Yes. you lerp.
First you need to make a fading mask.
You can take the height, make a 1 pixel line at about where the caustics should be most visible (let’s say 10m below water).
From that point you multiply or Power the result to get a nice falloff effect going that reaches all the way to shore, and however far down until it fades.
To make sure that the shore line is clear and that the effect doesn’t extend onto the terrain, simply keep and subtract the current mask, or even better, use the result of the first lerp into the learp you already have, and then lerp agian with the images to replace white and black.
You should really have the system work with a 2 point variable imho.
One for where to start fading below water, and one that’s automated to the shoreline fading about 5m and up.
Yeah as I mentioned I’ve learned all I know about UE4 materials this week XD. I do have a bottom cutoff and a top cutoff (the top I was planning to make automatic once the caustic function was fully complete. Where exactly would I lerp and where would I place the (Height-10) function to have it fade correctly? Sorry and thanks for the help!