 clouds. (Tested many combinations first.) Most of the water surface is a single sphere displaced as needed, with additional planes for the puddles. The render was divided over several tiles that took from 8 to 32 hours each, depending on the amount of water, the surface angle, and displacements. The slowest part was the bypass flume at left, next to the wooden crib, because of the low angle of the upper surface and the small displacements of the inclined surface. The rendering time may have been shortened by disabling water transparency, but I think that would have changed its appearance in the near foreground, around the boat. I don't mind waiting. Not too much anyway.